US2285985A

US2285985A - Step-by-step operated crossbar switch

Info

Publication number: US2285985A
Application number: US372080A
Authority: US
Inventors: Gerald V King
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1940-12-28
Filing date: 1940-12-28
Publication date: 1942-06-09
Anticipated expiration: 1959-06-09

Description

060i bll I \UUI H O Q 2 a 2 H 5 9 8 5 1942- G. v. KING 2,285,985

STEP-BY-STEP OPERATED CROSS-BAR SWITCH Filed Dec. 28, 1940 7 Sheets-Sheet l FIG. /0

[516.5 FIG. 5

FIG. 9

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June 9, 1942. v KlNG 2,285,985

STEP-BY'STEP OPERATED CROSS-BAR SWITCH Filed Dec. 28, 1940 7 Sheets-Sheet 2 INVENTDR G. I! KING TTORNE) June 9, 1942. v K 2,285,985

STEP-BY-STEP OPERATED CROSS-BAR SWITCH Filed Dec. 28, 1940 7 Sheets-Sheet I5 wvavron G. L KING ATTORNE) DBBTCH HO( JLIJ ILLLI Huh I,

June 9, 1942. v KlNG STEP-BY-STEP OPERATED CROSS-BAR swrrcu Filed Dec. 28, 1940 7 Sheets-Sheet 4 wvE/vmR By G. I! KIA (G ATmRNEV oearCn H0 119, ltLtrHuw 1 18 June 9, 1942. v, Kme

smEP-BY-sTEP OPERATED CROSS-BAR SWITCH Filed Dec. 28, 1940 7 Sheets-Sheet 5 wvvE/vmR G. l. KING- ATTORNEY QUUlbll |\U\ June 9, 1942. G. v. KING 2,285,985

sTw-BY-sTEP OPERATED CROSS-BAR SWITCH Filed Dec. 28. 1940 7 Sheets-Sheet 6 I H -EH H INVENTOR G. V KING .a' Q ATmRNEV VII Ilul June 9, 1942. a. v. KING STEP-BY$TEP OPERATED CROSS-BAR SWITCH Filed Dec. 28, 1940 7 Sheets-Sheet 7 ATTORNEY INVENTOR G. l! KING Patented June 9, 1942 Search Hoom STEP-BY-STEP OPERATED CROSSBAR WITC Gerald V. King, Chatham, N. J., asslgnor to Bell Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application December 28, 1940, Serial No. 372,080

7 Claims.

This invention relates to selective switches and particularly to switching devices useful in telephone systems of a type through w c an in- -coming line may be extended to an idle outgoing line of any one of a number of groups of such lines by directive and automatic action.

The object of the invention i to adapt the now well-known cross-bar type of switch to stepby-step operation. Applicant is aware that this object in general has been achieved by others but he has devised a new arrangement which has many economical and operating advantages whereby the present invention embodies a step forward in the art.

Broadly stated the present invention resides in the use of cross-bar switches of large sets of permanently paired contacts coordinately arranged accommodating incoming lines, links and outgoing lines whereby a plurality of paths are coincidentally established by the action of a pair of contact sets, one in the field of incoming lines and links and the other in the field of links and outgoing lines. Such a connection is established by control over an incoming line by directive selection of a group of outgoing lines and then an automatic selection of an idle line in the selected group. Since connections are now made to a plurality of outgoing lines including the selected one automatic means are employed to establish a connection from the incoming line to that one of the coincidentally established connections which leads to the selected outgoing line.

A feature of the invention is a means for automatically extending a connection from an incoming line to one of a plurality of coincidentally established connections through the contact sets of a cross-bar switch at a point before any of the switching points in the said switch.

Another feature, alternative to that set forth above, is a means for automatically extending a connection from an incoming line to one of a plurality of coincidentally established connections through the contact sets of a cross-bar switch at a point within the link circuit used as a path between the incoming line and the selected outgoing line.

Another feature of the invention is a multiple connection pattern for the outgoing line whereby each outgoing line appears in a plurality of contact sets in each of which appear a plurality of outgoing lines, no one outgoing line appearing more than once in a contact set.

