US2162892A

US2162892A - Telephone system

Info

Publication number: US2162892A
Application number: US141428A
Authority: US
Inventors: Charles D Koechling
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1937-05-08
Filing date: 1937-05-08
Publication date: 1939-06-20
Anticipated expiration: 1956-06-20

Description

Julie 20, 1939. c. D. KO EcHLlNG TELEPHONE SYSTEM 2 Sheets$heet 2 Filed May 8, 1937 FAN N NUFQQ at //v l ENTOR v C. 0. K05 CH1. ING

ATTORNEY Patented June 20, 1939 PATENT OFFICE TELEPHONE SYSTEM Charles Koechling, Floral Park, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application May 8, 1937, Serial No. 141,428

16 Claims.

This invention relates to telephone systems and particularly to semi-automatic systems.

It is an object of the invention to facilitate the completion of connections in a system comprising a dial, local and tandem office and a plurality of manual, local or toll o-flices.

According to this invention two-way trunk circuits are provided between a dial ofiice and each of a plurality of manual local or toll offices, each of the trunks being provided with a repeating coil which is included in the talking connection on calls originating or terminating in the dial ofiice and with switching means for by-passing the repeating coil on calls incoming to the dial onice from one of the manual local or toll offices and terminating in another of the manual local or toll oflices.

A feature of the invention is the provision of trunks between a dial, local and tandem, oihce and each of two manual ofiices, the line relay of each of the associated trunk circuits in the dial office being connected to terminals in the banks of local selectors for selection on calls originating in the dial office and to terminals in the banks of the incoming selectors associated with the trunks for selection on calls originating in one and terminating in the other of the two manual oflices. A polarized switching relay is provided for each trunk for connecting the conductors of the trunk to the impulse repeating relay and repeating coil of the associated trunk circuit or to the conductors of the associated incoming selector switch, the operating winding of the switching relay being connected in series with the line relay of the selected connector switch on calls terminating in the dial oflice and in series with the line relay of one of the trunks to the other of the two ofiices on calls from one to the other of these ofiices, the connections between each of the trunk circuits and the terminals in the banks of local selector switches being reversed with respect to the connections between these trunk circuits and the terminals in' the banks of incoming selector switches. The connections established between the conductors of an incoming selector and the conductors of the associated trunk by operation of the polarized switching relay of the trunk circuit, cancel the effect of the aforementioned reversal of the 50 connections between the terminals of the local selector switches and the terminals of incoming selector switches, so that the same supervision is given to the originating manual office on a tandem call as is given to this office on a call terminating in the dial ofiice.

A further feature is a two-way trunk circuit in a dial office for use in extending calls from subscribers in the dial ofice to an operator in a distant office and for use in extending calls from an operator in one distant oflice to an operator 5 in another distant ofiice, the trunk circuit being arranged to receive a signal from the answering operator and in response to this signal to reverse the current toward the calling operator or subscriber as an answering supervisory signal and ll) arranged to prevent this reversal of the current toward the calling subscriber if the calling line is a coin line.

The drawings which form a part of this specification disclose schematically a telephone sys- 15 tem in which the invention is embodied; and a clear and complete understanding of the invention may be obtained from the following description of this system.

Referring to the drawings: 0

'Fig. 1 shows a dial ofiice, designated Ofiice I, comprising a subscribers station A and line H,

a line-finder switch LP, a first selector switch S, and two two-way trunk circuits TI and T2;

Fig. 2 shows incoming selector switches IS--I 25 and IS2, a connector switch C and a called subscribers station B all in Office I;

Fig. 3 shows a manual office, designated Ofiice 2, comprising a two-way trunk circuit T3, which is connected by trunk 200 with trunk circuit TI 30 in Ofiice I Fig. 3 also shows a cord CD and an operators position equipment; and

. Fig. 4 shows a second manual OffiCG, designated Oflice 3, comprising a two-way trunkcircuit T4 which is connected by trunk 306 with trunk cir:- 351 cuit T2 in Office I.

The Ofiice I is an automatic ofiice provided with impulse controlled switches for establishing connections between subscribers lines and interofiice trunks. The telephone instruments pro- 40 vided at stations A and B are of the type usually employed in automatic telephone systems and include a dial or other impulse sender for use in establishing desired connections. The linefinder switch LF, selector switch S, intermediate selectors IS-l and 18-2, and connector switch C are all of the well-known two-motion step-bystep type. For a description of the structure of such switches and their operation when used as selectors and connectors reference may be had to the second edition of Automatic Telephony by Smith and Campbell, pages 53 to inclusive. For a description of the operation of such switches when used as line-finders reference may be had to Patent No. 1,799,654 granted to R. L. 65

Stokely April '7, 1931. The line-finder switch LF is represented by a set of three brushes and one set of terminals; the selector switch S is represented by a set of four brushes and two sets of terminals, 8 and 9; the intermediate selector switch IS-2 is represented by a single brush and a single terminal for each of two sets of terminals; and the connector switch C is represented by a set of brushes and one set of terminals. All magnets, relays and other circuit apparatus associated with switches LF, S, IS2 and C have been omitted. The selector IS-l is represented by its set of four brushes and two sets of terminals together with the magnets and other associated circuit apparatus.

Each of the two-way trunk equipments, such as Ti and T2, in Office l are connected to terminals in the banks of local selectors such as S and also to terminals in the banks of incoming selectors such as ISl and 18-2. A repeating coil RC! is provided in each of these trunk equipments for use on outgoing calls and for use on incoming calls which terminate in Office 5. A polarized relay, such as relay 2% in trunk equipment TI, is provided in each of these two-way trunk equipments for disconnecting the trunk from the repeating coil and connecting the trunk directly to the associated incoming selector switch on incoming calls which do not terminate in Oflice l but are completed through another similar two-way trunk to another manual office.

