US1613624A - Machine-switching telephone-exchange system - Google Patents

Description

Jan. 11,'1927. v 1,613,624

v R. L.. STOKELY MACHINE SWITCHING TELEHONE EXCHANGE SYSTEM OriginalA Filed SGPC- 25 1920 `9 vSneecs--Sheet 1 Jan. 11, 1927.

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RAY L. STOKELY, OF FLORAL PARK, NEW' YORK, ASSIGNOR T0 WESTERN' ELECTRIC COMPANY, INCORPORATED, F NEW YORK, N. Y., A. CORPORATEON 0F NEW YORK.

IVIACHNE-SWITCH1NG TELEPHONE-EXCHANGE SYSTEM.

Original application filed September 25, 1920, Serial No. 412,795.

Divided and this application led April 30, 1923. Serial No. 635,793.

This invention relates to telephone eX- change systems and more particularly to such systems employing machine switching equipment in the establishment of connections. This application is a division of application, Scrialllo. 412,795, iiled September 25, 1920.

It `is broadly an object of this invention to improve conditions and to expedite trafiic in systems of the above mentioned character.

This object is obtained in accordance with one feature of this invention by the pro vision of a circuit arrangement whereby a calling supervisory signal at a toll operators position is actuated in one manner if a selector fails to find an idle trunk in the selected group in the process of building vup a connection, and in another manner if the called line is found busy by a connector.

The invention will be readily understood from the following detail 4description made with reference to the accompanying drawings in which Fig. 1 shows a toll cord circuit. Fig. 2 shows a trunk circuit outgoing from the toll board to a full mechanical olice. Fig. 3 shows a selector circuit. Fig. 3A shows a fragmentary modiiication of Fig. 3; Fig. 4 shows the relay and repeating coil equipment associated with the toll transmission selector circuit. Fig. 5 shows the toll transmission selector circuit. Fig. 6 shows a combination toll and local connector circuit. Fig. 7 shows the combination toll and local connector circuit for party line working. Fig. 8 shows a. connector circuit for a P. B. X. working. Fig. 9 shows a socalled toll terminal loop connector circuit. F 10 is a diagram of the manner in which ,i the drawings should be placed together in order to'read the circuit.

In order to simplify thel description and to render the invention readily discernible, a detail description of the handling of a call over the system disclosed will be given.

The toll operator, having been informed of the number of the wanted line and assuming this lineto be in a nearby exchange, tests for an idle trunk by touching the tip of her plug TT to the sleeve of the jack T SJ of the toll switching trunk in the well known manner, and if she does not receive a click in her receiver she inserts the plug TT into the toll switching trunk jack TSJ. A circuit is thereupon closed to opthe plug also closes `the Jfollowing circuit to energize relay C2; free pole of battery, resistance 200, right hand winding of relay C2, conductor 201` armature 202 of relay G2, conductor 203, ring contacts of jack TSJ and plug TT, conductor 110, lower normal contact of ringing keyr BK, 4right hand winding of retardation coil 111, winding of relay B43, armature and back contact of relay E155, which is not operated when the plug` TT is inserted in the toll trunk switching jack, but only when it is inserted in a toll line leading ,to a distant oflice, left hand winding of retardation coil 111, upper normal contact of ringing key RK, front contact and armature of relayv E29, conductor 102, right hand normal make before break contact of relay E72, conductor 103, tip contacts of plug TT and jack TSJ, armature 204 and back contact of relay G2 and winding of relay A2 to ground. Relay A2 is marginal and does not operate in this circut. Relay C2 in attracting itsV armature closes the following circuit to operate relay A3, which is the impulse relay of the iirst selector shown in Fig. 3; 4frere pole of battery. lower winding of relay A2 (Fig. 3),

conductor 300. back contact and armature 301 of relay D2., conductor 302, conductor 205. conductor 206, outer left hand armature and back contact of relay H2, conductor 207, armature and front contact of relay C2, left hand winding of relay C2, conductors 208 and 209, front contact and inner right armature of relay B2. conductor 210, polarized relay F2, conductor 211, conductor 212, conductor 303, armature 304v and back contact of relay D3, conductor`305,

upper winding of relay A3, conductor 306,

normally closed contact of switch 307, (which is operated on the eleventh rotary step of the selector), to ground. The operator now throws the dialing and monitoring key DK whereupon an obvious circuit is closed to operate relay B34, Fig. 1, whichk in attracting its armature `causes the operators head set to be connected across the cord. She now rotates the dial D for the first digit of the desired number. The closure 'of the contact 104 of the dial as the dial moves oil normal shunts out relay B3, operates marginal relay E22 and releases .relay B34.. Relay E72 in attracting its left hand armature locks itself to ground at the Contact of the dialing key DK, which when actuated remains in its operated position until manually released by the operator. Relay E72 lin closingits right hand ,contact .connects the tree vpole o'l' battery `through the 4impulse Contact 108 of theldial :to the tip of the `plug interposing a break -in the tip conductor. rEhe interposition of this Vbreak in .the tip conductor 'opens the -cireuit heretofore traced through the right hand winding of relay C2.. Marginal relay A2 now `operates in series with the impulse contact of Athe dial. the circuit being` as fol- -lows.: ree fpole of battery, resistance 109, impulse contact 108. right hand armature .and stront Contact of relay E22. conductor 1,03, tip contacts of plug` TT and jack TSJ, .armature 204.- and back contact rot relay G2,

yconductor 213. and winding or relay A2 to ground. Relay VA2 in attracting its lett lhand armature bridges relay 12 across `.the tip and ring Aof the cord in parallel with the lett hand winding of relay C2. Relay l2 in attracting its armature closcsua circuit.

-to operate relay D2 as `follows: tree pole of battery, resistance .214` conductor 215r` winding of relay D2. conductor V9.16, right hand armature and front Contact of relay l2,

conductor 217, Contact 218 of relay G2 to ground. .Relay D2 in attracting its lett Aarmature short circuits the lett hand windl'ring :or` relay C2 which thereupon releases, thus opening one of the bridges to ,the impulse relay A3 .and leaving bridged across ,the .circuit .only relay l2. This circuit may be traced as follows: `tree pole .oi battery,

flower winding of relay A3. conductor 300.

