US2082586A - Automatic telephone system - Google Patents

Description

June 1, 1937. H. P. MAHONEY AUTOMATIC TELEPHONE SYSTEM Filed April 29, 1955 6' Sheets-Sheet l INVENTOR. HARRY F? MAHONEY W ATTORNEY.

awn-2E June 1, 1937. H. P. MAHONEY 2,082,586

AUTOMAT I C TELEPHONE SYSTEM Filed April 29, 1935 6 Sheets-Sheet 2 as Q S I N N 4. 2% N H $6 5! 2 N o x I a F w Q m 4 4 E :3 Hi. i? g m p m 1 I: V E

w m 9 Q N e: :I u N N N k9 41 Q N II 4 4 U Us *1 1 j CONNECTOR HARRY P. MAHONEY ATTORNEY. V

June 1, 1937. H. P. MAHONEY 2,082,586

AUTOMATIC TELEPHONE SYSTEM Filed April 29, 1955 6 Sheets-Sheet 3 J6] Ea x 4 CONNECTOR CONT.

- HARRY P. MAHQNEY ATTORNEY.

June 1, 1937. H. P. MAHONEY AUTOMATIC TELEPHONE SYSTEM 6 Sheets-Sheet 4 Filed April 29, 1935 June 1, 1937. H. P. MAHONEY AUTOMATIC TELEPHONE SYSTEM Y m R s o m t T w b m wE W A mm W U. W M R S o I t l q UK a nun 1.. W & \r 3E 5E m 6 1 H m w u H 5 Y B 1 &%2E fix? v l n v 1 m Q. TT ll MWMMMMMMMW A b 1 I... H j n 1% a 4. m3 2 8m F 5534 Q S. l 98 mNm 7 HI 1 1 I! A $325 w .f I11 E85 I 4! 223 IL I 3.5% T I b QE AB F 5 NB 1L w \le'.

0 Q h w m m N ATTORNEY.

June I, 1937. p, MAHONEY 2,082,586

AUTOMATIC TELEPHONE SYSTEM Filed April 29, 1935 6 Sheets-Sheet 6 H J l O 01 a a2e' sa1 529 sea 2 'i INVENTOR.

l HARRY P. MAHO NEY BY ATTORNEY.

Patented June I, 1937 UNITED STATES ATENT OFFICE mesne assignments, to

Associated Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application April 29, 1935, Serial No. 18,774

7 Claims.

The present invention relates in general to automatic telephone systems, but more especially to automatic systems of the Strowger step by step type, and the object of the invention is to produce a better and cheaper system for use in giving service in an exchange comprising between about three-hundred and six-hundred lines.

In further explanation of the object of the invention, it may be pointed out that the standard Strowger switch has a capacity of one-hundred lines. By using finders and connectors linked together in pairs an automatic switchboard for one-hundred lines may readily be constructed, and such is the common practice for small exchanges of this size. It has also been found feasible to equip the finders and connectors with two sets of wipers and thus increase their capacity to two-hundred lines, which is the largest sized exchange heretofore built, so far as is known, us-

2 ing finder connector links of the step-by-step type. 1

In the range extending from about threehundred lines to one-thousand lines it has been the practice to insert first selectors. A common arrangement is to use finders paired with the first selectors, and connectors arranged in groups accessible to the selectors, constituting what is commonly known as a one-thousand line system. This larger type of system is more expensive per line than the one-hundred line or two-hundred line system hereinbefore referred to, because it introduces an additional order of switches.

In view of the facts stated in the foregoing, it will be understood that the manufacturer is somewhat handicapped in selling automatic equipmerit for exchanges which are just a little too large for a simple finder connector link system. A system of the one-thousand line type has to be used, which results in a sudden rise in the cost per line, which although entirely justified by the equipment which has to be supplied, is nevertheless diflicult to satisfactorily explain to the customer.

More specifically it is the object of the present invention to devise a system which will fill the existing gap between the one-hundred line or two-hundred line system and the one-thousand line system, by producing an exchange in this capacity range which can be sold at a cost per line comparable with the cost per line of the smaller system and considerable less than the cost per line of the one-thousand line system.

The object is accomplished by new and improved arrangement for mounting the switching 5 equipment and by new and improved circuits which makes it possible to use finders and connectors of much larger capacity than has heretofore been considered possible. In a representative system, such as will be described herein, the switching equipment comprises finder connector links, each finder and each connector having four sets of wipers, which gives them access to four-hundred lines. Thus a system is produced capable of giving service in an exchange of this size, and at the same time the necessity for 'pro- 0 viding first selectors is obviated. The system is arranged so that additional banks and wipers may readily be added to increase the capacity to six-hundred lines whenever the occasion should arise. 15

Further details of the system will be explained hereinafter in connection with-the drawings, in the course of a full explanation of the equipment and circuits of which it is comprised.

Referring to the drawings, Figs. 1 to 5, inclusive, 20 are circuit drawings which show the circuits which are necessary to enable the system to be explained; while Fig. 10 shows how the circuit drawings are put together. Of these circuit drawings, Fig. 1 shows a line circuit and a finder switch, 25 Figs. 2 and 3 show a connector switch, while Figs. 4 and 5 show two allotters with the associated common start wires. Figs. 6 to 9, inclusive, show certain mechanical features of the system. Of these drawings, Fig. 6 shows a por- 30 tion of a switchboard with one of the link circuits mounted thereon, while Figs. 7, 8, and. 9 show certain mechanical details of the switches which cannot be shown clearly in Fig. 6.

The general arrangement of the system will 35 first be described briefly. There are four-hundred lines. The majority of these lines are subscribers lines, but a few of them maybe trunk lines extending to another exchange. Each line is provided with a line circuit comprising two relays. Thus 40 the line shown at the left of Fig. 1 comprising conductors IIlI and I02, is provided with line equipment consisting of relays I08 and IE1. Relay IEl'I is a combined line and cut-off relay, while relay lot is a lookout relay. From the line circuit conductors are extended to the multiple banks of the finder switches. There is also a branch for each line which extends to the banks of the connectors. Thus in the case of the line shown, 50 the branch which extends to the connector banks comprises conductors I03, I04, and I05.

All connections in the system are set up by means of finder connector links, each link comprising a finder switch and a connector switch.

' level of the finder switches.

These switches are of the well known Strowger vertical and rotary type. Each finder and each connector is provided with four sets of Wipers so that it may have access to all four hundred lines of the system. There may be around thirty links, more or less, depending on the amount of traffic.

The subscribers are assigned numbers beginning with the digits 2, 3, 4, and 5, that is, the second, third, fourth, and fifth hundreds are used. Subscribers numbers all have four digits, of which the first three are line selecting digits while the fourth is a party selecting or ringing current selecting digit. Trunks may have two, three, or four digit numbers, depending on factors which will be explained.

While the link circuits are all in one large group from the standpoint of each link being able to serve all the lines in the system, these link circuits are nevertheless divided into two groups as regards the arrangements which are provided for starting the finders. The lines are divided into groups A and B, the lines which have nunibers in the even hundreds constituting group A, and the lines which have numbers assigned in the odd hundreds constituting group B. The finders are divided into two corresponding groups, the basis of the division being that the finders of group A normally serve the lines in group A, while the finders in group B normally serve the lines in group B. It will be understood, however, that each finder has access to all the lines, as stated hereinbefore, and if no finder in group A is available at the time that a line in that group makes a call, then a finder in group B will be taken for use. The same is true as regards lines in group B calling when no finders in the associated group are available.

The starting of finders is controlled by means of two allotters. Fig. 4 shows allotter A which is associated with the finders of group A, Fig. 5 shows allotter B which is associated with the finders of group B. The finder switch which is shown in Fig. l is a finder in group A, and 'consequently is accessible from the bank of allotter A, Fig. 4, as indicated by the cable including conductors 458, etc. The allotter A may be a 25-point switch of the type which has a movement in a forward direction only. Only one set of contacts is shown, being the set of contacts which is assigned to the particular finder switch shown in Fig. 1. The other sets of contacts are individual to and are wired to the other finders of group A. Allotter B in Fig. 5 is similar to the allotter A, Fig. 4. Allotter B is associated with the finders of group B and the various sets of contacts in its bank are wired to the finders of that group, the same as the contact sets of allotter A are wired to the finders of group A.

For each group of lines there are ten common start leads. The common start leads for the lines of group A are shown appropriately labeled at the left of Fig. 4. There is one start lead for each tens group of lines, corresponding to each The common start wires are accordingly numbered for convenience from 1 to 0. Each common start lead is connected by way of a resistance to a main start conductor M3, which extends to the allotter A.

Each line circuit is provided with an individual start lead. The manner in which these individ ual start leads are connected will now be eX- plained. The individualstart lead for lines I I to H] of the second hundred. and for lines H to ID of the fourth hundred are connected to common start lead No. 1 of the A group, Fig. 4. The individual start leads for lines 2! to 20 of the second and fourth hundreds are connected to common start lead No. 2, while the individual start leads for lines 3! and 30 of the second and fourth hundreds are connected to the common start lead No. 3, and so on. Thus it will be seen that as regards the line shown, which belongs to the fourth hundred, the individual start lead H5 is connected to the No. 3 common start lead. The manner in which the other individual start wires of group A are connected up will be clear from the foregoing. As regards the individual start leads for the lines of group B, these are connected up to the common start leads B shown in Fig. 5 in the same way that the connections are made in group A.

The common start leads not only function as a means of starting the finder switches through the medium of the allotters, but they also serve to mark the levels in the finder banks in which calling lines are located. Each finder switch is provided with a so-called vertical bank, the vertical bank of the finder switch, Fig. 1, being indicated at 28. it will be seen that the energization of relay 48! associated with the allotter A is effective to extend the common start leads 5 to 53, inclusive, by way of cable di t to the vertical bank contacts l to 9, respectively, of vertical bank 28. The cable 414 is common to all finders of group A and the conductors thereof are multiplied into all the vertical banks such as 28 which are associated with such finders.