The Omces O2 and 03 are manual offices and may be either local or toll offices. The interoflice trunks including trunks 2G9 and Mil are jack ended at one or more operators positions, cords being provided for establishing desired connections. Trunks 2G9 and Bill) are arranged for twoway operation. Answering jacks AJ are provided for use on incoming calls; and outgoing jacks OJ and dial jacks DJ are provided for use on outgoing calls. The two-way trunk equipment T3 in Office 2 is shown in detail; but the trunk equipment T i in Office 3 is represented by the answering, outgoing and dial jacks, all of the associated circuit apparatus being omitted.

Assuming a call to have been originated at station A and assuming the extension of line Ll by line-finder switch LF and first selector switch S to the terminals. of the two-way trunk equipment Tl, line relay ii is operated by the current in a circuit from battery through the lamp resistor l2 and lower winding of relay l l, lower left winding of repeating coil RCl, inner lower back contacts of relays ltand i, terminal and brush of selector S, brush and terminal of line-finder LF, over line Li and through the telephone instrument at station A, top terminal and brush of line-finder LF, top brush and terminal of selector S, inner upper back contacts of relays l4 and 23, upper left winding of repeating coil RCl, upper winding of relay 5 i and through lamp resistor 55 to ground. Relay ii closes a circuit, which includes the lowermost back contact of relay l3 and back contact of relay it, for operating relay 1?. Relay l! closes, at its uppermost front contact a circuit for operating the slowto-release relay l8; closes, at its inner lower front contact, a circuit over conductor 23 for operating relay is; closes, at its middle lower front contact a circuit over conductor 25: for energizing the polarizing, lower winding of relay 25; and closes a circuit, for operating relay 2i, from battery through the winding and upper back contact of relay 2|, back contact of relay l3, lowermost front contact of relay ii, and through the back contact of relay 22 to ground. The ground at the middle lower front contact of relay H is further connected over conductor 24- to the test terminal and through the test brush of selector S to hold this selector and the line-finder switches in usual and well-known manner.

Conductors

23 and 24, already connected to ground by the operation of relay H are also connected to ground at front contacts of relay is. Relay 2! locks through its inner upper front contact; and, at its lower front contact, relay 25 connects the ringing current source 25 to and through condenser 27, thence through a back contact of relay 28, to the inner lower back contact of relay it, thereby transmitting an audible ringing signal to the calling station A. Normally the windings of relay 22 are connected through back contacts of relays ll, i i and 20, over the conductors of trunk 263, in series with the left windings of repeating coil RC2 and the windings of polarized line relay 25%| of incoming trunk equipment T3 in Office 2, the current in this circuit being insufficient to operate relay 22 in Office I and in a direction ineffective to operate relay 23l in Office 2. The aforementioned operation of relay 5! reverses the connection between the windings of relay 22 and the conductors of trunk 280 to cause the operation of the polarized relay 261. The operation of relay 253! causes the operation of relays 282 and 263. At its inner upper front contact, relay 2H2 closes a circuit for lighting the answering lamp 2%; and, at its lower front contact, relay 292 connects a busy marking potential to the sleeve of the jacks OJ to guard this trunk from seizure in Office 2. When an operator inserts the answering plug of a cord CD in the answering jack AJ, relay 205 is operated by the current in a circuit which includes both windings of relay 255, the right windings of repeating coil RC2, the tip and ring conductors of jack AJ and cord CD. Relay 205 closes a circuit for operating relay 28S and a circuit, through the lower winding of relay 291, for operating relay 253?. At its upper front contacts, relay 2% completes. the talking circuit, by bridging condenser 2&8 across the inner ends of the left-hand windings, of repeating coil RC2; and also short-circuits the lower, high resistance winding of relay 2c 1, thereby causing the operation of relay 22 of trunk equipment Ti. Relay 29'! looks, through its lower winding and lower front contact and the inner lower front contact of relay 2%, to ground at the front contact of relay 285; and locks through its upper winding and upper front contact to ground at the front contact of relay 253. Relay 2c? is, therefore, held operated under the joint control of relays 2%! and 205. At inner lower back contact, relay 2% opens the circuit for lighting lamp 2%; and at its outer back contact, relay 2% disconnects battery from the sleeve of jack AJ, the busy marking potential being supplied over the sleeve conductor of cord CD. The supervisory lamp (not shown) associated with the answering plug of cord CD does not light since the lower, high resistance winding of relay 2&5 is short-circuited by the outer upper front contact of relay 292.

The aforementioned operation of relay 22 of trunk equipment Tl, when an operator in Ofiice 2 answers the call from station A, closes a circuit through the upper windingand inner lower back contact of relay 28, outer upper front contact of relay 2|, and through the lower front contact of relay 22 to ground. Relay 28 is energized sufficiently by the current in this circuit to close its inner upper front contact and look, through its upper winding o-ver conductor 23 to ground at relay I8, before the operating circuit is opened at its inner lower back contact. At its outer lower back contact, relay 28 opens the audible ringing-tone connection; and, at its middle upper front contact, relay 28 closes a circuit for operating relay I4. Relay I4 interchanges the connections between the conductors of line LI and the windings of relay II, opens at its lower back contacts the short circuit around the right windings of repeating coil RCI, bridges the condenser 35 across the left windings of repeating coil RC I, and bridges condenser 36 across the right windings of repeating coil RCI to complete the talking circuit between station A and the cord CD in Ofiice 2.

