US2021286A - Telephone system - Google Patents

Description

' Nov. 19, 1935. E. D. BUTZ 2,021,286

TELEPHONE SYSTEM Filed Dec. 20, 1932 9 Sheets-Sheet 2 IIHIP MARG/NAL TH POT/Q) STEP INVENTOR E. D. BUT Z I i WW ATTORNEY Nov. .19, 1935. E. D. BUTZ I 'ELEPHONE SYSTEM 9 Sheets-Sheet 3 INVENTO/P E. D. 5U77 Filed Dec. 20, 1952 Br W -4W ATTORNEY Nov. 19, 1935. [1 gym 2,021,286

TELEPHONE SYSTEM Filed Dec. 20, 1932 9 Sheets-Sheet 4 INVENTOR E. D. BUTZ By W A T TORNE Y Nov. 19, 1935.

E D. BUTZ TELEPHONE SYSTEM Filed Dec. 20, 1952 9 Sheets-Sheet 5 INVENTOR E. D. BUTZ BY w www ATTORNEY Nov. 19, 1935.

FIG. 6

E. D. 'BUTZ TELEPHONE SYSTEM Filed DeC. 20, 1952 9 Sheets-Sheet 6 7'0 LINE FINDER BANKS INVENTOR E. D. BUTZ ATTORNEY Nov. 19, 1935. E. D. BUTZ TELEPHONE SYSTEM Filed Dec. 20, 1932 9 Sheets-Sheet 7 UDIJUUIJIJU I] u n [+----------n n u lNl/ENTOR ATTORNEY Nov. 19, 1935.

FIG. 8

MARG/NAL E. D. BUTZ 2,021,286

TELEPHONE SYSTEM Filed Dec. 20, 1932 9 Sheets-Sheet 8 ATTORNEY Nov. 19, 1935. E, D, BUTZ 2,021,286

TELEPHONE SYSTEM Filed Dec. 20, 1952 9 Sheets-Sheet 9 CCZ INVENTOR E D. BUTZ ATTORNEY Patented Nov. 19, 1935 PATENT OFFICE TELEPHONE SYSTEM Edward D. Butz, Palisade, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application December 20, 1932, Serial No. 648,052

11 Claims.

This invention relates to telephone systems and more particularly to trafiic intercepting equipment for use in automatic telephone systems.

The object of the invention is to provide an improved arrangement for extending intercepted calls to a centralized A switchboard.

In automatic telephone systems it is usual to connect an intercepting trunk to blank terminals in the selector and connector banks and also to provide an intercepting trunk from a plugging-up line for intercepting calls to a subscriber whose line is temporarily removed from service. The intercepting operators positions may be located in a distant office, in which case all intercepted calls may be extended over a single group of two-wire trunks to the intercepting switchboard. The inter-office trunks may terminate at the automatic ofiice in individual trunk finders which have access to the intercepting trunks from the connector and selector banks and from the plugging-up lines. This arrangement permits the economical use or" interoifice trunks for extending intercepted calls.

According to this invention, the outgoing and incoming ends of two-wire trunks between an automatic office and intercepting operators positions are arranged to transmit the necessary supervisory si nals dependent upon whether the intercepted call is a local call or a call from a toll operator. The supervisory bridge provided in the outgoing trunk circuit for connection across the line conductors from the trunk finder include a polarized relay and a relay having high and low resistance windings. If the intercepted call is from a toll operator, the polarized relay operates and the high resistance winding is thereby short circuited, the resulting low resistance bridge being efiective to give the toll operator a supervisory signal. If the intercepted call is from a local subscriber or operator, the polarized relay does not operate and the high resistance bridge is maintained across the trunk conductors to prevent operation of the supervisory relay in the connector and the charging of the calling subscriber in case the call is intercepted at a connector or over a plugging-up line. Flashing by the intercepting operator changes this bridge from a high resistance bridge to a low resistance bridge or vice versa depending upon whether the intercepted call is a toll or local call. If the call is intercepted at the bank of a local selector, release by the calling subscriber or originating local operator is effective to give the intercepting operator a disconnect signal. The trunk circuits are arranged to hold the trunk finder until the intercepting operator disconnects when the call is intercepted at a local selector or local connector or plugging-up line and to hold the trunk finder until both ends have disconnected when the call is intercepted at a toll connector or toll selector. 5 When the call is intercepted over a plugging-up line, or is intercepted at the terminals of a local selector, the trunk finder releases when the intercepting operator disconnects, irrespective of whether the calling end has or has not disconnected.

The invention will be better understood by considering a telephone system in which its features have been embodied, such a system being shown schematically in the drawings which form a part of this specification. The use of the invention is not limited, however, to the particular system illustrated and other applications of the invention will readily occur to one skilled in the art.

Referring to the drawings:

Fig. 1 represents schematically a toll line L, a toll operators cord circuit CCI, position equipment OP and an outgoing trunk circuit T for use in extending calls to a distant step-by-step ofiice;

Fig. 2 shows a toll selector TS in the step-bystep office for use in completing calls incoming from a manual toll ofiice;

Fig. 3 shows a toll connector circuit TC for use in completing calls incoming from a toll ofiice;

Fig. 3a shows a trunk circuit ITI for intercepte ing connections extended to blank terminals in the banks of toll selectors;

Fib. 3b shows a similar trunk circuit IT2 for intercepting connections extended to blank terininals in the banks of toll connectors;

Fig. 4 shows an automatic subscribers station A, a line finder LF and a first selector LS;

Fig. 5 shows a connector LC for completing local calls;

Fig. 5a shows a trunk circuit ITS for intercepting calls extended to blank terminals in the bank of local selectors;

Fig. 6 shows a plugging-up line circuit PL and an intercepting trunk circuit 1T5 from the plugging-up line for extending calls to an intercepting operator;

Fig. 6a shows a trunk circuit 1T4 for use in intercepting calls extended to blank terminals in the banks of local connectors;

Fig. 7 shows a trunk finder TF having access to the intercepting trunks from toll and local selectors, from toll and local connectors and from plugging-up lines;

Fig. 8 shows an outgoing trunk circuit OT associated with a trunk finder, such as is shown in Fig. '7, and used in extending intercepted calls to a centralized intercepting operators position in the same ofiice or in a distant ofiice;

Fig. 9 shows an incoming trunk circuit IT for receiving incoming intercepted calls;

Fig. 10 shows a cord circuit C02 for use in answering incoming intercepted calls; and

Fig. 11 shows the manner in which Figs. 1 to 10, inclusive, are to be connected to form an operative arrangement.

The toll operators cord and position circuits of Fig. 1 may be similar to those shown and described in the patent to R. C. Paine, No. 1,836,549, December 15, 1931. The selector and connector switches of Figs. 2, 3, 4 and 5 are of the well known two-motion step-by-step type as is also the trunk finder of Fig. 7. Reference may be had to pages 53 to 65 inclusive, of the second edition of Automatic telephony by Smith and Campbell, published in 1921, for a description in detail of the construction and operation of such switches.

The various intercepting trunks 1T1 from the bank toll selector TS, 1T2 from the bank of the toll connector TC, 1T3 from the bank of local selector LS, 1T4 from the bank of the local connector LC and 1T5 from the plugging-up line PL all terminate in the bank of the trunk finder TF and in the banks of similar trunk finders, each of which'is associated with a trunk terminating at the centralized intercepting switchboard. The operation of the system to extend intercepted calls to a centralized intercepting operators pc= sition will be described first for calls incoming from a, toll operators position and second for local calls.