The drawings consist of seven sheets of circuit diagram which may be arranged as indicated in Figs. 8, 9 and 10 to show three embodiments of the invention. Fig. 8 uses Figs. 1 and 2 and shows a single ten by ten six-wire cross-bar switch used as a selector and operated in a step-by-step manner. Fig. 9 uses Figs. 1, 3 and 4 and shows two ten by ten six-wire cross-bar switches arranged as a selector and operated in a step-bystep manner. Fig. 10 uses Figs. 5, 6 and 7 and shows the use of one ten by ten three-wire crossbar switch and one ten by ten six-wire crossbar switch arranged to operate as a selector in a step-by-step manner.

For a complete understanding of the mechanism of the cross-bar switch reference may be had to the following patents: 1,953,503, J. N. Reynolds, Apr. 3, 1934; 2,021,329, J. N. Reynolds, Nov. 19, 1935, and 2,040,334, J. N. Reynolds, May 12, 1936.

With Figs. 1 and 2 arranged as indicated in Fig. 8, a call will be traced from a calling substation to an idle trunk in a selected group. The substation I00 terminates at the central oflice in the usual line and cut-off relay combination and the terminals of a finder switch. The tip and ring conductors are connected to the windings of line relay IOI so that when the subscriber removes his receiver from its hook the relay IN is operated and the start circuit conductor I02 is grounded. This causes the brushes of the line finder I03, I04 and I05 to hunt for the calling line. The calling line will be characterized by a battery connection through the winding of cutoff relay I06 to the sleeve terminal I01. When the line has been found, the sleeve is grounded and the relay I06 is operated, whereby the relay IN is disconnected from the line. A slow releasing relay I00 is associated with the start circuit and temporarily places ground on the sleeve conductor I09. This ground is removed a short interval after the brushes I03 to I05 have made connection to the calling line. Thi action is standard line finder practice and it is explained fully in Patent 1,799,654, granted to R. L. Stokely April 7, 1931.

Thus, in the process of extending the line of substation I00 to the tip, ring and sleeve conductors leading to the selector switch forming the main part of the circuit diagram of Figs. 1 and 2, a ground is connected to conductor I09. Conductor I09 extends through the armature and back contact of relay I I0 and thence through armature I and back contact of relay III from which the circuit extends to the winding of start relay NZ to battery. Through the connection of ground to conductor I09 relay H2 is operated. If no other relay in the chain between relay H2 and relay H3 is operated, then relay H2 locks in a circuit through its front contact and armature 6 and thence through back contacts and similar armatures of the other relays in this series, including the back contact and armature 6 of relay H3, the back contact and armature 3 of relay I I4 to ground. Through the operation of relay H2, battery and ground through the dial tone transformer I I5 is connected through the windings of relay H6, the armatures I and 2 and their back contact of relay II4, armatures 2 and 3 and their front contacts of relay H2 to the tip and ring conductors leading to the calling subscribers line. The calling subscriber is thus given dial tone which indicates to him that the circuit is ready for the receipt of dialing impulses.

During this operation relay H is operated in a circuit from battery, the winding 01 relay H0, front contact and armature I of relay H2, back contact and armature I of relay H3, winding of relay II'I to ground. Relay H0 operates in this circuit and connects the sleeve conductor I09 through the armature and front contact of relay H0 and thus shunts relay Ill until the ground temporarily connected to this conductor is removed by relay I08. Thereafter the relay H0 is held in series with the winding of relay H'I. Through armature 4 of relay H2 ground is extended to the winding of relay III which now becomes operated. Relay III has one armature for each incoming circuit to the switch shown in Fig. 2 and, therefore, not only grounds the lead to the back contact of relay IIO but the leads to each of the corresponding back contacts of corresponding relays whereby ground is connected to the sleeves of all of these relays to render them temporarily busy during the ensuing dialing period.