If the station A is a coin station, relay 30 will have operated when the trunk equipment TI is seized by selector S, ground being permanently connected to the brush I of selectors associated with line-finders having access to coin lines. In this case, relay I4 closes a connection from the upper winding of tone source 32, through the upper contact of relay I9, condenser 33, a lower front contact of relay 30, a lower front contact of relay I4, and inner lower back contact of relay I3 to the left lower winding of repeating coil RCI; a tone is thereby transmitted to the answering operator in Office 2 to indicate that the calling station A is a coin station. When the slow-to-release relay I9 releases, due to the opening of its operating circuit at the back contact of relay I4, the tone circuit is opened. Should the answering operator wish to verify the tone, the plug of the cord CD is pulled out of jack AJ and then reinserted. Upon pulling out the plug, relays 205 and 206 of trunk equipment T3 release; the release of relay 206 opens the short circuit around thelower winding of relay 20I, so as to cause the release of relay 22 of trunk equipment TI; and the release of relay 22 causes.

the release of relay I4 and reoperation of relay I9. When the plug of cord CD is reinserted in jack AJ, relays 205, 206, 22 and I4 are ,reoper-- ated and the coin tone signal is repeated while relay I9 is again releasing. With relay 30 already operated on a call from a coin'line, the oper-,

ation of relay I4 upon answer of the call does not reverse the current over the calling line because the reversal of the connections between line LI and the windings of relay II at the contacts of relay I4 are neutralized by the further reversal at the contacts of relay 30. Were the current reversed on a call from a post-pay coin line when the called operator answers, it would cause the talking circuit to the calling station to be opened until a coin were deposited at the calling station, as is the case, for instance, in the arrangement shown in Patent 1,980,175 granted to W. M. Beaumont, November 13, 1934; but on calls to an operator, the talking connection should not be opened when the operator answers.

The calling subscriber may flash the operator by momentarily depressing the receiver hook. In this case relay II releases; and the resulting release of relay II interchanges the connections between the windings of relay 22 and the conductors of trunk T so as to cause the release of relay 20I of trunk equipment T3. The momentary release of relay 20I causes the release of

relays

202 and 203; and the release of relay 282 opens the short circuit around the lower, high resistance winding of relay 205 tolight the supervisory lamp (not shown) in cord CD. While relay ll of trunk equipment TI is released, relay I8 is held operated through the uppermost back contact of relay I1 and the lower front contact of relay 22.

When the calling subscriber replaces the receiver, relays II and I1 oftrunk equipment TI release, and relays 20I, 202 and 203 of trunk equipment T3 release. The release of relay 202 opens the short circuit around the lower winding of relay 205 tocause the lighting of the supervisory lamp (not shown) of cord CD as a disconnect signal. Relay I8 is held operated by relay 22 under control of the operator in Ofiice 2. When the plug of cord CD is removed from jack AJ, relays 205, 206 and 201 of trunk equipment T3 release. The release of relay 206 opens the short circuit around the lower winding of relay 20I to cause the release of relay 22 of trunk equipment TI. The release of relay 22 causes the release of relays I8 and I4; and the release of relay I8 causes the release of relays 2| and 28. The release of relay I8 also disconnects the holding ground potential from conductor 24 to cause the return of the line-finder and first selector switches LF and S to normal in usual and well-known manner.

If the operator is first to disconnect, relays 205, 206 and 201 of trunk equipment T3 release. The release of relay 206 causes the release of relays 22 and I4 of trunk equipment TI. When the calling subscriber releases the connection, relays II, II, I8, 2I and 28 release as above described.

Assume next a call from Ofiice 2 to station B in Office I. When an operator in Ofiice 2 inserts the calling plug of a cord CD in jack OJ, relay 205 is operated by the current through its windings in series with the right windings of repeating coil RC2 and the tip and ring conductors of jack OJ and cord CD. Relay 285 closes the circuits for operating

relays

206 and 201. When relay 206 operates, it short-circuits the upper, high resistance winding of relay 20I, thereby causing the operation of relay 22 of trunk equipment TI. W'hen relay 22 operates it causes the operation of relay I8 and relay I8 connects ground'potential over conductor 24 to energize the polarizing winding of relay 20 and to guard the trunk equipment TI against seizure'by any of the first selectors such as S by which this equipment might otherwise be selected. At its outer upper front contact, relay I8 connects ground to conductor 23, operating relay I9. Relay I9 closes a circuit 'for operating the line relay 30I of the associated toll intermediate selector circuit ISI of Fig. 3. This circuit is traced from battery through the lower winding of relay 30I, inner lower back contact of relay 306, conductor 42, inner upper back contact of relay 20, upper front contact of relay 22, a lower back contact of relay I3, a back contact of relay 2I and front contact of relay I8, upper winding and inner lower front contact of relay 20, conductor 4|, inner upper back contact of relay 306, and through the upper winding of relay 30I to ground. The current in this circuit is not in the direction to operate polarized relay 20. Relay 30I closes a circuit for operating relay 302. At its middle frontcontact, relay 302 connects the right winding of dial-tone source DT, over conductor 45, to the lower winding of relay 22, thereby transmitting dial tone to the calling operator The operator then inserts the plug of dialing cord DC in the dial jack DJ thereby connecting the impulse contacts of the dial D across the conductors of trunk T in series with the windings of relay 22, and at the same time opening the connection between the lower conductor of trunk T and the lower left winding of repeating coil RC2, and opening the connection through condenser 253 between the right windings of repeating coil RC2. After dialing the number of the called station in Ofiice or the number of the route to another manual ofiice, the plug of the dial cord is removed from jack DJ. When the operator dials the number of a wanted subscribers line, relay 2'2 releases at each opening of the impulse contacts. The first release of relay 22 closes a circuit for operating relay 34; this circuit is traced from ground at the back contact of relay 22, through the lower back contact of relay IT, lower front contact of relay l9, a lower back contact of relay i3, and through the winding of relay 34 to battery. Relay 34 is slow in releasing and remains operated while all of the impulses in the series are being received by relay 22. Being slow in releasing, relay l8 does not release during the response of relay 22 to dial impulses. Relay 34 connects the winding of relay IE to control conductor 44 between trunk equipment TI and the incoming selector IS-l, but relay I6 does not operate until relay 32$ operates as hereinafter described. Each release of relay 22 opens the circuit through the windings of relay 39! of the selector IS-i causing the release of relay 38!. Each release of relay 36H closes a circuit through the back contact of relay 3M, the upper front contact of relay 302 and the windings of relay 303 and the vertical-stepping magnet 3| I.