Referring to Fig. l, a call incoming over toll line L may be answered by inserting plug 101 of the cord CC! into jack 100. The talking key (not shown) is then operated to extend the connection to the operators position circuit OP. Upon inquiry the operator receives the number of the called subscriber with which the calling subscriber or operator desired connection. If the called subscribers line terminates in a distant automatic ofiice, the plug 103 of the cord circuit CC! is inserted in a jack connected to a trunk leading to the desired'ofiice, such for instance as the jack 110. The sleeve relay 111 of the outgoing trunk circuit T is thus operated by the energization of its lower winding in series with the supervisory lamp 104 of the cord circuit CCI, the current being insufficient to light the lamp. Upon operation of the dial key (not shown), a circuit is closed from battery (not shown) in the position circuit through the upper conductor of cord C01 and plug 103, upper spring of jack I 10, and through the upper back contact and winding of relay 112, to ground. Relay I 12 operates, locks under control of the sleeve relay 111, and closes the dialing circuit from battery at the back contact of the release magnet 240 of the toll selector TS, through the upper winding of line relay 201, upper outer back contact of relay 211, lower back contact of relay 206, left lower winding of repeating coil 250, over the lower conductor of theinteroffice trunk line 120, through the lower back contact of relay 111 in theoutgoing trunk circuit T, outer lower back contact of relay 113, inner upper front contact of relay 112, tip conductors of jack 110, plug 103 and cord CC1 through the interrupter contacts of the dial 105, back through the ring conductors of cord CCI, plug 103 and jack 110, lower front contact of relay 112, upper back contact of relay 113, winding of polarized relay 114, upper back contact of relay 117, over the upper conductor of trunk 120, outer upper back contact of relay 5 206, to ground at the inner upper back contact of relay 206. The line relay 201 of the selector TS operates thereby closing an obvious circuit for energizing release relay 202. Relay 202 connects ground at its upper front contact to con- 10 ductor 219, causing the operation of relay 210. The circuit for operating relay 210 is traced from battery through the winding of relay 210, inner upper back contact of relay 21 1, lowermost back contact of relay 208, to the ground on conductor 15 219.

When the toll operator dials the first digit of the called subscribers number the line relay 201 responds to the train of impulses thereby created, in the usual and well known manner. The first 20 release of relay 201 closes a circuit from battery through the winding of the vertical stepping magnet 220, winding of relay 203, upper back contact of relay 212, lower front contact of relay 292, to ground at the back contact of relay 201. 25 The vertical stepping magnet 220 and relay 203 both operate, the operation of the magnet being eifective to step the brushes 215, 216, 211 and 2&8 up to the first level of the terminal bank. Relay 203 closes a circuit from battery through 30 the winding of relay 204, inner front contact of relay 223, over conductor 219 to ground at relay 202. Relay 23 1 operates and it looks through its inner lower front contact and lowermost back contact of relay 212 to the ground on conductor 35 219. As soon as the shaft and brushes of the switch move out of normal position, the vertical off-normal springs VON are actuated, thereby closing a circuit for operating relay 205; this circuit is traced from battery through the back 40 contact of the release magnet 240, upper contacts of the VON springs, winding of relay 205, outer front contact of relay 203 to the ground on conductor 219. Relay 205 looks to ground at its left front contact, under control of the back con- 5 tact of the rotary stepping magnet 230, but independent of the continued operation of relay 203. The reoperation of relay 201 at the end of the first impulse causes the release of the magnet 220. Each succeeding release and reopera- 50 tion of line relay 20E in response to the dialing of the first digit of the called subscribers number causes a corresponding operation and release of the magnet 220, thereby stepping the selector brushes up to the level which corresponds to the 55 digit dialed. Being slow to release, relay 203 remains operated until all of the first train of impulses have been received. Relay 202 is also slow to release and remains operated during the receipt of dial impulses. 0

When relay 203 releases after all of the first train impulses incoming to relay 201 have been received, a circuit for operating the rotary stepping magnet 230 is traced from battery through the winding of magnet 230, right front contact 5 of relay 205, back contact of relay 203, over conductor 219 to ground at relay 202. The operation of the magnet 230 rotates the brushes 215, '216, 211 and 21 8 into engagement with the first set of terminals in the selected level and also 70 opens the circuit through the winding of relay 205. Relay 205 releases thereby opening the circuit through the winding of the magnet 230; and magnet 230 releases. The first set of terminals are now tested to determine whether they are idle or busy; the test circuit is traced from battery through the back contact of release magnet 2M], upper contact of the V ON springs, winding of relay see, back contact of rotary magnet 230, through the inner lower back contact of relay 2 i2, and through the sleeve or test brush 2 i? to the test terminal of the engaged set of terminals. If the first set of terminals is idle, the test terminal is not connected to ground and relay 252i is operated in a circuit from battery through the back contact of release magnet 2%, upper contact of the VON springs, winding of relay 285, back contact of rotary stepping magnet 238, winding of relay 2i2, over conductor 219 to ground at relay 232; being marginal, relay 235 does not operate in this circuit. If the first set of terminals is busy, the winding of relay H2 is short cireuited by the busy ground potential on the test terminal, which potential is effective to reoperate relay The rotary stepping magnet 236 is thus rcoperated to advance the brushes to the next set of terminals. Reoperation of relay and magnet continues as long as test brush 2 i l encounters the busy potential, but as soon as an idle set of terminals is reached, relay 2H2 operates as above described. Relay 2&2, operated, connects the ground on conductor 259, through its inner lower front contact, and through test brush ill to the test terminal to prevent selection of the trunk connected to these terminals by any other hunting selector having access thereto. The busy ground is also efiective as a holding potential connected through brush 2 Il and terminal 223 to hold the succeeding switches employed in establishing the desired connection.

The levels of the toll selector banks which represent assigned groups of telephone numbers may connect to intermediate toll selectors wl n'ch in turn have access to groups of toll connectors. In the drawin however, the terminals 23!, 232, 233 and are shown connected directly to the toll connector TC. intermediate selectors being omitted. The terminals 225, 222, 223 and 22d represent a level of the toll selector bank in which the terminals are connected to intercepting trunk circuits, the corresponding digit being one which represents an unassigned group of subscribers numbers.

Assume, first, that the call from the toll operators position in Fig. 1. is extended over trunk T and toll selector TS to the toll connector TC, the brushes of selector TS having been advanced into engagement with terminals 239, 232, 233 and res. With relay 2E2 operated, a circuit is closed for operating the line relay 3%! of connector TC; this circuit is traced from battery through the lower Winding of relay 3%, 1owermost back contact of relay terminal 232 and brush 2 it of selector TS, middle lower front contact of relay 2 lower front contact of relay 25.! I, inner lower back contact of relay 208, right lower winding of repeating coil 25d, resistance 253, upper front contact of relay 2%, upper right winding of repeating coil 25d, upper back contact of relay 2%, upper front contact of relay 2i2, brush are and terminal 23!; uppermost back contact of relay tilt, and through the upper winding of relay 3M to ground. Relay Sill closes an obvious circuit for operating the release relay Relay 3&2 looks through its inner upper front contact, the inner upper back contact of relay sec, conductor 3 i i, inner lower back contact of relay 3H6, conductor Sit, terminal 233 and brush 2 ll, inner lower front contact of relay 212, over conductor 2l9 to ground at relay 262. This ground is further extended from conductor 314 through terminal 234 and brush M3, the lowermost front contact of relay M2, and through the lower front contact of relay 264 to hold relay 29 i operated.

When the toll operator dials the next digit of the called subscribers number, relay 20! of selector TS alternately releases and reoperatcs causing the corresponding release and reoperation of relay 3M of connector TC, once for each dial impulse. The first release of relay 313i closes a circuit from ground at the inner upper back contact of relay 3%, back contact of relay 31H, inner lower front contact of relay 362, normally closed contacts of the vertical oif-normal springs VON, winding of relay 333, and through the Winding of the vertical stepping magnet 32% to battery. The magnet 32G operates thereby advancing the brushes 3H, 3G8 and 319 up to the first level of the terminal bank. :telay 393 also operates and as soon as the switch moves out of its normal position the circuit for energizing the windings of magnet and relay 3% is traced through the front contact of relay 353 and the upper front contact of the VON springs instead of through the normally closed contact of the VON springs. The magnet 32B releases when relay 30! reoperates at the end of the first impulse, each additional impulse causing the reoperation and release of magnet 532i to advance the connector switch brushes to the level corresponding to the digit dialed. Relay see is slow in releasing and remains operated until all of the impulses of the series have been received. Relay 392 is also slow in releasing and remains operated during receipt of dial impulses.

