US1902186A - Automatic telephone system - Google Patents

Description

March 21, 1933. N HSAUNDERg LQ28 AUTOMATIC TELEPHONE SYSTEM Original Filed Jan. 10, 1951 5 Sheets-Sheet 1 l D/FFEEEAlT/AL /z/ aura Ea g ll-mm? Norman H. Saunders March 31933. N. H. SAUNDERS AUTOMATIC TELEPHONE SYSTEM 5 Sheets-Sheet 2 Original Filed Jan. 10, 1951 rnuenlur Norman H. Saunders March y 1933- N. H. SAUNDERS 399@218@ AUTOMATIC TELEPHONE SYSTEM Original Fi led Jan. 10, 1931 5 Sheets-Sheet 5 U/VE BAN/Z5 am. awning Inventor Norman H. Saunders Mmh 23, 11933. N. H. SAUNDERS ilfifi AUTOMATIC TELEPHONE SYSTEM Original Filed Jan. 10, 1951' 5 Sheets-Sheet 4 Nun-nan H. Eaundars wmm March 21, 1933. "N. H. SAUNDERS AUTOMATIC TELEPHONE SYS TEM 5 Sheecs-Sheet 5 Original Filed Jan. 10, 1931 Jain iii T0 OVElFlOWl-IA/PEIS mo'mseswuas knvmmwwn Patented Mar. 21, 1933 UNITED STATES PATENT OFFICE.

NORMAN H. SAUNDERS, OF CHICAGO, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS,

TO ASSOCIATED ELECTRIC LABORATORIES, INC., OF CHICAGO, ILLINOIS, A CORPORA- TION OF DELAWARE AUTOMATIC TELEPHONE SYSTEM Application filed January 10, 1931, Serial No. 507,815. Renewed May 14, 1932.

The present invention relates, in general, to automatic telephone systems, but more )articularly to such systems in which line finders are employed to connect an idle selecting switch with a calling line; and the principal object of the invention, brlefly stated, is the production of new and improved circuit refinements in finder switch systems, the improvements tending to make the system more reliable, to give uniform high quality service, and to make it cheaper to install and maintain.

A feature of the invention relates to the rovision of a primary and partial secondary finder trunking arrangement, in which the primary finders of a primary line group are directly associated with selector switches, while the secondary finders, also directly associated with selector switches, have access to a plurality of primary line groups by way of multipled overflow primary finders.

One of the features of the invention relates to the novel means whereby an overflow finder starts an idle secondary finder and marks the contact terminating this overflow finder in the banks of the secondary finder at the time the overflow finder is started in search of a calling line.

Other objects and features incidental to carrying out the foregoing ones will become apparent from reading the detailed descrlption and claims which follow.

The drawings comprising Figs. 1 to 6, inclusive, when arranged with Fig. 1 to the left of Fig. 2 and Fig. 4 to the right of Fig. 3, show sufiicient detail to enable a clear understanding of this invention.

Referring now to Fig. 1, in more detail, the selector SA shown on the right-hand side is of the old and well-known type of Strowger selector and is included in a selectorfinder link. The finder switch FA is of the strowger vertical and rotary type, having wipers 230 to 235, inclusive, which are moved first in a vertical direction and then in a rotary direction to select the contacts of a calling line. The wipers of the finder FA are shown on the rightflhand side of Fig. 2. Since, in the present embodiment of this invention, a finder switch of 200-line capacity prises only the operating magnet, two switching relays and a start relay. The two switching relays are relays of the type disclosed in Patent 1,67 3,88 1, issued June 19, 1928, to H. E. Pye. The cores of these switching relays are provided with two windings which are separated by a magnetic spacing member, a projection of which extends back and forms a back stop against which the armature of the relay rests. The winding of the heel end of the relay is the magnetizing coil, and the'fiux produced thereby traversing the path including this magnetic iron back stop, which is in shunt of the air gap, and no amount of flux current in this magnetizing coil will cause the armature to operate. A very small current in the second operating winding of the relay, when in the same direction as the magnetizing winding, will cause the relay to operate. The use of these relays as switching relays permits the calling line to be marked in the finder bank with a potential of relatively high resistance and impedance, and prevents undesireddiscrepancies in the searching circuit upon the test wiper of the finder encountering booster battery metering potential on a test contact before reaching the test contacts of a calling line. All the relays of this type have been shown in the drawings with lugs extending from their center portion, and such relays hereinafter will be referred to as three-pole relays.

In the lower half of Fig. 1, there is shown the finder allotter DA comprising the stepping magnet 161, wipers 145 to 148, inclusive, and a. plurality of relays for controlling the various functions of the finder. The allotter DA is common to a plurality of findercircuit thereof has been altered in accordance with the present invention.

In Fig. 2 there is shown the subscribers lines S and S. Associated with each line are the usual line'and cut-ofl relays, the circuits of which have been modified and show a threepole line relay in place of the ordinary line cuited. The normal connections from connector banks are shown extending to the line and cut-oil relays associated with subscribers lines S and S. Inthe lower part of Fig. 2 is shown the vertical banks VA and VB, which, together with the wipers 262 and 263, determine the vertical designations to which the finder switches are to be operated. The vertical banks, as well as the line banks, are multipled to the banks of the overflow finders as will be more clearly described herein after. The overflow transfer relay 290 shown directly below the vertical bank. is provided for the purpose of transferring the start lead to the overflow finders when all the finders in the A and B groups, such as FA and FE, are busy. On the left-hand side of Fig. 2 the finder FB is represented by a rectangle and the allotter DB in the same manner with the exception that the busy common relay 262 is shown in order to explain the manner in which the starting circuit is transferred from one group of finders to another. The finder FB isidentical to the finder FA and it therefore need not be shown or described in detail. The same is also true of the allotter DB.

In Fig. 3, the line bank contacts and the vertical contacts VO shown to the left of Fig. 3 are multipled to the line banks and vertical banks as indicated by their associated reference characters. The overflow finder OF is somewhat similar to the finder FA. The circuits of the overflow finder have been changed somewhat in order to cooperate with the secondary finder shown in Fig. 4. The allotter DO for the overflow finders is also somewhat similar to the allotter DA and DB. The finder OF of a certain primary finder line group has access to the multiple bank contacts shown to subscribers line S and S. An overflow finder at one primary line group is multipled to other overflow finders in other primary line groups as will be more fully described in connection with Fig. 5. It will be noted by referring to Fig. 4 the multipled overflow finders terminate only in bank contacts and do not, therefore, have the customary line and cut-ofl equipment associated with switches of this type.

In Fig. 4 there is shown the secondary finder SF which is mechanically similar to the finders FA and OF. The finder SF also has two sets of wipers and as will be noted, thereis no step-by-step allotter associated therewith. The finders SF are provided with a chain starting arrangement and therefore need no allotter. It will also be noted that the control relays are individual to each of said finders. The overflow selectors SO, shown to the right of Fig. 4, are similar to the selectors SA. A busy chain circuit extends through normal open contacts in all of the secondary finders to 'a relay 471 which supplies busy holding battery to the trans fer relays, such'as relays 432. The relay 471 is not energized until all the relays 432 in all of the finders are energized. At the left-hand side of Fig. 4 the multiple connections of the line, release trunk, and start conductors,-are shown which extend to overflow finders in their primary line groups. Near the lower left-hand corner of this figure is shown the start conductors which extend to other overflow finders. As will be noted these start conductors mark the vertical banks of the secondar finders and start finders by Way of individual resistances, such as resistance 417, in the same manner as disclosed in Fig.2 only instead of the start circuit extending through an allotter it extends'through a transfer to a start relay in the secondary finder. This arrangement will be more fully described in connectioin with Fig. 6.