.back .Contact and armature 301 otrelay D3.y conductor 302, conductor Q05 and 206, outer flet hand armature and back Contact of relay H2, conductor V20T. conductor 298, .relay .12, `and left hand armature of relay A3., conductor 211, conductor 212, conductor .303, armature Y30a yand back contact ot relay D3, conductor .305, upper winding of relay .A3.and upper normal contacts 30T to ground. Relay D2 at Aits right hand armature and front Contact closes .the `following circuit. .to .operate relay E2: Yl'ree pole of battery, winding of relay E2, conductor 220, right .hand armature and Jiront contact ot relay D2, conductor 221, conductor "2922 and '228. inner left armature and front Contact et relay B2 to ground. YRelay E2 `in attracting its inner ri-git hand armature locks itselt to grounded conductor 242. The yfunctions of this relay `will be 'hereinafter described. Dial D, F ig. A1, in Vvreturning to "normal, interrupts at its impulse contact 108 the circuit of the impulse "rela-y A2, Fig. 2i, which at'its left .hand armature @intennupts the circuit of the impulse relay A3, Fig. 3, the number of times corresponding to the iirst digit of the desired number. Upon each retraction of `the armature off relay A3, the following circuit is closed for the vertical magnet 310 .of the first. selector: grounded .armature 311, Land iba-cli 'Contact of relay D3, conductor 312, Varmature and back contact of relay A3, :lower armature and front contact of slow releasing relay B3, winding of slow relay C3., ye'rticalmagnet 310, and free pole `of `battery l'to ground. On the irst step 'of the selector o ff normal springs 1313 close 'the following circuit for relay 314; free jpo'le of battery winding of relay 314. .conductor "315. off normal springs 313, conductors 316 and 317, armature and front Contact of relay C3 to to ground at the armature and front contact of relay B3. Relayv 314 in lattracting its upperarmature locks vvitself everthe I'following circuit: free pole of battery, winding ot relay 314, Vconductor 1315, toil? tnor-mal contact 313, conductor 1316,l armature `and back Contact of rotary magnet 318, conductor .319, conductor 320, upper armature and front Contact lof relay 314.1eonduct'or 321 to ground at the armature 311 and back Contact of relay D3. Upon the cessation of the impulses, however, relay `A3 remains energized and consequently relay 1C3, which is slow to release. after an interval, releases whereupon the `following circuit "is closed to energize the rotary magnet 318 ot the selector to step the Aselector brushes on 'to the first trunk in the selected level: ree pole of battery, magnet 318, :conductor Z322, 'front contact and lower armature of relay 3111, upper -normal contact of relay C3, front Contact and upper armature of relay B3 to ground. At the end o1' its stroke, the :rotary magnet 318 opens the locking-circuit itraced tor relay 314. Relay 314: in retracting'its lower armature opens the circuit :of the rotary magnet 318. If thelirs't trunk is busy` ground is present onxthe test :multiple 323 thereof, whereby the following circuit is close-dV to energize relay 314': `grounded multiple test vbrush '324H vconductor 325, armature 326 and back contact of 1relay D3, conductors 327 .and 319. back VContact and armature of magnet 318, conductors 310, contact 313. conductor 315. relay31ll ato tree pole of battery and ground. Relay 314511 attracting its upper armature Vagain locks itself through the back Contact off the rotary magnet 318 and in attracting its lower-'ardua ture again closes the circuit of the rot-airy magnet whereupon the selector brushes are stepped to the next trunk. This .action of H2 over the following circuit:

"ductor 222, right hand armature and back B 'of relay B3.

'in `attracting vits the relay 3 14 and rotary magnet is continued until an idle trunk is found which is indicated by the absence of ground on the test multiple 323 thereof. When the rotary magnet at the end of its stroke positions the brushes on to an idle trunk and no ground is present, relay 314 does not onergizebut relay D3 energizes over the following circuit: ground Ifree pole of battery, winding of relay 314, conductor 315, contact 313, conductor 316, armature and back contact of rotary magnet 318, conductor 319, conductor 327, conductor 328, winding of rela-y D2, conducto-r 329, lower normal con* tact of switch 307, conductor 330, to ground at the upper armature and front contact Relay 314 is marginal and does not operate in this circuit. Relay D3 armatures 304 and 301 eX- tends the talking conductors through to the lector brushes and cuts off impulse relay Assuming now that the selector has failed to find an idle trunk. In that event on the eleventh rotary step, switch 307 operates and opens at its uppermost contacts the circuit of the impluse relay A3 which causes the selector (Fig. 3) to restore. The opening of this loop circuit also causes relay I2 to be permanently deenergized. Relay A2 in remaining' energized and relay I2 being inert, the following. short circuit is closed about slow relay D2 to cause the same to release: ground, free pole ofI battery, resistance 214, right hand armature and front contact of relay A2, l-ay I2, conductor 217, contact 218, to ground. VIt will beunderstood that relay D2 is slow to release as shown, andholds up between the impulses ofone digit. RelayD2 in retract-ing its right armature operates relay ground, free pole of battery, winding of relay H2, concontact of relay D2, conductor 220,'inner right hand armature and front contact of relay E2 to ground on conductor 242. Relay H2 in attracting .its inner left hand'arinature locks itself up to grounded "conductor 242 and in attracting its inner rightarmature connects interrunter 223 to the inner left hand armature and front contact of relay E2 to shunt the resistance 200 and cause supervisory relay B23 in the cord circuit to flash the trunk and toll supervisory lamp 100 at the rate of 60 flashes per minute when the operator restores the key DK. This rate of flashing will indicate tothe operator that one of the switches has encountered a busy trunlf; group whereupon she will pull out plug TT andwill then wait and set up the connection later, or insert the other jack and again set up the connection by way of another trunk.V While the interrupting machine 223 is connected to the front armature and back contact of re plug into ancontact of relay H2,'as soon as relay D2 releases, this operation is not effective to flash the lamp until the operator, after having turned the dial for the last time, releases her dialing key DK, Fig. 1. The opening of the lowermost contact of this key releases relay E72 which in retracting its right armature again closes the loop circuit including the right hand winding of relay G2, Fig. 2, and the windings of relay A2, Fig. 2 and B13 (Fig. 1). It will,of course, be understood, if no idle trunk is found relay G2 is not energized. Relay H2 in attracting its outer left hand armature interposes a break in the loop ycircuit leading to the selector (Fig. 3) thus preventing the subsequent sets of impulses from operating the switches. Y n