When the next and last digit of the called number is dialed, the first release of relay Sill closes a circuit from ground at the inner upper back contact of relay back contact of relay till, inner lower front contact of relay upper front contact of the VON springs, back contact of relay 303, winding of relay 3535, and through the Winding of the rotary stepping magnet 33!] to battery. The operation of magnet advances the brushes 3M, 5358 and to the first set of terminals in the selected level and the operation of relay 3&5 connects the winding of test relay 3% to the sleeve brush tit. The magnet 33B releases when relay 395i reoperates at the end of the first impulse, each additional impulse causing the reoperation and release of magnet 336 to advance the brushes into engagement with the set of terminals corresponding to the digit dialed. Relay 365 is slow in releasing and remains operated until all of the impulses of the series have been received. Relay 3%, being seinewhat slow in operating, does not operate if the brush 3l9 engages a grounded test terminal during the advance of the brushes; but as soon as the brushes come to rest on the selected set of terminals, relay 3M operates in case the called line is busy as indicated by the presence of a ground potential on the test terminal.

Assuming that the called line is the line 3% connecting station C to terminals 33!, and 333 of the switch TC and that this line is idle when selected, the release of relay 3&5 closes a circuit from battery through the winding of the cut-off relay 38! of line see, through terminal 333 and brush 3E9, lower back contact of relay 3H5, inner lower back contact of relay 394, middle upper back contact of relay 3%, middle upper front contact of relay 382, through the upper winding of relay 3&6 to'the holding ground from relay 202 of selector TS on sleeve conductor 3I3. Relay 306 is sufliciently energized to close its inner lower front contact and thus lock through its lower winding to the holding ground. The operation of relay 306 extends the connection from the calling line through its outermost front contacts, the outermost front contacts of relay 332, the outermost back contacts of relay 304, and through brushes 3!! and 3I8 to the called line. The operation of relay 303 also disconnects control conductor 3I4 from sleeve conductor 3I3 thereby causing the release of relay 204 of the toll selector TS. The release of relay 204 closes a circuit from battery at the back contact of release magnet 243, lower front contacts of the VON springs, winding of relay 206, to ground. at the lowermost back contact of relay 204. Relay 206 operates, thereby reversing the current over trunk I20, the tip conductor of trunk I20 being connected through the upper left winding of repeating coil 250, the upper front contact of relay 20'5, resistance 25E, uppermost back contact of relay 2| I, upper winding of relay 20I, to battery at the back contact of release magnet 240; and the ring conductor of trunk I2 0 is connected through the lower left winding of repeating coil 250, inner lower front contact of relay 233, resistance 252, inner lower back contact of relay 2H, through the lower winding of relay 2%! to ground. This reversal of current is effective to operatethe polarized relay H4 of the trunk circuit T and a polarized relay (not shown) in the toll operators position equipment, thereby causing the dial I35 to be disconnected from the cord CCI. The operation of relay II 4 closes an obvious circuit for operating relay H3. Relay H3 locks under control of relay I I I and the connection from the line conductors of cord CCI is extended through the front contacts of relays H2 and H3 to the left-hand windings of repeating coil I IS. The inner end of the lower left-hand winding of coil H8 is further connected through the winding of relay H? to ground, this relay being under control of the ringing key (not shown) of the cord circuit. With relay I I3 operated, the supervisory relay H5 and right-hand windings of repeating coil I 58 are bridged across the conductors of trunk I23 leading to the toll selector TS in the distant step-by-step office, thereby operating relay H5 of trunk circuit T and maintaining the energization of the line relay 20I of the toll selector TS. The operation of relay H5 connects the upper winding of relay III in parallel with the lower winding, thus reducing the resistance of the sleeve circuit of the cord CCI sufficiently to light the supervisory lamp I04.

The aforementioned operation of relay 306 of the toll connector TC also causes the release of relay 35H but relay 302 is held operated through its upper winding and inner upper front contact, inner upper back contact of relay 334, control conductor 3M, terminal 234 and brush 2I8, the lowermost front contact of relay 2 I2, inner-lower back contact of relay 234, outer lower back contact of relay 2 I I, outer front contact of relay 21H outer lower back contact of relay 208, over conductor 2l9 to ground at release relay 202.

Further operation now awaits the operation of the ringing key at the toll operators position in response to which relay In of trunk circuit T is operated. Relay II I connects the alternating ringing current source I I9 across the outgoing conductors of trunk I23, thereby causing the operation of relay 20! of the toll selector TS. Relay 201 closes a circuit for operating relay 2108.

The operation of relay 208 disconnects the holding ground on conductor 2I9 from brush 2I8, thereby causing the release of relay 302 of the connector TO. The operation of relay 208 also causes the release of relay 2I0 and the release '5 of relay 2I0 reconnects the ground on conductor 2I9 to the brush 2I8; relay 2I0 is slow in releasing to insure the release of relay 302 of the connector. The release of relay 302 closes a ringing circuit from the source of ringing cur- 10' rent 325, middle lower front contact of relay 305,

lower winding and outer lower back contact of relay 302, outer lower back contact of relay 304, brush 3I8 and terminal 332, over line 380 and through the ringer (not shown) at station C, 15.

back through terminal 33I and brush 3I'I, outer upper back contacts of relays 304 and 302, to ground at the middle upper front contact of relay 306. When the ringing key at the toll operators position is released relays 201 and 208 release 20 and relay 2I0 reoperates. When the subscriber at station C removes the receiver to answer the call, relay 302 is operated by the current through its lower winding and this relay is again locked through its upper winding and inner upper front 25- contact over the control conductor 3I4 to ground at relay 202 of the toll selector TS. Talking current is now supplied to the called subscriber in a circuit from battery through the lowermost front contact of relay 2% of the toll selector TS, 80 lower winding of supervisory relay 2I3, middle lower back contact of relay 204, lower right Winding of repeating coil 250, inner lower back contact of relay 2%, lower front contact of relay 20I, middle lower front contact of relay 2I2, brush 35 2I6 and terminal 232, lowermost front contacts of relays 306 and 3592 of connector TC, lowermost back contact of relay 304, brush 3I8 and terminal 332, over line 300 and through the subscribers telephone at station C, back through terminal 40 33I and brush 3I'I, the uppermost back contact of relay 304, the uppermost front contacts of relays 302 and 306, through terminal 23I and brush 2I5, upper front contact of relay 2I2 of selector TS, upper back contact of relay 208, upper right 45 winding of repeating coil 250, upper back contact of relay 204, and through the upper winding of relay 2i3 to ground. The supervisory relay 2I3 operates to effect the operation of relay 2H. Relay 2H disconnects the windings of relay 20I 50 from the left windings of repeating coil 250 thereby causing the release of relay H5 of the trunk circuit T. With relay I I5 released the circuit through the upper winding of relay III is opened thus causing the supervisory lamp I04 to be extinguished. The voice currents are now transmitted through repeating coils I I8 and 250, the trunk I 23 having no direct current flowing thereover. Relay 20I of the toll selector is held operated by connecting resistance 2I4 in series with its windings, this connection being made at the next-to-the inner lower front contact of relay 2I I. The operation of relay 2H also causes the release of relay 2I3.

When the called subscriber replaces the receiver on the receiver hook, supervisory relay 2 I3 releases causing the release of relay 2H. Relay 20I now holds in the circuit over trunk I20 causing the reoperation of relay H5 of trunk circuit T and the lighting of supervisory lamp I04. Relay 2I0 reoperates. The operator may rering the called subscriber if this is found desirable. When the plug I03 is removed from jack H0, relays III, H2 and H3 release, thus restoring trunk circuit T to normal. The release of relay I I3 opens the bridge across trunk I20 causing the release of relay 20I of the selector TS followed by the release of relay 292. The release of relay 202 causes the release of relays H and 2I2 of selector TS and the release of relays 302 and 305 of the connector TC. The release of relay 292 closes a circuit from battery through the middle front contact of the VON springs, winding of release magnet 22!), through back contacts of relays 202 and 2m to ground. Magnet 2i0 operates causing the shaft and brushes of switch TS to be restored to normal in the usual manner and causing the release of relay 2%. When the shaft reaches normal the VON springs are restored to normal, releasing magnet 240.