By reference to Fig. 5 it will be observed that relay 59! has the function of connecting all the common start leads of group B by way of cable 414 to the vertical banks of the finders of group A. This relay 511i is energized whenever a finder in group A is started up to find a calling line in group B.

It should be pointed out also that there is a cable similar to cable li t which extends to the vertical banks of the finders in group B. Relays 592 and 82, under control of allotter B, serve to connect the common start leads of groups B and A to this cable. The conductors leading to the right from relay contacts of relays 492 and 502 are appropriately labeled to indicate the foregoing arrangement. All of this will be more clearly understood from the detailed explanation of the operation of the system.

The mechanical construction of the switchboard and link circuits will now be described, reference being made to Figs. 6 to 9, inclusive.

Referring to Fig. 6, the frame of the switchboard comprises two U-shaped channel members 2 and 5, which form the ends of the frame, and two intermediate members 3 and "3 of angle iron. These four frame members are secured together in the relative position shown in the drawings by means of a transverse channel member l l,together with a similar member near the top of the frame. There are also corresponding channel members directly opposite these members on the other side of the frame. The upright frame members 2, 3, 4, and 5 are attached at the bottom to foot members such as 6, 8, 9, and '1, respectively, by means of which the switchboard is secured to the floor. The various frame members are preferably secured together by welding. To give an idea of the dimensions of the frame it may be stated that the distance from the outside of channel mem her 2 to the outside of channel 5 is about 63 inches. The height of the frame is sufiicient By reference to Figs. 1 and 4 so that fifteen links similar to the one shown in Fig. 6 may be mounted one above the other. Since all these links are the same it has been considered necessary to show only the lower part of the frame with one link mounted.

On the opposite side of the frame mounting space is available for the line relays and for the necessary power and supervisory equipment such as is customarily furnished. At the top of the frame the necessary terminal strips are provided. These arrangements, however, are in accordance with standard practice and need not be shown. If the traflic is light enough so that fifteen links will take care of it, then all the equipment for the exchange may be mounted on one frame. In most cases, however, as many as 25 or 30 links will have to be provided to take care of the traffic, and it follows that two frames will have to be furnished.

Considering now the link which is shown in Fig. 6, the apparatus is mounted on a base plate Ill. This base plate is a U-shaped steel stamping corresponding in length to the distance between angle irons 3 and 4 and about 5 inches Wide. The plate is bent at right angles along the upper and lower edges shown in the drawings so that there is a rearwardly extending portion about three-fourths of an inch wide along each edge which bears against the face of the angles 3 and 4. By means of machine screws shown in the drawings the base plate It is secured in position on the angle irons 3 and 4. This base plate l0 carries the finder switch mechanism at the left, and the connector switch mechanism at the right, and the finder and connector relays, such as are shown in Figs. 1, 2, and 3 of the circuit drawings, in between.

The connector switch is of the usual vertical and rotary construction. Only the lower portion of the frame It is shown in the drawings, the rest of the switch mechanism, except for the shaft and wipers, being indicated by the rectangle l4. On the channel 5 there is secured a bracket 24 and between this bracket and the frame I6 of the switch extend the usual bank rods ll, except that these rods are, of course, much longer than is usually the practice and are secured firmly at both ends instead of being attached only at the switch frame. On the bank rods are mounted six banks such as IS in the usual manner. The switch shaft is indicated at 21. The shaft has a bearing in the upper end of the switch frame and also a bearing on the lower end of the frame, exactly as in the usual switch. In view of the length of the shaft an additional bearing is provided by the cross member 25, which extends between the two bank rods I7 and i8. On the shaft are mounted four sets of wipers, each set including two line wipers and a test wiper, and also the vertical wiper 329.

In order to provide for connections to the wipers a special arrangement is provided which comprises a strip 23, which is attached to the banks as shown in Fig. 9. The clamping plate 69 of the second bank from the left, Fig. 6, is provided with an ear 69, as is also the corresponding member of the fifth bank from the left. The strip 23 is secured to these ears 69 as shown in Fig. 9. On the strip 23 is mounted the vertical bank 328, and also the terminal blocks 2| and 22. The usual flexible wiper cords are run between the wipers and these terminal blocks. This avoids the use of the unusually long wiper cords which would otherwise be required.

The reference character 26 indicates the Well known rotary control bank. This comprises an arc shaped strip of metal which is drilled with one-hundred holes corresponding in position to the different positions of the wiper 326. These holes are tapped and threaded pins are inserted in the holes which correspond to switch positions in which the rotary control circuit is to be closed, as will be explained more fully hereinafter.

Associated with the connector there is a minor switch, indicated in Fig. 6 by the reference numeral I 5. This minor switch is of the usual well known construction and the circuit arrangement thereof is shown in Fig. 3. As indicated in Fig. 6 the minor switch 15 is mounted on the base plate i6 like the relays, and occupies the same space as two relays.

One object of mounting the links as shown, with the switches in a horizontal position, is to enable the vertical magnet to operate the shaft. In the usual arrangement, the shaft stands in a vertical position and the vertical magnet raises it against gravity, the shaft being restored by gravity upon the release of the switch. Due to the length of the shaft in the large capacity switch herein described, and the number of wipers which it carries, the shaft is much heavier, than is ordinarily the case and for that reason the horizontal mounting is much preferable. However, it can be seen that when the switch is mounted horizontally gravity cannot be depended on to restore the shaft and other means must be provided. This means is illustrated in Figs. 7 and 8 of the drawings. Referring to Fig. 7, this drawing shows the entire top or left-hand por tion of the connector, including the upper portion of the frame 16. The drawings incidentally show the manner in which the switch frame is attached to the base Hi. There is also shown the upper portion of the shaft 2! with the helical spring for restoring it to normal in a rotary direction. Also the normal post 4! and the comb-shaped member 42 for controlling the level springs such as 354. These details of the switch are Well known, but if necessary reference may be made to U. S. Patents Nos. 1,913,440 and 1,888,- 70.0.

The restoring means for the shaft comprises a bracket 46, seen in Figs. 7 and 8, which is held in place under the adjusting nuts for the vertical magnet coils. At the right end of member 66 there are two upwardly extending ears 4! and 48 between which is pivoted a lever #39. This lever is provided with an arm 50, and there is a spring 5! connected between the end of this arm and the forward end of bracket :36, as clearly shown in Fig. 7. The end of the lever 49 bears on the member 44 which is secured to the shaft 21. This member 44 is of standard construction except that it is provided with an ear as shown in Fig. 8. With this arrangement it will be clear that when the shaft 2'! is operated it will tension the spring 5| by means of lever d9. When the detent is withdrawn from the shaft upon release, spring 5! will restore the shaft by means of lever 49.

The finder switch mechanism mounted on the left of the base plate ii] is indicated by the rectangle Bi]. The mechanical construction of the finder is similar to that of the connector, except that no level springs are provided. The restoring means for the finder is the same as that of the connector. The-drawings show the finder shaft 3! and the wipers such as I28 and the associated banks, also the vertical bank 28 and the verticaltest wiper 29.

It will be observed that in the case of both the finder and the connector the switches are shown equipped with six banks, which is sufficient for a capacity oifour-hundred lines. Provision is made, however, for adding three more banks to each switch, so as to increase the capacity to six-hundred lines. In the case of the connector shown in Fig. 6, one of these additional banks would be added tothe left of the bearing member 25 and two of the banks would be added between this hearing member and the bracket 24. Thus the design of the links is such that the system may be installed with an initial capacity of either four, five, or six-hundred lines. The circuit shown in Figs. 1 to 5, inclusive, is arranged for a system of four-hundred lines, but can readily be adapted to take care of either fivehundred or six-hundred lines by a simple extension of the plan of wiper selection which is illustrated.

The operation of the equipment in setting up a number of representative connections will now be described. The first connection which will be considered is a call from station 43! 2, on line |0|l02, to another subscriber in the system whose number will be assumed to be 33 [2.

Upon removal of the receiver at station 43R, the subscribers talking equipment is bridged across the line, thereby closing a circuit over the line conductors iflli32 for the combined line and cut-off relay I01. It will be observed that the three windings of relay It! are connected across the line in series with the battery. The upper winding of relay I !ll is made of wire having high resistance, so that the relay is inefficient under these operating conditions and pulls up only part way, closing the contacts marked X and leaving the position of the other contacts unaltered. The closure of the upper contact X places battery potential through the middle winding of relay It}? on test contact H8, thus marking the line as calling in the banks of the finders such as the finder shown in Fig. 1. The closure or" the lower contact X places ground on the individual start wire H9.

Since the individual start wire H9 is connected to the No. 3 common start lead, Fig. 4, a circuit is completed which extends from the grounded common start lead by way of M0, M3, 428, and 425 to relay ist of the allotter A, Fig. 4. Relay 494 accordingly energizes. At 422 relay 4M closes a circuit for relay MN, and the latter relay upon operating connects all the common start leads by way of M4 to the vertical test banks of the finders in group A. Thus a ground is placed on the No. 3 test contacts in these vertical test banks, including the No. 3 test contact in bank 28, Fig. 1. The energization of relay lii i also opens the circuit of relay 495 at 52! and closes a circuit for relay 49! at 420. Upon energizing, relay 401 closes a locking circuit for itself at 833. In addition, relay iill closes a circuit for relay 689 at $34, and a circuit for relay M6 at 435. The latter circuit is to guard against release of relay 406 in the event that only one finder switch is available, as will be explained more fully later on. Relay lilil also shifts the circuit of wiper 453 at 43%} for reasons to be presently explained, prepares the test circuit at Q32 for test relay Mil, and at 43l places ground on the wiper 45L This latter operation grounds the individual start wire e56 extending to the finder shown in Fig. 1.