Fig. 5 diagrammatically represents the trunking layout of this system. Each primary line group such as 501, 502, 503, and 504, represented by rectangles are normally served by the primary finders FA and FE and their associated selectors SA and SB. Each primary line group has overflow finders associated therewith which are taken. into use after all of the primary finders FA and FE of that group are busy. As will be noted the overflow finder OF of the 501 group is multipled to the overflow finders of the 502 and 503 line groups and terminate in the bank contacts of the secondary finder SF in a set of bank contacts. Other overflow finders of other line groups are multipled in a similar manner and terminate in the bank contacts of the secondary finders. When an overflow finder is taken into use a secondary finder together with its associated overflow selector S0 is also taken into use and both finders then hunt for calling potential, the overflow finder hunting for the calling line potential while the secondary finder hunts for the calling potential supplied by the overflow finder in use.

Fig. 6 diagrammatically represents the manner in which the terminating bank con tacts of the overflow finders are multipled in the bank ofthe secondary finders. The overflow finders OF are represented by small rectangles and their associated bank contacts are multipled in the manner shown through the various secondary finder banks, said secondary finders being represented by small rectangles at the bottom of the figure. It will also be noted that the vertical bank of the secondary finders are slip multipled 1n the same manner as the line banks. The start circuits extending from the overflow finders are diagrammatically illustrated as extending to respective secondary finders in such a manner that the secondary finders taken into use over a particular start circuit normally are first choice to the overflow finder which has grounded its start lead. It will be noted that the start circuits form a sort of a chain so that if all of the secondary finders which are first choice to a particular group of overflow finders are all busy, then the start circuit is transferred to the group of secondary finders which are second choice to said overflow finders. By this starting arrangement a secondary finder which has the least movement to find the overflow finder'is taken into use and should be able to find the overflow finder in use at practically the same time or nearly so that the overflow finder finds the calling line.

Throughout the drawings a plurallty of batteries have been shown to avoid unnecessary complications, while in actual installations there would be but one battery, preferably with its positive pole grounded.

General description In order to enable a clear understanding of the invention, it will now be assumed that subscriber S initiates a call, and it will be further assumed that the finder FA has been preselected by the finder allotter DA in readiness to handle the call. Responsive to the removal of the receiver from the switchhook at substation S, line relay 201 associated with the line is energized to mark the line calling in the finder bank, and to place ground upon a start conductor 250. The grounding of start conductor 250 connects ground to the second contact of the bank VA, also closes a circuit for the start relay 163 in the finder allotter DA. The finder takes two vertical steps to reach the level pertaining to the calling line at which time the line wipers will be rotated into that level to select the contacts of the line A. When the line S is en countered, the battery potential applied to the test contacts associated with that line will cause the finder FA to stop thereon and switch through so that the calling line will be connected through to the selector SA.

When the finder switches through to the calling line, the switching relay in the finder operates and connects ground to the combined guard and kick-ofit' conductor 142 extending through the wiper 147 to the allotter, whereupon the allotter stepping magnet is operated to prepare the allotter to preselect another idle finder selector link.

In some instances due to faults, the finder may fail to switch and in such instances a relay in the allotter controlled by vibratin springs is energized. The energization 0 this relay lights a lamp to indicate to the attendant that there is a blocked call. Until this trouble is corrected, the calls originating in the A group are now handled by the B group allotter and finder selector links.

The allotter DA and finder-selector links, such as FA and SA in'the A group, normally handled all the calls from the subscribers in the A group. When all of the finder selector links in the A group become busy, the busy common relay 162 in the allotter is deenergized and the allotter DB and the finderselector links, such as FB and SB will be taken into use by the subscribers in the A group. The operation of the allotter DB and the finder-selector links in the B group are similar to the general operations just described for the A group finder-selector links and allotter.

In case all of the finder selector links in the A and B groups are busy, or in case the allotters DA and DB are locked out of service for the time being, the busy common-relay 162 in the allotter DA and the'busy-common relay 262 in the allotter DB are deenergized to cause the overflow transfer relay 290 to deenergize and transfer the start circuit from the A and B groups to the overflow finders by way of conductor 299. The allotter DO associated with the overflow finder operates in .the same manner as the allotter DA and also causes the preselected overflow finder to operate in the same manner as the finder FA. In additon, when the start relay 303 in the overflow finder is energized responsive to a call, it not only prepares the overflow finder for operation, but also marks its terminating contacts in the bank of the secondary finders. The start relay 303 also grounds the start conductor 416 which extends to the vertical banks of the secondary finders to mark this individual vertical bank and also completes a circuit through the resistance 417 to the start relay of an idle secondary finder. Both the overflow finder and the secondary finder hunt simultaneously and both finders will switch through when they have found the calling potentials, the overflow finder switching through when it finds the calling potential applied by the calling line and the secondary finder switching through when it- When the secthe system, a detailed description of its operation will now be given.

Assume now that the line S wishes to call. Responsive to the removal of the receiver, a circuit may be traced from ground through the left-hand winding of line relay 201, contacts 206, conductor 254, through the switchhook, receiver, transmitter, and calling device of substation S, conductor 255, contacts 209, and through the right-hand winding of line relay 201 to battery. It will be remembered that this line relay is a three-pole relay and therefore will only energize when the two windings are bridged together, and, therefore, the line relay 201 will not energize when either of the line conductors alone becomes grounded or in case both become grounded. Line relay 201, upon energizing, at armature 207 applies battery potential to the finder test contacts through the winding of the cut oil relay 202. The application of this battery to the test contacts of the line renders the line S selectable to the finder. At armature 205 line relay 201 connects ground to conductor 250 to ground the second vertical bank contact in banks VA and to complete a circ'uit extending from conductor 250 by way of resistance 251, conductor 260, armature 170 and its working contact of the normally energized busy common relay 162, and through the winding of the distributor start relay 163 to battery. Start relay 163, upon energizing, at armatures 181 closes a circuit through the lower winding of diiferential relay 167 which relay at armatures 187 and 188 starts the weighted springs vibrating to prepare a circuit for the differential slow-to-operate relay 168. Relay 168, being a slow-to-operate relay, will not operate as long as the weighted springs are vibrating and therefore will not operate until a predetermined time after the operation of relay 167. At armature 174, relay 163 completes a circuit for the distributor switching relay 164 as follows: from ground at armature 174, winding of relay 164, normally closed springs 172, interrupter springs 17 3, and through the windin" of the motor magnet 161 to battery. Due to the high resistance of relay 164, the motor magnet 161 is not energized in this circuit. In case, however, the allotter DA has not completed its preselecting operation at this time, the wiper 147 may be in engagement with a grounded contact and in this case the testing relay 164 would be short circuited by way of armature 180 and its resting contact, while a circuit would be completed through armature 17 2, interrupter springs 173 and through the winding of motor magnet 161 to battery. In this case, the motor magnet would step the wipers to the next finder-selector link and in case this finder-selector link was idle, wiper 147 would no longer encounter a ground potential and the switching relay 164 would energize in the manner previously described.

At armature 177, switching relay 164 closes a locking circuit for the upper windin of the busy common relay 162 as follows: om ground by way of armature 190 and its restlng contact, armature 171 and its normally closed springs, armature 177 and through the upper winding of busy common relay 162 to battery. The busy common relay 162 is maintained over this circuit so that in case the finder just seized is the last idle finder in this group, the busy common relay will be maintained in operated position until this finder has switched through. At armature 178, relay 164 prepares a locking circuit for the changeover relay 165; at armature 179 prepares an energizing circuit for changeover relay 165, at armature 180 and its working contacts prepares a circuit for the motor magnet 161, and at armature 186 completes a circuit for the start relay 106 as follows: from ground by way of armature 186, wiper 148, conductor 143, and through the winding of slow-to-release start relay 106 to battery. At armature 176, switching relay 164 also completes a circuit for energizing the vertical magnet 109 as follows: from ground by way of armature 17 6, armature 185, armature 182 and its resting contact, wiper 146, conductor 140, and through the winding of vertical magnet 109 to battery.

