US2371989A - Telephone system - Google Patents

Description

Mar 1945- M. E. GRlFFlNS ETAL TELEPHONE SYSTEM Filed Jan. 1, 1943 EOSQEPME hnn INVENTORS MORRIS E. GRIFFINS mm: MOLNAR 2% ma 2w pmmp 0mm mohamahwa hmmh 8N xmun 5E.

ATTORNEY A Patented Mar. 20, 1945 UNITED STATES PATENT OFFICE TELEPHONE SYSTEM Y Morris E. Griflins, Riverside, and Imre 'Molnar.

Chicago, Ill., assignors to Automatic Electric Laboratories, Inc., a corporation of Delaware Application January 1, 1943, Serial No. 470,952 17 Claims. (Cl. 179 -1752) usual to provide in the exchange a centralized test desk and automatic switching apparatus by means of which it is possible to extend a test circuit from the test desk directly to the line conductorsof any desired one of the subscribers lines. Facilities of this character ordinarily include some arrangement for clearing a subscribers line of attachments, i. e., for disconnecting from the line under test that part of the exchange equipment which is normally connected to the line conductors of such line and which,'if permitted to remain connected thereto, would. adversely effect the test. v

While the arrangements which heretofore have been provided for clearing a subscriber's line of attachments are quite satisfactory under most conditions encountered in practice, they usually are totally ineffective in the presence of certain abnormal conditions. If, for example, a connection is extended from the test desk to a subscriber's line at a time when a permanent conclition exists upon that line due to its conductors.

accidentally having become bridged and/or grounded, the conventional arrangementswill not disconnect the exchangeequip-ment attached to the line conductors, and accordingly it is not possible to perform a satisfactory test upon the line same arrangement is effective to clear a permanent line ofattachments whether; or notthat line is arranged to lock itself out in the eventof a permanent. I

1 According to another feature of the invention, a relay, which is connected to, the subscribers line and energized thereover due to a permanent condition of the character described, is caused to restore as a result of the differential action produced in its windings by means of a booster battery potential applied to thesubscribers line over the testconnection extended thereto.

Further objects and features of theinvention will be apparent from the following description,

reference being made to the accompanying drawing which discloses the circuits of an automatic telephone system embodying the invention.

Referring more in detail to the drawing, the telephone system shown therein includes a pluralityof subscribers substations, two of which are indicated at Hill and 300, and subscribercontrclled automaticv switching equipment for setting up connections to wanted substations suchas I99 and 3993. Thisswitching equipment includes links such as I41! and 340, each of which comprises afinder switch having access to calling lines and a selector switch having access. to called lines over atrain of one or more subse- 'quent switches, depending upon the number of subscribers in the system. For purposes of making routine tests upon the subscribers lines, a test desk Zlljll, is provided, which has access to said lines over operator-controlled automatic switchover the connection extended thereto from the test desk.

It is the general object of the present inven tion, therefore, to provide an improved arrangement for clearing a subscribers line of attachments, not only. under normal conditions; but under the abnormal conditions noted.

Inasmuch as the accidental bridging and/ or grounding of a subscribers line simulates a. calling condition, it usually resultsin the partial extension of a connection from the line over switching equipment which is common to a group of subscribers lines; it is another object ofthe inven: tion to provide an improved arrangement forbreaking down a connection-thus extended.

ing equipment including a test distributor 239 and a test connector such as 280. The bank of the test connector is connected in multiple to the banks of the standard, subscriber-controlled connectors by means of which calls are the variouslines. I

It will be'observed that the showing of test desk, the test distributor, the test connector and the finder-selector links is largely schematic, only such details having been included as are necesextended to .sary for the complete understanding of the present invention. Reference may be had to United States Patent No. 2,214,908, issued on September 17, 1940, to C. E. Lomax et al., for additional details of one suitable form of finder-selector link.

As is well known, provision is sometimes made for locking out a subscriber's line on which a permanent. condition exists; it is a further object of the invention to provide an arrangement for clearing a permanent line of attachments after such line has become locked out.