When the circuit of relay 409 is closed, this relay operates, at 43'! prepares a locking circuit for relay 4 l 0, at 439 closes an impulsing circuit for the finder, Fig. l, and at 438 attempts to close a circuit for relay 4| I. The contact engaged by spring 4-38, however, is weighted and upon the operation of relay 589 this contact is set into vibration with the result that the circuit to relay ii! is intermittently opened and closed. Relay iii cannot operate under these conditions. As a matter of fact, this relay never does operate if the calling line is found in the normal manner. The function of relay ll! will be fully explained later on.

The effect of grounding the individual start wire 456 is to operate the start relay I46 of the finder, Fig. 1. Upon energizing, relay H56 prepares a circuit for rotary magnet M4 at I59, disconnects conductor I'M from the conductor it! at I58, shifts the circuit or the guard wire #255 at 57 in order to prepare for energizing the stepping magnet 45!; of the allotter, prepares a circuit for test relay M2 at 55, and at 56 closes circuits through the polarizing windings of test relays MI and M2. These relays, however, do not operate at this time.

As already mentioned, the relay 499 of the allotter closes the impulsing circuit for the finder when it pulls up, so that the finder is started in its vertical movement by the time the so-called start relay 546 has pulled up. The circuit for the vertical magnet extends from ground by way of M8, 439, 336, 444, 454, and 459 to vertical magnet M5. On the closure of this circuit the vertical magnet of the finder energizes and advances all the sets of wipers into position opposite the first levels in their respective banks, at the same time shifting the ofi normal springs E68 and E65. understood that the vertical movement is in reality a horizontal movement in view of the way the switches are mounted, but it is thought that the explanation will be clearer if the familiar term vertical is retained. When the vertical magnet M5 energizes it also grounds conductor 468 at Mt, thereby operating the stepping relay 468 of the allotter. Upon energizing relay @598 opens the circuit of vertical magnet M5 at 436, whereupon the vertical magnet fa'lls back and opens the circuit of relay 4B8. Relay 488 then falls back and again closes the circuit of vertical magnet H55, causing the magnet to advance the switch wipers another step. This operation in which the vertical magnet and relay M33 are alternately energized continues until upon the third step of the vertical magnet the vertical test wiper 29 arrives at the No. 3 test contact in the vertical bank 28.

The operation of stopping the vertical move" ment will now be explained, Upon the third step relay 40!; of the allotter energizes by way of i5! and opens the vertical magnet circuit at 136. The vertical magnet accordingly falls back and breaks the circuit of relay 398 at 15L Relay 468, however, does not fall back but remains held up over a circuit which extends from the grounded No. 3 test contact in the vertical bank 28 by way of 29, .58, 453, Mill, upper winding of the test relay M0, 432, and winding of relay 308. Relay ME! energizes over the above circuit in series with relay 408, the latter relay holding up as stated prevents the circuit of the vertical magnet from again being closed.

Upon energizing, the test relay llll locks itself at MI and also closes a circuit for relay M2. The latter relay pulls up and attempts to close a circuit for relay il I, but without effect under normal conditions because the contact engaged by spring 449 is constructed similar to the contact It is engaged by spring 438 of relay 409, the operation of which was previously described. Relay II also opens the initial energizing circuit of relay 401 at 442, but relay dill holds up over its locking contact 433. By opening contact A43 relay Mil prevents the energization of relay MI by way of the circuit previously closed at contact 433 of relay see. At MM relay Mil shifts the impulse or operating circuit from conductor 59 to condoctor @82, thus accomplishing the change over from vertical to rotary operation at the finder, Fig. 1. At Mil, relay lifi grounds wiper 453 and also breaks the circuit which includes the upper winding of relay II!) and stepping relay 408. The latter relay now falls back in order to start the rotary movement of the finder switch, Fig. 1.

It will be understood now that all of the four sets of wipers with which the finder, Fig. l, is provided are standing opposite the third levels in their respective banks. Only two of these sets are connected up, however, because relay I III has not been energized. The wiper sets which are connected up are the set which comprises test wiper I20 and line wipers I22 and I23, this set having access to lines in the second hundred, and the set comprising test wiper I26 and line wipers I28 and I29, this latter wiper set having access to lines in the fourth hundred. The calling line. being a line in the fourth hundred, is accessible only to the latter set of wipers.

As mentioned hereinbefore, the rotary movement is started by the falling back of stepping relay 4B3, consequent upon the energization of test relay tit. The circuit for the rotary magnet extends from ground by way of M8, 439, 436, 464i, 462, I59, I53, and I58 to the rotary magnet I il. The rotary magnet controls the circuit of stepping relay I88 at I59 and consequently the stepping operation during the rotary movement is similar to that which takes place during the vertical movement. As the wipers are rotated step by step responsive to the operation of rotary magnet Hi l, the test wiper I20 searches for battery potential on the test contacts in the third level of its bank,'and the test wiper I26 likewise tests for battery potential on the test contacts of the third level of its bank. Test wiper I20 finds no battery potential, but as soon as test Wiper I25 engages test contact MB of the calling line battery potential is found and a circuit is closed for energizing test relay I il. Relay I l! operates over a circuit extending from ground at the allotter, Fig. 4, by way of M6, Q53, e53, upper winding of relay E li, wiper I28, H3, H3, and the middle winding of cut-off relay ID? to battery,

this circuit serving also to fully energize relay I07.

By the energization of relay I'll, the circuit of release magnet M3 is opened at I49, the rotary magnet circuit if opened at hill, the relay locks itself at Hi1, and at its two upper contacts the calling subscribers line is connected through to trunk conductors I79 and Ill.

The connecting through of the calling line to trunk conductors I1!) and I'll results in the energization of line relay 204 of the connector, Fig. 2. Upon energizing, relay 2M closes a circuit for the slow acting relay 236 at 236. Relay 2% accordingiy energizes and at 238 places ground on holding conductor I12. This operation completes a holding circuit for relays MI and Iil'i.

When relay Iiil pulls up in series with relay IM of the finder it disconnects ground from the start lead H9 at Md, and also disconnects its upper and lower windings from the subscribers line at III and H2. In addition, relay it: connects lockout relay I06 to the holding circuit at H3. It will be observed also that at this time the holding circuit for relay It? provides a ground potential for the test conductor I85 extending to the connector banks, where the calling line is made busy.

When ground is disconnected from individual start wire I I9, relay tilt of the allotter falls back, provided there is no other line in group A which is in calling condition. When relay 4% falls back it breaks the circuit of relay till which falls back also.

Returning now to the energization of test relay l ll of the finder, when this relay pulls up it closes at HIS a circuit which extends from the grounded impulse or operating conductor 452 by way of 59, I53, I48, I51 key K, 455, 555, and $39 to the stepping magnet 65 of the allotter A, Fig. 4. Stepping magnet 4G5 accordingly energizes and opens its interrupter contact, thus breaking the circuit of relay 401. Relay 40? therefore falls back and at 35 it removes ground from relay its, but the latter relay holds up over conductor itl. In addition relay iIll breaks the circuit of relay 489 at 434, opens its own locking circuit at $33, breaks the circuit of start relay I46 of the finder at 43I, and at 338 alters the circuit which was formerly traced over wiper 459 to the stepping magnet 465 so that this circuit includes the interrupter contact of the magnet. This interrupter contact being now open, for magnet 465 is energized, the foregoing shifting of the magnet circuit results in the opening of the circuit and the deenergizing of the magnet. When magnet 465 deenergizes, the wipers of the allotter are advanced one step into association with a set of contacts which is individual to the next finder. The allotter now proceeds to hunt for an idle finder under control of wiper $50. If the next finder is busy, there will be ground on the conductor corresponding to 355 and the stepping magnet 465 will reoperate to advance the wipers of the allotter into association with the next finder, this operation continuing until an idle finder is reached. It will be noted that relay 40! cannot pull up responsive to a new call as long as the-allotter is hunting for an idle finder, because the relay 4&1 will be short circuited by ground on contacts engaged by wiper 459.

When the circuit of relay 4539 is broken by the deenergization of relay lfll, the said relay 499 will fall back and break the circuits of relays 4H) and H2. These relays accordingly fall back also.

In the finder switch, Fig. 1, when ground is removed from conductor 655 by the falling back of relay lil'I in the allotter, relay Hi6 falls back. At I53 relay M6 prepares a circuit for release magnet I43. and at I5? ground from the off normal springs of the finder is extended to guard wire e55, thereby maintaining the finder in busy condition with respect to the allotter in Fig. 4.

The equipment is now ready for the calling subscriber at station Q3I2 to dial the number of the called station, but before proceeding with this operation, the explanation of the allotter and finder circuits will be. completed.

Referring to the allotter A, Fig. 4, it will be seen that relay 406 is normally energized over common conductor 45!. This conductor is common to all of the link circuits and has a branch at each link circuit which is normally grounded. Thus in the case of the link shown in the drawings, the branch of conductor Mil for that link circuit may betrased by way of off normal spring E50, key K, and spring I58 of relay M5, to conductor i1 2. Conductor I14 in turn may be traced by way of N2, Fig. 2, 249, 2M, and 291 to ground. Due to the fact that the connection between conductors I14 and Mil includes the serially related contacts of relay I46 and the on normal contact 169 (also contacts of busy key K), it will be appreciated that whenever the link circuit is in use the connection between these conductors will be broken and the conductor Mil will no longer be grounded at the link circuit shown. If there are other idle link circuits in group A, however, conductor 46! will still remain grounded.