Slow-to-release start relay 106, upon energizing, at armature 127 prepares the testing circuit for the three-pole switching relay 104; at armature 128 and its working contact prepares a circuit for the motor magnet of the allotter; at armature 130 prepares another point in the circuit for the magnet in the allotter; and at armature 131 and its working contact grounds the release-trunk conductor 135, and at its resting contact opens a point in the circuit to the release magnet 107. Armature 131 in addition to grounding the releasetrunk conductor also closes a circuit through the lower windings of the three-pole swiching relays 104 and 105'to polarize these relays to prepare such relays for operation.

By the operation of the vertical magnet 109 the wipers of the finder are raised one vertical step opposite the first level of bank contacts, and the off-normal springs 112, one of the multipled circuits for maintaining the busycommon rela 162 in the allotter energized, is opened. owever, at the other idle finders in this group the busy-common relay 162 is maintained over the following circuit: ground by way of test contact springs 192, armature 191, through the lower winding of busy-common relay 162, conductor 144 common to all of the finders in the A group, through the off-normal springs 112 in the idle finders of each group, and through the lower winding of the three-pole switching relays such as 104 and 105 in the idle finders. The busy-common relay 162 is therefore maintained energized as long as'there is an idle finder in the A group. At off-normal springs 129 a circuit is prepared for the grounding of the conductor 142 and at off-normal springs 132 a circuitis prepared for the release magnet 107. At armature 111 the vertical magnet 109 connects ground to the common interrupter conductor 141 for energizing the stepping relay 166. At armature 185, stepping relay 166 opens the circuit to the vertical magnet 109, whereupon the vertical magnet deenergizes and at armature 111 opens the circuit to the stepping relay 166. The deenergization of the stepping relay 166 again closes the circuit for the vertical magnet 109, whereupon the wipers of the finder are advanced another vertical step. This interaction between the vertical magnet 109 and stepping relay 166 takes place in the manner just described until the test wiper 262 of the finder FA finds the marking ground applied to the vertical bank contact. In this case, since the second vertical bank was grounded, the wiper 262 would encounter this ground potential on its second step and at that time a circuit may be traced from the grounded bank contact, vertical wiper 262, conductor 174, wiper 145, armature 183 and its resting contact, through the winding of changeover relay 165, armature 179, and through the winding of step ping relay 166 to battery. In case the armature 111 of the vertical magnet is not operated at this time, the changeover relay is energized over the above-traced circuit and completes a locking circuit for itself through grounded armature 178. The stepping relay 166 is maintained energized in series with the changeover relay until the changeover relay at armature 183 opens its own original energizin circuit at its back contact and at its working contact prepares the circuit for the three-pole switching relay 105. At armature 182 and its resting contact the circuit extending to the vertical magnet 109 is opened and at the working contact of this armature the impulsing circuit is transferred to the rotary magnet 108. At armature 184 changeover relay transfers the energizing circuit from the lower winding of differential relay 167 to its upper winding thereby causing the differential relay to kick down and again energize to restart the vibrating springs. In the normal operation of the finder and allotter, the changeover relay will operate before the vibrating springs of relay 167 have stopped vibrating and therefore before relay 168 can energize. The differential relay 167 is now energized over its upper winding and due to the vibration of the springs 187 and 188, the differential sloW-to-operate relay 168 will not operate unless the finder fails to switch through on account of some fault. When stepping relay 166 deenergizes responsive to the energization of changeover relay 165, a circuit may be traced from grounded armature 176, armature 185, armature 182 and its working contact, common conductor 139, armature 130, armature 158 and its resting contact, armature 152 and its resting contact, and through the winding of rotary magnet 108 to battery. Rotary magnet 108, upon energizing, rotates the wipers 230 to 235, inclusive, into engagement with the first set of line bank contacts, and rotates the vertical test wiper 262 out of engagement with the vertical bank. At armature 110, rotary magnet 108 completes a circuit for the stepping relay 166 over common conductor 141. At this point further rotation of the wipers of the finder FA are dependent upon whether the test wipers 231 or 234 encounter a negative battery calling potential or not. In case ne ative battery potential is not on either of the test contacts with which the test wipers are in engagement, neither of the switching relays 104 or 105 will energize. Therefore, when the rotary magnet 108 energizes the .stepping relay 166, the stepping relay 166 in turn opens the circuit of the rotary magnet 108 and the rotary magnet in turn will open the circuit of the stepping relay 166, whereupon the stepping relay deenergizes and again closes a circuit for the rotary magnet 108. This cycle of operation continues until one of the test wipers 231 or 234 encounters a negative battery potential.

Assuming that no other line in the second level of the finder bank terminals are calling, except subscriber S, then when test wiper 231 is rotated into engagement with this set of contacts, the test wiper 231 will encounter a calling potential which is applied thereto through the winding of the cut-off relay 202. A circuit for energizing the three-pole switching relay 105 may be traced as follows from ground by way of the working contact of armature 183 and said armature, wiper 145, upper winding of switching relay 105, test wiper 231, conduct0r 2'56, armature 207, and through the winding of cut-01f relay 202 to battery. The switching relay 105 and the cut-off relay 202 energize over the above-traced circuit. The circuit just traced through the upper winding of the switching relayil05 assists the circuit previously traced through the polarizing winding with the result that the switching relay energizes very quickly to stop the rotation of the wipers.

It might also be mentioned at this time that in case either of the test wipers 231 or 235 should encounter a booster battery metering potential or a busy ground potential during their rotation before the calling line is reached, the booster battery potential or the ground potential encountered would be in opposition to the circuit through the polarizing winding with the result that the switching relay would not energize.

The cut-oil relay 202 at armatures 206 and 209 disconnects the line relay 201 from the line conductor and at armature 208 completes a locking circuit for itself independent of armature 207. Line relay 201, upon deenergizing, at armature 205 removes ground from the start conductor 250.

Returning now to the finder FA and at a time when line switching relay 105 energ zes in series with the cut-off relay 202, it should be stated that armature 152 operates very quickly and opens the circuit to the rotary magnet in order to prevent the wipers from rotating an extra step. At armature 151, relay 105 connects the release-trunk conductor 135 to test wiper 231; at armature 152 and its working contact connects ground to the combined guard and kick-ofl' conductor 142; and at armature 153 opens a further point in the circuit of the release magnet 107. At armatures 150 and 154 relay 105 connects the subscribers talking conductors 254 and 255 to conductors 134 and 137, thereby causing the energization of the line relay 102 of the selector SA in the wellknown manner. The operation of the line relay 102 in the selector causes the energizationof the release relay 101 to apply ground potential at armature 120 to the release trunk conductor 135 before the ground potential applied thereto in the finder is removed. When the switching relay 105 connects the line conductors of the calling line S to conductors 134 and 137 dial tone is connected over these conductors to the calling line in the well-known manner, and when the calling subscriber S hears the dial tone, the subscriber may then proceed to set u the desired connection to the called party. ince the operation of the switch SA and the remaining switches in the switch train tothe called line is old and well known, it is therefore not necessary to describe or show their operation.