The seizure of the toll transmission selector, Fig. 5, with which the relay and repeating coil equipment'of Fig. 4 is associated, causes the closure of the following circuit for impulse relay A5, Fig. 5 of the toll transmission selector: ground, free pole'or batter'y, right hand windingof relay A5, conductol' 500, conductor 400, conductor 401, back Contact and outer left armature of relay Bt, conductor 402, contact 403 of relay F 2, conductors 404 and 405, upper left hand winding of repeating coil 406, conductor 407, `multiple terminal` 351, brush 350, conductor 352, front contact and arma-- ture 304 of relay D3, conductors 303, 212 and 211, left hand armature and front contact Vof relay A2, winding of relay I2, conductors 298, 207, baclccontact and outer left hand armature of relay H2, con-. ductors206, 205 and 302, armature301 and front contact of relay D2, conductor 332, brush 333, multiple terminal 334, conductor 403, lower left hand winding of repeating coil 406, conductor 409, contact 410 of relay F4, `conductor 411, contact 412 of relay t, conductor 413, conductor 501, through the left hand winding of relay A5 to ground Vat the lower normal contact of the switch 502 which` is operated on `the eleventh rotary step of the transmission selector. rIhe impulse relay A5 in attracting its right hand-armature energizes slow relay B5. This, relay in attracting its left armature closes a circuit for relay 336 (Fig. 3) which in attracting its armatures applies a local ground to the test multiple 323 to cause this trunk to test busy. Relay 336 is provided when the transmission selectoris not located in the sameol'lice as the selector circuit of Fig. 3, to take care of differences in ground potentials and trunk resistances. If the. toll selector is in the same oflice, ground from the outer left armature and front Contact of relay B5 is transmitted to the test multiple 323, and relay 336 is omitted, as indicated in the drawing Fig. 3A. When the relay B operates it closes, at its right "65 back `Contact of relay F5,

hand armature, the following circuit for relay D'1 in the relay .fand repeating `coil cir- Y cuit, Fig. 4: ground, right `armature and .front contact of relay B5, conductors 503 and 518, conductor 504, conductor 505, contact 506 of relay D5, conductor 507 and 414, outer right hand armature and back Contact of relay F4, conductor v415, winding of re layD, free pole of battery to ground.

.The second operation of the dial by the operator'transmits the :seconddigit of the called line causing relay A2, Fig. 2 to open and close the loop circuit lfor relay A5, which, in vibrating its right hand armature, 4,transmits impulses over the following circuit to the vertical magnet 503 of the toll transmission selector: ground, right hand armature and back Contact of relay A5, inner armature and front contact of relay B5, conductor 509, armature 510 and back 'contact of relay D5, conductor 511, slow relay C5 magnet 508 to free pole of battery and ground. The brushes of the toll transmisvsion selector are thus elevated to the desired level. lflhen the dial returns to normal and maintains the relay A5 energized, 'relay A5 remains energized and, after a slight interval, slow relay C5 releases. Ylhenlthe relay C5 operatedv on the first impulse and Vthe selector' toolr its first step, relay E5 corresponding to relay 314 (Fig. 3) -.o.perated over the following circuit: ground, free pole of battery, winding of relay E5, 'upper kContact of off normal switch 515, conductor 516, armature andV front Contact of relay C5, conductor 517 conductor 518, conlductor503 to ground `at the right armature and lfront Contact of relay B5.' `rIn attractn ing its inner armature, relay locks itself w to the 'upper armature and back contact of Yslow relay F5, this `circuit including `the armature and back contact of rotary magnet 519. These circuits are similar to those -of Vthe selector of Fig. 3. Upon the cessation of the impulses vand thefrelease of slow relay C5, the circuit of the rotary magnet is closed as follows: free pole of battery, magnet 519, outer armature and frontcontact of Arelay E5, normal contact of relay C5, conductor 517 conductor 518, conductor 503, right armature and front contact of slow relay B5 to ground. The rot-ary magnet advances the brushes on to the terminals `of the first .trunk and at the end of its stroke vopens the locking circuit of the relay E5 which releases, opening'the circuit of the rotary magnet. If 4the trunk is busy, relay E5 again energizes over the following circuittground, free pole of battery relay E5, upper lcontact. of switch 515, conductor 516, conductor 520, back contact and armature of rotary magnet- 519. conductor 521` conductor 522, back contact and armature 523 of relay D5. conductor 524, lowermost armature and conductor 525, test Cil rselector circuit, Fig. 3.