Relay 393 and magnet 3! l operate. Being slow in releasing, relay 3&3 remains operated until all of the impulses in the series have been received by relay 30!; and, being slow in releasing, relay 302 does not release during the response of relay 33! to dial impulses. Each operation of magnet 3H raises the brushes of selector IS-I one step, to select the desired group of terminals. The vertical off-normal springs VON are actuated when the shaft is raised out of normal position by the first opera-' tion of magnet 3H, thereby closing a circuit through the winding of relay 335, the upper contact of springs VON, the front contact of relay 303, over

conductors

43 and 24, to ground at relay l8. Relay 385, operated by the current in this circuit, closes a locking circuit through the upper contact of the VON springs, back contact of the rotary-stepping magnet 3l2, upper front contact of relay 335, to ground at the outer upper back contact of relay 3%. When relay 363 releases after all of the impulses in the series have been received by relay em the rotary-stepping magnet 3l2 is energized by the current in a circuit which includes the lower front contact of relay 355, the back contact of relay 3&3, and conductor 43. The operation of magnet 3l2 rotates the brushes of selector ISI into engagement with the first set of contacts in the selected level and causes the release of relay 305. The release of relay 395 causes the release of magnet 312. If the first set of terminals is idle, relay 336 is operated by the current in a circuit from battery through the winding of relay 3B5, upper contact of the VON springs, contact of magnet 3l2, winding of relay 306, over conductor 4&3 to ground at relay l8. Being marginal, relay 325 does not reoperate in series with relay 3%. If, however, this first set of terminals is busy, the ground potential encountered by the sleeve brush 323 short-circuits and thereby prevents theoperation of relay 306 and causes the reope'ration of relay 3935. Relay 3135 again closes the circuit for operating magnet 312 and the operation of relay 3l2 advances the brushes into engagement with the second set of terminals in the selected level. Relay 305 and magnet 3l2 are in this manner eifective to step the brushes from one set of terminals to the next until an idle set of terminals is reached, at which time relay 3% operates to prevent further advance of the brushes. When relay 3835 operates, its connects the control conductor 44 of trunk equipment TI to brush 32 i; connects the holding ground potential at relay l8 of trunk equipment Tl, over conductor 53, to the sleeve brush 323 thereby marking the selected trunk or connector as busy, and transfers the talking conductors 4i and 42 of trunk equipment Tl from the windings of relay 3M to the brushes 32l and 322. Relay 305 also disconnects ground from the armature of relay 39! so that release of relay 3!)! will be ineffective to cause another operation of magnet 3i i.

If all of the terminals in the selected level are found busy, the brushes of the switch are advanced to the eleventh rotary position in which contacts 330 are actuated and relay 3% operated. Relay 366 operates and relays 3M and 3322 release as above described. Before relay 3i52 releases, a circuit is traced from ground at its lower front contact, through the upper front contact of relay 39 1, over conductor dd, through the outer lower back contact of relay 34, through contact l and the winding of relay E3 to battery. Relay l3 operates, closing its locking contact 52 before contact 5! is opened. At contact 53, relay l3 opens the impulse repeating loop across conductors 4i and 42; and, at its inner front contacts, relay is connects conductors M and 42 to the windings of relay ll. Relay l3 also closes a circuit through the lower winding of relay l I, resistor 5t and a back contact of relay for operating relay H; and closes a circuit, which includes the lower front contact of relay 22 for operating relay M. Relay lt'locks through its middle lower front contact, the inner lower back contact of relay 2 l, the uppermost back contact of relay ll to ground at the lower front contact of relay 22". Relay l4 opens the short circuits around the right windings of repeating coil RC! and bridges condenser across the inner ends of the left windings and condenser 36 across the inner ends of the right windings of repeating coil RCI. Relay it also causes the release of relay l9. With relay l3 operated and as soon as relay 332 releases, relay 304 is held operated and relay 28 is operated by the current in a circuit from battery through the winding of relay 8%, contact 338, upper front contact of relay 3%, conductor i i, outer lower back contact of relay 35, lower winding of relay 28, contact 52 of relay E3 to ground at relay l8. Relay 28 locks through its upper winding and front contact over conductor 23 to ground atrelay it. With relay 28 operated, the circuit through resistor 5'4 is opened and the energization of the lower winding of relay H is controlled by, interrupter 335. The energizing circuit is traced from battery through lamp resistor l2, lower winding of relay ll, lower left winding of repeating coil RC1, inner lower front contact of relay l3, upper front contact of relay 22 in parallel with the middle upper front contact of relay l4, inner upper back contact of relay 20, conductor 42, resistor 3H1, lower front contact of relay 366i, and through interrupter 33l to ground. After relay 28 operates, each operatact of relay 28.