Returning now to the allotter DA and at a time when the switching relay 105 operated, a circuit for operating the motor magnet 161 of the latter may be traced as follows: from ground by way of armature 176, armature 185, armature 182 and its working contact, common conductor 139, armature 130, armature 158 and its resting contact, armature 152 and its working contact, working contact of armature 128 and said armature, common guard and kick-oft conductor 142, wiper 147, armature 180 and its working contact, and through the winding of stepping magnet 161 to battery. Stepping magnet 161 operates its pawl (not shown) preparatory to stepping the allotter and at interrupter springs 173 opens the circuit of relay 164, whereupon thev latter relay deenergizes. The circuit of relay 164 is also opened at another point at armature 174 when the relay 163. deenergizes responsive to the removal of ground from the start conductor 250 by the deenergization of the line relay 201. At armature 177 the locking circuit to the upper winding of busycommon relay 162 is open and if all the finders in the A group are busy, the busy common relay will release. At armature 178 the looking circuit of changeover relay 165 is opened whereupon the latter relay deenergizes. At armature 186 the circuit extendin to the start relay 106 is opened and this relay after an interval of time also deenergizes. At armature 176 and 180 the circuit extending to the motor magnet 161 is opened, whereupon the magnet deenergizes and connects the wipers of the allotter to the contacts of the next finder in the group. In the finder FA, the slowto-release relay 106 deener izes and at armature 127, removes groundrom the upper winding of relay 104; at armature 128 opens up the kick-off circuit and at itsresting contact connects ground to conductor 142 by way of off-normal springs 129 and its working contact, and at armature 131 prepares the circuit to the release magnet 107. In case the'wipers of the allotter DA should be standing on a busy finder, wiper 147 will encounter a ground potential, where upon a circuit may be traced from wiper 147, armature 180 and its resting contact, armature 172, interrupter spring 17 3, and through the motor magnet 116, to battery. The motor magnet is energized over this circuit and steps the wipers until the wiper 147 no longer encounters a ground potential. In this manner the allotter preselects the 'next idle finder in the A group. When the start relay 163 deenergizes responsive to the removal of ground from the start conductor, armature 181 removes ground from difierential relay 167 with results that this relay deenergizes fault, however, the changeover relay 165 may fail to function in the proper manner with the result that after an interval of time the relay 168 is energized over an obvious circuit and at armature 190 completes a circuit through the call block lamp 196 to indicate to the attendant that a call has been blocked ,through some fault. At the restingcontacts.

of armature 190 the locking circuit prepared by the energization of relay 164 for busycommon relay 162 is opened, and at armature 191 the locking circuit of the lower winding of the busy-common relay 162 is opened, whereupon the busy-common relay releases. Busy-common relay 162 at armature 169 opens one of the circuits for maintaining overflow transfer relay 290 in energized position, at armature 170 opens a point in the start circuit for relay 163 and transfers the start circuit by way of conductor 194 and armature 297 to the B group; and at armature I 172 opens the circuit of relay 164. The calls now ori inating in the A group are handled by the group finders and allotters until the fault is corrected by the attendant.

Since the finder FA is a 200-point finder and therefore has two sets of wipers it may so happen that test wiper 234 instead of test wiper 231 may encounter the negative battery callin potential of the calling line. In this case t e finder is operated in the same manner as previously described, and when wiper 234 encounters a negative battery calling potential on the test contact, associated with the calling line, a circuit will be completed for operating switching relay 104 as follows: from ground by way of armature 127, upper winding of switching relay 104, test wiper 234 to negative battery calling potential. Switching relay 104, upon energizing, at armatures 156 and 160 connects the lower sets of wipers for use. At armature 157, switching relay 104 disconnects the release-trunk conductor 135 from armature 151 and also connects the release-trunk conductor 135 to test wiper 234; at armature 158 completes the kick-off circuit for operating the motor magnet 161 of the allotter; and at armature 159 opens another point in the circuit of the release magnet 107. The switching relays, when either one or both are en ergized, are maintained energized alone over their lower winding by ground on the releasetrunk conductor 135. The finder allotter DA then preselects another idle finder in the same manner as previously described.

In case both test wipers 231 and 234 should simultaneously encounter a calling potential, both switching relays will energize and the energization of the switching relay 105 willbe ineffective because the switching relay 104 disconnects the upper set of wipers.

After conversation and responsive to the calling subscriber replacing the receiver, ground is removed from the release trunk conductor in the well-known manner, whereupon the switching relay 103 of the selector SA 'deenergizes to release the selector. The switching relays in the finder also deenergize responsive to the removal of ground from the release-trunk conductors. Since the start relay 106 has previously deenergized when the allotter kicked off of this finder, a circuit may be traced from grounded armature 131 by way of its back contact, armature 159, finder test springs 113, armature 153, off-normal springs 132, and through the winding of release magnet 107 to battery. B the operation of the release magnet 10 the shaft and wipers 'of the finder are returned to their normal position at which time the off-normal springs also return to their normal position. Finder test jack springs are provided in order to inform the attendant which set of wipers are engaged in the connection set up. In case the attendant wishes to know which set of wipers is in use, the attendant will operate the test jack spring 113 to its upper position. Now if the upper set of wipers is in use in the connection, a circuit may be traced from ground at armature 131, armature 159, test jack 113 in its operating position, common conductor 138, through lamp 175 to battery. The operation of the lamp indicates to the attendant that the upper set of wipers in this finder is in use. In case the lower set of Wipers were in use, then.

armature. 159 would have been operated and the light 175 would not operate.

The test jack 192 associated with the al lotter DA is provided in order for the attendant to routine test the allotters and finders in the A and B groups. Responsive to short circuiting the test jack spring 192 and its associated upper spring, the start test conductor 195 is grounded. This ground at spring 192 extends by way of conductor 195,

resistance 251, start conductor 260, armature 170 and through the winding of start relayf 163 to battery. Start relay 163 will be energized over the above-traced circuit and will operate the allotter and the finder in the same manner as previously described. In this case thefinder will be advanced to its fifth level where the vertical wiper 262 cucounters the vertical bank contact marked by conductor 195 and rotates off of the fifth level in case no subscribers therein are calling. As soon as the finder rotates off of any level the cam springs 155 are operated to complete a circuit for switching relay 105 as follows: from ground by way of armature 183, wiper 145, upper winding of switching relay 105, cam springs 155, and through the winding of rotary magnet 108 to battery. Switching relay 105 energizes over the above-traced circuit because the upper winding now assists the lower winding, while the rotary magnet, due to the high resistance of the upper winding of the switching relay, does not energize over the circuit. The switching relay 105 causes the allotter to kick off and select another idle finder in the same manner as previously described. Now when slow-acting relay 106 deenergizes responsive to the operation of the allotter, ground is removed from switching relay 105 and said relay deenergizes because no holding ground'is sent relay 162 would be opened and said relay would release and transfer the start circuit to the allotter DB, whereupon the finders FE and allotterDB are operated in the manner just described-for the purposes of testing the same. It is also obvious that the finder in the A group and the allotter DA may be taken out of 'servicemerely by insulating the grounded jack spring 192 from its lower associated jack spring. This operation causes the release of the busy-common relay 162 so that any calls originating in the A group will be handled by the B group.

In some instances in order to more fully routine test the operation of the finders and allotters, it may be desirable to provide a test subscribers line to which the finders are operated and switched through instead of rotating the finders ofi of the level to switch through. The finders and allotters, inthis case, are operated in the same manner as previously described to find the test line after which they are released.

From the foregoing it will be seen that calls from the A group subscriber are first handled by the A group finders and in case all of the A group finders are busy, then the calls are handled by the B group finders. Under certain condition both the A and B group finders may all be busy, and under these conditions the calls from the A and B groups are then handled by overflow finders.