.brush 526 to ground on the test multiple 527. Relay E5, in attaching its inner armature again locks up through the up er armature and back contact of relay E5 and at the other armature again closes the circuit of the rotary magnet which .advances the brushes to the next trunk and at the end o t' its stroke opens the locking circuit of relay E5 which in retracting its armature opens the circuit of the rotary magnet 519. The switch 502 of the toll transmission selector, Fig. 5, corresponds to the switch 307 of the lts function is to open the circuit of the impulse relay A5 on the eleventh rotary step of the toll transmission selector, that is to say, yif all the trunks in the group are busy.V rlhe opening of this circuit releases the switch and causes relay l2 Fig. 2te become permanently inert which causes the release of slow relay D2 and prepares a circuit for the interrupter 223 which results in the flashing of the ytrunk and toll supervisory lamp 100 when the operator restores her dialing key as described in detail in connection with Fig. 3. If, however, an idle trunk is found, relay D5, which corresponds to relay D3 Fig. 3, operates over the following circuit: ground, free pole of battery, `relay E5, upper Contact of switch 515, conductor 516., conductor 520` back Contact and `armature of magnet 519, conductors 521 and 522, winding of relay D5, upper normal contact of switch 502, conductors 530 `and 503 to ground at .the right hand armature and front 'contact of relay 502. Relay E5 is marginal and does not operate in this circuit in Aseries with the relay D5. Relay D5 then operates Aand in attracting its armatures 531 and 532 extends the talking conductors through to the talking lbrushes 533 and 534. The attraction of Athe armature 523 of relay D5 grounds the test brush 526 and consequently test multiple 527 of the selected Vtrunk `causing the same to test busy to other selectors. The contact 535 isV made before the contact 506 is broken by the Varmature 537 of the relay D5. Consequently relayDt Fig. 4 in the relay and repeating coil equipment is maintained energized over the' following circuit: ground, free pole of battery, wind ing of relay Dt, conductor 415, baci: contact and outer right hand armature of relay F5, conductor 414, conductor 507, contact 535, conductor 538, brush 539, multiple 540, control conductorA 541, conductor 600, conductor 501,`back contact and armature 602 of relay K5, conductor 603, sleeve conductor 650, conductor 542, multiple 527, brush 526, conductor 525, back Contact and lowermostarmature of relay F5,'conductor 524', 4armature 523 `and front Contact of relay D5, conductor 513, vconductor 503, to ground Vat the right hand armature and front contact of slow relay B5. Thus, the circuit for relay D* (Fig. 4) is maintained closed as the circuit is extended from switch to switch. As Will hereafter appear, relay F4 is not operated until the desired line is `icund idle and seized, when it reverses the direction of current flow in the circuit leading back to the toll operators position to light the supervisory lamp 100 to indicate to her the idle condition oi' the line, whereuponV she will cause the connector to begin the automatic ringing operation. The switch of Fig. 6 to which the connection has been extended is a combination toll and local connector containingmultiples or" ordinary lines and its bank. This switch is accessible not only to the toll transmission selectors of Fig. 5 but also to the local selectors which are used by the subscribers in building up their own local connections. Theseizure of the connector causes the closing ot the following circuit for the impulse relay A6: ground, free pole of battery, upper winding of relay A, conductor 604, conductor 605, left winding of slow relay J6, conductors 606 and 607, back Contact and lowermost armature of relay K, ring conductor 646, conductor 543, multiple 544, brush 534, conductor 545, front contact and armature 532 and front Contact of relay D5, left hand armature and front contact of relay A5, ring conductor 546, conductor 416, inner lower armature and back contact of relay K4, conductor 419, lowermost armature and back contactof relay H4, conductor 421, lower right hand winding of the repeating coil 406, resistance 460, conductor 422, left hand armature and Jiront contact of relay D4, resistance 423, conductor 424, resistance 461, upper right hand wind-v ing of repeating coil 406, back Contact and upper armature ot relayHl, conductor 425, back contact and uppermost armature of relay K4, tip conductor 426, conductor 547, armature 531 and front Contact oi' relay D5, conductor 548, brush 533, multiple 549, tip conductor 550, conductor 610, upper armature and back contact of relay l 6, conductor 611, conductor 612, lower `winding of relay A6 to ground. Relays J G and A6 operate in this circuit, the former at its innermost-right armature closing a 4locking circuit for itself as follows ground, free pole ot battery, right hand winding and right innermost armature and front contact of relay Je, conductors 614, 631 and 615 to ground a-t the armature 616, and front contact of slow relay BG which is energized upon the energization of the impulse relay AG. Relay B6 grounds the sleeve wire 617, leading to the test multiples in the local selectors, this circuit leading from grounded armature 616, conductor 615, to conductor 617. The returnot the dial to normal after the operation of trans mitting the tens digit of the desired num* ber interrupts the circuit of relay A2, Fig. 2which in turn` interrupts the circuit of the vthe winding of relay K6.

impulse relay A5, Fig. 5 which, in Vibrating its armatures, causes the impulse relay A or' the connector to transmit impulses to the Vertical magnet 618 of the connector over the following circuit: ground, .free poleof battery, winding or' magnet 618, winding oi" slow relay 619, right contact of oft' normal switch 620, conductor 621, front contact and lower armature vof relay B6 to ground at the armature and back contact of the impulse relay AG. At the iirst step of the connector, the ott normal springs 620 are shifted and the succeeding impulses are transmitted by way of the upper armature and front con`` tact of relay 619 and the contact 622 now closed at the off normaly springs 620. The selector' brushes are thus lifted to the desired level and upon the cessation of' the impulses, impulse `relay A remains energized and relay 619 in series with the Vertical magnet 618 releases, preparing the circuit of the rotary'mafgnet 623. The units impulses pass through the back contact of the im, pulse relay AG, lower armature` and front contact of relay B6, conductor 621, olf nor mal contact 622, upper armature and back contact or slow relay 619, conductor 624, inner left hand armature and back contact of relay G, conductor 625, back contact and uppermost armature of relay H5, Winding orotary magnet 623, 'ree pole of battery to ground. rlhe connector is thus stepped around into engagement with the desired line.

1f this line is idle, potential is present on its test multiple 626 through the cut ott winding of the line switch and, the following circuit is closedfto operate relay H6; multiple 626, brush 627, Conductor 628, right hand armature and back contact of relay F6, conductor 629, upper Winding of relay H, conductor 630, back contact and right hand armature of relay Gr, conductors 631 and 615, armature 616 of relay BG to ground. Relay H in attracting its armature 632 locks itself to the grounded sleeve wire 650 and extends this grounded conductor over conductor 633, middle right armature and front contact of relay J6, conductor 634 to Relay K6 inattracting its armature 602 disconnects the grounded sleeve wire 650 from the control lead 600 leadingy back to the relay D4, Fig. 4 of `the relay and repeating coil equipment circuit. Relay D'1 in retracting its outer right hand armature operates relay F4, Fig. 4, over the following circuit: ground, tree pole of battery, winding of relay F4, conductor 428, back contact and outer right hand armature of relay D4, conductor 429, conductor 550, armature 523 and front contact of relay D5, conductor 518 to ground at the right hand armature and front contact of relay B5. Relay Ft in attracting its Outer right hand armature closes a :sub-

stitute ground to 'hold up! the relay F6 to prevent ringing from occurring at this time: ground, right hand armature and back contact of relay tact and 'right hand armature of relay B4, outer right 'armature iront Contact and outer right hand armature of relay F4, control conductors 414 and 507, contact 535 and uppermost arma-ture of relay D2, conductor 538, brush 539, multiple 540, conductor 541, conductor 600, front contact, armature 635 and lower winding of relay F2 to 'ree pole of battery and ground. Relay F2 was energized upon the rst impulse to the vertical magnet,`this circuit being as follows gro-und, tree pole of battery, lower winding of 'relay F, lower armature and irontV Contact of slow relay 619, innermost right hand armature Iand front contact of relay J6, conarmature and ductor 614, conductors 631 and 615 to ground at the upper, `inner armature and rontwcontact of relay B4. When energized, relay FG locks by way` of its armature 635 and front contact, conductor 601, back contact and armature 602 oi' relay K6 to grounded sleeve wire 650. Consequently, the `operation of relay K4 to cause the reversal of direction of the current 'How in the loop leading back to the toll operators position would deenergize relay FG and unless a substitute circuit is pro-vided or holding up relay FG the ringing operation would automatically take place. This is prevented by applying ground `to the control conductor 600 over the circuit traced to hold Athe relay F4 until the operator, by depressing a key as will be explained, releases relay FG to start the automatic ringing operation. The release ot the relay D4 andthe consequent energization of relay F4 as described reverses the direction ot current flow in the talking conductors leading backto the operators position. After having turned the dial for the last time, 'the operator restores her dialing key DK which releases-relay E72 which in turn disconnects the dial from the tip oi the plug causing the release of the relay A2 Fig. 2 and causes the closure of an energizing circuit "r'or the right hand winding or relay C2, relay B43 and relay A2. Relay A2 it will be remembered, releases under this condition and in retracting its left armature deenergizes relay I2, which in Vreleasing causes the release or relay B2. The polarized relay F2 is now bridged across the vfollowing circuit: upper Vtalking conductor 212 Fig. 2, conductor 211, windings of polarized relay F2, conductor 210, inner right hand armature and front Contact of relay B2, conductor 209, conductor 208, lett hand winding oi relay C2, front contact and armature of relay. C2, conductor 207, outer lett hand back Contact of `relay H2, conductor 206 to lower talking conductor 205.