According to one feature of the invention, the

Likewise, reference may be had to United States Patent No. 1,691,269, issued on November 13, 1928, to, T. F. Crocker. for additional details of one suitable form of test distributor and test connector.

The general procedure involved in making tests upon various subscribers lines is fully set forth tests as he desires upon the line I 9| in the last-mentioned patent. This procedure will be outlined briefly, it being assumed for this purpose that the test operator wishes to test the line If leading to substation I99. To do this, he first closes contacts 22I, 222 and 223 (which may be accomplished by inserting a plug in a jack, by operating a manual switch key, or by any like measure) thereby to seize the test distributor 2119, he operates the test distributor to seize a test connector such as 280, and then operates the test connector to move its wipers 29!, 292 and 293 into engagement with bank contacts 294, 295 and 296, respectively, of the line IUI.

As explained in detail in the Crocker patent,

relay 2-50 in the test distributor is operated dur ing the final setting of the test connector wipers upon the line to be tested, and it releases upon completion of that setting operation. Accordingly, while operated, relay 250 maintains the slow-to-release relay 260 operated over contact 252, thereby to hold the test circuit open at contacts 29I and 292 during the setting of the test connector wipers. When relay 250 restores at the end of the setting operation, it closes contact 25I and, at contact 252, opens the circuit for relay 259. Because of its sl-ow-to-release characteristic, relay 269 remains operated for a brief interval after its circuit is opened, and then restores; during this interval, in order to determine whether the line IBI is busy or idle, the test relay 249 is connected to contact 296 in the bank of the test connector, over the following circuit; earth, battery, winding of relay 240, contacts 25I and 263, wiper 213 of the test distributor, and wiper 293 of the test connector. It is self-evident that relay 240 will operate over the above circuit only if contact 295 is at earth po tential.

Assuming that the subscribers line Ifll is idle, contact 295 normally will not be at earth potential, and hence relay 249 will not operate. Relay 289, upon restoring, opens the above-described circuit for the test relay 240 at contact 263, and at the same time completes the following circuit over contact 264: earth,,contacts 24I and 264, wiper 213 of the test distributor, wiper 293 of the test connector, contact 296, conductor I I9, middle winding of two-step relay I29, battery and earth. Responsive to its energization over this circuit, relay I28 operates all of its contacts; at contacts I2I and I22 it disconnects itself from the conductors H5 and III; of the line MI in order to.

clear the line of attachments. The opening of contact I24 insures that no finder switch will be set in motion with line I9 I At contacts 26! and 262 the test circuit 2"! is switched through so that conductors 2I I and H2 are in direct connection with conductors H5 and H6, respectively. Accordingly, by means of appropriate testing equipment which may be connected to the conductors 2H and 2I2 at the test desk, the test operator now is able to make such Suitable test desk equipment is shown in the Crocker patent.

Assuming now that the subscriber's line I!" is not idle at the time the test operator extends the connection to it over his test'switch trains but instead is engaged in a. call, contact 295 in the bank of the test connector will be at earth potential as is well known. The operations in this case will be the same as those previously'described up to the point where relay 2'50 restores. When this occurs, test relay 249 will operate due 23!]. Next, by means of a dial at the test desk to the presence of earth potential on bank contact 295, and will prepare an alternate circuit for itself by closing contact 242. Accordingly,

upon the release of relay 290 a moment later,

relay 240 will remain operated due to its energization over the following circuit: earth, battery, winding of relay 249, contacts 242 and 264, wiper 213 of the test distributor, wiper 293 of the test connector, and earth on the bank contact 299.

Theoperation of relay 240 brings in a signal at the test desk to notify the operator that the line with which connection has been made tests busy. He will then associate his telephone set with the conductors 2H and 2I2, and, by listen- I ing for speech, verify the fact that the line is in use.

Finding a call to be in progress, he may for the moment abandon his attempt to test the line and release the connection which he has established thereto, or, alternatively, he may wait for the line to become idle. It will be assumed that he elects to follow the latter course.