It will now be assumed that all of the finders in the A and B groups are busy and that subscriber S initiates a call. Under these conditions, the busy-common relay 162 in the allotter DA and the busy-common relay 262 in the allotter DB are in denergized position and have opened the circuit to relay 290, whereupon overflow transfer relay 290 has deenergized in order to prepare the start circuit to the overflow distributor DO. When line relay 201 energizes, said relay at armature 205' grounds the start conductors 250 and instead of energizing a start relay in either of the distributor DA and DB, the start relay 351 in the allotter D0 is energized over the following circuit: ground at start conductor 260, armature 170 and its resting con tact, conductor 194, armature 297 and its resting contact, overflow start conductor 299, Fig. 3, armature 357, and through the winding of start relay 351 to battery. Since the allotter D0 is similar to allotter DA, only a brief description of its operation will be given. At armature 363, start relay 351 energizes switching relay 352 by way of armature 359 and magnet 361. At armature 392, relay 352 closes a circuit for energizing the start relay 303 in the finder OF; atarmature 365 com p etes a circuit for energizing the vertical magnet 305 of the finder; and at armature 367 prepares a circuit for the changeover relay 353. Start relay 303 in the finder OF upon energizing, at armature 324 completes a locking circuit for itself; at armature 321 and its working contact prepares a circuit for the cut-off relay 304 and. at spring 322 and the back contact of armature 321 connects ground through the lower windings of the three-pole switching relays 301 and 302 to polarize such relays; at armature 323 prepares a testing circuit for switching relays 302'; at

armature 325 prepares a kick-ofl' circuit extending to the motor magnet 360 of the allotter DO; at armature 326 prepares a point in the circuit extending to the rotary magnet 306; at armature 327 and its resting contact opens a point in the circuit of the release magnet 300, and at its working contact connects ground to start conductor 416 by way of armature 331 for starting an idle secondary finder, such as finder SF. At armature 328, relay 303 bridges a loop circuit, including the resistance R, across the talking conductors 393 and 395 in order to hold the secondary finder SF and selector SO in case the secondary finder should find this overflow finder before the overflow finder has found the calling line S. The circuit for energizing the vertical magnet 305 may be traced as follows ground by way of armature 365, armature 374, arma-- ture 370 and its resting contact, wiper 341, conductor 337, and winding of vertical magnet to battery. Responsive to the operation of the vertical magnet 305 the oif- normal springs 332, 320, and 318 are operated on the first vertical step of the shaft and wipers. The wipers 344 to 349, inclusive, and the vertical test wipers 339 are operated one step opposite the first level of bank contacts. At armature 327, vertical magnet 305 grounds the common interrupter conductor'336 in order to energize stepping relay 354. Stepping relay 354 at armature 374 opens the circuit to the vertical magnet 305, whereupon the vertical magnet deenergizes and opens the circuit of the stepping relay. This interaction between the vertical magnet and stepping relay continues until the vertical test wiper 339 encounters a ground potential on one of the vertical banks. In this case since the Wiper 339 encounters a ground potential on the first vertical bank contact, a circuit may be traced from the grounded armature 205 associated with the line relay 201, conductor 250, the multipled connections between the vertical banks of the A, B, and overflow vertical banks indicated by numeral 1 in the circle, vertical wiper 339, wiper 340 of the al.0tter, armature 371 and its rest-ing contact; through the lower winding of changeover relay 353, armature 368, and through the winding of stepping relay 354 to battery. Changeover relay 353 is'energized and the stepping is maintained energized over this circuit. The stepping relay maintains the circuit to the vertical magnet open and at armature 370 the changeover relay transfers the impulsing circuit from the vertical magnet to the rotary a a i ll 1' l m mu tact changeover relay 353 opens its original energizing circuit and the circuit of stepping relay 354 and at its working contact connects 5 ground to the upper winding of the switching relay 301 to prepare the switch through circuitfor the latter relay. At armature 372 changeover relay completes an obvious locking circuit for itself, and at armature 373 transfers the ground connection from the lower to the upper winding of differential relay 355 to restart the springs vibrating in the same manner as described for the vibrating springs in allotter DA. Stepping relay 354, upon deenergizing, at armature 374 completes a circuit for energizing the rotary magnet 306 as follows: from ground by way of armature 365, armature 374, armature 370 and its working contact, common conductor 338, armature 326, armature 315 and its resting contact, armature 309 and its resting contact, and through the winding of rotary magnet 306 to battery. By the operation of the rotary magnet 306 the wipers 344 to 349, inclusive, are rotated into engagement with the first set of bank contacts in the level indicated Mult. A2 and Mult. A1 which are multipled to corresponding bank contacts similarly indicated in Fig. 2. At armature 326, rotary magnet 306 grounds conductor 336 to cause the energization of stepping relay 354 and the latter relay at armature 374 interrupts the circuit extending to the rotary magnet 306. Further rotation of these Wipers now depend upon whether the test wipers 345 or 348 encounter a calling negative battery potential or not. In case neither test wipers encounter anegative battery potential, the rotary magnet 306 and stepping relay 354 cause the wipers to be rotated into engagement with successive bank contacts in this level until one of the test wipers encounters the test contact marked by the calling line. In this case, test wiper 345 completes a circuit for the switching relay 301 as follows: from ground by way of the working contact of armature 371 and said armature, wiper 340, upper winding of three-pole test relay 301, test wiper 345 and engaged test contact, conductor 256, Fig. 2, armature 207, and through the winding of cut-off relay 202 to battery. Cut-01f relay 202 energizes in series with switching relay 301 and at armatures 206 and 209 opens the circuit of the line relay 201 which deenergizes and at armature 208 prepares a locking circuit for itself as well as preparing a guarding circuit extending to the connector banks. Line relay 201 upon deenergizing, removes ground from the start conductor 299 at armature 205 with the result that the start relay 351 in the allottcr D0 will deenergize in case no other call is being made at this time. Switching relay 301, upon energizing, at armatures 308 connects the test wiper 345 to release-trunk conductor which is grounded at llllll llllll [Hill llllfllll] relay 202 in energized position; at armature 309 and its resting contact opens the circuit to the rotary magnet and at its working contact closes the kick-off circuit extending from grounded armature 365 by way of armatures 374, 370, 326, 315, 309, 325, and 369 to the motor magnet 361 of the allotter to cause the allotter D0 to open the circuit of the switching relay 352 and cause the advance of the allotter D0 to pre-select another idle overflow finder in the same manner as described for the allotter DA. At armature 311, switching relay 301 opens a pointin the release circuit of release magnet 300 and at armatures 307 and 312 connects the upper set of talking wipers to the talking conductors 393 and 395. Although the upper winding of switching relay 301 is momentarily short circuited, the lower winding is suflicient to hold the switchin relay in energized position after it has once en operated.