tion of relay ll under control of interrupter 33! causes the operation of relay ll. The circuit for operating relay I! includes the upper back contact of relay [6 and the uppermost frontcon- Each operation of relay I! interchanges the connections between the windings of relay 22 and the conductors of trunk 200 to cause the release of polarized relay20| of trunk equipment T3. Each release of relay 20! causes the release of

relays

202 and 203; and each release of relay 202 opens the short circuit around the lower, high resistance winding of relay 205 to cause the lighting of the supervisory lamp (not shown) in cord CD. The flashing of this lamp informs the calling operator in Omce 2 that'an all-trunks-busy condition has been encountered. Relay 22 may momentarily release each time relay I'l operates or releases; but relay I4 is slow in releasing so that the temporary release of relay 22 does not interfere with the interrupter control of relay H. When the calling operator disconnects by removing the plug from jack OJ, relays 205 and 203 release, opening the short circuit around the high resistance winding of relay 2M and thereby causing the release of relay 22. The release of relay 22 causes the release of relays I4 and I8. The release of relay It causes the release of relays I3, 28, 304 and 303 and causes the return of switches S and LP to normal in usual manner. The release of relay 306 causes the operation of release magnet 313 thereby restoring selector switch ISI to normal. 7

Assuming that the selector ISI finds an idle set of terminals in the selected level, the aforementioned operation of relay 306 connects

conductors

4E, 42, 43 arid 44 through brushes 32!, 322, 323 and 324 to a connector switch C. If the called line is a party line, the connector may be similar to that shown in Fig. 2 and described in the specification of Patent No. 1,849,662 granted to B. G. Dunham, March 15, 1932. The impulse repeating loop through the upper contacts of relay 22 of trunk equipment Tl isv thereby extended through brushes 32l and 322 to the windings of the line relay (not shown) of the connector C; and the impulses created by the dialing of the last two digits of the called subscribers number, and the party identifying digit if the called line is a party line, are repeated by the upper contact of relay 22 to this line relay. The connector C is thereby operated to select and test the called line L2. If the line is idle, ground is connected through a resistor to the terminal with which control brush 324 is in engagement, thence through brush 324, lower most front contact of relay 306, conductor 44, to the lower armature of relay 34. If at that time relay 22 is repeating impulses created by the dialing of a party identifying digit, relay 34 is operated and this connection over conductor 44 is extended through the lower front contact of relay 34 to the winding of relay I 3; but relay i6 is marginal and does not operate. If relay 34 is not operated, or as soon as relay 34 releases, the connection is extended through the outer lower back contact of relay 34, and through contact 5! to the winding of relay l3. Relay l3 operates, locks through contact 52, opens the impulse repeating loop at contact 53, connects the windings of relay H to the talking conductors 4i and 42 leading to selector IS-l, closes the circuit through the lower winding of relay H and resistor 54, and closes the circuit for operating relay !4. Relay l4 locks as hereinbefore described, opens the short circuit around each of the right windings of repeating coil RCI, and completes a talking circuit through the coil by bridging condensers 35 and 36 across its windings. The called subscriber is signaled in usual manner, audible ringing tone being transmitted from the connector C through either or both of brushes 32! and 322 and conductors 4| and 42, through repeating coil RC! over trunk 200 tothe calling operator. When the call is answered the ground potential connected to the terminal with which brush 324 is in engagement is disconnected and battery is connected through the winding of a supervisory relay (not shown) in the connector C through brush 324, front contact-of relay 306, conductor 44, outer lower back contact of relay 34, lower winding of relay 28, contact 52 of relay l3, to ground at relay l8. Relay 28, operated by the current in this circuit, locks'through its upper winding and inner upper front contact to ground at relay H3. The aforementioned supervisory relay in the connector also operates,'thereby completing a connection from battery through the lower winding of relay H, lower left winding of repeating coil RCI, inner lower front contact of relay l3, upper front contact of relay 22 in r parallel with the middle upper front contact of relay l4, inner upper back contact of relay 20, conductor 42, inner lower front contact of relay 306, brush 322, through connector C and brush 352, over line L2 and through the instrument 'at station B, brush 35l and through connector C, brush 32 l, inner upper front contact of relay 303, conductor 4|, inner lower backcontact ofrelay 20, inner upper front contact of relay l3, upper left winding of coil RC1 and upper winding of relay II to ground. With relays 23 and H operated, relay I! is energized thereby reversing the current over the conductors of trunk 200 'to cause operation of the polarized relay 20L Relay 2% causes the operation of relays 2 02 and 203, and