When the apparatus involved in the intersubscriber connection is released upon termination of the call, it removes earth from contact 296 in the bank of the test connector. There- 'upon, relay 249 will restore, and at contact 2:

will complete the following circuit for operating the two-step relay I20: earth, contacts 2M and 294, wiper 213 of the test distributor, wiper 293 of the test connector, bank contact 298, conductor H9, middle winding of relay I23, battery and earth. As previously explained, relay I20 operates all of its contacts when it is energized over this circuit. Accordingly, it disconnects itself from the line II at contacts I2I and I22 and opens contact I24 to insure that no finder switch will be started searching for the line WI. The disconnection 'of relay I20 from the line conductors clears the line of attachments, and therefore the test operator may now proceed with his test over the conductors 2H and H2, as in the case already described.

The procedure involved in making a test upon the subscribers line MI is substantially the same as that for testing the line IIH. Obviously, in this case the test connector will be operated to set its wipers 29!, 292 and 293 upon bank, contacts 291, 298 and 299, respectively. If the line 39I is busy, bank contact 299 will be at earth potential, and test relay 240 will be operated upon the restoration of relay 259, as should be clear from the previous description; if, on the other hand, the line is idle, there normally will be no earth potential upon contact 299 and relay 249 will not be operated.

Assuming first that line 3DI is idle, the followingcircuit will be established upon the release of relay 263 in the test distributor: earth, contacts 2M and 264, wiper 213 of the test distributor, wiper 293 of the test connector, bank contact 299, conductor 3I9, contact 32I, winding of relay 325, battery and earth. Relay 325 operates responsive-to energization over this circuit, and at contacts 324 and 326 disconnects relay 320 from conductors 3I5 and 3I6 thereby to clear the line 30I 'of attachments. Relay 325 also closes contact 306, causing relay 395 to operate, but the latter relay performs no useful function at this time. The closing of contacts 26I and 262 in the test distributor completes a direct connection from conductors 2H and 2I2 of the test circuit to conductors 3| 5 and 3H5, respectively. of line 39I, so that the test operator may proceed with his test in the usual way. Had the line 3DI been busy instead of idle, test relay 240 in the onbank contact 299 until the line became: idle,"

asexplained in connection with the test made upon line I I; responsive to theremoval of earth from contact 299 when line 30I became idle, testrelay 240 would restore, and, by closing contact 24I would operate relay 325 over the circuit set forth above. This places the line in. proper-condition for testing by disconnecting relay 3.20 from it.

After the operator has extendeda connection over the test switch train to a subscriber's line in the waydescribed and has received anindication that the line testsbusy, it sometimes happens that, by means of his listening test, he .determines that no conversation is in progress; Under such circumstances he will, of course, wish to proceed with the usual tests upon the line. Ordinarily, however certain attachments are bridged across the subscriber's line in the exchange; in the past the operator has been unable to remove such attachments from the line,

and hence he frequently has been compelled to abandon his attempt to test the line over the connection extended thereto from the test desk, and has had, instead, to resort to the inconvenient practice of testing the line directly atthe main distributing frame, where the attachments can beremoved by opening the H3, H4 or 3I8, 3I4).

The reasons for this difficulty will be made clearer by an explanation of what takes place jumpers (such as when a permanent exists on a subscribers line.

As is well known, a permanent may result fromthe line conductors being accidentally bridged as shown at X, from one of the conductors being accidentally grounded as shown at Y, or from a combination of these twolcauses. In all such cases, the same result is produced. It will be assumed, therefore, in order to illustrate the problem, that the conductors III and N2 of line IOI have become bridged as shown at'X. This bridge simulates a calling condition by completing the following circuit: earth, lower winding of the two-step relay I20, contact I22, conductor I I6, jumper II 4 at themain distributing frame,

I20, .battery and earth. Responsive to energize-r tion over this circuit-,JreIay I20 now takes its 1 second -step,thereby operating the remainder of its'contacts; at contact; I 24' it opens the start circuit extending to the distributor over conductor'I31, while at contacts I2I and I22 it disconnects itself from conductors. III and 112 of thesubscribers line. v