E4, conductor 430, back con-Y neiaeea The reversal of the direction vof current in these talking conductors due to the operation of relay F4 causes the relay F2 lto cooperate, closing the following circuit l'or relay G2 ground: free pole of battery, winding off relay G2, conductor Q24, `contact 225 and armature of relay F2, conductors 226, 227, 22S, inner left hand armatureand front Contact of relay` B2 to ground. Relay G2 locks itself up over the following circuit: ground, free pole or' battery winding of relay G2, conductor 224, conductor 229, front contact and armature 230 of relay G2, conductors 231, 227 and 228-to ground at the inner left hand armature of relay B2. Relay G2 connects the talking 'conductors oi Fig. '2 through to the talking conductors of Fig. l whereupon the trunk and toll relay B43 operates in series with the relay A5 (Fig. 5) and lights the supervisory lamp 100 as a ringing signal to the toll operator. Relay G2 (Fig. 2) cuts off the bridge including relays C2 'and A2. The operator now operates her ringing key RK which impresses alternating current upon the talking conductors and operates the alternating current relay G4 which in attracting its armature operates the relay E4 in an obvious circuit. This relay in attracting its right armature opens the circuit heretot'ore traced, which has been holding relay F2, (Fig. 6) energized. This relay in retracting its `armature 637 connects ringing lcurrent to the called line through the upper winding of relay FG. This ringing current is automatically continued until the called party removes his receiver, resulting in vthe 'increase in the current through the upper winding ol relay F 2 causing the same to operate removing the ringing current. The Vattraction of the armature 635 of this relay closes'a locking circuit for the same over control conductor 600. The extension of the tip and ring conductors by relay F(s to the called line operates relay A4 over the winding of which talking current is i'ed Yto the `called line. Relay A4 in operating energizes relay B4 which in attracting its right hand armature applies ground to the conductor 414. to hold up relay F4, (Fig. 6) independently of the relay E4. Relay B4 :in attracting its left hand armature opens the connection of battery through the windings lof relay A2, (Fig. 5) to the talking conductors 407, 408, leading back to thev operators `position which causes the deenergization of supervisory relay B42. This lrelay .in retracting its armature extinguishes the supervisory lamp 100 which notifies the operator that the subscriber has responded. Talking current is fed to the called line over the winding of relay A4 andthe repeating coil 406. This 4talking circuit is a standard repeating coil transmission circuit used in long distance connections. Talking current rau Y operator instead.

is -fed to the callin line from the calling distant exchange.' uring conversation the trunk leading from the left hand windings of repeating coil 406 through the right hand winding ot' the repeating coil (not shown) at the distant oflice is dry, in accordance with standard practice.

Assuming now that the desired linewhen selected by the connector is busy. In that condition the test multiple 626 Fig. 6 is grounded. TWhen test wiper 627 is set on the busy multiple 626, ground is extended over brush 627, conductor 628 right hand armature and contact 6407otI relay E, conductor 641, armature 642 and back contact of relay H6, conductor 643 winding of relay G, free pole of battery to ground. Relay G6 energizes and when relay EG releases locks itself up over the following circuit: ground, free pole of battery, relay GG, conductor 643, back contact and armature 642 of relay HG, conductor 641, make before break contact ot relay EG, front contact and right hand armature of relay G6, conductor 631, Conductor 615 to ground ati the armature 616 and front contact of relay B6. Relay GG in the case of a local call connects busy tone from the source 645 tothe Calling line. ln the case of a toll call this busy tone is not used, a flashing signal being given to the By reason of the ground connection to the multiple 626 of the selected line relay H6 does not operate. Consequently, relay K is not energized to open the circuit of relay D4 (Fig. 4) as described in the case of an idle line. Inasmuch as relay D4 vremains energized, relay F4, whose circuit is maintained open at the outer right hand armature andv back Contact ot' relay D1 is not operated and nocurrent reversal in the trunk leading back to the operators position occurs. Polarized relay F2 (Fig. 2), is n'ot operated in this case and relay G2 remains inert. Since the relay E2 is locked up at this time and relay G2 is inert, when the operator restores her dialing heyv DK the following circuit is closed from interrupter 233 of 120 impulses per minute to shunt out resistance 200 to cause the supervisory relay B43 to flash the lamp 100,120 times per minute, which indicates to the operator that the selected line is busy, whereupon she pulls out the plug TT from the trunk switching jack TSJ .which results in the release of all switches and the normal condition oli all the apparatus including the various locked up relays. Durw ing existence ot a connection in order to recall the operator the called subscriber by moving his receiver Vhook up and down causes the supervisory lamp at the toll operators position to flash as iny manual practice without releasing the switches. This is apparent from the preceding description inasmuch as relay A4 is in circuit with the called line and each time it attracts its armature, operates the relayV B4 which removes battery and ground from the trunk conductors leading back to the su-y pervisory relay B43 vand puts a bridge across the relay A5 to holdv it operated as long as the subscriber has his receiver oli the hook. When the called subscriber replaces his receiver he lights the lamp 100 at the toll operators position Fig. 1; i The operator may rering the subscriber it necessary, if she desires to recall, by actuating her ringing key RK, which in operating actuates relay C4 to operate relay E, which in attracting its right hand armature again releases relay Fs which initiates the automatic ringing operation. The control of this relay FP was removed from the relay F# by the attraction of the rightv armature ot' relay B4 whenV the called sub scriber responded and was restored to the relay E4 and consequently `to the operatorV when the called subscriber replaced the-receiver and deenergized relay B4. When the operator. desires to break Vdown the connection after the called subscriber has replaced his receiver, she removes the plug TT from the toll switching jack TSJ. This releases relay A5 Fig. 5 which causes the restoration of -all the switches. lf, however, the operator pulls out the plug while the called subscriber still has hisreceiver 'off the switchhoolnrthe switches are not released since relay A5 which controls the release lis maintained energized over the 'following circuit: grounded battery, right hand winding` of relay A5, conductor 500,

conductors 400 and 401, resist-ance 435, in-

ner left Vhand armature and front contact of relay B", conductors 413 and 501, left windingof relay A to ground at the lower normal contact of contacts 502, it being noted that relay B4 which controls this loop'circuit is itself controlled by relay A4 in circuit with the called line and controlled at the switchhook of said line.