The release of relays 302 and 328 of connector TC closes a circuit from battery through the winding of release magnet 340, lower front contact of the VON springs, inner lower back contact of relay back contact of relay 30I, to ground at the inner upper back contact of relay Magnet operates causing the shaft and brushes of switch TC to be restored to normal. When the shaft reaches normal the VON springs are restored to normal releasing magnet *4 Should the called line 380 be busy when seized by the switch TC as hereinbefore described, the operation of test relay "Sti l disconnects the tip and ring conductors of the connector from the brushes SI? and 3 I0 to prevent interference with the call already in progress over the called line. When relay 325 releases, a locking circuit for relay 353 3 is closed before the operating circuit is opened, the locking circuit being traced from battery through the winding of relay silt, back contact of the continuity springs of relay 305, inner lower front contact of relay 3%, middle upper back contact of relay 3%, middle upper front contact of relay 302, upper winding of relay 3%, to the holding ground from selector TS on conductor M3. Relay 326 is sufficiently energized to close its inner lower front contact thus locking through its lower winding to the ground on conductor Slit. The operation of relay 306 connects ground through its inner upper front contact to the inner lower armature of relay 304 to hold relay 304. With relay 305 operated, relay 302 holds through its inner upper front contact and the inner upper front contact of relay 304 to the holding ground on conductor EH3. The operaticn of relay also causes the release of relay 30! and disconnects the holding ground on conductor 3&3 from the control conductor 3 I4 thereby causing the release of relay 2% of the toll selector TS. The release of relay 224 causes the operation of relay 2%, reversing the current over trunk I26. This reversal of current operates relay li t of trunk circuit T and causes the dial I25 to be disconnected. Relay H3 operates to connect the left-hand windings of repeating coil M8 to the cord CCI and to bridge the winding of relay H5 across the conductors of trunk I20 as hereinbefore described. With relay 204 of the toll selector TS released a circuit is closed from ground through interrupter 3H5 of the toll connector TC, through the lowermost front contacts of relays and terminal 232 and brush 2E6 of the toll selector TS, middle lower front contact of relay 252, lower front contact of relay middle lower back contact of relay 228, right lower winding of repeating coil 250, middle lower back contact of relay 204, lower winding of relay 283, and through the lowermost front contact of relay 200 to battery. The alternate closing and opening of this circuit under control of interrupter 3I5 causes the alternate operation and release of relays 2I3 and 2! i. Relay 2 thus alternately opens and closes the connection from battery and ground through the windings of relay 20I to the conductors of trunk I20 to cause the alternate release and reoperation of relay H5 of trunk circuit and the flashing of lamp I04 to indicate that the called line is busy. When the toll operator removes plug I23 from jack IIO, the trunk circuit T, toll selector TS and connector TC are restored to normal in the same manner as hereinbefore described, the release of relay 300 of the connector TC causing the release of relay 304.

Assume, next that the call from the toll operators position in Fig. l is extended over trunk T and through toll selector TS to the intercepting trunk circuit ITi in Fig. 3a, the brushes of switch TS having been advanced into engagement with terminals 22!, 222, 223 and 224. Since relay 2% requires a locking circuit through its lower front contact and brush 2I8 in order to remain operated after relay 2 i2 operates and since the trunk ITl has no conductor connected to terminal 228 with which brush 2I8 is in contact, the aforementioned operation of relay 2I2 causes the release of relay 294. With relay 204 released, relay 20% operates as hereinbefore described thereby connecting battery through the lowermost front contact of relay 206, lower winding of relay 2I3, middle lower back contact of relay 2%, lower right winding of the repeating coil 25d, inner lower back contact of relay 208, lower front contact of relay 20L middle lower front contact of relay 2| 2, brush 2I6 and terminal 222 to the ring conductor 352 of trunk ITI and connecting ground through the upper winding of relay 2I3, upper back contact of relay 204, upper right winding of repeating coil 250, upper back contact of relay 208, upper front contact of relay 2I2, brush 2I5 and terminal Hi to the tip conductor 35I of trunk ITI. The operation of relay 205 is also effective to reverse the current over trunk I 20 and thus cause the disconnection of dial Hi5, the extension of the line conductors of cord CCI to the windings of repeating coil H8, the lighting of supervisory lamp I04, and the connection of the winding of relay H5 across the conductors of trunk I20, all as hereinbefore described. Further operation of the dial is ineffective and the lighting of lamp I04 prior to the completion of dialing indicates that the call is being intercepted and the ringing key will not be operated.

Upon seizure of the trunk circuit ITI, a circuit is closed from the busy and holding ground connected to the test terminal 223, over test conductor see, through the lower back contact of relay 355 of trunk circuit ITI and through the winding of trunk relay 3% to battery. Relay 354 operates thereby connecting the winding of cut-off relay 3% over the sleeve conductor 353 of trunk ITI to test terminals in the banks of the trunk finders which have access to this trunk. Thus, the line conductors 35! and 352 of trunk IT! are connected to terminals 'IIi H2 in one of the terminal banks of finder TF and the sleeve conductor is connected to the corresponding test terminal lit in the test bank of finder TF. Relay 35 l also closes a circuit from ground through the upper back contact of relay 255, the upper front contact of relay sti l, over the group conductor I00, through the winding of group relay IM to battery. Group relay I! operates thereby connecting ground through its right front contact, over conductor I02, to the corresponding segment of the vertical commutators of all of the trunk finders having access to the group of trunks which includes the trunk ITI. In the drawings this is shown as the second segment of commutator I03 and corresponding to the second level of the bank of switch TF.

Assuming the trunk finder TF to be the first idle trunk finder in the group, the operation of relay IOI also closes a circuit for operating relay I05; this circuit is from ground at the left front contact of relay I05, over the start conductor I04, through the inner upper back contact of relay I08 and winding of relay I05 to battery. Relay I05 connects ground through its inner lower front contact over conductor W3 to the sleeve conductor of the outgoing trunk circuit OT in Fig. 8 and closes a circuit, for operating relay I0I, from battery through the uppermost back contact of relay I08, upper winding of relay I07, back contacts of the rotary stepping magnet I30 and vertical stepping magnet l20, to ground at the lowermost front contact of relay I05. Relay I0I operates thereby closing a circuit from battery at the uppermost back contact of relay I08, winding of the vertical stepping magnet I20, lowermost back contact of relay I00, front contact of relay I01 to ground at the lowermost front contact of relay I05. The magnet I20 operates, thereby stepping the two sets of brushes IOI, I62 and I63 and I64, I65 and I56 up to the first level of terminals in the associated banks. The vertical commutator brush I l I is also stepped. up to make contact with the first segment of the commutator I03. The operation of magnet I20 also causes the release of relay I01; and the release of relay I0? causes the release of magnet I20.

Although the calling trunk may be connected to terminals in the banks associated with brushes 16!, I62 and I63 or to terminals in the banks associated with brushes I64, I65 and I66, the intercepting trunks ITI, 1T2, 1T3, 1T4 and 1T5 are all shown connected to terminals in the second level of the banks with which the brushes I6I, I62 and I03 are associated and description of the terminal hunting operating of the trunk finder will, therefore, be limited to the case where the calling trunk is encountered by the latter set of brushes. Since the trunk, for which the trunk finder TF is seeking, is connected to terminals in the second level, the commutator brush III does not encounter ground potential on the first commutator segment to stop further hunting.

