US1355635A

US1355635A - Telephone-exchange system

Info

Publication number: US1355635A
Authority: US
Publication date: 1920-10-12
Anticipated expiration: 1937-10-12

Description

S. B., WILLIAMS, In.

TELEPHONE EXCHANGE s'vs'rzm; 7 APPLICATION FILED nmzz. ms. 1,355,635, .Patented Oct. 12,1920.

2 SHEETS-SHEET I.

S. B. WILLIAMS, Jn. TELEPHONE EXCHANGE SYSTEM. wucmou FILED DEC. 21. 1918.

v 1,355,635. Patented Oct. 12,1920.

2 SHEETS-SHEET 2.

lawman? 4 QlFrwIiJH 1 JEMIEJE 2 UNITED STATES PIATENT OFFICE.

SAMUEL B, WILLIAMS, JR, 033 IBRGOKLYN, NEIV YQRK, ASSIGNOR TO WESTERN ELEC- TR-IC COMPANY, INGORPDRATED, CF NEW YQRK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Specification of Letters Patent.

Patented Oct. 12, 1920.

Application filed December 27, 1918. Serial No. 268,501.

T all whom it may concern Be it known that I, Snsitmn B. WILLIAMS, J r., a citizen of the United States, residing at Brooklyn, in the county of Kings, State of New York, have invented certain new and useful Improvements in Telephone-Exchange Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to an improvement in telephone exchange systems and has particular reference to a semi-mechanical private branch exchange system employing rotary line and selector switches.

An object of the invention is to provide an improved selector switch arranged to serve a plurality of groups of trunks, any one of which may be selected by a directive movement of the brushes of the switch, the terminals of the trunks in certain of said groups being interspersed either periodi cally or promiscuously and in such a manner as to materially reduce the automatic trunk-hunting operation in the groups necessary before finding an idle trunk in the selected group.

Another object is the provision of a terminal bank for a selector switch wherein certain of the terminals are each allotted for determining the selection of one of a plurality of groups of trunks having connection with other terminals of said bank. In accordance with this arrangement, the brushes of the switch may, during the directive and automatic movements thereof in seizing an idle trunk in the selected group, pass over the terminals allotted for group selection and also terminals of trunks in non-selected groups, the test for an idle trunk in the selected group depending upon the finding of two terminals within the same set simultaneously free from ground.

The inventive idea involved is capable of receiving a variety of expressions, one of which, for the purpose of illustrating the invention, is shown in the accompanying drawings, but it is to be expressly understood that said drawings are employed merely for the pupose of illustrating the invention as a whole and not to define the limits thereof, reference being had to the appended claims for this purpose.

In the drawings, Figures 1 and 2 combined, with Fig. 2 at the right of Fig. 1, illustrate diagrammatically the various circuits of the private branch exchange system; Fig. 3 is a diagrammatic view of the trunking arrangement employed in connection with the invention.

In carrying out the invention, switches of the rotary type having contacts arranged in a complete circle are preferably employed for interconnecting the telephone lines. In Fig. 3, wherein the trunking arrangement is disclosed, a subscribers substation A is shown in association with a line switch B, the brushes of which are caused to move over the terminal bank by the removal of the receiver at substation A and automatically select an idle trunk, whereby the line is extended to a first selector switch C. The multiple bank of this switch consists of a plurality of terminals, certain of which are available for trunks divided into groups. Two of these groups 0 and 0 are available for automatically extending a'connection to selecton switches D when interconnecting calling and called subscribers within the private branch exchange. The terminals of said groups in the multiple bank of switch C are shown as arranged alternately but it is to be understood that said terminals may be promiscuously interspersed or disposed at random without departing from the spirit and scope of the invention. The multiple of the several banks is such that a different trunk appears as the first trunk in each multiple bank or group of multiple banks. By this arrangement, the selectors will not be required to hunt over all'the busy trunks, and the number of busy trunks passed over will be on the average the same when calling through the first group as when calling through the second group. The other two groups of trunks c and a may be used in establishing connections to a private branch exchange operators position and to a central ofiice exchange, respectively. The terminals in the trunks of each of these groups, in contra-distinction to the terminals. of groups of trunks c and 0 are preferably arranged in the ordinary manner.