Assuming, howeventhat the called subscriber'has replaced his receiver, when the operator removes lthe plug, relay A5 in re leasing deenergizes relay B5. Relay B5 in 'retracting its outer lett hand armature removes ground rom the sleeve conductor 551 leading over the sleeve conductor 436 to relay 336 which in releasing its armature removes ground from the sleeve wire 325. The removal of this ground releases relay D3 whereupon the release magnet 340 operates as follows: ground, free pole of battery, vwinding of magnet 340, off normal switch contact 341, lower armatures and back contacts oit' relays B3 and A3 to ground at armature 311 and back contact of relay D3. VThus the irst selector is restored and upon reaching its normal position opens the olf normal springs 313 and 341. Thel removal of ground from conductor 503, by the retraction of right hand armature ol' relay B releases relayY D5 and the retraction oit the right hand armature olrelay A5 and inner left hand armature of relay energized. in parallel with the release niag- Cil net and opens the circuit for the test brush '.526 during restoration at its lowermost armature. At its armature 554, relay F5 short, circuits the: letthand winding of relay A5'. Atits upper armature-it closes a lool;- uing circuit for itself which is opened when the ott normal switch assumes its normal position. The opening'ol the circuit o'fthe tip and ring. conductors 610 and 6&6 causes the release of relays AG, B6, JG, (Fig. 6)

` which results Ain the closure of the circuit ol' release magnet 686: lree pole of battery, magnet 686, lett hand contact of oil normal switch 620, back contact and lowerinost armature ol relay D, lower armatures and back contacts of relays B6 and AG to ground. The connector upon reaching normal position restores the od' normal switch 620.

Referring now to Fig. 7, this represents a combination Vtoll and local connector for party line working. The arrangement for party line working shown employs' what is known as segregated grouping, each connectorV having a generator of a certain character associated with it and only the stations on the line having bells responsive to this generator appear in the multiple bank of tiis connector, in accordance with the well lrnown practice. The only difference between the circuits of Fig. 6 and Fig.

f' 7. is that a so-called pick-up relay Z7 is provided to insure that the ringing will commence at the beginning of the cod-e. lt will be remembered that it the line isidle relay H7 operates, andl in operating operatesrelay' K7 which causes the reversal of the current flow in the circuit leading back' to the toll operators position to light the lamp: 100 as a ringing signal to` her. She

thereupon presses the ringing lrey whereupon relay C4 (Fig. el) operates to energize re-` lay E4 (Fig. 4) which in operating causesV the release of relay F7. However, when this circuit releases relay F7 does not alone impress ringing current on the called line but instead prepares a circuit for a pickup relay Z7 as follows: ground, free pole or' battery, winding of relay Z7, uppermost armature and back contact ot'- relay F7, normal contact of relay Z7, conductor 701, armature 702 and front contact of relay H7, interrupter 7.00 to: ground if' the inter-A irupter brushes are on=` the metallic segment.

grounded sleeve wire 714. In attracting its.

lowerarmature relay Z7 prepares the ringing circuit andL upon the ringing machine reaching its ringingposition ringing current is impressed Von the called line overthev following circuit: ringing machine 703, upperwinding of relay. F7, lower armature. and. front contact of. relay Z7, armature 704V and back contact of. relay F7, armature 705,. biuslr706, multiple` 707, through the bell at the called.. station, returning over the upper talking-conductor, multiple 708, brush 7 09?,A front contact andarmature 710.v ol relay H7, armature. 7.1.1, and back contact of relay F7 to .grounded battery pole of the'. generator; This code ringing continues until the called party answers, whereupon the ringing cutoll relay F7 operates connecting the calling and` called ends ofV the talking conductors to gether and locking itself to the control. conductor 712. From this point the operations are the saineas those described in connection with Fig. 6.

.Referring now to Fig. 9. This Vligure represents a toll connector circuit, that isto say connectors which are accessible only to the toll` transmission selectors of Fig. 5 and not to` local selectors. are provided where certain lineshave an unusually' large amount of toll trafli'c.

Then the tolltransmission. selector of Fig. 5-

scizes a. connector of Fig. 9, the ground on sleeve conductor 542 is transmitted over con-- ductor 911, armature 900 and back Contact of relay l)9 to the cont-rol. conductor 901, conductor 541,. armature 537 and front con-- tact ci relay D5, control. conductor 507 to hold the relay D4 (Fig. 4)y energized.

VWhen the toll connector is selected! by the` toll transmission selector, relay A9 isv ener-- gized over the loop leading back to the circuit ot Fig; l as described, and the interrup-` tion of thisloop due-tothef operation. of they dial causes relay A9 to transmitimpulses over.