It will be assumed now that all of the links except one are busy, and that the remaining idle link circuit is the one shown in the drawings. The allotter A will have its wipers associated with this link circuit, due to the fact that the guard wires such as 455 of all the other link circuits will be grounded. If a call comes in now from one of the lines in group A, relay 406 will operate over conductor 413 as previously explained, followed by the energization of relay 401. The finder, Fig. l, is operated to connect with the calling line in the manner described,

. and at the beginning of the operation the last stead of dill.

ground is removed from conductor 46! by the energization of start relay M6. Relay 406 in the allotter does not fall back, however, because it is held up temporarily at contact 435 of relay 301. As soon as the finder completes its operation, ground is placed on guard wire 555 as previously explained, and the stepping magnet 455 is energized to break the circuit of relay 491. This relay then falls back as in the case previously described, but now it breaks the circuit of relay @136, since conductor 4M is no longer grounded. Relay 406 thereupon falls back and at 421 breaks the automatic hunting circuit of the allotter stepping magnet 465. Since all the link circuits are now busy all of the guard wires 455 will be grounded and unless the circuit of 665 were opened the allotter would continue to hunt indefinitely. In addition to the foregoing relay 4B6 transfers the starting circuits, as will now be explained.

Assuming now that another line in group A makes a call, a circuit will be completed over the main start conductor M3 by way of 4238 (relay iill deenergized) 513, 529, 525, and relay 505 of the allotter B, Fig. 5. Relay accordingly pulls up and controls the allotter B through the medium of relay 591 to start up an idle finder in group B. The finders in group B are just like the group A finder which is shown in Fig. 1, and the allotter B is like the allotter A, so that the ensuing operation need not further be described. It should be noted, however, that relay 505 of allotter B closes a circuit for relay 402 in- By the energization of relay 402 the common start leads of group A lines are connected to the vertical banks of the group B finders. This is obviously essential because the calling line is starting a finder of group B rather than a finder of group A.

The handling of a call from a line in group B will now be explained briefly. When the receiver is removed from a line in group B, groundis placed on one of the common start leads B shown at the left of Fig. 5 thereby closing a circuit over the associated resistance and main start wire 513, to relay 594 of the allotter B.

Relay 504 controls the allotter B through the medium of relay 581 in order to start up an idle finder switch of group B. It will be observed that relay 5% also closes a circuit for relay 562, by means of which the common start leads of group B are connected up in the vertical banks of the group B finders.

Assuming now that all of the finders of group B become busy, ground will be removed from the common conductor 56L which corresponds to conductor 585 of Fig. 4, and as the last finder completes its operation, relay 561 of the allotter will fall back and permit the release of relay 5%. Upon relay 5% deenergizing, the main start wire M3 is transferred by way of 528, 51!, 429, and 42! to relay 405 of allotter A. Accordingly, another call coming in from a line in group B will cause the energization of relay 405 of allotter A, which will start up a finder switch in group A. Relay 05 closes a circuit for relay 551, which connects the common start leads of group B into the vertical banks of the finders of group A.

Attention is directed to the fact that whenever a line in group B makes a call, the finder which is started up to connect with the calling line must undergo a wiper switching operation, since the finder wipers which are normally connected are those which serve the lines of group A. This wiper switching operation is performed by a relay such as relay 145, Fig. 1. Assume, for instance, that a calling line of group B starts up a finder in group A by means of relay 405 of the allotter, Fig. 4. When relay Q95 energizes it grounds wiper 452 at 423, thereby closing a circuit over conductor 51 of the finder in use to relay I40 of such finder. In a similar manner when a line in group B makes a call and starts a finder in group B by means of relay 5534 of the allotter B. relay 5% will connect ground at its contact 523 to the conductor 551 of the finder in use, and will energize the relay of such finder which corresponds to relay 15G of the finder shown in Fig. 1.

In case all of the links of both groups A and B are in use, a circuit is completed for placing a busy tone on all the subscribers lines so that any subscriber upon removing the receiver will hear the busy signal. When all the links are in use relays M36 and 5% will both be deenergized. If another call comes in now from group A a circuit will be completed over conductor M3 by Way of 622, 513, 529, and 512, to relay 403. This relay accordingly energizes and applies a busy tone to all the subscribers lines which are not engaged in conversation. Of course, any line which is actually involved in a connection will have its relay such as 101 energized so that the associated line will be clear. A similar circuit to the foregoing may be graced by way of the main start wire 513 to relay 403 and is eifective in a similar manner if a call should be made from a line in group B.

It will be recalled now that when the operation of the allotter A was being described it was explained that relay 4! i tried to operate at the initiation of the vertical movement of the finder and also at the initiation of the rotary movement, but was prevented from so doing because of the special construction of the contacts engaged by springs 43B and M9, which introduce a delay in the response of relay 4H. In the ordinary operation of the system relay ill never operates because its first circuit is opened at MS upon the completion of the vertical movement of the finder, and its second circuit is opened at 449 by the falling back of relay M2 upon the completion of the rotary movement of the finder. In the event that something should go wrong, however, which will prevent the starting of a finder, or the completion of its vertical or rotary movement, relay til will energize. When relay 4H operates it disconnects at 541 the common ground conductor dfil from relay 5B5, opens the impulsing circuit at M3, at 4% locks the relay 4% to the branch conductor 5% of the common ground conductor 555i associated with the allotter B, and at 445 also closes an alarm circuit to call the attention of the attendant to the fact that trouble has occurred. Also at 555 relay ill closes a circuit for stepping magnet $85, which energizes and breaks the circuit of relay 4M. Relay 451 falls back and alters the stepping circuit of magnet 465 to include its interrupter contact, so that the magnet deenergizes and advances the allotter one step. Relay till falling back also opens the circuit of relay 556. After 451 falls back relay M19 remains held up by 515 and 55!, as stated. In this manner the allotter A is held out of service, and at the same time by the deenergization of relay 5% the main start wire 5 l 3 is transferred to allotter B, so that calls from group A may be handled by finders of group B. If the group B finders should all become busy, then ground is removed from conductors 55! and 515 with the result that relays M?! and 5| l are deenergized and subsequent calls will try to get through by way of allotter A. In the meantime the trouble will no doubt have been fixed. At any rate, the next call will get a different finder due to the fact that the allotter has been advanced.

The key K, Fig. 1, is a link busy key provided for the purpose of rendering the associated link circuit busy. When this key is operated it disconnects conductor l'M from the common ground conductor lfil, and at the same time it connects conductor H 5 to the guard wire 455 so as to make the associated link circuit test busy in the bank of the allotter.

Key K2, Fig. 4, is a busy key for the allotter A. When this key is operated it opens the branch 515 of conductor 5 so as to drop back relay and if energized, and it disconnects the common ground conductor 45! from relay 455 so as to release this relay and transfer the main start wire ll-i to allotter B. The allotter B, Fig. 5, is provided with a similar busy key K3.

Returning now to the point where the calling line was extended by means of the finder, Fig. 1, to the connector, Figs; 2 and 3, it was described how the line relay 2% was energized, followed by the energization of relay 256 for the purpose of placing ground on the holding conductor I12. An additional result of the energization of relay 255 is the energization of relay 258, the circuit extending from the grounded conductor H2 by way of 259 to relay 2%. Upon energizing, relay locks itself at 248, and at 246 completes a circuit which extends through the vertical off normal contacts 0N4 to relay 2l3. Upon energizing, relay 2&3 locks itself at 219, prepares a circuit 1 for relay 255 at 282, and at 233 closes a circuit for relay 262. Upon energizing, relay 2l2 prepares a circuit for the vertical magnet 2M at 218, and at 2'55 connects dial tone to the calling subscribers line. The latter operation gives the caliing party an audible signal which notifies him that he can begin to dial the desired station.

It will be assumed, however, that for some reason or other the calling subscriber fails to dial, and the operations which take place under this condition will be described. Fig. 2 of the drawings shows two cams 284 and 285. These cams are mounted on a constantly rotating shaft, and make about one revolution per minute. These cams and the associated contact springs are common to all the link circuits. When relay 2 l 3 of the connector pulls up responsive to the seizure of the link, it prepares a circuit for relay 205 at contact 282 as explained above, and if the subscriber fails to dial, cam 284 will presently close a circuit for relay 2&5, the circuit extending from ground by way of 0N5, contacts controlled by 231, 282, and upper winding of relay 255. Upon energizing, relay 205 locks itself at 237, and at 235 substitutes the ground which is associated with the springs of cam 285 for the ground which was formerly connected to the holding conductor I12 by relay 295. About one minute later, cam 285 Will operate its associated contact springs, thereby inserting a booster battery in the holding circuit including conductor H2. This operation raises the potential sufiicient to operate relay H26 in the subscribers line circuit. Upon energizing, relay Hi5 locks itself across the line at cont-acts I58 and HE disconnects the line conductor it. from the finder bank at I08, and disconnects the test conductor H15 from relay H3! at I59, at the same time placing ground on this test conductor to maintain the line busy. The opening of the line conductor lill causes the line relay 25 in the connector to fall back, followed by the deenergization of relays 206, 268, M3, M2, and 2%. Relay 265 on falling back removes ground from the holding conductor [12, which permits relay MI of the finder and relay l0! of the subscribers line circuit to fall back also. Relay l ll. upon deenergizing closes a circuit at I i-5 for the release magnet I43 of the finder. The operation of the release magnet restores the switch shaft to normal, and the circuit of the magnet is broken at off normal springs I when the shaft is completely restored.