7 In the final selector switch D, three groups of trunks (Z, (Z and 0Z are shown, and de-' pending upon the number of tens impulses transmitted by the sender at substation A in making an automatic connection to a called substation, the brushes of the final selector are stepped around to one of three terminals. The units digits of numbers in the first two groups are selected by the dial impulses, but when a number in the last group is called, a group relay operates on the completion of the impulses for the tens digit, as will appear later, causing the steppingmagnet of the final selector to automatically step the brushes around to the last group, and the dialing of the units digit of the number then selects the desired trunk in this group.

The operation may be briefly stated as follows: Should a subscriber at substation A desire a connection to the central office exchange, the removal of his receiver will first operate line switch B to seize. an idle trunk. The impulse sender is then manipulated to transmit one impulse which will step the brushes of the first selector switch 0 to the second terminal of the multiple I bank and thus select the group of central office trunks 0 By this selection the terminals of all the other groups of trunks are rendered non-selectable and the brushes of theswitch will be stepped over these terminalsand caused to hunt for an idle trunk in the group 0 whereupon the connection will be extended to the central office.

If it is desired to automatically establish a connection between two subscribers within the private branch exchange, the calling subscriber will, by removing his receiver, seize an idle trunk connected to the line switch, and by operating the sender to transmit two or three impulses, depending upon which of the groups 0 or c is to be selected,

, the brushes of the selector C will be stepped to the corresponding terminal in the selector bank allotted to the particular group, whereupon a trunk-hunting operation will proceed over the terminals of the group of erator, the digit 0 is dialed to send trunks selected. 7 V

7 As previously stated in connection with the trunk hunting in group 0*, the terminals of all the other groups, with the exception of the one in which trunk hunting is now proceeding will likewise be made non-selectable so that should all the trunks in the selected group'be busy, the brushes of the selector will travel over the groups of trunks c and'o in order that a busy tone will be transmitted to a subscriber at substation A. Upon the seizing of atrunk in'either of the two groups 0 or 0 the line is extended to the final selector switch which is operated, as briefly referred to above, connect the calling and called subscribers.

To call the private branch exchange opten impulses after a connection" has been extended from the line switch and the brushes of the selector are stepped to the terminal of the bank in association with the groups of trunks 0 at which time a trunk-hunting operation would again take place to select an: idle trunk leading to the operators position. Again, as described in connection filed on December 27,

r 202, back 'with the trunk-hunting operations in other groups, the terminals thereof, in this instance, will be rendered non-selectable in order that trunks therein will not be seized.

The trunking arrangement above described forms the subject-matter claimed in the present application, and the means herein shown and described for establishing the different connections have been disclosed and claimed in a Samuel B. WVilliams and Bert G. Dunham,

Serial No. 268,468.

It is believed that the invention will now be best understood from a detailed description of the operation in establishing a connection from a calling subscriber to a called subscriber and also to central office and private branch exchange trunks. Upon the removal of the receiver at substation A, in initiating a call, line relay 200 of the line switch 13 is energized over a circuit from grounded battery, winding of relay 200, back contact and innermost lower armature of'cutofl' relay 201, substation apparatus, upper armature and back contact of relay 201 to ground. The marginal stepping magnet 202 is then energized over the circuit from grounded battery, winding of said magnet, armature and back contact thereof, front contact and armature of line relay 200 and lowermost brush 203 to ground at the normal terminal thereof, whereupon the brushes of the switch will he stepped to the second set of terminals, the trunks of which lead to one of the first selector switches Should the selector switch connected to the separate application to,

1918, and bearing first test terminal be busy, brush 203 of the grounded battery, winding of'said magnet,

armature and back contact thereof, front contact and armature of relay 200, brush 203, armature and back contact of the line relay of said other line switch to ground. Magnet 202 being self-interrupting, will again step the brushes of the line switch over the terminal bank until an idle trunk is found, whereupon a circuit is established from grounded battery, winding of magnet contact and armature thereof, winding of relay201 in series with said magnet, brush 204, conductor 30%, winding of low resistance relay 307, brush 308 of the selector switch, backcontact and innermost right armature of test relay 303, and right armature of relay 301 to ground. ,Magnet 202 being marginal and in series with relay 7 contact grounds the test terminal and makes the trunk test busy to all other line switches.