202 and 203 and the lighting of the supervisory lamp in the cord CD as a disconnect signal. When the plug of cord CD is removed from jack OJ relays 205, 206 and 20'! release. The release of relay 206 opens the short circuit around the lower high resistance winding of relay 20! causing the release of relay 22 in Office I. The release of relay 22 causes the release of relays l4 and H8. The release of relay l8'causes the release of relays 28 and E3, the release of relay 303 of the intermediate selector IS-l and the release of the connector C. The release of relay 306 causes-the operation of release magnet 3l3 and return of equipment Tl has released, .in which case the connection of ground to conductor 44 causes the operation of relay [3; but, if the called station is served by a single line or a party line the testing of the busy condition and connection of ground through brush 324 to conductor 44 occurs while relay 34 is operated, and in this case the marginal relay I5 is operated. When relay 34 releases, relay 56 (if operated) is held through the inner lower back contact of relay 34 and the lower front contact of relay it, over conductor 23, to ground at relay l8; and the ground on conductor 44 is then extended through the outer lower back contact of relay 34, and contact 5! to the winding of relay 13. When operated, relay l3 locks, closes the talking circuit through coil RCI, causes the operation of relay ii, and causes the operation of relay l4 and release of relay l9, all as hereinbefore described. If relay i6 is operated, the release of relay 34 connects the winding of relay I! through the upper front contact of relay l6, upper back contact of relay 34, lowermost front contact of relay l4, .back contact of relay [9 to interrupter 3|. Relay I! is thereby alternately released and reoperated to reverse the current over trunk 200 and flash the calling operators supervisory lamp; and a busy tone is transmitted from the connector C through coil RC! over trunk 200 to the operator. If the connector is arranged to hunt for an idle line in a private branch exchange group, it is also arranged to connect ground to the control conductor for a brief interval if the called line is busy or if all lines in a called group are busy, and then connect battery to this conductor; and in this case, relay 34 having released, relay I3 is operated over conductor 44 to ground in the com nector and locks to ground at relay !8; and, as soonas battery is connected to the control conductor in the connector, the lower winding of relay 28 is energized. Relay 28 operates, locks, connects the winding of relay I! to the contact of relay H and relay H is alternately operated and released under the control of an interrupter associated with connector C. Relay ll follows the operation of relay l I, thereby flashing the calling operators supervisory lamp; and a busy tone is transmitted through coil RCI to the operator. When the operator disconnects cord CD from jack OJ the various relays and switches are restored to normal.

Assume next a call from Office 2 to Office 3. In this case, the incoming selector IS-l is operated under control of the calling operators dial to select a set of terminals connected to a trunk equipment T2 and trunk 3013. When relay 3% of selector IS-l operates, the impulse repeating loop through the upper winding of relay 2i! and the upper front contact of relay 22 is extended through brushes 32I and 322 over conductors 6i and B2 to the winding of the line relay (not shown) of trunk equipment T2. The ground potential at relay 18 of trunk equipment Tl is ex: tended over

conductors

24 and 43, through the middle lower front contact of relay 3%, and

brush 323, to the sleeve conductor 63 of trunk equipment T2 thereby temporarily guarding against seizure of this trunk by any other local or incoming selector. The terminal with which brush 324 is in engagement has no conductor connected thereto, the fourth terminal of each terminal set being of use only on those levels which give access to connector switches. Now it is particularly to be noted that conductors 6i and 62 of trunk equipment T2 are connected to the terminals in the banks of the incoming selectors including the selector IS-l in reversed relation to that in which they are connected to the terminals in the banks of the local selectors including the selector S. Consequently when relay 306 operates and completes the connection between the line relay of trunk equipment T2 and the impulse repeating loop of trunk equipment Tl, the direction of the current through the upper winding of relay 20 of trunk equipment TI is reversed with respect to its direction While connected in series with the windings of relay Sill of selector IS-l. Therefore relay 2!! of trunk equipment TI operates, disconnecting the conductors of trunk 20!] from relay 22 and coil RC! and connecting these conductors directly to the line conductors of selector IS| and thence through brushes 32! and 322 to the line relay of trunk equipment T2. At its outer lower front contact relay 26 shunts the impulse repeating contacts of relay 22 so that, although relay 22 releases, the complete operation of relay 253 is assured. The release of relay 22 causes release of relay l8. Operation of the line relay of trunk equipment T2 causes ground potential to be connected to conductor 63 in the same manner that operation of relay H of trunk equipment TI causes ground potential to be connected to conductor 24. This ground potential connected to conductor 63 guards the trunk equipment T2 against seizure by any other selector after relay ill of trunk equipment Tl releases. This ground connection is further extended through brush 323 of selector IS-l, middle lower front contact of relay 3%, and conductor 43 to hold the lower winding of relay 20 energized; and relay 26 is held operated by its lower winding after the circuit through its upper winding is opened upon transfer of trunk 29? from the windings of relay 22 of trunk equipment TI tothe winding of the line relay (not shown) of trunk equipment T2. The trunk equipments T2 and T4 function in like manner to that in which trunk equipments TI and T3 function as hereinbefore described on a call from station A to Office 2. Operation of the line relay of trunk equipment T2 causes a reversal of the current over trunk 300 to operate the polarized line relay of trunk equipment T4 and light an answering lamp associated therewith. Answer of the call by inserting the plug of a cord in jack AJ associated with trunk equipment T4 increases the current over trunk 300 to operate a supervisory relay (similar to relay 22) in trunk equipment T2 and thereby cause the reversal of current over conductors 6.! and 62 and trunk 200 to operate polarized relay 20! of trunk equipment T3 in O lfice 2. The talking connection is completed through the repeating coil (not shown) of trunk equipment T2, but the repeating coil RCl of trunk equipment TI is not included. Supervisory signals from the calling operator are received over trunk 28% and conductors 6i and 62 by the line relay of trunk equipment T2 and are repeated by a reversal of current over trunk 309 to the polarized line relay of trunk equipment T4. Supervisory signals from the answering operator are received over trunk 38% by the supervisory relay (similar to relay 22) of trunk equipment T2 and are repeated by a reversal of current over conductors El and E2 and trunk 200 to the polarized relay 2d! of trunk equipment T3. Disconnect signals are thereby given to each of the operators.

When the calling operator removes the plug of cord CD from the jack OJ associated with trunk equipment T3, the line relay .of trunk equipment T2 releases; and when the answering operator removes the plug from jack AJ associated with trunk equipment T4, the supervisory relay (similar to relay 22) in trunk equipment T2 releases. With both the calling and called supervisory relays (similar to relays I! and 22) in trunk equipment T2 released, holding ground potential is disconnected from conductor 63 thereby causing the release of relay of trunk equipment TI and the release of relay 3% of selector ISI. The selector 13-! is thereupon restored to normal as hereinbefore described.