It will be appreciated that the purpose of the arrangement described in the foregoing is to prevent the link from being tied up when it is not actually being used in setting up a connection. The apparatus functions as described not only if a calling subscriber should delay dialling but also if the receiver should be accidentally displaced from the hook, or if the line should be short circuited at any point. Any of these occurrences will cause the link circuit to be taken for use the same as on a regular call, but if no dialling occurs the link is very shortly freed and the line is locked out by means of the associated relay H t. It will be noted that the locked out condition depends on the maintaining of a bridge across the line, so that whenever the trouble becomes cleared the lock out relay will automatically be released and the line circuit will be restored to normal condition. 7

Attention is directed also to the fact that the lower winding of relay 235, Fig. 2, is connected to a conductor coming from the power panel where it is connected to the individual fuse alarm terminal for this particular link circuit. If the fuse which is individual to the link circuit should become broken or blown out battery will be placed on this conductor, resulting in the energization of relay 255 over its lower winding. If the link circuit is in use at the time, the connection or partial connection will be released as described in the foregoing and the calling line will be locked out, requiring the subscriber to replace his receiver before he can call again. In any event,

the link is made busy at 236, where ground is applied to the guard wire 455.

Returning again to the point where the calling line was extended to the connector, Figs. 2 and 3,. it will be assumed that dialling begins. The number of the called station, it will be remembered, is Still, and therefore the first digit to be dialled is the digit 3. It will be assumed, however, that by some mischance the calling subscriber dials- 13 digit i instead of the digit 3. This may happen by reason of faulty manipulation of the dial. A single impulse or interruption corresponding to the digit 8 may also be produced by an accidental momentary depression of the switchhook.

When the single interruption corresponding to the digit l occurs, the line relay 2% of the connector, falls back momentarily. Relay 206 is slow to release and remains operated during the momentar 1 interruption of its circuit. When relay 23 falls back it transmits an impulse over a circuit which extends from ground by way of 233, 2 3i, 2E3, 233, and 218 to the vertical magnet 2 M. Responsive to this impulse, the vertical magnet 25d operates and advances the shaft of the connector one step. When the shaft moves off normal, the various oif normal springs are shifted, including ON i, but relay 2H3 remains locked up by way of 2 53, 259, and 2'53. The movement of the switch shaft also brings the vertical wiper 323, Fig. 3, into engagement with the first contact in the vertical bank 323. Relay 332 is energized in parallel with the vertical magnet. Shortly after the vertical magnet has op erated, relay 332 falls back and closes a circuit for the connector release magnet 255, the circuit extending from ground by way of 236, 3I3, 258, wiper 323 and contact engaged thereby, and 0N2 (now shifted), to the release magnet 2E5. Responsive to the closure of the above circuit the release magnet energizes and restores the switch shaft to normal. It will be noted that when the release magnet 2 l 5 energizes it breaks its own operating circuit at 299. These springs do not-open, however, until the armature is nearly operated and do not prevent the effective operation of the release magnet, because only a momentary energization of the magnet is required to disengage the usual double-dog of the switch and lock it under the release link. This construction is well known and need not be further explained.

It will be seen from the foregoing that if the first digit dialled is the digit l, the only result is to operate and then immediately release the switch, thus absorbing or cancelling the digit.

It will be assumed now that the dialling of the called number proceeds in the proper manner, the first digit dialled being the digit 3. When the digit 3 dialled three momentary interruptions are produced in the circuit of the line relay 26d, and this relay accordingly falls back momentarily three times, transmitting three impulses over the previously traced circuit to vertical magnet 2M and relay 332 in parallel. Vertical magnet 2M operates three times and advances the switch shaft three steps. The vertical wiper 323 is thus positioned on the third contact in the vertical bank Relay 332 is slow acting and holds up during the series of impulses.

When the series of impulses is finished, ,relay 382 very shortly deenergizes and completes a circuit for wiper selecting relay 303. This circuit extends from ground by way of 246, 3l3, 258, 298, and wiper 329 and contact engaged thereby, to

relay 303. Upon energizing, relay 303 locks itself at 324, and at 348 closes a circuit for the release magnet H5. The release magnet circuit extends from ground by way of 246, 313, 258, 348, and ON 2 to the release magnet 2l5. Responsive to the closure of the foregoing circuit, release magnet 2l5 operates and disconnects wiper 329 at 299. Also at 299 the release magnet closes a circuit for on" normal relay 2| 0 which extends from ground by way of 233, 3l3, 258, 299, 345 (relay 333 being now energized), upper winding of relay 213, and winding of release magnet 2l5 to battery. Relay 2H) cannot operate over the above circuit just at this time because the winding of the relay is short circuited by ground on the operating circuit which was formerly traced to the release magnet by way of ON 2. However, an instant later the switch shaft will be restored due to the operation of the release magnet and the on. normal springs 0N2 will be shifted back to normal position, opening the operating circuit for the release magnet 2l5. This removes the short circuit from the upper winding of relay 2"] and this relay accordingly operates over the circuit traced. Upon energizing, relay 210 looks itself at 23!, and at 258 breaks the circuit which includes its upper winding and the release magnet 2l5, thus permitting the release magnet to deenergize. The energization of relay Zlfi opens the dial tone circuit at 257, and also alters some other circuits which will be explained later.

It will be seen as a result of dialling the first digit 3 of the called number the connector switch is operated to the third level and immediately released again. Moreover, the operation of the switch results in the energization of the wiper selecting relay 303, which remains locked up after the switch releases. The energization of relay 333 selects and connects up the set of wipers which comprises test wiper 33I and the two line wipers 334i and 335. This set of wipers has access to lines in the third hundred, one of which is the line of the called subscriber.

The calling subscriber may now dial the next digit of the called number, which is also the digit 3. Accordingly the line relay 204 falls back momentarily three times, and at 23 2 again delivers three impulses to the vertical magnet 2M and to the slow acting relay 382 in parallel. The vertical magnet 2| c advances the switch shaft three steps as before. Relay 332 energizes in parallel with the vertical magnet and holds up during the series of impulses. At the first step of the switch shaft the off normal springs are shifted, and the shifting of DNA opens the initial energizing circuit of relay 2| 3. The previously described locking circuit for relay 2! 3 is now open at 259, due to relay 2H) having energized, but relay 2I3 holds up for the time being over another locking circuit which extends from ground by way of 246, 3l3, and 279 to relay 2l3. At the end of the series of impulses the slow acting relay 332 falls back in due time. The deenergization of this relay does not now ground the vertical Wiper 323 nor close the circuit of the release magnet H5, because contact 258 of relay 219 is now open. However, the falling back of relay 392 does break the circuit of relay 2l3, permitting this relay to deenergize. Upon deenergizing, relay 213 breaks the circuit of relay 2! 2, which falls back also. The only result of the deenergization of relays M3 and M2, which needs to be noted at this time, is the transfer of the impulsing circuit at 238 of relay 212 from the vertical magnet 214 to the rotary magnet 343.

The calling subscriber may now dial the next digit of the called number, which is the digit 1. The line relay 204 therefore falls backs once momentarily and transmits an impulse to the rotary magnet 343 in parallel with the slow acting relay 302. The rotary magnet responds to this impulse and rotates the switch shaft and wipers one step, so that the various sets of wipers are brought into engagement with the first con tacts of the third levels of their respective banks. Relay 302 operates in parallel with the rotary magnet 343. Relay 2E2 being now deenergized, when relay 302 operates it closes a circuit for the slow acting relay 305, said circuit extending from ground by way of 246, M3, 205, and 211 to relay 305. Upon energizing, relay 305 closes a circuit for relay 306 which extends from ground by way of 246, 280, 261, winding of relay 306, and 310 to relay 305. Relay 300 cannot energize over this circuit because it is short circuited for the time being by the previously described circuit to ground for energizing relay 305.

Shortly after the operation of the rotary magnet is completed, relay 302 will fall back and break the circuit of relay 305. This operation also removes the short circuit from relay 300 and the latter relay energizes in series with relay 305; Upon energizing, relay 300 locks itself at 322 and also breaks the circuit of relay 305, which accordingly deenergizes. In addition to the foregoing, at 323 relay 300 transfers the impulsing circuit from the rotary magnet 343 of the connector to the stepping magnet 321 of the minor switch.

Summing up the operations which have taken place so far, as a result of the dialling of the first three digits, 3, 3, and l, a particular set of wipers in the connector has been selected and these wipers have been operated first by the vertical magnet 2M and then by the rotary magnet 343 and thereby brought into engagement with the terminals of the called line. The wiper set selected is the set comprising wipers 33 I, 334, and 335. By the operations referred to, this wiper set is now in engagement with the terminal set to which test conductor 353 and line conductors 354 and 355 of the called line are connected. Although the called line has been selected the line is not tested at this time, as the testing operation is deferred until after the operation of the minor switch has been completed.

The calling subscriber now dials the last digit of the called number, which is the digit 2. Accordingly, the line relay 204 will fall back twice momentarily and will transmit two impulses to stepping magnet 321 of the minor switch in parallel with the slow acting relay 302. Responsive to these impulses, stepping magnet 321 will advance the wipers 350, 35L and 352 of the minor switch two steps, so that each wiper engages the second contact in its associated bank. Relay 302 operates in parallel with the stepping magnet 321 and upon energizing closes a circuit for relay 305. Relay 305 accordingly energizes also. At the end of the series of impulses which operates the stepping magnet 321, slow acting relay 302 falls back and thereby connects test relay 209 to the test wiper 33 l. The test circuit may be traced from the test contact to which test conductor 353 of the called line is connected, by way of test wiper 531, contacts of relay 304 and 303, wiper 352 of the minor switch, 3M, 318, (relay 305 being still energized), winding of test relay 209, to battery. Relay 209 accordingly tests the called line for the presence or absence of ground potential on its associated test contacts.