. With magnet I20 released, relay I08 reoperates again closing the circuit for operating magnet I20. The brushes are thus stepped up to the second level of the terminal banks. Since trunk ITI is connected to terminals in the second level, a circuit is closed for energizing relay I09 as soon as the commutator brush Ill comes in contact with the second commutator segment; this circuit is traced from battery through the uppermost back contact of relay 700, upper winding of relay 101, back contact of magnet I30, upper winding of relay I09, commutator brush I II, second commutator segment, conductor I02 to ground at the right front contact of group relay I0! This circuit is also effective to hold relay I0I operated. Relay 309 is slow in operating to ensure proper positioning of the brushes before the first rotary step. Relay I09 opens the circuit through the winding of magnet I20 so that magnet I20 releases. Relay I09 also closes a circuit, for operating the rotary stepping magnet I30, from battery through the winding of magnet I30, lowermost front contact of relay I09, front contact of relay 101 to ground at the lowermost front contact of relay I05. The operation of magnet I30 steps the two sets of brushes into contact with the first set of terminals in the second level of each of the associated banks. The circuit through the upper windings of relays 101 and I09 is opened when magnet I30 operates and is also opened at the commutator due to brush I I I being rotated out of alignment with the segments. Relay I0I releases but relay I09 is held operated in a circuit from battery through the upper most back contact of relay 108, winding of magnet I20, lower winding and inner lower front contact of relay I00, to ground at the lowermost front contact of relay I05; the current in this circuit is not suflicient to operate the magnet I20. If the first set of terminals in the second level is not the set to which the calling trunk ITI is connected, magnet I30 releases when relay I0I releases; relay I01 reoperates when magnet I30 releases and causes the reoperation of magnet T30 to advance the brushes into engagement with the second set of terminals. The alternate reoperation and release of relay I07 and rotary stepping magnet 730 continues until the test brush I63 encounters test terminal II3 to which conductor 353 is connected; at which time a circuit is closed from battery through the winding of the cut-off relay 355 of trunk circuit ITI, lower front contact of relay 354, conductor 353, terminal II3, brush I63, lower winding of relay IIO, lowermost back contact of relay I08, lower winding of relay I01 to ground at the inner lower front contact of relay I05. Relay I0! is held energized, and relay I I 0 is operated in this circuit sufficiently to close its inner upper front contact. Relay H0 is thus fully energized and locked operated in the circuit from battery through its upper winding and inner upper front contact, conductor "4, front contact of magnet I30, front contact of relay 101, to ground at the lowermost front contact of relay I05. Magnet I30 is held operated under control of relays I09 and 101. The cut-01f relay 355 of trunk circuit ITI is also operated by closure of the above circuit through brush I63 and terminal II 3, thereby disconnecting the ground at the upper back contact of relay 355 from group conductor I00. The operation of relay 355 also causes the release of relay 354, thereby extending the holding ground at the upper front contact of relay 202 of toll selector TS, over conductors 2I9 and 350, through the inner front contact of relay 355 and inner back contact of relay 354, to hold relay 355; and from conductor 350 through the outer front contact of relay 355 and the lowermost back contact of relay 354 to sleeve conductor 353 to hold the trunk finder TF in its operated position. The aforementioned operation of relay IIO extends the connection from the toll operators position, over conductors 35I and 352 of trunk ITI through terminals HI and I I2 and brushes I6I and I62, outer back contacts of relay I05, outer front contacts of relay H0, over conductors III and TI2 of the trunk finder TF to the outgoing trunk circuit OT. Relay H0 also closes a circuit from battery through the lower winding of relay I03, middle upper front contact of relay H0, over conductor 110 to ground at the lower front contact of the vertical off-normal springs VON; the VON springs were operated when the shaft and brushes stepped up to the first level. The operation of relay I08 causes the release of relay I05 and extends the holding ground on sleeve conductor 353 (from the toll selector TS) through terminal H3 and brush 163, through the inner lower front contact of relay 7 It, the inner lower back contact of relay lilo, and the lowermost front contact of relay 7513 to the sleeve conductor T13 leading to the outgoing trunk circuit OT. This holding ground is further extended from conductor l? through the inner lower front contact of relay 733, over conductor TN, to hold relay 'Ilfi operated. Relay 158 also disconnects the battery at its uppermost back contact from the windings of relay fill and magnet 725 and short circuits the lower winding of relay 7%? thereby causing the release of relays l! and 199. The group relay it! releases when relay 355 of the trunk circuit IT-I releases unless another trunk in the same group is awaiting connection to another outgoing trunk, in which case the ground at the left front contact of relay TM is extended over conductor 7%, through the outer upper front contact of relay 708, over conductor 769 to the next trunk finder (not shown) in the group. The rotary magnet 130 releases when relay We releases leaving only relays 108 and Fill operated during the further extension of the connection to the intercepting operator.

With conductors 354 and 352 of intercepting trunk ITl extended over conductors TH and ll? to the outgoing trunk circuit OT, and with relays 294 and 288 of the toll selector normal, relay 8%2 of the outgoing trunk circuit OT is operated in a circuit from ground at the upper back contact of relay 523, resistance 825, lower winding of relay 852, lower back contact of relay 82 3, conductor N2 of trunk finder lowermost front contact of relay Fill, lowermost back contact of relay 1%, brush Hi2, terminal H2, conductor 352 of intercepting trunk ITi terminal 222 and brush 2% of toll selector TS, middle lower front contact of relay 2E2, lower front contact of relay 25 I, inner lower back contact of relay right lower winding of repeating coil 25E, middle lower back contact of relay roe, lower winding of relay 2l3, lowermost front contact of relay 2%, to battery. The re istance 325 is high enough to prevent the operation of relay 2 l3 this circuit. The operation of relay 3 32 closes an obvious circuit for operating relay 8G7. Relay 85'! connects ground to sleeve conductor 833 and looks through its lower front contact and lower back contacts of relays 3M and 823 to same ground. Relay 83'! also closes a circuit for operating relay 858. Relay closes a circuit for operating relay 8&9, and relay 5% closes a circuit for operating relay 8H3. Relay closes a circuit for operating relay Relay 8% also connects ground to sleeve conductor 833 and closes a circuit for operating relay 8H3. Relay 2H9 closes a circuit for operating relay iii, from battery through the winding of relay 8 i i, upper front contact of relay BIB, upper back contact of relay M5, to the ground on conductor 833. With relay 8M operated, battery and ground are connected to the tip and ring conductors of the interoflice trunk see leading to the centralized intercepting switchboard to cause the operation of the line relay till at the distant end of the trunk. The circuit for operating relay is traced from battery through the upper winding of relay are, upper front contact of relay 8M, right upperwinding of repeating coil 635, conductor 83! and upper conductor of trunk the leading to the intercepting switchboard, upper back contact of relay 956, winding of relay Bill, lower back contact of relay 9%, ring conductor of trunk 980, conductor 832, right lower winding of repeating coil 830, inner lower front contact of relay 8 l 4, lower winding of relay 8 l 5 to ground. Relay 3 l 5 is marginal and does not operate in this circuit. Relay QOI closes a circuit for lighting the answering lamp 5 902.

When an operator at the intercepting switchboardinserts the plug of an answering cord in jack 903 to answer the call and assuming the cord CO2 to be the one used in answering, a cir- 10 cult is closed from battery through the upper back contact of relay 853, winding of relay 952, lower back contact of relay 955, ring conductor of plug 951 and jack 9% through the lower winding of relay to ground. Relay 5%. is marginal and does not operate; but relay G52 operates, thereby closing a circuit for operating relay 953 from battery through the lower back contact of relay 959, winding and front contact of the continuity springs of relay 953, to ground at the front contact of relay 952. Relay 553 looks through the front contact of its continuity springs, over the sleeve conductor of plug 55! and jack 9113 through the winding of relay 986 to ground, thereby operating relay 966. Relay 953 also closes a circuit for operating relay 954 and relay 954 closes a circuit for operating relay 955. The aforementioned operation of relay e96 disconnects relay Stl from the conductors of trunk 95!] and extends those conductors through the front contacts of relay 9% and the back contacts of relay 955, through the windings of relay 9%! to battery and ground. Relay 855 of the outgoing trunk circuit OT and relay Q9! of the incoming trunk circuit IT are thus operated by the energization of their upper windings in series and their lower windings in series. With relay 901 of the trunk circuit IT and relay 955 of the cord circuit (702 both operated, a circuit is closed from battery through the upper winding of relay 954 and front contact of relay 946? of trunk IT, through the tip conductors of jack E593 and plug 95I, retard coil 95 5, windings of relays Q51 and 958, lower back contact of flashing key 96!, lower front contact of relay 955, through the ring conductors of plug ilfil and jack 853, and through the lower winding of relay to ground. Relay 95'! operates, but relay set does not operate because it is polarized and the marginal relay 904 does not operate because the current in this cir- 5O cuit is insuiiicient.