Through armature of the start relay H2 a ground connection is extended to the selector magnet 200 to prepare the contact sets I, 202 and 203 for operation. These contact sets represent ten such contact sets which are associated with the line terminating in line finder brushes I03, I04 and I05.

Through the connection of relay H6 to the calling line a slow releasing relay H0 is operated and at this point the circuit is completely ready for the receipt of dial pulses. Let it be assumed that the digit now dialed is 9. The armature of relay IIB will, therefore, vibrate between its front and back contacts and make nine trips to the back contact, each of short duration, corresponding to nine interruptions of the subscriber's line from the substation I00. Upon each connection established between the armature and back contact of relay H6 an impulse will be sent from ground through the armature and back contact of relay H6, the left-hand armature and front contact of relay IIB, the winding of relay H9 and the winding of stepping magnet I20 to battery. Relay II9 will operate upon the first of these impulses and will remain operated steadily throughout this train of impulses and for a short time thereafter due to its slow releasing characteristics. Each of those impulses will operate the stepping magnet I20 to rotate the brush I2I which, in accordance with our assumption, will now come to rest on its ninth contact. After this series of impulses, when relay H9 returns to normal, a circuit will be established from ground, right-hand armature and front contact of relay H8, back contact and armature of relay |I9, brush I2I and its ninth contact, conductor I22 to the winding of relay I23. Relay I23, in operating, closes a circuit from ground through the winding of select magnet 204 which now prepares the contact sets 205, 206 and 201 for operation.

Before proceeding with the description of the circuit changes which take place, a brief explanation of the arrangement of this cross-bar switch will be given. This switch is known as a ten by ten six-wire switch. There are one hundred cross-point contact sets, such as 20I, 202 and 203, arranged in ten rows of ten each. Each horizontal row is controlled by a select magnet. such as 200 and 204 described as now being operated. Each vertical row is controlled by a hold magnet, such as 208, 209 and 2 I0.

The first five horizontal rows of these contact sets, starting from the top, are associated with incoming trunks and the last five rows are associated with outgoing trunks. Since three wires are suflicient for a trunk circuit, the lower five rows of contact sets will accommodate one hundred trunks, that is, ten rows of ten trunks each, The lower horizontal row of cross-point contacts 2| I, 2 I 2 and 2|3 will accommodate trunks II to I0, inclusive, and trunks 2| to 20. inclusive, the numbering system here being used running from 1 to 0, corresponding, in fact, from 1 to 10 in each case. Through the operation of the step-by-step switch having the brush |2| any particular level may be selected. As described herein, the ninth level will be selected since the brush I2I has been placed on its ninth contact and since the selecting magnet 204, having control over the ninth and tenth levels, will be operated. At a later period, as will be described hereinafter, some one of the

hold magnets

208, 209 and 2|0 will be operated, let us say 209 by way of example, whereupon the contact sets 202 and 206 will be operated. Thereafter the

select magnets

200 and 204 will be released and the connection will be held through the continued operation of the hold magnet 209. Since the ninth level has been selected by the brush I2I, then the circuit through the lower three contacts of the set 206 and the lower three contacts of the set 202 will become effective through the automatic operation of relay 24. as will be hereinafter described. Had the tenth level been selected, whereby trunk No. 02 would be used instead of trunk 92, then the upper three contacts of the set 206 and the upper three conductors of the set 202 would have become effective through the failure of relay I24 to operate.