Line relay 309 of the selector switch will energize immediately upon energization of relay 307 due to a circuit extending from grounded battery, right winding of relay 309, armature and front contact of relay 307 to ground. A circuit for relay 309 will be maintained from grounded battery, right winding of relay 309, back contact and innermost lower armature of cutoff relay 310, lower side of the subscribers line, substation apparatus, upper side of subscribers line, back contact and upper armature of relay 310, left winding of relay 309, brush 311 and coil 312 to ground. First slow-torelease relay 305 is then energized by a circuit extending from grounded battery, winding of relay 305, and front contact and armature of line relay 309 to ground. Operation of relay 305 establishes a holding circuit for relay 201 extending from grounded battery, winding of magnet 202, armature and contact thereof, winding of relay 201, brush 20%, conductor 30% and left armature of relay 305 to ground. A dial tone is furnished by coil 312 to inform the subscriber that he may now operate his sending device. If the subscriber desires to establish a connection to another P. B. X. subscriber, he will now transmit two or three impulses, depending upon which group of trunks c or 0 is to be selected for the trunk-hunting operation. Interruption of the circuit of line relay 309 by the sending device causes the armature thereof to vibrate, and upon each retraction a circuit is closed for the stepping magnet 313, extending from grounded battery, winding of magnet 313, winding of slow-to-release relay 301, right armature of slow-to-release relay 305, which remains energized during the line interruptions, back contact and outermost lower armature of cutoff relay 310 and back contact of the armature of relay 309 to ground. The brushes of the selector are stepped from their normal terminals in accordance with the number of impulses sent, and upon deenergization of relay 301 at the termination of the transmission of impulses, one of the two

roup relays

311 and 315 is energized. ssuming that the two impulses were sent to select the group of trunks 0', group relay 314 will be energized over a circuit extending from grounded battery, winding of relay 314, brush 308 which now rests upon the third terminal in its row, back contact and innermost right-hand armature of test relay 303 and right armature of relay 301 to ground. Relay 314 in attracting its right armature, energizes test relay 303 over a circuit extending from grounded battery, right winding of said relay, lowermost brush 316, the third terminal in the row associated with said brush, front contact and right armature of relay 314 to ground. After test relay 303 is energized, relay 31 1 isheld up until an idle trunk is found, over a circuit extending from grounded battery, winding of relay 314:, left armature and front contact thereof and left armature of slow-to-release relay 305 to ground Stepping magnet 313 is now operated over a circuit extending from grounded battery, winding of said magnet, armature and back contact thereof, front contact and outer left armature of relay 303, front contact and right armature of relay 314 to ground. It is to be noted that the continued energization of relay 31 1 has removed the ground at its right armature from the terminals 0f the selected group 0 traversed by the brush 316, but that as long as the test brush 317 of the selector is moving over busy trunks, test relay 303 is held up over a circuit from grounded battery, left winding of relay 303, front contact and inner left armature thereof, test brush 317 to ground at the busy final selector. It is therefore apparent that relay 303 will not release until

brushes

316 and 317 engage two terminals simultaneously free from ground, and consequently stepping magnet 313 continues to operate until an idle trunk is found. During the energization of test relay 303, a ground is placed upon the conductor 302 except when relay 301 is energized, and this ground provides an additional guarding potential which will prevent seizure of the selector by another line switch when the latter is hunting for an idle trunk. lVhen brushes 316 and 317 simultaneously engage two terminals free from ground, test relay 303 will retract its armatures and break the circuit for stepping magnet 313, and brushes of the selector will come to rest upon the selected terminals. Cutoff relay 310 is immediately energized by the circuit extending from grounded battery, winding of relay 310, back contact and outer right armature of test relay 303, brush 308, back contact and inner right armature of test relay 303, and back contact and armature of relay 301 to ground, and the line is thus extended to the final selector switch 1). Upon the operation of cutoff relay 310, line relay 309 and slow-- to-release relay 305 deenergize but the upper and inner lower armatures of relay 310 being of the makeebefore-break type, the connection is cut. through and ground is found at the final selector for relay 201 and group relay'314l before the ground at relay 305 is removed, and said relays thus remain energized.