Returning to the operation of switching'relay 160 in the finder, it will be seen that this, at

contacts IBI and I62, extends the line loop to the line relay I110 of theselector switch. Thereupon relay I10 operates over the'following circuit: earth, lower winding of relay I10, contact I32, finder switch wiper I35, bank contact I 32, conductor IIB, jumper II4, conductor II-2,- the bridge X, conductor I I I, jumper II3, conductor 1 I I5, bank contact I3I, finder switch wiper I34, contact IBI, upper winding of relay I10, battery and earth. Relay llfl closes contact "I thereby operatingthe slow release relay I80, and the. latter in turn closes contact I81. It should. be mentioned that certain known arrangements, for example the one shown-in the l conductor II2, the bridge X, conductor III, jumper H3 at the main distributing frame, conductor H5, contact I2I, upper winding of relay I20, middle winding of relay I20, battery and earth. Responsive to itsenergization over this circuit, relay I20 takes its first step, operating contacts I23 and I25, but no others. acterizes the subscribers line IIiI in the banks of finder switches having access to that line, by completing a circuit from earth via battery, the middle winding of relay I20, conductor I I9, and contact I23 to finder switch bank contacts such as I33. At the same time contact I25 completes an obvious circuit over conductor I31 for causing the distributor I to start a finder switch of one of the links searching for the characterized line.

Assuming that the distributor has connected with the finder switch of link I40 over a hunter switch I55, that finder switch will move its wipers I34, I35 and I33 until they engaged the bank Contact I23 char-' contacts I3I, I32 and I33, respectively, of the above-mentioned patent to Lomax et al., depart from the mode of operation just described to the, extent that the relay I10 is operated overa preenergizing circuit (not shown), before contacts IIiI and I62 are closed; when this practice is followed, however, the said pre-energizingcircuit is opened after the line IIII has been switched through to relay I10 by the closure of contacts NH and I62, so that relay I10 is maintained energized over the line loop, as described. In either event, the operation of relay I 'due to the closing of contact I1I occurs before earth is removed from conductor I'6.5,.so that, upon such'removal, relays I60 and I20 are maintained operated from earth at contact Isl. The holding circuit for relay I60 may be traced from earth; over contact I8I, contact I64, winding of relay I60, and'battery to earth. The holding circuit forthe relay I20 may be traced from earth over contact IBI, contact I63, finder switch wiper I36, bank contact I33, contact I23, conductor II9, middle winding of relay I20, and battery to earth.

It will be appreciated that the operations 'described above, which have taken place as a result of the conductors III and H2 becoming bridged at X, are exactly the same aswould have taken place if a bona fide call had been originated by 5 the subscriber removing the telephone receiver at substation I00 from its switchhook. They bring about the conditioning of the selector switch to receive the call-directing impulses which, in the case of a bona fide call, would now betransmitted from substation I00 by the subscribers operation of the dial. Quite obviously no such impulses will be transmitted in the case under consideration, and accordingly, unless some special steps are taken, the apparatus will .remain in .the

condition described so longas the bridge at X persists.

Let it now beassumed that this case is the" status of the equipment at the time the test operator extends'a connection to line l0I over the test distributor and test connector.

the final setting of the test connector wipers, the

usual test is made to determine whether line'i's busy or idle; this test results in the operation of test relay 240 over the following circuit: earth, battery, winding of relay'240, contacts'25I and 263,-'\viper 213 of the test distributor, wiper 233 Upon the release of relay 250 in'the test distributor after thereupon opens contact I8I.

earth. It will be seen that now relays I20, I60

and 240 all are maintained operated by the earth at contact I8I of the selector switch.

The operator of test relay 240 brings in the busy signal at the test deskas previously explained, whereupon, by associating his telephone set with the test circuit 2I0, the operator can determine that no conversation is in progress. Although the test circuit is in direct connection with conductors H5 and H6 of the subscribers line, the fact that relay I is also connected to conductors H5 and 'I I6 militates against the operator making a satisfactory test upon the line. It is this fact which has, in the past, made it necessary for permanent lines to be tested at the main distributing frame with the exchange equipment disconnected, rather than over the test switch train.