Assuming that the called line is busy, there will be a ground potential on the test contact with which wiper 553i is in engagement and test relay 209 will energize. Shortly after this occurs, the slow acting relay 305 will fall back, as its circuit was broken by the deenergization of relay 302. When relay 303 deenergizes, a locking circuit is completed for the test relay 209 which extends from ground by way of 232, 253, and contacts controlled by 3E8, to relay 209. In energized position, relay 209 opens the impulsingcircuit at 253 and closes the busy signalling circuit at 250. The latter operation gives the calling subscriber an audible busy signal to notify him that the called line is busy.

On finding the called line busy, the calling subscriber will hang up his receiver. This results in the deenergization of line relay 204, followed by the deenergization of relays 200 and 208. The latter relay opens holding circuits for the various other relays in the connector that have been energized and relay 206 takes ground off the holding conductor I12. As a result of the ungrounding of conductor I12 relays l4! and I01 are deenergized. The switches are released by their respective release magnets in the well understood manner. The circuit of the release magnet of the connector may be traced from ground by way of 291, 244, 249, and N2 to the connector release magnet 215. In parallel with the release magnet 2 i is the release magnet 344 of the minor switch, the circuit of which extends from ground by way of 291, 244, 249, and the minor switch off normal springs MSON to release magnet 244. As soon as the connector is restored by the operation of release magnet 2l5, the off normal springs 0N2 are shifted to normal position and the circuit from ground at 291 is transferred to conductor I14 of the finder switch to operate the release magnet I43. i '1 Thus all of the equipment in the link circuit is restored to normal.

Returning now to the point where the busy test relay 209 was connected up by the deenergization of slow acting relay 302, at the end of the impulses which operated the minor switch, it will be assumed that the called line is idle. Under these circumstances there will be no ground on the test contact engaged by test wiper 33I and test relay 209 will not pull up. Shortly after relay 302 falls back the slow acting relay 305 will fall back, and now since the test relay 209 is not energized a circuit will be completed for the switching relay 2! I. This circuit extends from ground by way of 202, 256, 255,1ower winding of relay 21 I, 318,3l4, 352, contacts of relays 303 and 304, relay 303 being energized, test wiper 33l and contact engaged thereby, test conductor 353 and the winding of the cut-off relay of the called line to battery. The line circuit of the called line is not shown in the drawings but is similar to the line circuit which is shown in Fig. 1. On the closure of the above circuit the switching relay 2 of the connector and the cut-off relay of the called line operate in series, the operation of the latter relay serving to clear the called line in the usual manner.

When relay 2 energizes it looks itself at 212. Relay 2 also cuts in the upper winding of line relay 204 at 233, and at 26'! opens the circuit of relay 300. Since the minor switch has been advanced only two steps, relay 306 has no circuit through wiper 35l, and therefore it deenergizes. Relay 21 I also closes points in the talking circuit at 204 and 265, and at 210 closes a circuit for the pick-uprelay 30! in order to start the ringing operation. The latter circuit extends from ground by way of 298, 210, contacts controlled by 3| 2, 28!, and interrupter contacts of rotary magnet 343, to relay 30!. Relay 30! energizes and locks itself at 3l2.

The results of the energization of relay 305 are the closure of the ringing circuit at 301 and 300, and the closing of a circuit at 309 for transmitting ring back tone to the calling subscriber. The ringing circuit may be traced from ground by way of generator GEN, interrupter I, ringing conductor labeled FREQZ, wiper 350 of the minor switch, 32I, 308, 215, 235, 22L and contacts of relays 303 and 304 to line wiper 335. From this point the circuit extends out over conductor 355 of the called line and to ground or to the other side of the line, depending on how the ringer at the called station is connected. If the ringer is bridged across the line, the return path of the ringer current will be by way of the other line conductor 354, line wiper 334, contacts of relays 304 and 303, 220, 264, 274, 307, 320, and lower winding of ring cut-on" relay 2l3 to battery and ground.

When the called subscriber removes his receiver, relay 2|3 pulls up in the usual manner and locks itself at 219. Relay 2 is now energized so that this locking circuit can be established by way of ground, 246, 266, and 219. At 28I relay 2|3 breaks the circuit of relay 3M, and the latter relay falls back. Relay 213 also closes a circuit for relay H2 at 283. Upon energizing, relay 2I2 completes the talking circuit at 214 and 215. The talking circuit is shown in heavy lines and need not be traced in detail. Upon the closure of the talking circuit the back bridge relay 203 will pull up over the called line. Upon energizing relay 203 reverses the direction of current flow in the calling line at 23| and 232. This is a standard operation which is introduced in order to give supervision to an operator if the calling line is a trunk from an operators position. In the connection under discussion the. reversal of current has no particular function. The required connection having been established, the calling and called subscribers may converse as desired. When the conversation is finished, the subscribers will replace their receivers. The release of the connection is controlled by the hanging up of the receiver at the calling station, which causes line relay 204 to fall back. This breaks the circuit of relay 200 which falls back-and-breaksthe circuit of relay 203. The connection is accordingly released in the manner previously described.

In the foregoing explanation it was not specified if the called line was an individual line or a party line. The fact is that it could be either, as the. operation is the same. This means that individual and party lines may be arranged indiscriminately, and have similar four digit numbers assigned. In case of an individualline the last digit, of course, would preferably be assigned in accordance with the frequency ofringing current which is used to ring the individual lines, this being usually the No. 2 frequency. In case of party lines the last digit of the number determines the ringing current or party selection. There may be as many as ten stations on a party line. At five of the stations the ringers would be connected between one side of the line and ground, while at the other five stations the ringers would be connected between the other side of the line and ground. In accordance with this arrangement, the'circuit of relay 306 is arranged so that when the switchingrelay 2H pulls up relay 306 will dropback if wiper 35! of the minor switch is standing onany position from I to 5, inclusive. Thus the ringing current frequency selected by the wiper 350 is projected out over the lower side of the subscribers line. However, if wiper 3% has been positioned on any contact from 6 to 0, inclusive, relay 305 will hold up by way of said wiper 35l after the relay 2 has energized, with the result that the ringing circuit connections to the line are reversed at 320 and 32!, so that ringing current is projected out over the other side of the line.

The lines of the fourth and fifth hundreds are called in the same Way as the lines in the third hundred, except, of course, that a different set of wipers is selected at the connector in use. In selecting a line in the fourth hundred the first digit dialled is the digit 4 and it follows that the vertical wiper 329 will be set on the fourth contact in its bank when the first digit is dialled, resulting in the energization of relay 304 instead of relay 303. The operation of relay 304 connects up the set of wipers which comprises test wiper 336 and line wipe'rs 228 and 339. In calling a line in the fifth hundred, the first digit dialled will be the digit 5. Since the Verti-- cal wiper 329 is set on the fifth contact in its bank responsive to this digit, both relays 303 and 304 will be energized. By the operation of both these relays simultaneously the set of wipers which comprises test wiper 331 and line wipers 340 and 34! is connected up. Otherwise the operations are the same as the operations which have already been described. The lines in the second hundred are called by means of the normally connected set of wipers which comprises test wiper 330 and line Wipers 332 and 333. Since this set of wipers is normally connected, the calling of a line in the second hundred does not involve the operation of any relay such as 303 or 304, and consequently is somewhat difierent. This can conveniently be explained later in the course of the description of the establishment of a trunk connection, as the groups of trunk lines are assigned numbers in the second hundred and are accessible to the normally connected set of wipers.

Before taking up the establishment of trunk connections an additional feature of the regular exchange operation will be described. This feature is the handling of revertive calls on party lines. A revertive call is a call from one subscriber on a party line to another subscriber on the same line, and is made by dialling the regular directory number of the called subscriber. In order to explain the operations which take place in this type of call it Will be assumed that the subscriber at station 43.12, Fig. 1, desires to call the subscriber at station 4317 on the same line.

In order to establish the above connection, the subscriber at station 4312 will remove his receiver and dial the number of the called station. The removal of the receiver takes an idle link into use and the finder thereof connects with'the calling line. The subscriber then dials the four digits of the called number and the connector of the link is operated the same as has been previously described. Assuming that the link which is used is the one shown in the drawings, relay 304 of the connector, Figs. 2 and 3, will be operated so as to select the set of wipers comprising 336, 338, and 339, which are then positioned on the first set of contacts in the third level of their associated banks. This set of bank contacts is the set to which normal conductors I05, I03 and I04, extending back to the line circuit, Fig. l, are connected. It will be noted also that the minor Switch is operated responsive to the last digit to position its various wipers on the seventh contacts in their respective banks. Aside from these differences, theoperation of the connector is the same as it was before.

Taking up the detailed description atthis point, when relay 302 falls back at the end of the impulses for the last digit, a circuit is completed over which the test relay 209 is connected to the test wiper 336, which is now in engagement with the test contact of the called line. since the called line is also the calling line, there will be a ground potential on conductor I05 and the test relay 209 will pull up. Relay 209 remains locked up after relay 305 falls back and at 250 connects a busy tone to the calling line. So far, therefore, the operation corresponds to the normal operation in calling a busy line.

In this case, however, the calling subscriber expects to hear the busy signal, as he knows that he is calling another subscriber on his own line, so he merely replaces his receiver for a short interval, long enough to signal the called party. When the receiver is hung up at the calling station, the line relay 204 falls back and breaks the circuit of the slow acting relay 206. Line relay 204 also places ground on the test wiper 330 in order to provide a holding circuit for maintaining the connection after relay 206 falls back, this holding circuit extending from ground by way of 234, 222, 241, 253, (busy relay 200 being now energized), wiper 352, contacts of relays 303 and 304, test wiper 336, conductor I05, I00, Fig. 1, H3, H8, wiper I26, I41, and I52 to holding conductor I12. Ground on the holding conductor I12 will hold up relays MI and I01, Fig. 1. Also a branch may be traced from conductor I12 by way of 223, 243, and 248 to relay 200, which serves to hold up relay 208 after relay 206 has deenergized. When relay 206 falls back, it closes a circuit for relay 202 at 238, said circuit including the contacts 25I of the now Upon energizing, re-

energized busy relay 209.