What is claimed is:

1. In a multi-office telephone system, subscribers lines, a trunk between a first ofiice and a second o-fiice, a selector in said first oifice for use on calls incoming over said trunk, a repeating coil in said first ofiice normally connected to said trunk, a trunk connected to terminals in the bank of said selector for use onccalls to a third ofiice, and relay means effective upon interconnection of said trunks by the operation of said selector for switching said repeating coil out of the connection.

2. In a multi-oifice telephone system, subscribers lines, a trunk between a first office and a second ofiice, a selector in said first ofiice for use on calls incoming over said trunk, a repeating coil in said first office normally connected to said trunk, a trunk connected to terminals in the bank of said selector for use on calls to a third ofiice, a switch connected to other terminals in the bank of said selector for use, on calls to lines in said first ofiioe, relaymeans ineffective on a call incoming over the trunk from the second oflice to a subscriber in said first ofiice and effective upon interconnection of said trunks by said selector on a call from said second office to said third oflice for switching said repeating coil out of the connection.

3. In a telephone system, a first ofiice, a second office, a trunk between said ofiices, an incoming selector associated with said trunk, impulse repeating means for receiving impulses incoming over said trunk and repeating the impulses to the conductors of said selector, two sets of terminals in the bank of said selector, and a polarized switching relay for connecting the conductors of said trunk either to said impulse repeating means or to the conductors of said selector, the operating winding of said switching rclay being non-operatively energized in series with said conductors of the selector upon selection of one of said sets of terminals and operatively energized in series with said conductors of the selector upon selection of the other of said sets of terminals.

4. In a telephone system, a first office, said office comprising subscribers lines and automatic switches for use in completing calls originating and terminating in said first office, a second ofiice, said second oifice comprising an operators position arranged for sending switch-controlling impulses, a third ofiice, a two-way trunk between said first and second ofiices, a trunk between said.

first and third ofiices, means in said first olfice for seizing either of said trunks on calls originating in said first ofiice, an incoming selector switch associated with said two-way trunk for use on calls incoming over said two-way trunk, a connector switch in said first oifice for selecting called lines, said connector switch and said trunk between said first and third ofiices each being connected to terminals in the bank of said incoming selector switch, circuit means for repeating imtrunk between said first and third ofiices, the 7 operating winding of said switching relay being operatively connected in series with said line relay upon seizure of said trunk between said first and third offices by said incoming selector switch, the operation of said switching relay being effective to connect the conductors of said twoway trunk directly to the line relay of the trunk between said first and third oflices.

5. In a multi-office telephone system, a first trunk, said first trunk extending between a first oifice and a second ofiice, a second trunk, said second trunk extending between said first oflice and a third ofiice, means in said first ofiice for selecting and seizing either of said trunks on calls originating in said first office, a connector switch for use in completing calls terminating in said first ofiice, an incoming selector switch in said first ofiice associated with said first trunk, said connector switch and second trunk being connected to terminals in the bank of said incoming selector switch, a repeating coil and an impulse repeating relay in said first o-ifice, a polarized switching relay for connecting the conductors of said first trunk to said coil and impulse repeating relay or to the conductors of said incoming selector switch, a circuit including theoperating winding of said switching relay for repeating impulses received by said impulse repeating relay to said connector switch, said switching relay being operatively unaffected by the current in said impulse repeating circuit, and a circuit including contacts of said impulse repeating relay and the operating winding of said switching relay for operating said switching relay, the last-mentioned circuit being closed upon seizure of said second trunk by said incoming selector switch.

6. In a telephone system, a first ofiice, a second ofiice, a third ofiice, a first trunk, said first trunk extending between said first and second ofiices,

a second trunk, said second trunk extending between said first and third offices, means in said first office for seizing either one of said trunks on calls originating in said first oifice, means in said second office for seizing said first trunk on calls outgoing from said second oflice, an incoming selector in said first ofiice for said first trunk, a connector switch in said first ofiice for selecting called lines, said connector switch and said second trunk being connected to terminals in the bank of said incoming selector, a polarized switching relay in said first oifice for said first trunk, a

repeating coil in said first office for each of said trunks, means comprising contacts of said relay normally connecting said first trunk to its repeating coil, means comprising normally'open contacts of said switching relay and said incoming selector switch for connecting said first trunk directly to the repeating coil of said second trunk, circuit means for repeating impulses received over said first trunk to said incoming selector and connector switches, the operating winding of said switching relay being included in the impulse repeating circuit but operatively unafiected by the current therein, and circuit means including:

a line relay for said second trunk for sending a seizure signal to said third oifice responsive to seizure of said trunk by said incoming selector, the operating winding of said switching relay being included in circuit with said line relay and operatively affected by the current therein to cause operation of said switching relay.

7. In a multi-ofiice telephone system, a first trunk, said trunk extending between a first ofiice and a second ofiice, a second trunk, said second trunk extending between said first ofiice and a third office, a local selector switch in said first office for use on calls from lines in said first office, said trunks being connected to terminals in the bank of said local selector switch, a connector switch for use in completing calls terminating in said first ofiice, an incoming selector switch in said first oflice associated with said first trunk, said connector and said second trunk being connected to terminals in the bank of said incoming selector switch, an impulse repeating relay in said first ofiice for said first trunk, a line relay for said connector switch, a line relay in said first office for said second trunk for operation I upon seizure of said second trunk in said first office, a polarized switching relay for connecting the conductors of said first trunk to said impulse repeating relay or to said incoming selector switch, means comprising said impulse repeating relay 'for connecting the operating winding of said switching relay in series with the line relay of said connector switch on calls incoming over said first trunk and terminating in said first ofiice, and means comprising said impulse repeating relay for connecting the operating winding of said switching relay in series with the line relay of said second trunk on calls incoming over said first trunk and outgoing over said second trunk, the connection between the line relay of said second trunk and the terminals in the bank of said incoming selector switch being reversed with respect to the connections between the line relay of said second trunk and the terminals in the bank of said local selector, the circuit through the operating winding of said switching relay being efiective to operate said switching relay on calls incoming over said first trunk and outgoing over said second trunk and ineffective to operate said switching relay on calls incoming over said first trunk and terminating in said first oiTice.