Each of the trunks leading from the contact sets 205 to 201, inclusive, presents under normal conditions a battery connection on its sleeve much as the normal battery connection to the sleeve I09 through the winding of relay II2, as hereinbefore described. Since the select magnet 204 has been operated and it is desired to pick an idle trunk in the ninth level, the trunks 9|, 92 to 90. inclusive, will be automatically tested. This is done through the connection of the sleeves Ol these trunks through the armatures of relay I23 to the test relays associated therewith. Thus, the sleeve of trunk 9| may be traced through the front contact and armature of relay I23, the armature and back contact of holding magnet 208 to the winding of test relay 2I4. Similarly, the sleeve of trunk 92 will be connected to test relay 2|5 and the sleeve of trunk will be connected to the test relay 2|6. If trunk No. 9| is busy, its sleeve will be grounded and, hence, the test relay 2|4 will not operate. If the vertical row controlled by hold magnet 209 i busy, although trunk 92 is not busy, the normal connection to the test relay 2I5 through the armature and back contact of the magnet 209 will be broken. Let it be assumed, however, that this vertical link is idle. Hence, relay 2I5, which may be of high resistance so as to operate to the battery on the sleeve of trunk 92 but not to cause the operation of the sleeve, will now operate. Relay 2I5 now becomes locked in a circuit through its front contact and armature 3, the back contact and armature 3 of relay 2I4, the front contact and armature 8 of relay II2 to battery. Another circuit is now established from the winding of hold magnet 209 through the front contact and armature 2 of relay 2I5, the back contact and armature 2 of relay 2I4, the front contact and right-hand armature of relay I25 to ground. Relay I25 is operated from the armature 4 of relay I23. Holding magnet 209 operates and becomes energized and, therefore, operates the contact sets 202 and 206 which have been prepared for operation by

select magnets

200 and 204, respectively. A circuit is also established from battery, the winding of relay 2II, front contact and armature I 01 relay 2I5, back contact and armature I of rela- 2I4, armature I and front contact of relay I23, front contact and left-hand armature of relay I25 to ground. Relay 2II extends the ground for its operation over its front contact and left-hand armature to the sleeve of trunk No. 92 and thereafter remains locked to the sleeve of this trunk even after the ground provided by the operation of relay I25 has been disconnected. Likewise, through the movement of the right-hand armature of relay 2I'I the hold magnet 209 is connected to the sleeve of trunk 92 so that the continued operation of this cross-bar switch depends upon the ground coming over the sleeve of trunk 92.

At the same time a ground is connected over armature 6 and front contact of relay I23,

- through armature I and front contact of relay II2, to the winding of relay I24. Relay I24 becomes operated and locks to the sleeve of trunk 92. Through the operation of the upper three armatures of relay I 24 the trunk ending in brushes I03, I04 and I05 is now connected through the lower three contacts of the set 202 and thence through the lower three contacts of the set 206 to trunk 92. While it is true that trunk No. 02 is connected through the upper three contacts of set 206 and the upper three contacts of contact set 202, this connection is ineffective due to the operation of the upper three armatures of relay I24.

Since the connection has been extended to trunk 92 the ground from the sleeve of this trunk may be traced back to the armature and front contact of relay IIO to hold this relay operated but it will at the same time result in the shunting of relay III so that this relay becomes released. Therefore, a connection from the front contact of holding magnet 209 which extends back through the armature of relay I23 to the sleeve of trunk 92 to ground will, therefore, be extended over the front contact and armature 4 of relay 2I5, the back contact and armature 4 of relay 2I4, to the winding of relay H4 and thence to battery. Relay II4 now becomes operated and disconnects the windings of relay I I6 from the tip and ring conductors leading to the subscriber's substation I00. At the same time the holding ground for relay H2 is removed and \JUUI bll this relay becomes deenerglzed. Through the release of relay II6 the slow release of relay II8 will shortly take place, whereupon a circuit will be extended from ground, the armature and .back contact of relay II6, the left-hand armature and back contact of relay II8, the off-normal contact I26, to the relay magnet I 21, whereby the brush I2I is returned to normal. Through the release of start relay II2 the test relay 2I5 is returned to normal and through the release of brush I2I the group relay I23 is released. Therefore, the

select magnets

200 and 204 are in turn released and the connection is held by the holding magnet 209. In this condition relay I24 and relay IIO, individual to the incoming trunk, are operated and all other relays are returned to normal. In Fig. 2 the holding magnet 209 is held operated and relay 2I'I is held operated, both under control of the sleeve of trunk 92. When the connection is released and the ground removed from the sleeve of this trunk, all of these relays will immediately be released and the connection restored to normal.