The aforementioned operation of marginal relay 815 of the outgoing trunk circuit OT as a result of the answer of the call by an operator at the intercepting switchboard, causes the re- 55 lease of relay 8M and the operation of relay 823. The release of relay 8M disconnects the windings of relay 355 from conductors 83! and 832 and connects a supervisory bridge, comprising resistances 82! and 822! and the windings of relays 8&6 and 8H, across these conductors. The upper windings of relays tilt and 8H are of low resistance and the lower windings of these relays are of high resistance, the lower windings and resistance 322 being short circuited by the upper front contact of relay SID. Relay 816 is polarized and does not operate, but relay 8H is operated by the current through its upper winding in series with the line relay Bill of the incoming trunk circuit IT. Relay 8!! provides a 7() ground connection for holding relay 818 operated after relay 5 raeases. Relay 815 does not release, when relay 8M releases, being locked through its upper winding and upper front contact to ground on sleeve conductor 833, the hold- 7 ing ground being supplied from the front contact of relay 8I8 and also from the release relay of the toll selector TS. Relay 823 closes a circuit for operating relay S24, thereby disconnecting relays 8m and 8&2 from the tip and ring conductors ill and iii. The release of relay 802 causes the release of relay 837 since its locking circuit is open at the lowermost contacts of relay 823. The release of relay 807 causes the release of relays 838, 899 and BIB. With relay 823 operated and before relay 8% releases, the ring conductor W2 is extended through the lower back contact of relay 8%, the lower front contacts of relays i323 and 839, and through resistance M3 to ground; the resistance 8I3 is low enough to cause the operation of the tripping relay on calls intercepted at connector switches arranged to transmit ringing current over the intercepting trunk. When relay see releases, the resistance iiifi is disconnected from conductor I12 and a supervisory loop is closed from the tip conductor I?! of trunk finder Ti through the upper back contact of relay 8%, left upper winding of repeating coil 83%, windings of relay BIZ, winding of relay ii I, left lower winding of repeating coil 835, lower back contact of relay 8'09, lower front contact of relay 823, lower back contact of relay 806 to the ring conductor N2 of trunk finder TF. Relay 852 operates and since the current in this circuit is in the operating direction for polarized relay iii I, this relay also operates. The operation of relay til short circuits the high resistance lower winding of relay 8I2, thereby increasing the current in the supervisory circuit sufficiently to operate the marginal supervisory relay 2E3 of the toll selector as an indication that the call has been answered. When relay 2I3 of the toll selector operates, it closes a circuit for operating relay 2H, thereby disconnecting the winding of relay 2%! from the conductors of trunk I253, but holding relay 2i operated by bridging resistance 2M across its windings. With battery and ground disconnected from trunk 929, relay I 55 of the trunk circuit T releases thereby causing the supervisory lamp I04 of cord circuit CCl to be extinguished.

With the talking key 9 50 of cord 0C2 operated, conversation may be carried on between the toll operator and the intercepting operator. The connection is under the joint control of the two operators. Should it be necessary for the intercepting operator to attract the toll operators attention, the flashing key QEI of cord circuit C02 is alternately operated and released thereby intermittently eliminating the windings of relays 557 and 958 from the bridge across the tip and ring conductors of cord CO2 to cause the alternate operation and release of the marginal relay tilt of the trunk circuit IT. The operation of relay 9% closes a circuit for operating relay 9'35 and relay 9635 interchan es the connections between the conductors of trunk 90!) and the windings of relay set so as to cause the current over trunk see to be reversed and thus operate the polarized relay 356 of the outgoing trunk circuit OT. The alternate operation and release of relay it, under control of the flashing key, causes the short circuit around the lower winding of relay 8E2 to be intermittently opened, thereby causing the alternate release and reoperation of relay N3 of the toll selector TS. Relay 2! I is thus alternately released and reoperated to cause the alternate operation and r l of relay I I5 of the trunk circuit T which result in the flashing of the supervisory lamp I04 of the cord circuit CCI.

Upon release of the connection at the calling end by the removal of the plug I03 from jack IIO, relay III releases thereby causing the release of relays I I2 and I I3. The release of relay II3 opens the bridge across the conductors of trunk I20, but further release of the connection is under control of the intercepting operator. Since no disconnect signal is given the intercepting operator when the toll operator releases the connection, the plug 95! of cord 002 should be removed from jack 903, as soon as conversation is completed. Upon removal of plug 95I, relay 953 of the cord circuit and relay 906 of trunk circuit IT both release; relay 951 also releases; The release of relay 953 is followed by the release of relays 954 and 955 thus restoring the cord circuit 0C2 to normal. Relay 906 disconnects the conductors of trunk 900 from the windings of relay 901 and reconnects the winding of relay SQI across the trunk. Relay 901 of the incoming trunk circuit IT and relay 8II of the outgoing trunk circuit OT are thus released. The release of relay 8H causes the release of relay 858. The release of relay 8I8 disconnects the ground on its lower armature from sleeve conductor 833 and causes the release of relay BIB. Relay 8!!! opens the short circuit around the high resistance winding of relay M2 to release the supervisory relay 2I3 of the toll selector TS. The release of relay 2I3 is followed by the successive release of relays 2II, I and 202. The release of relay 202 disconnects the holding ground from conductor 2I9 and causes the return of the toll selector TS to normal in the usual manner. The release of relay 20I causes the release of relays 8H and 8I2 of the outgoing trunk circuit OT. With holding ground disconnected from sleeve conductor 2I9 of selector TS due to the release of relay 202 and with holding ground disconnected from sleeve conductor 833 of the outgoing trunk circuit OT due to the release of relay 8I8 (both the toll and the intercepting operators having released the connection) relay 355 of the trunk circuit ITI, relay iii! of the trunk finder TF and relay 8I5 of the outgoing trunk circuit OT release. The release of relay 8I5 causes the successive release of relays 823 and 824. When relay H0 of the trunk finder TF releases, a circuit is closed from battery through the winding of release magnet I40, upper front contact of the VON springs, inner upper back contact of relay I09, upper back con-' tact of relay-H0, back contact of relay I05, to ground at the lower front contact of the VON springs. The release magnet M0 is thus operated to return the trunk finder to normal. When the shaft reaches normal, the circuits through the winding of the release magnet I40 and the lower winding of relay I08 are opened. If the start conductor I64 is free from ground potential when the circuit through the lower winding of relay I08 is opened, or as soon thereafter as conductor I04 is free from ground potential, relay I08 releases. All of the various circuit units involved in extending a call intercepted at the bank of a toll selector to an operator at a central intercepting switchboard have now been restored to normal.

Should the called line number be an unassigned number in a partially assigned group of one hundred line numbers, the connection is extended by the operation of the toll selector TS and a toll connector TC, the terminals corresponding to unassigned numbers in the bank of connector TC being connected to one or more in-' tercepting trunks. Such a trunk is shown connected to terminals 321, 322 and 323 in the bank of switch TC, the associated trunk circuit IT2 shown in Fig. 31) being similar to the trunk circuit ITI of Fig. 3a. The trunk 1T2 connects to terminals 12 I, 122 and 123 of trunk finder TF and the further extension of the connection to an intercepting operators position is completed in a similar manner to that hereinbefore described for the call intercepted by trunk 1T1 except that relay 802 receives ringing current from connector TO. The direct current path for operating relay 802 during the silent interval of the ringing cycle is through the lower winding of this relay and resistance 826 to ground at the upper back contact of relay 823; and the alternating current path is traced from conductor 112 through condenser 804, and the upper winding of relay 802 to ground. When resistance 813 is temporarily connected to conductor 112 in response to the answer of the intercepting operator, as hereinbefore described, the tripping relay 302 of connector TC operates to complete the supervisory circuit between the toll selector TS and the outgoing trunk OT. The supervisory operations are similar to those on a call intercepted over trunk 1T1, the connector TC being released when the selector TS releases in the usual and well known manner.