If all of the trunks in the group are found to be busy, test relay 303 remains energized until the brushes of the switch have been stepped onto the last set of terminals, at which time brush 317, no longer finding ground, will cause relay 303 to denergize,

and upon therelease of relay 303, cutoff relay 310 is energized over a circuit extending from grounded battery, winding of relay 310, back contact and outer right armatureof relay 303, brush 317, inner left-hand armature and back contact of relay 303, normal contact and left-hand armature of relay 301, left-hand armature and alternate contact of relay 305 to ground. Upon energization of cutoff relay 310, a busy tone is placed on the calling line bya circuit extending from grounded battery, right winding of line relay 309, brush 318, lower side of the telephone line, substation apparatus A, upper side of the telephone line, brush 319 and coil of busy tone device'B Z to ground. Through this circuit, relay 309 is held energized until the receiver at substation A is replaced upon its hook. Line relay 309 then releases whereupon slow-to-release relay 305 will become deenergized. This latter relay opens a circuit for relay 310 at its left-hand front contact above described. The release of relay 310 closes a circuit from ground, armature and back contact of relay 309, lower armature and back contact of relay 310,,right-hand armature and back contact of relay305, brush 316,

right-hand winding of relay 303to grounded battery. The energization of relay 303 closes a circuit for stepping magnet 313 from groundedjbattery, the winding, armature and back contact of said magnet, left D becomes energized over a circuit extending from grounded battery, right winding of relay 400,.lower side of the telephone line, sub station apparatus A, upper side of the telephone line and left winding of relay 400 to ground. In attracting its armature, relay 400 closes the clrcuit for slow-to-release relay 401 which extends from grounded battery, winding of relay 401, front contact I left armature of relay 401.

number is within the groups of trunks (Z or.

and armature of relay 400 to ground. Relay 401 attracts its left armature and establishes the ground previously referred to in connection with the holding circuit for relay 201 and group relay 314. lVhenrelay 401 is energized, relay 402 is also energized over a circuit extending from grounded battery, winding of relay 402, brush 403 in its normal position, conductor 404 to ground at the If the desired (Z of the final selector switch D, shown in Fig. 3, the impulse-sending device at substation A is operated to transmit either one or nine impulses, depending in which group the trunk-selecting operation is to take place. Assuming that the called numberis in group cl, the sending device is operated to transmit one impulse, andin response thereto the armature of relay 400 will be retracted and close a circuit for the stepping magnet 405 extending from grounded batter winding of magnet 405, front contact anc inner left armature ofrelay 402, winding of slow-to-release relay 406, back contact and left armature of relay 407, right arma ture of slow-to-release relay 401 and back contact and armature of relay 400 to ground. The brushes of the switch are thereby stepped onto the second set of terminals. Upon energization of relay 406 in response to the impulse transmitted a circuit was closed for relay 408 extending from grounded battery, winding of said relay and right armature of relay 406 to ground, and said relay 408 locked up through its outermost lower armature and front contact, armature and backcontact of relay 409 and left armature of slow-to-release relay 40lto ground. The group of trunks cl has now been se lected, and at the termination of the. impulse, slo'w-to-release relay 406 deenergizes, but relay 402 remains energized over a cir-' cuit extending from grounded'battery, windingof relay 402, brush 403, conductor 404 and left armature of slow-to-release relay 401 to ground. Upon transmitting the units impulses to select the desired line in the group cl, stepping magnet 405 is again operated over the previously described cir-' cuit to step the brushes of the switch. Itis to be noted that as soon as the brush 403 leaves the second terminal, ground will no longer be found for relay 402 at the left armature of slow-to-release relay 401, but relay 402 will remain energized over a circuit extending from grounded battery, winding of said relay, left armature and back contact of group relay 410 and left armature of slow-to-release relay 406 to ground. Re-

lay 406 remains energized during the transmission of impulses. Stepping magnet 405 will thus continue to operate in accordance with the impulses transmitted until the brushes have been stepped upon the desired set of terminals.- If the line selected is found to bebusy, relay 402 will'find ground at the-left armature of slow-torelease relay 406 until the same becomes deen'ergized at thectermination of the impulses, whereupon the circuit for relay 402 will be extended from the back contact of the left armature of.

relay 406, through relay 407, inner right armature and back contact thereof, front contact and outer left armature of relay 402, brush 411 to ground at the busy terminal of the called line. Relay 407 will lock up through its inner right armature to ground at the left armature of relay 401. Attraction of the outer right armature of relay 40'? furnishes a busy tone to the calling line extending from grounded battery, right winding line relay 400, lower side of the subscribers line substation apparatus A, upper side of subscribers line, outer right armature of relay 407 and coil 15 Z to ground.