Relay 202 also dislay 202 locks itself at 229. connects ground from line relay 204 at 225, and opens the trunk conductors I10 and HI at 226 and 221. Finally, at 230 relay 202 closes a circuit for relay 2II, which energizes and locks itself at 212. Relay 2II upon energizing breaks one circuit of relay 306 at 261, but relay 306 holds up over another circuit including wiper 35I of the minor switch, now setting on its seventh contact. Relay 2 also closes at 210a circuit for relay I, which locks itself at 3I2 and completes the ringing circuit in the manner formerly described. I i

The bell at the called station now begins to ring intermittently in the usual manner. After a short interval the calling subscriber will again remove his receiver, and the called subscriber will also take off his receiver in order to answer the call. A bridge is accordingly placed across the line which operates the ring cut-off relay 2 I3. Relay 2I3 locks itself at 216, breaks the circuit of relay 300 at 280, and breaks the circuit of relay 30I at 28I. Relays 306 and 30I accordingly fall back. Relay 2I3 also closes the circuit of relay 2I2, which accordingly energizes and closes the heavy talking conductors at 214 and 215. This latter operation connects up the back bridge relay203, which energizes over the line circuit through the connector wipers, feeding current for the transmitters at the calling and called stations. Upon energizing, relay 203 closes acircuit for relay 201 at 233. Relay 201 operates when its circuit is closed and locks itself at 24I. At 240 and 242 relay 201 supplies holding ground for various energized relays in the connector, thus providing against the deenergization of relay 200. For a similar reason relay 201 opens the release magnet circuits at 244, and at 286 places a shunt around contact 241 of relay 208. This latter is to maintain ground on the test wiper. The circuit of relay 200 is broken at 243 when relay 201 energizes and relay 208 therefore falls back, but the connection is not released owing to the continued energization of relay 20?. The maintaining of the connection therefore depends on the continued energization of back bridge relay 203, which controls relay 201.

The calling and called subscribers may now converse,'and when they get through they will both replace their receivers. This brings about the deenergization of back-bridge relay 203. Relay 203 falling back breaks the circuit of relay 201. When relay 201 deenergizes, the link circuit is released in the manner previously explained.

The operations involved in making certain representative trunk calls will now be explained. It will be assumed that the exchange being described is connected with a distant manual ex- 1' terminated in the first five sets of contacts in 1- the third level of the second hundred. These trunks are therefore accessible to the wiper set comprising test wiper 330 and, line wipers 332 and 333. -The first trunk of the group is indicated in the drawings, Fig. 3, and comprises conductors 350, I, and 352. Each trunk may have a. line circuit similar to the line circuit-shown in Fig. 1, and at the manual exchange may ter minate in a jack and drop, or similar well known ring down signalling equipment. From the location of the trunks in the connector banks as explained, the line selecting digits assigned will be 2, 3 andl. Adding the digit 1 to operate the minor switch, the complete number of the trunk group will be 2311.

Assuming that the subscriber at station I3I2 desires to extend a call to the manual exchange, he removes the receiver, whereupon an idle link circuit is taken into use in the manner previously explained. Assuming that the link shown inthe drawings is the one which handles the call, the finder, Fig. 1, will connect with the calling line and extend it to the connector, Figs. 2 and 3. The line relay 204 will therefore energize, followed by the energization of relays 206, 200, 2I3, and '2I2, all as previously explained.

The calling subscriber will now start to dial, the first signal dialled being the digit 2. Line relay 204 therefore falls back twice momentarily and sendstwo impulses to the vertical magnet 2I4 and to the slow acting relay 302 in parallel therewith. Responsive to these impulses, the vertical magnet advances the switch shaft two steps, thereby bringing the vertical wiper 320 into engagement with the second contact in its bank. The slow acting, relay 302 holds up during the impulses and falls back after the impulses cease. Upon deenergizing, relay 302 closes a circuit for relay 2II by way of 246, 3I3, 258, 290,

wiper .320-and contact engaged thereby, and

'- followed by the deenergization of relay 2 I2.

upper winding of relay 2| l to'battery. Upon en'- ergizing, relay 2H locks itself at 212. In addition, relay 2H closes a circuit for the release magnet 2I5, this circuit extending from ground by Way of 246, M3, 258, 213, and off normal contact N2, to the release magnet 2|5. Upon energizing, the release magnet 215 restores the switch shaft in the usual manner. Also the release magnet closes a circuit for operating relay 210, which extends from ground by way of 246, 3l3, 258, 299, 21!, upper winding of 2H), and release magnet 2|5 to battery. Relay 2l0 operates in the above circuit as soon as the off normal springs 0N2 shift back on the restoration of the shaft and locks itself at 26!. Relay 2l0 also breaks the locking circuit of relay 2| I at 260, and breaks the circuit including its own upper wind ing and the release magnet at 258. Accordingly relay 2 and release magnet 2l5 deenergize.

It will be seen that as a result of the dialling of the digit 2 the connector switch has been operated and released and that the ofi normal relay 210 has been energized and locked up. It will be appreciated that this has been accomplished without energizing either of the wiper selecting relays 303 and 304. The connector therefore now has access to all lines in the second hundred, which are reached by way of the normally connected set of wipers.

The calling subscriber maynow dial the next digit 3. As a result, the switch shaft is advanced three steps by means of the vertical magnet 2M. At the end of this operation, relay M3 is deenergized in the manner previously explained, Thus the impulsing circuit istransferred to the rotary magnet 303.

The calling subscriber may now dial the next digit 1, as a result of which the rotary magnet 343 is operated to rotate the switch shaft one step, bringing the wipers 330, 332, and 333 into engagement with the first set of contacts in the third level of their respective banks. Relay 302 of course is operated in parallel with the rotary magnet 343 and operates relay 305, which in turn brings about the energization of relay 306 in the manner previously explained. Relay 300 transfers the impulsing circuit to the stepping magnet 32'! of the minor switch.

The calling subscriber may now dial the last digit of the number, which is also the digit 1. From this point on somewhat different operations are involved, and the explanation will be given more in detail. Responsive to the dialling of the digit 1, relay 204 falls back once and sends one impulse to the stepping magnet 32'! and slow acting relay 302 in parallel, the stepping magnet 32! operating to advance the wipers of the minor switch one step. Relay 302 operates and closes a circuit for relay 305, which operates also. After the impulse ceases, relay 302 falls back and closes the usual test circuit, which in this case extends from the test wiper 330 by way of normally closed contacts of relays 304 and 303, wiper 352 of the 7 minor switch, 3M and 348, to test relay 209. As-

suming now that the first trunk line is busy, conductor 350 will be grounded, test wiper 330 will encounter ground potential, and the busy relay 209 will energize. Upon energizing, relay 209 closes a circuit for relay 3!", which will now operate as a stepping relay for the rotary magnet 343. The circuit of relay 30I extends'from ground by way of 349, 341, rotary control bank 26, the first pin in the third level, now engaged by wiper 326, wiper 320, 3H, 254, contacts controlledby3l2',

28 I, interrupter contact of rotary magnet 343, and winding of relay 30 to battery. Upon the closure 'of the above circuit by the busy relay, relay 30! operates and closes a circuit for the rotary magnet 343 at 3. Relay 30! also closes a circuit for slow-acting relay 305 at 3 I 0, thus maintaining this relay energized in order to maintain the busy relay 209 connected to the test wiper. On the closure of its circuit by relay 30l, the rotary magnet 343 operates'and rotates the connector wipers one step, at the same time opening the circuit'of relay 30L Relay 30I accordingly falls back and breaks the circuit of the rotary magnet. If the second trunk of the group is busy also the busy relay 209 will remain energized and the operation will continue, relay 3!]! and the rotary magnet 343 operating alternately, the latter rotating the wipers step by step in search of an idle trunk line.

When an idle trunk line is found, relay 209 will fall back due to the absence of ground on the test contact'engaged by wiper 330 and the circuit of relay 30l will be broken. This relay therefore cannot again energize and the rotation will cease. Slow-acting relay 305 falls back, as it will receive no more impulses from relay 30l, and the usual circuit is therefore completed for relay 2| I. Relay 2 now pulls up in series with the cut-off relay of the selected trunk line. The remaining operations, including the transmission of ringing current over the trunk line, are the same as have been previously explained.

Some additional explanation will now be made in respect of the rotary control bank. This bank and the associated wiper 326 have been neglected so far because in any connection involving the operation of either relay 303 or relay 304 the ground connection to the rotary control bank is broken and the wiper 326 consequently can have no function. The rotary control bank therefore is in use only when a line in the second hundred is being called, or when the normally connectedset of wipers is being used. The circuit drawings, Fig. 3, shows only the third level ofthis bank, as this is the level in which the group of trunks to the manual exchange is terminated. There being five trunks in this group, terminated in contacts I to of the third level, as stated, there will be four pins inserted at positions I to 4, inclusive, of the third level of the rotary control bank, as indicated in the drawings. Wiper 320 therefore can maintain the circuit to the stepping relay 3M through successive pins as long as busy trunk lines are encountered and the busy relay 209 is held up. The

fifth pin, corresponding to the last trunk line of the group, is omitted, so that when the wipers are advanced to the fifth set of contacts wipers 320 will find no pin to engage and the circuit of relay 30| will be broken, whether the fifth trunk line is busy or not. If the fifth trunk line is busy, relay 209 will hold up and will lock itself when relay 305 falls back, and the busy signal will be transmitted to the calling party in the usual manner.