8. In a telephone system, a first oifice, a second office,a third office, a first two-way trunk, a sec ond two-way trunk, said first trunk extending between said first and second ofiices, said second trunk extending between said first and third ofiices, a local selector switch in said first ofiice for selecting and seizing either one of said trunks on calls originating in said first ofiice, an incoming selector switch in said first ofiice for each of said trunks for use in completing incoming calls, a connector switch for completing calls terminating in said first ofiice, said connector switch being multipled to terminals in the banks of each of said incoming selector switches, each of said trunks being connected to terminals in the bank 'of incoming selector switch associated with the other of said trunks, an impulse repeating relay and a repeating coil and a polarized switching relay in said first office for each of said trunks, normally closed contacts on each of said switching relays for connecting the conductors of the associated trunk with the repeating coil and impulse repeating relay, normally open contacts on .each of said switching relays for connecting the 1' conductors. of the associated trunk directly to the associated incoming selector switch, a line relay for said connector switch, a line relay in said first oifice for each of said trunks for operation upon seizure of the trunk in said first ofilce, means comprising the impulse repeating relay associated with one of said trunks for connecting the operating winding of the switching relay associated with said one of the trunks in series with the line relay of said connector on calls terminating in said first office, means comprising the impulse repeating relay associated with said one of said trunks for connecting the operating winding of the switching relay associated with said one of the trunks in series with the line relay of the other of said trunks on calls between said second and third ofiices, the connections between the line relays of said trunks and the terminals in the bank of said incoming selector switches being reversed with respect to the connections between the line relays of said trunks and the terminals in the bank of said local selector, the current through the operating winding of the switching relay associated with said one of said trunks being inefiective to operate said switching relay on calls terminating in said first ofiice and efiective to operate said switching relay on calls incoming over said one and outgoing over the other of said trunks.

9. In a multi-office telephone system according to claim 7, a polarized line relay in said second ofilce associated with said first trunk, a circuit including said line relay of said second trunk, contacts of said switching relay and said polarized line relay in said second ofiice, the current in said circuit being inefiective to operate said polarized supervisory relay.

10. In a multi-ofiice telephone system according to claim 7, a polarized line relay in said secline relay in said second ofiice, the current in said circuit being inefiective to operate said polarized supervisory relay and means in said first omce associated with said second trunk and operatively responsive to the answer of a call over said second trunk to said third oifice for reversing the connections between the windings of said line relay of said second trunk and the terminals in the bank of said local and incoming selectors, said reversal being effective on a call from said second office to operate said polarized line relay.

11. In a telephone system, a first office comprising subscribers lines including a coin line, a second office, a trunk between said offices, means for connecting a calling line in said first oflice to said trunk, means including an operators cord in said second ofiice for answering a call incoming over said trunk and for thereupon transmitting a. supervisory signal over the trunk to the first ofiice, means in the first ofiice responsive to said signal for reversing the current over the calling line, and means effective if the calling line is a coin line for preventing the reversing of the current over the calling line responsive to said signal.

12. In a telephone system, a dial ofiice comprising subscribers lines including a coin line, a first manual ofiice, a second manual oifice, a first trunk, a second trunk, said first trunk extending between said dial and first manual office, said second trunk extending between said dial and second manual office, means for connecting a calling subscribers line in said dial ofiice to said first trunk, means for connecting said second trunk to said first trunk, means including an operators cord for answering a call incoming to said first manual oflice over said first trunk and for trans- :mitting an answering signal over said first trunk to said dial ofiice, means responsive to said answering signal for reversing the current over said second trunk on a call originating in said second manual ofiice and for reversing the current over the calling line on a call originating in said dial ofiice, and means efiective only if the calling line in said dial oflice is a coin line for preventing said reversal of current responsive to said an- {swering signal.

13. In a telephone system, an automatic office :comprising subscribers lines including coin lines, a manual office, a first trunk, said first trunk extending between said automatic and manual oflices, other interoflice trunks terminating in said automatic ofiice, means comprising said first trunk for connecting a calling one of said lines .or a calling one of said other interoffice trunks to said first trunk, means in said manual office for answering a call incoming over said first trunk and for transmitting an answering signal to said automatic ofiice, means responsive to said answering signal for reversing the current over the calling line or calling one of said other trunks, and means associated with said first trunk in said automatic office for preventing a reversal of the current over a calling coin line in response tosaid answering signal.

14. In a telephone system according to claim 7, means comprising another winding of said switching relay for holding said relay operated after the conductors of said first trunk are connected to said incoming selector switch by the operation of said switching relay.

15. In a telephone system according to claim '7, contacts effective upon actuation of said switching relay to connect the conductors of said first trunk to said incoming selector and the line relay of said second trunk without reversing the current over the conductors of said first trunk.

16. In a telephone system according to claim 7, contacts of said switching relay effective upon operation of said switching relay to connect the conductors of said first trunk to said incoming selector and the line relay of said second trunk 20 without reversing the current over the conductors of said first trunk, and means in said second trunk responsive to the answer of a call in said third oflice for reversing the current in the conductors of said first trunk.

CHARLES D. KOECHLING.