Thus, a single ten by ten six-wire cross-bar switch will operate to extend calls from five incoming trunks to one hundred outgoing trunks arranged in ten groups of ten each.

With Figs. 1, 3 and 4 arranged as indicated in Fig. 9 another embodiment of the invention is illustrated. In this case the eight contact sets 30I to 308, inclusive, in Fig. 3 represent one ten by ten six-wire cross-bar switch. That is, these contact sets represent one hundred such contact sets arranged in ten rows of ten each. There will be ten such select magnets as that numbered 300 and ten such holding magnets as that numbered 309. In Fig. 4 the contact sets 40I to 408, inclusive, represent a ten by ten sixwire cross-bar switch. In other words, these eight contact sets represent one hundred such sets arranged in ten rows of ten each. In this case there will also be ten such select magnets as that numbered 400 and ten such hold magnets as that numbered 409. The vertical links of these two switches are connected together so that effectually, and particularly since the hold magnets 309 and 409 are multiplied together, a single cross-bar switch twenty by ten is formed. Ten incoming trunks, such as the trunk leading from the finder brush-es I03, I04 and I05, are served by the cross-bar switch of Fig. 3. One hundred outgoing trunks are served by the cross bar switch of Fig. 4. Since each contact set controls six pairs of contacts and only three are needed for an outgoing trunk, there are effectually two hundred outlets. In order to make the so-called coverage better, only one hundred outgoing trunks are used and each trunk is served by two different contact sets each in a different vertical. Thus, trunk No. I2 is served by the upper three contacts of set 405 and the lower three contacts of set 406. Likewise, trunk No. II is served by the lower three contacts of set No 405 and the upper three contacts of set No. 406

The outgoing trunks are numbered according to the usual step-by-step numbering plan, that is, all of the trunks on the first level served by contacts sets 405, 406, 40! and 408 begin with the digit for indicating the first level. All of the trunks served by the other row of contact sets 40I to 404, inclusive, begin with the digit 0, that is, they are in the tenth level. Other levels, two to nine, inclusive, are indicated by the multiple connections to the vertical wires. Likewise, all of the trunks in the first vertical row IIUU situated on the lower three contacts of the sets end with the digit 1 and those in the second row in a similar position end with the digit 2. It is believed that without further explanation the numbering of these trunks will be clear.

A call is established by substation I in the manner hereinbefore described and the select magnet 300 is operated. Let us assume in this case that the digit 0 is dialed. Thereupon the steering switch controlled by the stepping magnet I20 will place its wiper on its tenth or 0 contact whereupon relay I28 becomes operated. Relay I28 connects the sleeves of the various trunks 0| to 00, inclusive, to the conductors 4l0 which have also been numbered 1 to 9 and 0 in accordance with the last digit of the trunk to which they are connected. If we assume that trunk No. 0| is busy, then a connection will be extended from ground through the lower armature and back contact of hold magnet 409 to the Winding of odd test relay 4H and this relay will fail to operate. If we assume that the even trunk No. I2 is idle, then the battery on its sleeve will be connected over the inner armature and back contact of hold magnet 409 to the winding of the even test relay 4I2.

If we assume that the second link, controlled by the hold magnet M3 is busy, then neither one of the test relays 4I4 or 4I5 will be operated since connections to their windings are broken by the operation of hold magnet 4|3. If magnet 4|3 is not operated, then the winding of test relay 4| 5 will be in parallel with the winding of test relay 4H and both of these relays will operate.