Should the called line be idle, relay 402 releases at the end of the impulses, since upon deenergization of relay 406, the ground at the left armature of the latter relay will be removed. Upon the release of relay 402, relay 412 becomes energized over a circuit extending from grounded battery, winding of relay 412, right armature and back contact of relay 402, back contact and innermost right armature of group relay 410, brush 413 and back contact and right armature of slow-to release relay 406 to ground. Energization of relay 412 extends the line to the selected terminals and closes a circuit extending from the ringing current generator 414, right winding of relay 409, front contact and inner lower armature of relay 40S, lower armature and front contact of relay 412, ringer apparatus at the called substation E, front contact and upper armature of relay 412 and inner upper armature of relay 408 to ground. Ringing cur rent is thus applied to the line and is also induced into the secondary winding of relay 409 for the purpose of furnishing a ringing tone to the calling station, the circuit for this ringing tone extending from grounded battery, left winding of relay 415, lower side of the telephone line, substation apparatus A, upper side of the telephone line, right winding of relay 415 and left winding of relay 409 to ground. Relay 409 is marginal and will not attract its armature as long as the resistance of the substation bell is in its circuit, but when the receiver at the called substation E is removed, said relay will become energized and break the circuit for relay 408 which extended through the armature and back contact of said relay 409. Relay 408, in releasing, disconnects the ringing current and closes the talking circuit at the innermost upper and lower armatures and back contacts, and conversation may proceed. 7

If the trunk for the called line had been located in group (Z it would have been necessary to transmit nine impulses to the final selector, to step the brushes thereof onto the tenth terminal shown in the bank of the selector D in Fig. 3 and in so stepping the brushes, the operation would be precisely the same as that set forth above. It should be noted that no line numbered 91 appears, since the terminal which should have been allotted for line No. 91 is, in-

stead, allotted for the selection of group d Should the tens digit of the called number be 0, the brushes are stepped around as previously described until they engage the eleventh terminal shown in Fig. 3, whereupon, as soon as relay 406 releases at the end of the impulses, group relay 410 is energized by a circuit extending from grounded battery,

winding of relay 410, conductor 416, brush 413, back contact and armature of relay 406 to ground; The op'erationof relay 410 energizes relay 402 over a circuit extending from grounded battery, winding of relay over a circuit extending from grounded bat- V tery, winding of relay 410, front contact and innermost right armature thereof, conductor 417, brush 418, back contact and armature of relay 406 to ground. The stepping operation of the brushes continues until brush 413 reaches the terminal having no connection to the conductor 417, whereupon said brushes come to rest on this set of terminals. Relay 410 releases, but relay 402 continues to be energized over a circuit from grounded battery, winding of relay 402, brush 403, conductor 404 and left armature of slow-to-release relay 401 to ground. In response to the units impulses, the brushes are again stepped around in the trunk selecting movement in group d in the same manner as previously described for calling a number in group cl.

Should the subscriber, after initiating 'a call, hang up his receiver before an idle trunk leading to the selector switch has been seized, it will be apparent that the line switch will continue to hunt for the idle trunk, and upon finding it, cutoff relay' 201 will be energized as previously described. Relay 304', being in series with relay 201, also energizes, and at its front contact, closes a circuit for line relay 309, which in attracting its armature, energizes slow-torelease relay 305, thus grounding conductor 304, leading from cutoff relay 201, at the left armature of relay 305, instead of at the back contact and right armature of relay 301 and thereby shunting relay 307. Release of this relay d *nergizesline relay 309, since the circuit has been broken by replacing the receiver, and armature of relay 309 loses the circuit of stepping magnet 813 extending over the previously traced circuit,

and the brushes are stepped onto the second set of terminals. In response to the continued deenergization of line relay 309, re-

lay 305 becomes deenergized and after an interval, relay 301 follows. Group relay 320 is then energized over a circuit extending from grounded battery, winding of relay 320, brush 308, back contact and inner right armature of test relay 303, back contact and right armature of slow-to-release relay 301 to ground. The right armature of group relay 320 puts ground on the set ,of test'terminalsassociated therewith, and

closes a. circuit for stepping magnet 313 from grounded battery, winding of magnet 313, armature and back contact thereof,