Referring now to Fig. 4 and at a time when the start relay 303 of finder OF at armature 327 grounded the start conductor 416, a circuit may now be traced for energizing a start relay in a secondary finder as follows: from grounded start conductor 416,- resistance 417, conductor 464, to the secondary finder in which the banks of the overflow finder appear as first choice or in case this finder should be busy the circuit would extend by way of an armature spring similar to the armature springs 450 and to the startout conductor in this finder similar to the start-out conductor 492 which extends to the next secondary finder. Assuming that the first finder SF is not busy, then the circuit extends by way of conductor 464, normally closed springs controlled by armature 450, and through the winding of start relay 433 to battery. Start relay 433 is energized over the above-traced circuit, and at armature 452 opens a point in the circuit of the release magnet 446 at its working contact, and at its working contact closes a circuit to the vertical magnet 437 and at armature 455 grounds the release trunk conductor 466 and also completes the circuit to the lower polarizing win dings of the three-pole switching relays 430 and 431. The circuit for energizing the ver tical magnet 437 may be traced as follows: from ground by way of armature 443 and its resting contact, test jack springs 419, armature 439 and its resting contact, armature 452 and its working contact, through the normally closed springs controlled by armature 456, armature 460 and its resting contact, and through the winding of vertical magnet 437 to battery. By the operation of the vertical magnet 437, the wipers 420 to 425, inclusive, and the vertical test wiper 426 are raised opposite the first level of bank contacts. Olfnormal springs 447 prepare a point in the circuit to the release magnet 446 and offnormal springs 454 prepares a circuit for maintaining the transfer relay 432 energized through its upper winding. At armature 45S, vertical magnet 437 com letes a circuit for energizing the stepping re ay 434 and the latter relay at armature 456 opens the circuit extending to the vertical magnet, whereupon the vertical magnet deenergizes and in turn opens the circuit of stepping relay 434. Further operation of the finder is now dependent upon whether the vertical test wiper 426 is in engagement with a grounded bank contact or not. In case wiper 426 is not in engagement with a grounded vertical bank contact, the stepping relay 434 deenergizes and again closes the circuit of the vertical magnet, whereupon the wipers are advanced another step. As soon as wiper 426 encounters ground potential, a circuit may be traced for the changeover relay 435 and for maintaining the stepping relay 434 energized as follows: from grounded start conductor 416, vertical bank contact 418 and test wiper 426, armature 463 and its resting contact, through the upper winding of changeover relay 435 and through the winding of stepping relay 434 to battery. The stepping relay 434 is maintained energized over this circuit to prevent the wipers from taking an additional vertical step. Changeover relay 435 at armature 461 completes a locking circuit for itself from ground at armature 443; at armature 462 prepares a testing circuit for three-pole switching relay 431 at armature 463 prepares a testing circuit for the three-pole switching relay 430 at its working contact, and at its resting contact opens the circuit of the changeover and stepping relays 435 and'434. At armature 460 changeover relay 435 transfers the impulsing circuit from the vertical magnet 437 to the rotary magnet 436. \Vhen stepping relay 434 deenergizes responsive to the operation of the changeover relay, the stepping relay at armature 456 again completes the impulsing circuit, this time to the rotary magnet 436. The

rotary magnet 436, upon energizing, rotates the wipers 420 to 425 into engagement with the first set of bank contacts in the level to which the wipers have been operated. At armature 457, rotary magnet 436 energizes the stepping relay 434 to again open the impulsing circuit at armature 456. Further rotation of the wipers now depends upon whether either the test wiper 421 or 424 are in engagement with a test contact having a call-- ing potential or negative battery potential thereon. In case neither of the contacts upon which the test wipers are now resting have negative battery potential thereon, the rotary magnet 436 will deenergize and open the circuit of stepping relay 434, whereupon the stepping relay 434 deenergizes and at armature 456 again completes the circuit for the rotary magnet to again rotate the Wipers. This interaction between the rotary magnet 436 and stepping relay 434 continues until either of the test wipers encounter a calling potential. In this case since a calling potential was supplied to test contact 414 by way of conductor 394, armature 321, and through the winding of cut-ofi' relay 304 to negative battery, then when wiper 424 reaches this contact, or contact 414, switching relay 430 will be energized from battery through the cutoil' relay 304, test wiper 424, upper winding of test relay 430, and armature 463 to ground. The direction of current through the upper winding of the three-pole switching relay is in the proper direction to assist that through its lower winding and accordingly the switching relay 430 energizes very quickly and at armature 439 opens the impulsing circuit to the rotary magnet 436. At armature 439 and its working contact, a circuit may be traced for energizing the transfer relay 432 as follows: from ground by way of armature 443 and its resting contact, test jack contact 419, armature 439 and its working contact and through the upper winding of transfer relay 432 to battery. At armature 440, switching relay 430 connects the grounded release-trunk conductor 466 to wiper 424 by way of the normally closed springs controlled by armature 444. At armatures 438 and 441 relay 430 connects the wipers 423 and 425 to conductors 465 and 467 extending to the line relay of the selector SO. Line relay 473 of the selector S0 is energized either over the subscribers calling loop or over the loop circuit in the overflow finder including the resistance R and said relay in turn causes the energization of release relay 474 which operates and connects ground to release-trunk conductor 466 at armature 479 before the slowacting start relay 433 has had time to deenergize. Transfer relay 432, upon energizing, over the above-traced circuit, at armature. 450 transfers the start-in conductor 464 to the start-out conductor 492; at the normally closed springs controlled by armature 450 opens the circuit of the start relay 433, whereupon such relay deenergizes; at armature 451 closes one. point in the busy-chain circuit 468 for the busy-chain relay 471; and at armatures 450 and 448 complete a locking circuit for maintaining the transfer relay energized by way of its lower winding as long as ground is maintained on either the start-in conductor 464 or the start-out conductor 492. At armature 452, relay 433, upon deenergizing, opens a point in the impulsing circuit at its working contact, and at its resting contact closes a point in the circuit to the release magnet 466; at armature 453 closes a circuit for maintaining the transfer relay energized over its upper winding; and at armature 455 removes one of the ground potentials from releasetrunk conductor 466.

Referring now to the overflow finder 0B in Fig. 3 and at a time when the switching relay 430 energized in series with the cutoff relay 304 in response to the test wlper 424 encountering the calling battery potential placed on test contact 414 through the winding of the cut-off relay; the cut-off relay 304, upon energizing over the previously-traced circuit, at armature 329 connects the releasetrunk conductor 394 to test wiper 345. Ground can now be traced extending back from the release-trunk conductor 466 of Fig. 4 for holding the switching relays in the secondary finder SF energized and extending by way of test wiper 424 and test contact 414 to release-trunk conductor 394 for maintaining the switching relay 301 in the overflow finder energized and extending by way of test'wiper 345 to the cut-off relay 202 for maintaining the ,cut-ofl relay energized and a the subscribers line busy. At armature 331,

cut-ofl' relay 304 opens the grounded start conductor 416 to prevent another secondary finder from starting in response to the operation of the transfer relay 432; At armature 330, cut-off relay-304 opens the locking circuit of the start relay 303, whereupon the latter relay deenergizes. At armature 321 and its working contact, relay 303 opens the circuit of the cut-off relay 304, whereupon the latter relay releases, and at armature 321 and its resting contacts disconnects the grounded spring 322 from the lower winding of the switching relays 301 and 302, only after the resting contact of armature 321 has engaged said armature so that the ground on the release-trunk conductor 394 now maintains the switching relay energized and the calling line busy. At armature 324 relay 303 opens another point in its locking circuit, whereupon the start relay 303 can only now be energized by way of the allotter DO. At armature 325 and its resting contact, relay 303 grounds the combined guard and kick-off conductor 335 in order to maintain the finder OF unselectable by the allotter DO and at armature 327 and its working contact disconnects the ground from armature-331 and at its resting contact prepares a circuit for the release 'magnet 300. At armature 328, relay 303 removes the bridge including the resistance R from across the talking conductors 393 and 395, because, at this time, the calling subscribers loop is bridged across the conductors 393 and 395 and this bridged loop is not needed to maintain the line relay of the selector SO energized. When both the overflow finder OF and the secondary finder SF have switched through in the manner just described, the calling subscriber may complete the connection to the called subscriber in the well-known manner.