If we had assumed that, for instance, the test relay M6 were the first to operate, then chain circuits would have been established through the whole line of test relays 4|2, 4I5, etc. It has been assumed, however, that test relay 4|2 becomes operated. This relay, therefore, locks through its front contact and inner lower armature and the front contact and armature 8 of relay ||2. Through its upper armature relay 4|2 extends ground from the front contact and right-hand armature of relay I25 to conductor 4|! which leads in parallel to the windings of holding magnets 309 and 409 whereby these two magnets become operated, in turn causing the operation of contact sets 30I and MI. It will be noted that relay 4|8 does not become operated at this time since its winding is opened at the front contact and uppermost armature of relay 4. Through its lower outer armature and front contact relay 4I2 extends a connection from the winding of relay M4 to the conductor No. 2 in the bundle designated 4|0 which leads through one of the armatures of relay I28 to the sleeve of trunk No. 02. Since this sleeve is by this time grounded, in accordance with standard practice, relay II4 will respond as soon as relay II'I releases. Since trunk No. 02 is an evennumbered trunk and since conductor 4|9 has not been further extended, relay I24 will remain in its normal position so that a connection is extended from trunk No. 02 through the upper three contacts of set 40I, the upper three contacts of set 30I, the back contacts and upper armatures of relay I24 to the circuit including the brushes I03, I04 and I05. Ground from the sleeve of trunk 02 is now extended over this circuit to the sleeve conductor I09 whence it extends through the armature and front contact of relay 0 to maintain this relay operated and at the same time shunts the winding of relay III.

tit)

Relay Ill becoming released causes the operation of relay III which signifies the fact that the connection has been successfully established and, therefore, controls the release of all common relays in the manner hereinbefore described. During the maintenance of the connection relay H0 in Fig. 1 will remain operated and locked to the sleeve and in Figs. 3 and 4 the hold magnets 309 and 409 will remain looked through the upper armature and back contact of relay M8 to the sleeve of trunk 02.

It will be noted that if, contrary to the preceding description, trunk 0| had been idle and trunk 02 had been busy, then the odd test relay 4II would have been operated. In this case the relay 4I8 would have been operated through the front contact and upper outer armature of relay 4 and conductor 4|9 would have been grounded, resulting in the operation of relay 124. Therefore, trunk 0| would have been connected through the lower three contacts of set 40l. the lower three contacts of set 30I, the front contacts and upper three armatures of relay I24. to the trunk terminating in brushes I03, I04 and I05. In this case, during the maintenance of the connection, relays I24 and H0 of Fig. i would have been locked to the sleeve of trunk 0| and in Figs. 3 and 4 the hold magnets 309 and 409 and the relay 4I8 would have been locked to the sleeve of trunk 0|.

Figs. 5, 6 and 7, when arranged in the manner indicated in Fig. 10, illustrates a third embodiment of the present invention. The characteristic feature of this embodiment is that the relay which automatically determines the proper link circuit to use is inserted not before the incoming trunk enters the cross-bar switch but rather in the link itself. Thus, the contact sets SM. 602, 603 and 604 represent a ten by ten three-wire cross-bar switch, that is, a cross-bar switch in which there are one hundred sets of contacts arranged in ten rows of ten each. There are ten select magnets, such as that numbered 600. and ten holding magnets, such as that numbered 605. The switch illustrated in Fig. 7 is a ten by ten six-wire cross-bar switch. The contact sets IOI to I04, inclusive, represent one hundred such cross-bar contact sets arranged in ten rows or ten each. There are likewise ten select magnets. such as that numbered I00, and ten holding magnets, such as that numbered I05. The connections between the crossbar contact sets l. 603, 'IOI and I03 is known as a link. This link is in the form of three wires through the crossbar of Fig. 6 where they extend to the armatures of a relay 606 which performs a similar function to the relay I24 of Fig. 1. The contacts cooperating with the armature of relay 606 extend to six wires leading through the contact sets represented by those designated 'IOI and 103.

The trunks leading from the contact sets l0| to I04, inclusive, will be two hundred in number since there are one hundred such contact sets and since each such contact set accommodates two trunks. Thus. contact sets I03 and 104. which we will assume to be in the first level. will accommodate trunks II to I0, inclusive, and III to IIO, inclusive, and contact sets IOI and 102. representing the tenth level, will accommodate trunks 0| to 00, inclusive, and |0| to I00. inclusive.