front contact and outer left armature of relay 303, back contact and left armature of slow-torelease relay 305 to ground, relay 305 having become deiinergized upon the release of line relay 309. The brushes are now stepped to the next set of terminals and thisaction, takes place each time the brush 316 engages one of the terminals which is connected to ground at the right armature of group relay 320. lVhen engaging the test terminals of the different groups 6', 0 and c brush 316 finds ground for test relay 303 at the back contacts and armatures of the respective group relays. When relay 320 is energized, ground for the group of terminals 0" extends from the armature and backcontact of relay 300, outer lower armature and back contact of relay 310, right armature and back contact of relay 305, outermost and middle left armatures and front contacts of relay 320 to said terminals. Stepping magnet 313 continues to operate until the last set of ter-' minals is reached, whereupon the switch is stepped to normal, as previously described. It is to be understood that the terminals indicated bydotted lines over which brush 316 moves are connected to the other terminals of the respective groups in the same manner as shown in full lines, Upon the shunting of relay 307 as previously .de

scribed, relays 309 and 305 will release,-and

the holding circuit for relay 201 will be broken at the left armature of relay 305,

Stepping; magnet 202 will then operate to step the switch B to normal over the circuit extending from grounded battery, winding of magnet 202, armature and back contact thereof, lowermost armature and back contact of relay 201 and brush 205 to ground at the armature and back contact of line relay 200.

At the termination of a conversatiomin the event that a connection has been established between the calling and called substations, the hanging up of the receiver at substation A releases line relay 400 of the final selector switch D which also causes slow-to-release relay 401 to deenergize. Relay 410 now energizes over the circuit extending from grounded battery, winding of relay 410, brush 418, back contact and right armature of slow-to-release relay 401, back contact and armature'of relay 400 to ground. Energization'of relay 410 breaks, at its in nermost right armature and back contact, the (ircuit for cutoff relay 412 causing this relay to release. Stepping magnet 405 now operated over the circuit extending from grounded battery, winding of magnet 405, armature and back contact thereof, outermost right armature and front contact of relay 410, brush 418, back contact and right armature of slow-to-release relay 401,

back contact and armature of relay 400 to ground, and stepping magnet 405 continues to operate until the switch is stepped to its normal position where the circuits for said magnet and relay 410 are broken.

In order to preventthe selector switch D from being seized during the return'of the switch to its normal position, it being understood that the busy ground has been removed by the decnergization of slow-torelease relay 401, a ground is provided at the middle right armature and front contact of relay 410. r

The removal of ground at relay 401 releases group relay 314 of selector switch C and places ground on all trunks of the selected group associated with said relay and thereby energizes test relay 303 over a circuit extending from grounded battery, right winding of relay 303, brush 316, termnal of the selected trunk, back contact and right armature of relay 314 to ground. Test r lay 303, pulling up, opens at is right armature and back contact, the circuit for cutoff relay 310 and closes the circuit for stepping magnet 313 extending from grounded battery, winding of magnet 313, armature and back contact thereof, front contact and outer left armature of relay 303, back contact and left armature of relay 305 to ground, and stepping magnet 3 13 continues to operate as long as brush 316 engages a terminal which finds ground at the right armature of relay 314, and will also operate upon each engagement' of brush 316 with the test terminals associated with group relays 315, 320 and 321, which are deenergized. If the brushes have selected an idle trunk in groups 0 and 0 before reaching the terminal to which they would be steppediwhen selecting group of trunks c relay 303, said terminal, will be energized by the circuit extending from grounded battery, right winding of relay 303, brush 316, conductor 322, back contact and left armature of relay in passing over 305 to ground, and stepping magnet 313 will thus again step the brushes onto the next set of terminals.

Line switch B is also returned to normal by the removal of ground at left armature of slow-to-release relay 101 which causes the release of cutoff relay 201, this relay having been held energized by the circuit extending from grounded battery, winding of stepping magnet 202, armature and back contact thereof, winding of relay 201, brush 204, conductor 30st, left armature and back contact of relay 301, back contact and inner left armature of relay 303, brush 317 and left armature of relay 401 to ground. The release of relay 201 energizes stepping magnet 202 over a circuit extending from grounded battery, winding of magnet 20 2, armature and back contact thereof, lowermost armature and back contact of relay 201 and brush 205 to ground at the armature and back contact of line relay 200. Stepping magnet 202 continues to operate until the brushes thereof engage the normal terminals, whereupon the operating circuit of said magnet will be broken and the switch will come to rest.