Aft-er conversation and responsive to the replacement of the receiver by the subscriber S, ground is removed from the release trunk conductor 466 in the well-known manner, with the result that the switching relay 430 in the secondary finder SF, the switching relay 301 in the overflow finder OF, and the cut-off relay 202 in the subscribers line circuit are deenergized. Responsive to the deenergization of the switching relay 301 in the overflow finder OF, a circuit may now be traced for the release magnet 300 as follows: from ground by way of armature 327 and its resting contact, armature 316, test jack springs 319, armature 311, and through the off-normal springs 318, and through the winding of release magnet 300 to battery. By the operation of the release magnet 300, the shaft and wipers of the overflow finder are restored to their normal positions. When the shaft reaches its normal position, the

normal springs 332, 320, and 318 are operated to the positions shown in the drawings, the off-normal springs 332 to maintain one of the circuits to the busy-common relay 350; the off-normal springs 320 to remove the guarding potential from the combined guard and kick-01f conductor 335; and the offnormal springs 318 to open the circuit of the release magnet 300. The overflow finder OF is now returned to its normal position and may be used in other calls.

Responsive to the deenergization of the switching relay 430 in the secondary finder SF, a circuit may be traced for the release magnet 446 as follows: from ground by way of armature 443 and its resting contact, test jack springs 419, armature 439 and its resting contact, armature 452 and its resting contact, off-normal springs 447, and through the winding of release magnet 446 to battery. By the operation of the release magnet 446 the shaft and wipers of the finder SF are returned to their normal positions at which time the off-normalsprings 447 opensthe circuit of the release magnet 446 and the oil'- normal springs 454 open the circuit extending through the upper winding of the transfer relay 432. The transfer relay 432, however, is only deenergized at this time in case there is no ground potential on the start-in conductor 464 or start-out conductor 492. In case there is ground on either one of these conductors the transfer relay 432 is maintained over its lower winding in order to prevent the finder SF from stealing a call away from the succeeding finders. When ground is removed from the start-in conductor 464 or start-out conductor 492, the transfer relay 432 is deenergized and the secondary finder is now returned to its normal position and may be used for other calls. The busy-chain relay 471 is provided for the purpose of removing the holding battery from the lower windings of transfer relays 432 so that all of the transfer relays in the secondary finders which are in normal position may .be deenergized to provide a secondary finder for an incoming call.

It will also be noted that both the overflow finder OF and the secondary finder SF are provided with test jack springs 319 and 419 to enable the attendant to determine which set of wipers are in use in a connection. It will also be noted that the allotter D0 is provided with a test jack spring 381 for routine testing the overflow finders, and since this operation is practically the same as that previously described for the allotter DA and finder FA, it is believed that no detailed description of the function performed thereby need be described.

Having described the invention what is considered to .be new and is desired to have protected by Letters Patent, will be set forth in the following claims.

What is claimed is:

1. In a telephone system, a plurality of groups of lines, primary and overflow finders for each group, a single set of bank contacts comprising a test and line terminals terminating a plurality of overflow finders in different line groups, other similar sets of bank contacts'terminating other multipled overflow finders, secondary finders having access to said set and other similar sets of bank contacts, a start relay in an overflow finder energized responsive to a call for initiating the operation of such overflow finder in case all the primary finders in the group of the calling line are busy, means controlled by said relay for applying a calling potential to the terminating test terminal of such overflow finder, means also responsive to the energization of said relay. for initiating the operation of an idle secondary finder, and means for simultaneously operating said overflow and secondary finders in search of the calling line and said applied calling potential, respectively.

2. In a. trunking system, a plurality of lines divided into groups and each group divided into two sub-groups, two groups of primary finders associated with each line group and having access to the lines therein, each group of primary finders being first choice to the lines of one sub-group in the associated line group, overflow finders associated with each line group and having access to the lines therein, said overflow finders being third choice to the lines of a group, multiple connections connecting corresponding overflow finders in different line groups, secondary finders having access to said overflow finders by way of said multiple connections, and a numerical switch associated with each primary and secondary finder for extending connections.

3. In a trunking system, a plurality of subscribers line groups, primary finders associated with each subscribers line group and having access thereto, numerical switches, a trunk line leading from each primary finder to a numerical switch. overflow finders associated with each subscribers line group and having access thereto, multiple connections connecting corresponding overflow finders in different subscribers line groups, secondary finders having access to said overflow finders by way of said multiple connections, and other trunk lines leading from said secondary finders to numerical switches.

4. In a telephone system, a plurality of line groups, primary finders for each group of lines and having access thereto, secondary finders, sets of bank contacts terminating in the banks of the secondary finders, multiple .connections, a single one of said sets comprising only a test contact and line contacts and terminating a plurality of said corresponding primary finders in different line groups by way of said multiple connections, and means responsive to a call by a line in one of said groups for operating an idle primary finder of that group to find the calling line and for operating an idle secondary finder to find the primary finder in use by way of its set of bank contacts and multiple connection.

5. In a telephone wherein a grou of subscribers lines are normally served y a first group of finders as first choice, by a second group of finders as second choice, and by a group of overflow finders as third choice, secondary finders having access to only said overflow finders, and means responsive to a call by a calling line for starting one of said overflow finders to hunt for the calling line in case the first and second group finders are all busy and for starting an idle one of said secondary finders having the least movement to find the overflow finder in use.

6. In a telephone system wherein a plurality of roups of subscribers lines are each served y a first group of finders as first choice, by a second group of finders as second choice, and by a group of overflow finders as third choice, secondary finders, a plurality of trunk lines, each of said trunk lines terminating in said secondary finders and in a plurality of said overflow finders in different line groups, each secondary finder having access to said trunk lines in a different order, and means responsive to a call in one of said line groups for starting an idle overflow finder to hunt for the calling line in case the first and second groups of finders of that group are busy and for starting an idle secondary finder having the least movement in accordance with said order to hunt for the overflow finder in use.

7. In a telephone system, a plurality of secondary finders, a plurality of sub-groups of overflow finders terminating in said secondary finders, a chain circuit sequentially including all said secondary finders, a start circuit common to each sub-group of overflow finders for starting said secondary finders, each start circuit including a resistance and connected to said chain circuit at predetermined oints, and means in each overflow finder or completing the start circuit to a particular secondary finder dependent upon the point at which said start circuit is connected to said chain circuit.-

8. In a telephone system, a group of subscribers lines, a group of finders having access tosaid lines, a combined guard and kickoff conductor associated with each finder, an allotter having access to said finders by way of said conductors, busy ones of said finders characterized by a ground potential applied to their associated guard and kickofi conductors, means including a motor magnet in said allotter for preselecting a finder dependent upon the absence of ground potential on its associated conductor, means responsive to the initiation of a call on one of said lines for operating the preselected finder to find the calling line, means responsive to the finder finding the calling line for causing said finder to switch through and extend the connection from the calling line, means responsive to the switch-through operation of the finder for operating said motor magnet over the associated guard and kick-oif conductor, and means in said allotter controlled by the operation of said magnet for causing said allotter to preselect another idle finder.

9. In a telephone system, a group of subscribers lines, a group of finders having access to said lines, a combined guard and kickoff conductor associated with each finder, an allotter having access to said finders by way of saidconductors, busy ones of said finders characterized by a ground potential applied to their associated guard and kick-ofi' conductors, means including a motor magnet in said allotter for preselecting a finder depend ent upon the absence of ground potential on its associated conductor, an impulsing circuit for said finders controlled by said allotter, means in said allotter responsive to the initiation of a call on one of said lines for operating the preselected finder over said impulsing circuit to find the calling line, means responsive to the finder finding the calling line for causing said finder to switch through and extend the connection from the calling line, means responsive to the switchthrough operation of the finder for operating said motor magnet over a circuit including said impulsing circuit and the associated guard and kick-oil conductor in series, and means in said allotter responsive thereto for causing said allotter to preselect another idle finder.