The operation of the circuit of Fig. 5 is similar to the operation of the circuit in Fig. l and. since the relays therein have been given corresponding numbers. no further particular description of the operation of the circuit of Fig. 5 will be given. It should be noted that a relay corresponding to relay I24 of Fig. 1 is missing and that the armatures and contacts of

relays

523 and 520 corresponding to relays I23 and I29, used in the one case for operating the relay I24 and in the other case for extending a ground from the left-hand armature of relay I25, are missing. The reason for this will be apparent as the description proceeds.

When a call has been established the select magnet 600 is operated and if the first digit dialed is then the select magnet 100 is operated. Let it be assumed, by way of example, that trunk |0| is busy but that trunk 0| is idle. Then the groundedsleeve of trunk |0| will be extend-- ed through one of the armatures of relay 528, thence through the lower outer armature and back contact of hold magnet I to the winding of test relay I05. Test relay I06 will not operate in this circuit. The sleeve of trunk 0|, however, being connected to battery since this trunk is assumed to be idle, will be connected through the inner lower armature of magnet I05 to the winding of test relay I01, whereupon this relay will become operated. Relay 101 will extend ground from the front contact and armature of relay 525 through the armature 2 and back contact of relay I06, armature I and front contact of relay I01, to conductor I00 which leads to the hold magnet 105 and the hold magnet 605, whereupon these magnets become operated. The trunk 0| will now be connected through the lower three contacts of set IN, the back contacts and armatures of relay 605, the contact set GM, to the trunk terminating in finder brushes 503, 504 and 505.

Through its armature 2, relay I0I locks to battery from armature I of relay 5I2 until this relay is returned to normal. Through its armature 3, test relay 101 extends the sleeve of trunk 0| to the winding of relay 5|4 so that this relay will become operated as soon as relay 5|I is deenergized. Relay 5|I responds to the completion of the connection from trunk 0| to the trunk circuit of Fig. 5, through the extension of ground from the sleeve now placed on conductor 509, through the armature and front contact of relay 5I0, to the winding of relay 5|I, whereby relay 5| I is shunted and releases its armature. As in the same manner hereinbefore described, the energization of relay 5|4 signifies the fact that the trunk has been successfully extended and that the common apparatus is no longer needed.

During the maintenance of the connection relay 5|0 of Fig. 5 will be tied to the sleeve of the trunk and in Figs. 6 and 7 the holding magnets 605 and I05 will be likewise tied to the sleeve of the trunk.

It should be noted that if trunk 0|, for instance, had been busy and trunk |0I had been idle, then test relay I06 would have been energized. 111 this case relay I06 through its armature I will extend ground to conductor I09 for the operation of relay 606. Thus, trunk IIlI would have been connected through the upper three contacts of set IOI, through the front contacts of relay 606, the contact set GM, to the trunk terminating in finder brushes 503 to 505, inclusive, and during the maintenance of the connection relay 606 will be tied to the sleeve of the trunk as well as the hold magnets 605 and I05.

In either case, when the conversation is terminated and the ground removed from the sleeve of trunk 0| or |0|, the relays noted as beingenergized at this time will return to normal and the entire connection will be instantly broken down.

What is claimed is: 1. A selective switch comprising coordinate rows of sets of permanently paired contacts, in-

coming lines appearing in certain of said rows. ou going es appearing in other certain of said rows, said rows of incoming line contacts and said outgoing line contacts being parallel to each other, link circuits appearing in sets of contacts of rows r rows of incoming and outgoing line contacts, a plurality of outgoing lines and a corresponding plurality of links appearing in each set of contacts in the said outgoing line rows, means for directively selecting a row of outgoing line contacts, means for automatically selecting a link and automatic means for establishing a connection from an incoming line through said selected link to an outgoing line in said selected row of outgoing lines.

2. A selective switch comprising coordi nate rows of sets of permanently paired contacts, incoming lines appearing in certain of said rows, outgoing lines appearing in other certain of said rows, said rows of incoming line contacts and said outgoing line contacts being parallel to each other, each said incoming line having alternative paths through each set of contacts in a row, link circuits appearing in sets of contacts of rows crossing said rows of incoming and outgoing line contacts, a plurality of outgoing lines appearing in each set of contacts in the said outgoing line rows, means for directively selecting a row of outgoing line contacts, means for automatically selecting a link and automatic means for connecting a said incoming line to that alternative path leading to the said selected outgoing line.