In addition to the ring down trunks extending to the manual exchange, there may be various other groups of trunk lines, including a group of dial trunks extending to an automatic exchange. The operations involved in setting up a connection to an automatic exchange will therefore be described. It will be assumed that there is a group of five one way dialling trunks terminating in the first five contact sets of the ninth level of the banks of the second hundred.

That is, these trunks terminate in the ninth level of the banks which are associated with the normally connected set of wipers comprising wipers 330, 332, and 333. These trunk lines differ from the ring down trunks in that they do not have line circuits such as is shown in Fig. l, but the three trunk conductors of each trunk line extend directly from the connector banks to a standard two-wire repeater. There will be accordingly five repeaters associated with the five trunk lines, respectively, and from the outgoing side of each repeater there will be a two conductor trunk line extending to the automatic exchange. At the automatic exchange these trunk lines may terminate in line switches or incoming selectors. Since the group of trunk lines terminates in the ninth level of the connector banks, and occupies the first five contact sets in that level, the number assigned to the group is the number 91.

Assuming now that the subscriber at station 4312 desires to extend a call to the distant automatic exchange, he will remove his receiver, whereupon an idle link circuit is taken for use. Assuming that the link circuit shown in the drawings is the one which is taken for use, the finder, Fig. 1, will connect with the calling line and extend it to the connector, Figs. 2 and 3. The connector line relay 204 and other relays will pull up responsive to the call in the manner previously described.

The calling subscriber will now dial the first digit of the number, which is the digit 9. The line relay 204 accordingly falls back momentarily nine times and sends nine impulses to the vertical magnet 214 and the slow acting relay 302 in parallel. The vertical magnet 214 steps the connector shaft nine steps, advancing the various sets of wipers carried by the shaft until they stand opposite the ninth levels of their respective banks. The vertical wiper 329 is positioned in engagement with the ninth contact in the vertical bank 328. Also the shaft springs 354 and 355 are operated, the comb 41, Fig. 7, being arranged to close these springs on the ninth level. The slow acting relay 302 responds to the first series of impulses in parallel with the vertical magnet 214 and holds up throughout the series of impulses, falling back after the impulses cease. On deenergizing, relay 302 closes a circuit for the off normal relay 210 which may be traced from ground by way of 246, 313, 258, 299, vertical wiper 329 and the ninth contact engaged thereby, and

thence through the lower winding of relay 210 to battery. Upon energizing, relay 210 locks itself at 261. In addition relay 210 performs its usual functions. It also unlocks relay 213 at 259. Relay 213 accordingly falls back and permits relay 212 to deenergize. Relay 212 transfers the impulsing circuit from the vertical magnet 214 to the rotary magnet 343.

The calling subscriber may now dial the second digit of the number, which is the digit 1. Accordingly the line relay 204 falls back once momentarily and transmits an impulse to the rotary magnet 343 in parallel with the slow-acting relay 302. The rotary magnet 343 responds by rotating the switch shaft one step, bringing the wipers 330, 332, and 333 into engagement with the first trunk line of the group. Relay 302 operates in parallel with the rotary magnet 343, and now since relay 2 I 2 has fallen back a circuit is completed for slow acting relay 305, which operates also. Upon energizing, relay 305 closes at 319 a circuit for the lower winding of switching relay 201, the circuit extending from ground by way of 349, 341, 355, 319, and the lower winding of relay 201 to battery. The lower winding of relay 201 is an inefficient winding and consequently the relay operates only far enough to close its contact marked X. The closure of contact X completes a circuit for the upper winding of relay 201 which extends from ground by way of 2152, 256, contact X, and the upper and lower windings of relay 201 in series to battery. It will be seen that the upper winding of relay 201 is short circuited over the previously traced circuit for the lower winding and consequently the relay remains only partly energized for the time being.

Shortly after the cessation of the impulse to the rotary magnet 343, the slow acting relay 302 will fall back, and thereby a circuit is closed for connecting the busy relay 209 to the test wiper 330. This circuit may be traced from test wiper 330 by way of normally closed contacts of relays 304 and 303 to the minor switch bank associated with wiper 352. From this point the circuit is completed by way of 356, 346, 354, 314, and 318 to the busy relay 209. If the first trunk line of the group is busy, relay 209 will energize because of the ground on the contact engaged by wiper 330, closing a circuit for relay 301. In explanation of this circuit it should be stated that the ninth level of the rotary control bank 26 is arranged as regards the first five positions in exactly the same way that the third level, shown in the drawings, Fig. 3, is arranged. That is, pins are inserted at positions 1 to 4, inclusive, of the ninth level. Accordingly, wiper 326 will now be in engagement with the first pin of this group and the circuit for relay 301 will extend from ground by way of 349, 341, rotary control bank 29, first pin of the ninth level, wiper 326, 311, 254, contacts controlled by 312, 291, and interrupter contacts of the rotary magnet 343 to relay 301.

Relay 301 operates as formerly described, closing a circuit for the rotary magnet at 3| I, and also closing a circuit for the slow acting relay 305 at 310. The switch wipers are accordingly rotated step by step until an idle trunk line is found, whereupon busy relay 209 will fall back, breaking the circuit of relay 301 at 254, and the rotation of the switch will cease. Relay 305 now falls back also, since it no longer receives impulses from relay 30I. Upon deenergizing, relay 305 breaks the circuit of the lower winding of relay 201 at 319, thus removing the short circuit from the upper winding of relay 201. During the rotary operation, the ground connection to the upper Winding of relay 201 through contact X was temporarily disconnected by energization of relay 209, but this connection has now been re-established by the falling back of relay 209, and accordingly relay 201 now energizes fully over the circuit which extends from ground by way of 262, 256, contact X, and both windings of the relay in series to battery. Upon energizing relay 201 looks itself to the holding conductor 112. Relay 201 also opens the release magnet circuit at 291, opens the impulsing circuit at 222, and at 223 it disconnects the holding conductor 1'12 from the slow acting relay 208 and connects it instead to the test wiper 330. In addition, relay 201 connects the trunk conductors 1'10 and 111 direct to the wipers 332 and 333, respectively, at contacts 220 and 221, at the same time disconnecting these trunk conductors from the line relay 204. Relay 204 a cordingly falls back and breaks the circuit of relay .206.

The two trunk conductors I10 and Ill and the holding conductor "2 now extend via the connector wipersto three conductors of the selected trunk. It follows that before the relay 206 of the connector can fall back, the line and release relays'of the repeater associated with the selected trunk will energize, and the latter relay will place ground on the holding conductor to maintain the connection.

The calling subscriber will now dial the necessary remaining digits to complete the connection in the automatic exchange and these digits are repeated by the repeater in the well known mariner. Release of the connection is accomplished by hanging up the receiver at the calling station, which drops the line and release relays of the repeater. The release relay falling' back removes ground from the holding circuit including conductor I12 and the link circuit is restored as previously described.

From the preceding explanationit will be clear that another group of ring down trunks could be terminated in the sixth, 7th, 8th, orlOth level and could be reached by dialling a three digit number. Such a group of trunks might be a group of toll trunks leading to the toll board in an adjacent exchange. Assuming these trunks are terminated in the 10th level (of the second hundred), the number assigned would be 011. In calling the toll operator over one of these trunks, the first digit 0 will operate the connector shaft to the 10th level and at the same time will operate relay 2H1 by means of wiper 329. The second digit 1 will rotate the connector shaft one step, whereby wipers 33B, 332, and 333 are set on the first trunk line of the group. The third digit 1 will operate the minor switch, whereupon automatic trunk hunting will take place and an idle'trunk will be selected. The hunting movement is controlled through the rotary control bank, which has pins inserted at the 10th level, as explained in the case of the 3rd and 9th levels.

The invention having been described, that which is considered tobe new and for which the protection of Letters Patent is desired will be pointed out in the appended claims.

What is claimed is:

1. In an automatic exchange switchboard, a frame comprising four upright members secured in spaced relation to each other, thereby forming a central mounting space for switches and a mounting space for banks on each side thereof, a series of base plates secured one above the other in said central space, each plate having mounted thereon a finder and a connector, means for mounting finder banks in the space on one side of said central space, and means for mounting connector banks on the other side.

2. In an automatic exchange switchboard, a frame comprising four spaced upright members, a link comprising a finder switch and a connector switch, a base secured to the two inner upright members and supporting said finder at one end and said connector at the other, and banks supported between the respective switches and adjacent outer upright members of the frame.

3. In an automatic exchange switchboard, a plurality of links each comprising a finder switch and a connector switch, a base for each link on which the two switches thereof are mounted together to form a unit and a frame on which said units are mounted one above the other in horizontal position.

4:. In an automatic exchange switchboard, a link comprising a finder switch and a connector switch, each having a wiper shaft, a base plate, means securing the finder switch to said base plate at one end thereof with the shaft extending beyond the end of the base plate, means for similarly securing the connector switch to the said base plate at the other end, and relays for controlling said switches mounted on said base plate between the switches.

5. In an article of manufacture, a switching unit comprising a base plate, a finder switch mounted on one end of said plate, a connector switch mounted on the other end, said finder and connector each having a wiper shaft, relays mounted on said plate between the switches for controlling the same, and means including certain of said relays for directly connecting the wipers of the finder with the wipers of the connector.

6. A large capacity switch and mounting therefor comprising a base on which the frame of the switch is secured, a frame including two upright members to which said base is secured, said frame including a third upright member, bank rods extending between said third upright and the switch frame, banks supported on said rods, and a bearing for the switch shaft also supported on said rods.

7. A large capacity switch comprising a plurality of sets of banks and wipers, also a vertical bank for controlling wiper selection, a metallic strip secured to two of said banks, means for mounting said vertical bank on said strip, terminal blocks also mounted on said strip, and wires connecting the wipers of the switch with said terminal blocks.

HARRY P. MAHONEY.

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