If it is desired to establish a connection to a central office, subscriber at substation A, by removing his receiver, will operate line switch B to select an idle trunk leading to one of the first selectors, and upon transitting a single impulse, the brushes of said selector will be stepped, as previously described, onto the second set of terminals and thus select the group of trunks c for the trunk hunting operation which automatically takes place in the same manner as described in connection with the extension of a call through group of trunks 0, group relay 320, in this instance, becoming energized.

k Should the service of substation A be restricted a conductor 207 is employed to connect the middle lower armature of cutoff relay 201 of the line switch with brush 206, so that if an attempt is made to call the central office from this station, energization of cutoff relay 201 will apply said ground to the magnet 313 will therefore central oilice trunks and cause the same to test busy, said ground extending through the brush 206, conductor 323, front contact and middle left-armature of group relay 320, which has become energized, to the terminals of the central office trunks.

continue to operate until the last set of terminals is reached, whereupon test relay 303 will be energized over a circuit extending from grounded battery, right winding of relay 303, brush 316, the last test terminal, outermost left armature and front contact of re lay 320, conductor 323, brush 206 and middle lower armature and front contact of relay 201 to ground, thus causing the stepping Stepping magnet to again operate and return the switch to normal position. Line switch 13, however, remains in its actuated position as long as the receiver is off the switchhook and the subscriber may again manipulate his dial to call the private branch exchange operator.

To establish a connection to the private branch exchange operators position, the sending device at substation A is actuated, after the seizure of an idle trunk by the line switch B, to transmit ten impulses to step the brushes onto the eleventh set of terminals, whereupon group of trunks 0 will be selected for the trunk hunting operation, and in this case group relay 321 will be energized to remove ground from the terminals of the private branch exchange trunks over which test brush 316 passes and one of the trunks will be seized in the same manner as previously described.

IVhat is claimed is:

1. In a telephone system, a trunking arrangcment for switches including a bank and groups of trunks terminating in said bank and having their terminals interspersed, other terminals of the bank being allotted for group selection.

2. In a telephone system, a trunking arrangement for switches including a bank, and groups of trunks terminating in said bank and having their terminals interspersed, whereby terminals of one group of trunks are passed over in selecting a trunk in another group, other terminals of said bank being allotted for group selection.

In a telephone system, a trunking arrangement for switches including a bank, and groups of trunks terminating in said bank and having their terminals inter spersed, whereby terminals of one group of trunks are passed over in selecting a trunk in another group, other terminals of said bank being allotted for group selection, the latter terminals being initially passed over in selecting a group of trunks.

it. In a telephone system, a trunking arran ement including a terminal bank, groups of trunks connected to terminals of said bank and having their terminals interspersed, and other groups of trunks connected to other terminals of said bank, certain other terminals of the bank being allotted for group selection.

5. In a telephone system, a trunking arrangement including groups of trunks connected to terminals of said bank and having their terminals interspersed, and other groups of trunks connected to other ter iinals of said bank, certain other terminals of the bank being allotted. for group selection, one of the latter terminals being arranged between terminals of the first named groups.

6. In a telephone system, a trunking ara terminal bank,

rangement including a terminal bank, groups of trunks connected to terminals of said bank and having their terminals interspersed, and other groups of trunks connected to other terminals of said bank, certain other terminals of the bank being allotted for group selection and being initially passed over in selecting one of said groups.

7. In a telephone system, a trunking arrangement including a terminal bank, groups of trunks connected to terminals of said bank and having their terminals interspersed, and other groups of trunks connected to other terminals of said bank, certain other terminals of the bank being allotted for group selection and being initially passed over in selecting one of the first named groups.

8. In a telephone system, a trunking arrangement including a terminal bank, groups of trunks connected to terminals of said bank and having their terminals interspersed, and other groups of trunks connected to other terminals of said bank, certain rangement including a terminal bank,

groups'of trunks connected to terminals of said bank and having their terminals interspersed, and other groups or" trunks connected to other terminals of said bank, certain other terminals of the bank being allotted for group selection, one of the latter terminals being arranged between terminals of the first named groups, others of said certain terminals and the terminals of the first named groups being passed over when selecting the group of trunks allotted to the terminal which is arranged between terminals of said first named groups.

In witness whereof I hereunto subscribe my name this 23rd day of December, A. D. 1918.

SAMUEL B. WILLIAMS, JR.