the following circuit tothe vertical magnet, 902 of the connector: ground, armature 903A and back contact of relay D9, right handl armature and: back contact. of. relay Altoonductor 919, outer left hand armature and'v front contact of relay F9,.contact 904 of or1 normal switch 905, winding of slow relay C, winding. of vert-ical magnet 902, free pole ot battery to. ground. RelayF-9 energizes over. its right handz winding. andi the ing to these impulses at the irst step opens code These switches:

olf normal switch 905, but relay C9 remains operated over Contact 906 at its armatur and front contact. Relay C9 is slow to release andholds itself energized between the impulses, but restores at the end of the first series of impulses and shifts vthe impulse circuitto the frotary magnet. The impulses corresponding to the units digit now pass over the bach Contact of the relay C9. Relay E9 in the rotary stepping eircuit, being slow to release, holds up between the impulses and the second and succeeding impulses pass through the rotary magnet 959, ,over the lower armature and front contact of relay E9; Relay E9 in operating connects relay D9' to the test brush 907. lf the line is idle however, relay B9 is not open ated, since there is no ground on the multiple 908 thereof, but full potential through the cut-olf winding of the called line switch. This current is transmitted over the armature 909 and bach contact of relay E9, inner' left hand armature and back contact of relay B9, conductor 912, conductor 913, upper winding of relay D9 to the grounded sleeve Relay D9 gets sutlicient current ough thev bridge cutoff winding to operiliciently to make its contact Y when "aver windingis brought into circuit i permits it to energizesufliciently to il iet i its armatures., In attracting its armatures it disconnects the grounded sleeve conductor 911 from the control conductor 901 to deenergize relay D4 (Fig. 4), which causes the` current to be Areversed in the trunk leading back to the toll operators position to cause the lamp 100 to beV lighted asa ringing signal as described heretofore in detail. ln'attracting armatures 914 and 915 it connects the incoming and outgoing tip and ring conductors together and disconnects relay A9; the armature 915, however, closes a circuit through resistance 916 to hold the relay A9 energized. While the attraction of armature 900 of relay D9 removed ground from the holding winding of relay F9, ground is returned over the Vcontrol conductor 901 to the. holding winding to hold the same energized and prevent ring` ing until the operator depresses her ringing hey. lllhen she presses her ringing hey e operates relay @t l) which in turn operates relayllt (Fig. l) to remove this ji und from the control lead. Relay F9 "hereupon releases and transfers the called line from the trunk to the machine ringing circuit. The ringing circuit is as follows: ground at generator 9&0, lett hand winding of relay F9, left hand` armature and front contact of relay A9, outer right hand armature and back contact of relay F9,.lower talking conductor, through the substation,

'upper talking conductor, inner left hand.

rature and back contact of relay F9 to groundedbattery at the armature andback coil 406 as in'Figs. l to 6 and the called subscriber controls supervisory lamp 100 at the switch hook contacts.

When the Connection is broken down relays D9 and F9 release. Relay D9 releases relay A9 andthe circuit of the release magnet 918 is closed as follows ground, free pole of battery, magnet 918, upper make contacts of olf normal switch 905, outer left hand armature and bach contact of relay F9, conductor 919, bach Contact and right rmature of relay 119 to ground at the armature' 903 of relay D9. When the switch reaches its normal position the off normal switch 905 is restored to normal. 'y

If the selected line is 'busy slow relay .B9 Vis operated from ground at the multiple 908, test brush 907, armature 909 and front contact of relay E9, winding of slow relay VB9 to free .pole of battery and ground.` Re

lay B9 then locks itself over make before break contact 910 at its inne' right hand armature and front Contact to the grounded sleeve wire 911. rlhus no circuit is closed through the winding of the relay D9 to operate the same to release relay DAk (Fig. Ll) to reverse the direction of current flow in the circuit leading bach to the operators position. Consequently relay G2 (Fig. 2)

'1s not operated and the interrupter 233 is connected in shunt of the resistance 200 to intermittently operate relay B49 in the operators cord circuit when she restores her dialing key Dl. Thus, the supervisory lamp is flashed to indicate that the line isv busy as particularly described in connection with Fig. 6.

Referring now to Fig. 8, this figure shows a toll rotary connector, that is to say a switch which is only reached from the roll transmission selectors and in which eac-h subscriber may have a numberk of lines running to his station. llllhen this connection is seized by the toll transmission selector, impulse relay A9 operates over the loop and Operates slow relay B8. VTens impulses pass from ground at thearmature 800 and back contact of relay B8, armature and back contactof impulse relay A9, left hand armature and front contact of relay B9, contact 801 of olf normal switch 802, winding of 1nagnet 803, winding of slow relay `D9 to free p ole of battery and ground. Thus, the connector is lifted tothe desired level. Upon the termination of the tens impulses, the

reo

relay CS releases. The units impulses pass Vfrom ground at the armature 800 and baci; Contact of relay DS, armature and back conn tact ot relay A8 left hand armature and front Contact ot relay B8, contact 804 of the off normal switch 802, armature 805 and back contact of slow relay CS, conductor 806, conductor 807, armature 808 and back contact ot relay K8, conductors 810 and 811, armature 812, and back Contact of relay HS, conductor 818, winding ot rotary magnet V814i to free pole of ybattery' and ground.

lvlagnet 814 rotates the connector intoengagement with the first l). B. 1X.. trunk. Slow relay E8 remains energized while the impulses are beingV transmitted. lt the first l). B. X. trunk is busy, test multiples 815 and 816 will be grounded. The ground on multiple 816 is transmitted over test brush 817, conductors 818 and 840, armature 819, and front Contact of slow relay ES, conductor v820, armature 821, and back cont et of relay Hconductor 822 and relay lis to free pole of battery and ground. Relay Vl@V energizes and locks itself in the followand back contact ot rela E3, conductor 881 Y a test brush 882 to grounded multiple 815. lelay S in attracting'armature 883 disconnects'relay iig tti-om the grounded sleeve wire and connects relay HS over conductors 884 and 818 to grounded multiple 810. llelay GS closes the following circuit tor the rotary magnet 814, to rotate the connectorv on to the next trunk: ground, tree pole ot battery, winding otrotary mar/net 814, conductor. 860, conductor 813. armature 812 and back contact oi' relay lil?, conductor 811, lower armature and front contact ot' relay (is. conductor 886 to grounded sleeve wire 837. Rotary magnet 814 at the end ot itsY stroke breaks thc circuit. ot relays G and CS. Relay G8 in retracting its lower armature opens the circuit ot' the rotary magnet. Relay C8 opens the energizing circuit of relay KS, which is released when brush 817 reaches the idle trunk. Assuming that this trunk is idle, potential. on the test terminal 888 thereof through the bridge cut-oilI winding of the line is transmitted by brush 81T conductor 818, conduct-or 840, `armature 819 and back contact .of relay Econductor 841,` the Viippgn windingot relay Hl'conductor L842,