3. A selective switch comprising coordinate rows of sets of permanently paired contacts, incoming lines appearing in certain of said rows,

outgoing lines appearing in other certain of said rows, said rows of incoming line contacts and said outgoing line contacts being parallel to each other, link circuits appearing in sets of contacts of rows crossing said rows of incoming and outgoing line contacts, a plurality of lines and links appearing in each said set of contacts, means for directively selecting a group of outgoing lines, means for automatically selecting a line of said selected group of outgoing lines and means for rendering a single path from an incoming line through a link to a selected outgoing line out of a plurality established by the actuation of an incoming line-link contact set and a corresponding link-outgoing line contact set effective.

4. A selective switch comprising coordinate rows of sets of permanently paired contacts, incoming lines appearing in certain of said rows, outgoing lines appearing in other certain of said rows, said rows of incoming line contacts and said outgoing line contacts being parallel to each other, link circuits appearing in sets of contacts of rows crossing said rows of incoming and outgoing line contacts, a plurality of lines and links appearing in each said set of contacts, each said outgoing line appearing in a plurality of said sets of contacts, means for directively selecting a group of outgoing lines, means for automatically selecting a line of said selected group of outgoing lines and means for automatically connecting an incoming line to that one of said plurality of paths through said sets of contacts leading to said selected outgoing line.

5. A selective switch comprising coordinate rows of sets of permanently paired contacts, incoming lines appearing in certain of said rows, outgoing lines appearing in other certain of said rows, said rows of incoming line contacts and said outgoing line contacts being parallel to each other, link circuits appearing in sets of contacts of rows crossing said rows of incoming and outgoing line contacts, a connection from an incoming line to an outgoing line being established through said switch by the coincident operation of two of said sets of contacts each in a row defined by a link circuit, each said set of contacts acting to connect a plurality of lines to a plurality of links, means for directively selecting a group of outgoing lines, means [or automatically selecting an outgoing line from said selected group and means for automatically connecting an incoming line to that one of said paths established through the operation of said pair of sets of contacts leading-o said selected outgoing line.

6. A selective switch comprising coordinate rows of sets of permanently paired contacts, incoming lines appearing in certain of said rows, outgoi'ng lines appearing in other certain of said rows, said rows of incoming line contacts and said outgoing line contacts being parallel to each other, link circuits appearing in sets of contacts of rows crossing said rows of incoming and outgoing line contacts, a connection from an incoming line to an outgoing line being established through said switch by the coincidental operation of two of said sets of contacts each in a row defined by a link circuit, each said set of contacts acting to connect a plurality of lines to a plurality of links, each outgoing line appearing in a plurality of contact sets in each of which appear a plurality of outgoing lines, no one outgoing line appearing more than once in a contact set. means for directively selecting a group of outgoing lines, means for automatically selecting an outgoing line from said selected group and means for automatically connecting an incoming line to that one of said paths established through the operation of said pair of sets of contacts leading to said selected outgoing line.

7. A selective switch comprising coordinate rows of sets of permanently paired contacts, incoming lines appearing in certain of said rows. outgoing lines appearing in other certain of said rows, said rows of incoming line contacts and said outgoing line contacts being parallel to each other, link circuits appearing in sets of contacts of rows crossing said rows of incoming and outgoing line contacts, a connection from an incoming line to an outgoing line being established through said switch by the coincidental operation of two of said sets of contacts each in a row defined by a link circuit, each said set of contacts in the link circuit outgoing line field acting to connect a plurality of lines to a plurality of links, each said set of contacts in the link circuit incoming line field acting to connect a single link to a single incoming line, means for directively selecting a group of outgoing lines, means for automatically selecting an outgoing line from said selected group and means for automatically connecting an incoming line to that one of said paths established through the operation of said contact set in said link circuit outgoing line field leading to said selected line.

GERALD V, KING.