Consider next a call originated by the subsoriber at station A in Fig. 4. The telephone set at station A may be of any type suitable for use in an automatic telephone system, the dial 400 being provided for dialing the number of any subscribers line with which connection is desired. The line 401 connects station A to the usual line circuit (not shown) in the central ofiice and also to terminals in the banks of a group of line finders one of which designated LF is represented by the brushes 402 and the associated terminals. This line finder may also be of the well known Strowger type. For a disclosure of such a finder and a description of its operation, reference may be had to the patent to H. Hovland No. 1,711,682 granted May '7, 1929.

Assume the line 401 to have been extended through the brushes 402 of line finder LE to the line relay 403 of the associated first selector LS. Relay 403 operates closing an obvious circuit for operating the release relay 404. Relay 404 connects ground through its lower front contact to sleeve conductor 413 to hold the line finder LF in its operated position and to hold the cut-01f relay (not shown) of the line 401 in the well known manner. The dialing of the first digit by the subscriber at station A causes the alternate release and reoperation of relay 403 in response to the dial impulses thus created. The first release of relay 403 closes a circuit from ground through the uppermost back contact of relay 406, back contact of relay 403, the upper front contact of relay 404, winding of relay 405, and through the winding of the vertical stepping magnet 420 to battery. The relay 405 and mag net 420 operate, the operation of the magnet causing the shaft and brushes of switch LS to be stepped up to the first level of the terminal bank. The reoperation of relay 403 at the end of the first impulse causes the release of magnet 420. Relay .405 is slow in releasing and remains operated until all of the impulses in the train have been received. Relay 404 is also slow in releasing and remains operated during the receipt of dial impulses. Each succeeding release and reoperation of relay 403 in response to dial impulses are effective to cause a corresponding operation of magnet 420, the brushes 411, 4 I 8 and 419 being thereby stepped up to the level of terminals corresponding to the digit dialed. When the shaft of switch LS is moved out of its normal position upon receipt of the first dial impulse, the vertical off-normal springs VON are actuated and with relay 404 operated as above described, a circuit is closed from battery 10 through the winding of relay 401, upper contact of the VON springs, front contact of relay 405, to the holding ground on conductor 413. Relay 401 closes a locking circuit traced from the upper contact of the VON springs, through the bank contact of the rotary stepping magnet 430, conductor 403, and the outer front contact of relay 401 to ground at the uppermost back contact of relay 406. When relay 405 releases after all of the impulses corresponding to the first digit have been received, a circuit is closed from batterythrough the winding of magnet 430, inner front contact of relay 401, back contact of relay 405, to ground on sleeve conductor 413. The operation of magnet 430 advances the brushes of switch LS into contact with the first set of terminals in the selected level and opens the circuit through the winding of relay 401. The release of relay 401 causes the release oi. magnet 430. The release of magnet 430 connects the winding of relay 401, through the upper contact of the VON springs, back contact of magnet 430, to conductor 409 thence through the lowermost back contact of relay 406 to sleeve brush 419 and also from conductor 409 through the winding of relay 406 and the lower back contact of the 11th ROTARY STEP springs to the holding ground on conductor 413. If the first set of contacts is idle, relay 406 operates in series with relay 401. Relay 401 ismarginal and 0 does not operate unless the first set of terminals is busy, in which case the brush 419 encounters ground potential on the terminal with which it is in contact, the winding of relay 400 being short circuited. With relay 401 reoperated, the rotary stepping magnet 430 reoperates thereby advancing the brushes of switch LS to the next set of terminals in the selected level. Relay 401 and magnet 430 thus continue their cycle of operations as above described to advance the brushes of switch LS until an idle set of terminals is encountered at which time relay 406 operates to extend the connection from line 401 through its inner front contacts to brushes 411 and 418. With relay 406 operated the sleeve conductor 413 is connected through the lowermost front contact of relay 406 to sleeve brush 429. The operation of relay 406 also causes the release of relays 403 and 404. Relay 404 being slow in releasing maintains the holding 6o ground on conductor 413 until a holding ground has been supplied through brush 419 from the succeeding switch or trunk as a result of its seizure as hereinafter described. Relay 406 is thus held operated, after relay 404 releases, by the holding ground supplied through brush 419. The levels of the local selector banks which represent assigned groups of telephone numbers may connect to intermediate selectors which in turn have access to groups of 'local connectors. 7 In Fig. 4, however, the terminals 431, 432 and 433' are shown connected directly to the local connector LC of Fig. 5. The terminals 421, 422 and 423 represent a level of the first selector bank in which the. terminals are connected to interof relay 501.

cepting trunk circuits. the corresponding digit being one which represents an unassigned group of subscribers numbers.

Assuming first that the call is for an assigned number and that brushes M1, M8 and 419 have been advanced into engagement with terminals 43L 432 and 033, the connection from line MI is extended through brush-es 481 and M8 and terminals 43| and 432, and through the inner back contacts of relay 504 of connector LC to the windings of line relay 50|. Relay 50| operates, in turn causing the operation of relay Relay 502 connects ground through its: lower front contact over sleeve conductor M3 to test terminal 4-33 to hold relay 403 of the selector LS and also to hold the line finder LF in its operated position and to hold the cut-off relay (not shown) of the line 40! all in the well known manner. When the calling subscriber dials the penultimate digit of the called subscribers number, relay 50| is alternately released and reoperated in response to the dial impulses thus created. The first release of relay Sill closes a circuit from ground at its back contact, through the innerv upper front contact of relay 502,, normally closed contact of the vertical off-normal springs VON, winding of relay 5 03 and through the winding of the vertical stepping magnet 52% to battery. The relay 503 and magnet 525 both operate, the operation of the magnet stepping the shaft and brushes of switch LC up to the first level of the terminal bank. When the relay 50l reoperates, magnet releases, but relay 503 is slow in releasing and remains operated until all of the impulses in the train have been received. Relay 502 is'also slow in releasingandremains operated until the connection is released by the calling subscriber. Each succeeding release of relay 50|causes the reoperation of magnet 520 thereby advancing the brushes 5H, hi0 and 55a up to the level corresponding to the digit dialed. After the switch is advanced from its normal position in response to the first impulse, the circuit for holding relay 503 and reoperating magnet520 is traced through the upper front contact of the vertical ofi-normal springs VON and the front contact of relay 503 instead of through the normally closed contact of the VON springs.

When relay 5 0i releases in response to the first impulse created by the dialing of the last digit of the called subscribers number, relay 505 and the rotary stepping magnet 530 are operated in a circuit from battery through the winding of magnet'530 and outer upper back contact of relay 55! in parallel with battery through the winding of relay 505, through the upper back contact of relay 501, back contact of relay 503, upper front contact of the VON springs, inner upper front contact of relay 502, to ground at the back contact of relay 50!. The operation of relay 505 renders the energization of this relay and magnet 530 independent of relay 501, the upper front contact of relay 505 being in parallel with the upper back contact The operation of magnet 530 advances the brushes 5, 5(8 and 5| 9 into contact with the first set of terminals in the selected level. The reoperation of relay 50| at the end of the first impulse causes the release of magnet 530. Each succeeding release of relay 50| causes the reoperation of magnet 530, thereby advancing the brushes of switch TC into engagementwith the set of terminals connected to the line of the called subscriber. Relay 505 is slow in releasing and remains operated until all of the impulses have been received. Before relay 505 releases, a busy test circuit is traced from battery through the winding of relay 501,

inner upper back contact of relay 5, lower 5 front contact of relay 505, through sleeve brush 5|!) to the sleeve terminal of the selected line. If the line is busy, relay 501 operates due to there being a busy-ground potential on this terminal.

If relay 50'! operates, it remains operated after 10 relay 505 releases, the holding circuit being traced through the inner back contact of relay 505 and the front contact of relay 501 over conductor 5| 3 to ground at the lower front contact of relay 502. A busy tone is transmitted to 15 the calling station by connecting the left-hand. winding of the tone source 5|2 through the inner lower front contact of relay 50! to the lower one of talking condensers 500.