10. In a telephone system, a group of subscribers lines, a first group of primary finders, a second group of primary finders, and a group of overflow finders having access to said lines, an allotter for each group of finders, a start circuit common to said group of lines and extending vto the allotter associated with the first group of finders, means for making said first oup of finders busy and for transferring sai start circuit to the allotter associated with the second group offinders, an overflow transfer relay, means for making said second group of finders busy and for operating said relay in case the finders in the first group are still means responsive to said finder finding the\ calling line for causing said allotter to preselect another finder, a test jack having springs associated with said allotter, and means responsive to, short circuiting the springs of said test jack for grounding said start conductor to cause the finders of said group to be successively selected, operated, and released to simulate calls.

'12. In a telephone system, a first and a second group of subscribers lines, a first and a second group of finders having access to said lines, an allotter common to said first group of finders and an allotter common to said second group of finders for preselecting successive ones of said finder for use in their respective groups, a start conductor common to eachgroup of lines and extending to its associated allotter, means responsive to a call on one of said lines in the first group for grounding the first start conductor, means responsive thereto for operating the preselected finder of the first group to find the calling line, means responsive to the finder finding the calling line for causing the first allotter to preselect another finder in the group, a test jack having springs associated with the first allotter, means responsive to short circuiting the springs of said test jack for grounding said first start conductor to cause the finders in the first group to be successively selected, operated, and released to simulate calls, and means responsive to the operation of the springs of said test jack for making the finders in the first group artificially busy and for grounding the second start conductor to cause the finders in the second group to be successively selected by the secondallotter, and operated and released to simulate calls.

13. In a telephone system, a group of finders, anupper and a'lower set of wipers associated with each finder for completing connections, means for operating said finders, and for connecting either one of said sets of wipers to complete a connection, a test jack associated with each finder. and means common to all said finders for indicating the set of wipers in use in a connection responsive to the actuation of the test jack associated with the finder in use.

14. In a telephone system. a plurality of groups of lines, groups of primary finders having access thereto, a plurality of secondary finders. trunk lines, a test conductor of each trunk line terminating in a test contact in the banks of the secondary finders. a plurality of overflow finders: associated with each line group and having access to the lines therein. each of said trunk lines multipled to an overflow finder in each line group. a start relay in each overflow finder, means for making the primary finders in a group busy, means responsive to the initiation of a call by a calling line in one of said line groups when all the primary finders associated therewith are busy for initiating the operation of one of the overflow finders associated with said group and for energizing the start relay therein, means controlled by said relay for connecting a calling potential to the test contact of the trunk line multipled to said overflow finder and for initiating the operation of an idle one of said secondary finders, means for continuing the operation of the said overflow finder to find the calling line. and means for continuing the operation of said secondary finder to find said calling potential and to connect with said overflow finder in use over said trunk line.

15. In a telephone system, a plurality of groups of lines, groups of primary finders having access thereto, a plurality of secondary finders, trunk lines, a test conductor of each trunk line terminating in a test contact in the banks of the secondary finders, a plurality of overflow finders associated with each group and having access to the lines therein, each of said trunk lines multipled to an overflow finder in each line group, a start conductor in each trunk line, a start relay and a cutoff relay in each overflow finder, means for making the primary finders in a group busy, means responsive to the initiation of a call by a calling line in one of said groups when all the primary finders associated therewith are busy for initiating the operation of one of the overflow finders associated with said group and for energizing said start relay therein, means controlled by the energization of said relay for completing a locking circuit for itself, for continuing the operation of said overflow finder to find the calling line, for connecting a calling potential through the winding of said cut-ofl' relay to the test contact of the trunk line multipled to said overflow finder, and for grounding the start conductor of said trunk line to initiate the operation of an idle secondary finder, means for continuing the operation of said secondary finder to find said calling potential and connect with said overflow finder over said trunk line, means for energizing sald cut-off relay responsive to said connection, and means ing and the other being an operating winding, said windings being connected to opposite poles of battery, a pair of line conductors extending through normally closed contacts on said cut-ofl relay and terminating in said windings, said line relay inoperative responsive to one or. both line conductors being grounded but operative responsive to the connection of one line conductor to the other when the subscriber initiates a call, and means responsive to the operation of said line relay for preparing a circuit for said cut-ofl relay.

17. In a telephone subscribers line circuit, a line relay, two windings on said relay, one being a polarizing winding and the other being an operating winding, said windings being connected to opposite poles of battery a pair of line conductors terminating in sald windings, said line relay inoperative responsive to one or both of said conductors being grounded, and means responsive to the subscriber initiating a call for connecting one conductor with the other conductor to opcrate said relay.

18. In a telephone system, a plurality of groups of lines, a group of primary and overflow finders for each line group and having access thereto, a group of secondary finders, each secondary finder having access to all said overflow finders in all said groups, means responsive to a call by a line in one of said groups for operating an idle overflow finder of that group to search for the calling line in case all the primary finders of that group are busy, and means for operating any idle one of said secondary finders to find the overflow finder searching for the calling line.

19. In a telephone system, a group of lines, primary and overflow, finders having access to said lines, secondary finders having access to said overflow finders, means responsive to a call by one of said lines for selecting an idle one of said overflow finders in case all said primary finders are busy, means responsive to said selection for initiating the operation of an idle secondary finder, and means for operating said secondary finder first in a primary movement and then in a secondary movement in search of said overflow finder.

20. In a telephone system, a plurality of groups of lines, primary and overflow finders for each group, secondary finders having access to said overflow finders, means in an overflow finder operated responsive to a call in case all the primary finders in the group of the calling line are busy for initiating the operation of an idle secondary finder, and means for operating said secondary finder to find the overflow finder in use.

21. In a telephone system, a group of lines, primary and overflow finders for said group, secondary finders having access to said overflow finders, means responsive to a call by a calling line for selecting an idle one of said overflow switches in case all the primary finders are busy, means in said selected overflow finder operated responsive to said selection for initiating the operation of an idle secondary finder, and means for operating said secondary finder to find said overflow der.

22. In a telephone system, a group of lines, primary and overflow finders for said group, secondary finders having access to said overflow finders, means responsive to a call by a calling line for selecting an idle one of said overflow switches in case all the primary finders are busy, means in said selected overflow finder operated responsive to said selection for initiating the operation of an idle secondary finder, and means for simultaneously operating said overflow and secondary finders in search of said calling line and said overflow finder, respectively.

23. In a telephone system wherein a plurality of groups of subscribers lines are each served by a separate group of overflow finders, secondary finders, a plurality of trunk lines, and each of said trunk lines terminating in a secondary finder and in a plurality of said overflow finders in different line groups;

24. In a telephone-system, aplurality of finders, a chain circuit sequentially including all said finders, start circuits for starting said finders, each start circuit including a resistance and connected to said chain circuit at predetermined points, and means for completing the start circuit to a particular finder dependent upon the point at which said start circuit is connected to said chain circuit.

25. In a telephone system, a group of subscribers lines, a group of finders having access to said lines, a start conductor common to said group of lines, means responsive to a call on one of said lines for grounding said start conductor, means responsive thereto for operating a finder in said group to find the calling line, a test jack having springs common to said finders, and means responsive to short circuitlng the springs of said test jack for ounding said start conductor to cause the ders of said group to be successively operated and released to simulate calls.

26. In a telephone system, a group of lines, a group of primary finders having access to said lines, a plurality of secondary finders, test conductors extending from said primary finders and terminating in the banks of said In witness whereof, I hereunto subscribe my name this 6th day of January. A. D. 1931.

NORMAN H. SAUNDERS.

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