upper outer armature and back contact of' relay KS, conductor 843, outer armature and front Contact ot relay BS to ground. Relay H8 in attracting its armature 845 locks itsel't to grounded sleeve wire V837 and extends this ground over conductor 847 to relay Dg which in operating cuts ott' impulse relay A? and disconnects grounded sleeve conductor 887 from the control conductor 848, at its armature 849. Thus, the deenergization of relay D4, (Fig. 4) follows which causes the current to be reversed in the trunlr leading back to the toll operators position, which results in the lighting or the lamp 100 as a ringing signal to the operator. Relay F? was operated upon the operation of relay BS when the toll transmission selector seized the connector. The operation ot relay DS in attracting its armature 850 opens the original circuit for the relay F8 but before this relay which is slow can .be energized, a substitute circuit is closed over control conductor 848 as described. The armature 854 of relay H8 ap plies a direct ground over conductor 818 to `the test multiple 838 ot the seized line and d CIV this ground is transmitted by the conductor 855 to the test multiple 856. Thus this trunk will test busy to other connectors. lWhen the operator depresses her ringing hey it operates alternating current relay U1 t0 energize relay E4 which removes ground from the control lead and consequently relay FB releases connecting at its armatures 851 and 852 the ringing machine in rcircuit with the called line to signal the subscriber. Upon the response ot the subscriberrelay F8 operates by means of its lower winding Vand again locks up to grounded control wire 848. Current is i'ed to the called line relay A4' and the repeating coil 406 (Fig. 4).

The called subscriber by operating his switch hook flashes the supervisory lamp l0() at the toll operators position. After the called subscriber replaces his receiver, the operator can, actuating her ringing lrey lll', again cause the connector to start the ringing operation until the called party answers. W hen the called subscriber replaces his receiver, relay 'A4' releases, deenergizing u relay il* which again connects current-to the trunk Vleading back to the operators position to operate relay B43 to light the supervisory lamp 100 permanently as a disconnect signal. The operator thereupon removes the plug which result-s in the release ot' the switches as described. The release circuit of the l). l. X. connector as tollows: ground, battery, winding ot release magnet 853, lower malte contact of oil? normal switch 802, left hand armature and back contact ot relay BS, lower armature and back Contact of relay AS, armature 800 and back 'contactot Vrelay D8 to ground. The ori' normal switch is restored when the connecto'r shaft reaches its normal position.

inn

lSt)

lit)

Relay H4 is provided to permit the toll operator to manually apply ringing current to the selected private branchV exchange line to signal the operator thereat. This relay is operated when the relay is operated due to the actuation of the ringing key by the toll operator. The circuit tor operating relay H4 extendsiifrom grounded battery, winding of relay H4, left hand contacts of relay E4 to ground at the contacts otk relay A4. Relay H4 is not operated Whenlre-ring ing on the line, other than a private branch exchange line, because in such a case, there is no bridge across theT and R conductors to energize relay At. It' relay A4 is not operated, relay H4 cannot be operatedwhen relay C4 is energized because the ground at the contacts of relay A* is not in circuit with the winding of relay H4.. ln private branch exchange working the called subscriber may hang up his receiver, but due to the bridge at the P. B. X. operators board the relay A4 remains operated and thus no .signal is given to the toll operator. Circuits for private brancli-excl1anges where a bridge is placed across the operators cord-circuit., when the subscriber atthe private branch hangs, up his receiver, are old and well known in the art for example, as shown in Patent No. 1,232,507, otl July l0, 1917, to H. L. Darrah.

What is claimed is:

l. in a telephone exchange system, the combination with telephone lines, automa-tic switches, groups ottrunk lines terminating therein, an operators position, a lamp thereat, means controlled irom said position for setting said switches to interconnect said :lines over said trunks, means controlled l,by the busy condition of the selected line for flashing said lamp in one manner and means controlled by the busy condition ot a selected trunk group for flashing said lamp in another manner.

2. lin a telephone exchange system,A the combination with an automatic otlice ineluding' automatic switches, subscribers lines terminating therein, a toll operators position including a cord circuit having a supervisor lam 3 therein a dial associated therewith, means actuated in case one ot said switches fails to tind anidle trunk tor flashing` said lamp in a certain manner, and means actuated in case the connector finds the selected line busy :for flashing said lamp in a diii'erent manner.

3. in a telephone exchange system, the combination with telephone lines, automatic switches, groups oi? trunks terminating therein, an operators position, a lamp thereat, means at said position for controlling said switches to interconnect said lines over said trunks, means controlled by the idle condition of the selected line for lighting said lamp as a ringing signal, means controlled by the operator 'tor causing ringing current to be applied tothe selected line, means controlled by the response of the called party for cutting oil' the ringing` current, means controlled by the busy .condition oi' a selected trunk group for flashing said lamp at a certain rate, and means controlled by the busy condition of the called line Jr'or flashing said lamp at a differentrate.`

i. in a te ephone exchange system, the combination with telephone lines, lautoifnatic switches, groups of trunks terminating therein, an operators position, mea'nsfat said position for controlling said switches to int rconnect said lines over said trunks, a su pervisory lamp at said position a supervisory 'clay controlling the samea polarized relay kbridged across one ot said trunks, means controlled by the idle condition of the selected line for operating said polarized relay to cause the energization of said supervisory relay, means controlled by the busy conditio-n of said line 'for closing an interrupted circuit Vthrough said supervisory relay to iiash said lamp at a certainl rate, and means controlled by thel busy condition ot a selected trunk group for closing an interrupted cirtif:

till

titl

cuit to intermittentlyV energize said supervisory relay to flash said lamp at a vdiilerent rate. Y y

5. In va telephone system, telephone line, automatic switches, a trunk circuit, an operators position, a cordcircuit thereat having means torr controllingsaid switches to build up a connection over said trunk lines to a selected line, a supervisorylamp in said cord, a supervisoryrelay in said cord, a polarized relay in one of said trunks, means controlled by the idle condition ot the selected line for operating said polarized relay 4to close the circuitoii said supervisory relay,

means controlled by the Abusy condition of, the selected line for preventing the operation of said polarized relay `and for closing aninterrupted circuit to said supervisory relay to iiash said lamp at a certain rate, and means controlled by the busy condition et a selected trunk group for closing an int rrupted circuit to said supervisory relay to flash said lamp at a different rate.

6.111 a telephone system, the conjibnation with telephone lines, groups ottrunk lines including auton'iatic switches, au operatoi"s position, means at said position 'for building up a connection to a called line over said trunks and switchcs,`a supervisory signal said position, a supe visory relay therefor, a lcv at said position, an interrupted circuit 'tor said relay prepared during the building' up of a connection. a second interrupted circuit, means controlled by the busy condition the called vline and said key 'lor connecting said first circuit to said relay to

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