Assuming that the called line is the line 580 go connecting the station B to the terminals 54|, 542 and 543 and that this line is idle, the release of relay 505 closes a circuit from battery through the winding of the cut-off relay (not shown) of line 5530, through terminal 543 and 35 brush 5|9, outer back contact of relay 505, lower winding of relay 5| I, lower back contact of relay 501 to ground at relay 502. Relay 5H is sufficiently energized by the current through its lower Winding to close its inner upper front contact. The circuit from battery through its upper winding and inner upper front contact over conductor 5|4 to ground at the uppermost front contact of relay 502 is effective to complete the operation of relay 5| With relay 5| operated, 35 ground is connected through its next to the outer lower front contact, to sleeve brush 5|9 as a line busy condition. With relay 5| operated,

a signaling circuit is closed from the ringing current source 525, through the inner lower 40 front contact of relay 5H, lower winding and lower back contact of relay 500, lowermost front contact of relay 5| I, brush 5|8, terminal 542, over the line 530 and through the ringer (not shown) at station E, back through terminal MI and 45 brush 5|l, uppermost front contact of relay 5! to ground at the outer upper back contact of relay 506. When the subscriber at station E removes the receiver, relay 506 is energized sufficiently by the current through its lower Wind- 5 ing to operate its inner upper front contact thereby closing a circuit from battery through its upper winding and inner upper front contact to ground on conductor 5|4. The operation of relay 500 connects a source of talking 55 current to the line 580; battery is connected through the upper winding of relay 504 and uppermost front contacts of relays 506 and 5 to brush 5|"! and ground is connected through the lower winding of relay 504 and lowermost 60 front contacts of relays 506 and 5 to brush 5|3. With the receiver removed from the receiver hook at station B relay 504 is operated thereby reversing the connections between the windings of relay 50! and the line conductors incoming to the connector LC. The current is thus reversed over the calling line circuit to indicate that the called subscriber has answered the call. Talking current is furnished to the calling station through the windings of relay 7 55 the voice frequency currents being transmitted through condensers 500.

When the connection is released by the subscriber at station A, relay 50| releases and when the receiver is replaced at station B relay 504 75 releases. The release of relay 501 causes the release of relay 502. Relays 506 and are held until relays 502 and 503 are both released. With relays 50l, 502 and 5| l normal, a circuit is closed from battery through the winding of release magnet 540, lower contact of the VON springs, lower back contact of relay 5H, and upper back contacts of relays 502 and 50] to ground. The operation of magnet 540 causes the switch to restore to normal in the usual manner. When the shaft and brushes reach normal position, the circuit through the winding of magnet 540 is opened at the VON springs.

Upon release of relay 502, as above described, the holding ground is disconnected from conductor 513 thereby causing the release ofrelay 405 of the selector LS, the release of the line finder LF, and the release of the cut-off relay (not shown) of line 401, the line finder Ll? being restored to normal in the usual manner. The release of relay 406 closes a circuit from battery through the winding of release magnet 440, lower contact of the VON springs and upper back contacts of relays 404, 403 and 406 to ground. The operation of magnet 440' causes the switch LS to restore to normal in the usual manner. When the shaft and brushes reach normal position, the circuit through the winding of magnet 440 is opened at the VON springs,

If the selector LS is advanced to a level of the terminal bank which represents an unassigned group of subscribers numbers, the call is ex tended to an intercepting operator, the terminals in this level being connectedto one or more intercepting trunks. Thus, the terminals 421, 422 and 423 in the bank of selector LS are shown connected to the intercepting trunk IT3 in Fig. 5d. Since the local selectors have no means for signaling over a selected trunk, as do the connectors and tool selectors, the trunk IT3 is arranged to respond to its seizure to initiate the further extension of the connection to the intercepting operator and to hold the selector and line finder switches in their operated positions. Upon seizure of trunk IT3, the calling line loop is extended through brushes 411 and 418, terminals 42I and 422, and through the back contacts of relay 558 to the windings of line relay 55L The operation of relay 55| causes the successive operation of relays 552, 553 and 554. The operation of relay 553 connects ground through its outer lower front contact over sleeve conductor 569 to sleeve terminal 423 to hold relay 406 of selector LS and to hold the line finder LF and cut-oil" relay (not shown) of line 400 in the usual manner. The trunk IT3 is shown connected to terminals 13I, 132 and 133 in the bank of trunk finder TF and is shown as being in the same group of trunks as are the trunks ITI and 1T2, having the common group relays The operation of relay 553 connects ground through its inner lower front contact, the lower back contact of relay 555 and the uppermost back contact of relay 551 to conductor 100 thereby operating the group relay PM. The operation of relay 554 connects battery through the winding of the cutoff relay 555 in parallel with resistance 559, through the upper front contact of relay 554 and the inner upper back contact of relay 551, over the sleeve conductor 503 to terminal 133 in the bank of finder IT. The trunk finder TF, or a similar finder having access to trunk IT3, is thereupon operated in the manner hereinbefore described to step its brushes up to the level in which the terminals of trunk IT3 are located and to rotate its brushes into engagement with these terminals. When brushes 16!, 152 and 163 engage the terminals 13l, 132 and 133, the connection from the winding of the cut-off relay 555 is extended through brush 153, the lower winding of relay 1I0, lower back contact of relay 108, lower winding of relay 101, to ground at the inner lower front contact of relay 105. The finder switch TF is thus stopped on the terminals in question to extend the connection from trunk IT3 to the outgoing trunk circuit OT. The operation of relay 555 connects the source of ringing current 500 through the lower front contact of relay 555 and through condenser 561 to one of the incoming line conductors thereby transmitting a ringing tone to the calling subscriber. Relay 555 also disconnects the ground at relay 553 from group conductor 100. The operation of relay 555 closes a circuit from battery through the winding of relay 555 through the upper front contact of relay 555, and the lower back contact of relay 551, conductor 562, through terminal 132 and brush 162 to conductor 112 of the outgoing trunk circuit OT, to effect the operation of relay 852. Relay 553 is marginal and does not operate in this circuit. The operation of relay 802 causes the further extension of the intercepted call through trunk circuit OT out over trunk 900 to the incoming trunk circuit IT at the intercepting operators position in the manner hereinbefore described. When the operator answers the call the connection of the tripping resistance 8l3 to the conductor 112 as hereinbefore described causes the operation of relay 556. Relay 555 locks through its inner upper front contact and resistance 554, over sleeve conductor 553, through terminal 133 and brush 153, through the inner lower front contact of re lay 1l0, inner lower back contact of relay 105, outer lower front contact of relay 108, sleeve conductor 113 of trunk finder TF and over sleeve conductor 833 of the outgoing trunk circuit OT to ground at the lower front contact of relay 818. The operation of relay 550 also causes the operation of relay 551. Relay 551 locks under control of relay 554, and causes the release of relay 555 to disconnect the audible ringing tone. With relays 556 and 551 operated, a supervisory circuit is closed from battery through the upper winding of relay 558 of trunk IT3, outer upper front contacts of relays 553 and 556, over conductor 55!, through terminal 13! and brush 16! of trunk finder TF, uppermost back contact of relay 106, uppermost front contact of relay H0, conductor 11!, upper back contact of relay 805 of the outgoing trunk circuit OT, upper left winding of repeating coil 830, windings of relay 8l2, winding of relay 8! l, lower left winding of repeating coil 030, lower back contact of relay 809, lower front contact of relay 823, lower back contact of relay 8%, conductor 112, lowermost front contact of relay 1H3, lowermost back contact of relay 106, brush 152'! and terminal 132 of trunk finder TF, conductor 562, lowermost front contact of relay through the lower winding of relay 558 to ground. Relay BIZ operates in this circuit but relay 8H being polarized does not operate since the connection of battery to the tip conductor 55| of trunk IT3 and ground to the ring conductor 552 results in current in the non-operating direction. With relay 8 non-operated, the high resistance lower winding of relay 8l2 is not short circuited and relay 558 of trunk IT3 being marginal the latter relay does not operate. The voice currents between

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