According to the present invention it is possible for the test operator to free the line IOI of attachments despite the existence of the permanent condition thereon, and to proceed with his test over the test switch train. To do this, he momentarily operates the manual switch key 2 I 5 at the test desk. This completes a circuit extending from earth, over resistance 2I8, switch contact 2I6, conductor 2| I, contact 221, contact 26I, test distributor wiper 2', test connector wiper 29I, bank contact 294, conductors H1 and I I5, finder switch bank contact I 3 I, finder switch wiper I34, contact IBI, upper winding of relay I10, and battery to earth; it also completes the following circuit: earth, booster battery, resistance 2I9, switch contact 2", conductor 2I2, contact 222, contact 262, wiper 212 of the test distributor, wiper 292 of the test connector, bank contact 295, conductors II 8 and H6, bank contact I32, finder switch wiper I35, contact I62, lower winding of relay I10, and earth. The first of these two circuits insures that current will continue to flow over the upper winding of relay I10 in the same direction that it did before switch key 2I5 was operated, while the latter circuit causes a reversal of the current flow through the lower winding of relay I10. Whereas the two windings of relay I10 previousl aided one another, the now are in opposition, resulting in a differential action which causes the relay to restore. In consequence thereof, contact I'II is opened, permitting relay I80 to restore, which The opening of contact I8I initiates the release of relays I60, I20 and 240.

Relay I60 restores first, thereby opening its contacts and also, in the well known way, initiating the release of the finder switch. Next, relays I 20 and 240 restore substantially simultaneously. Relay 240 upon restoring closes contact 24!, which completes a'previously traced path for reenergizing the middle winding of relay I20. Therefore, relay I20 immediately reoperate all of its contacts. It will be seen that the release conductors of the subscribers line.

of relay I60 has disconnected relay I10 from the conductors of the subscribers line, first by opening contacts I6I and I62 and then, shortly afterward, by the restoration of the finder switch Wipers I34, I35 and I36 to normal. In View of this fact, and the additional fact that relay I20 now has also been disconnected from the line conductors due to the opening of contacts I 2I and I22, the subscribers line is free of attachments in the exchange. Accordingly, the operator, having restored the key 2I5 to normal, may proceed with his test upon the line in the usual way by means of equipment at the test desk which he associates with the test circuit 2I0.

Turning now to an examination of what takes place when a permanent exists upon subscriber's line 30I which is provided with an arrangement for lockingv out that line, it will be assumed for illustrative purposes that the line has accidentally become grounded as shown at Y, This completes the following circuit: earth, at Y, conductor 3I I, jumper 3I3 at the main distributing frame, conductor 3I5, contact 324, upper winding of relay 320, battery and earth. Relay 320 operates responsive to its energization over this circuit, and

.at contact 329 connects earth to conductor 3I9 to characterize the line as busy in the banks of connector switches. At contact 322 it characterizes the subscribers line 30l in the banks of finder switches having access to that line, by completing a circuit from earth via battery, winding of relay 325, contacts 302 and 322 to finder switch bank contacts such as 333; at the same time, by closing contact 323, it completes a start circuit over contact 304 and conductor 331 to the distributor 350. Thereupon the distributor causes the finder switch of one of the links, say 340, to search for the characterized line.

When the finder switch wipers 334, 335 and 336 come into engagement with contacts 33 I, 332 and 334, respectively, their movement is halted in the known manneryand relay 360 is operated by earth connected for a brief interval to conductor 365. Relay 360 upon operating completes the following circuit for relay 325: earth on conductor 365, contacts 384 and 363, finder switch wiper 336, bank contact 333, contacts 322 and 302, winding of relay 325, battery and earth. Relay 325 operates, and at contact 321 closes an alternate circuit for its own winding so that it will remain operated independently of contacts 302 and 322, which are soon'to open. At contact 306 relay 325 completes an obvious circuit for relay 305, while at contacts 324 and 326 it disconnects relay 320 from the line Relay 320 releases, thereby interrupting the start circuit to the distributor by opening contact 323, It also interrupts the original operating circuit for relay 325 by opening contact 322, but this is without effect since, as already pointed out, relay 325 will remain energized over its own contact 321. Earth now is maintained on conductor 319 over contacts 32I and 321. Relay 305 operates due to the closing of contact 306. At contact303 it prepares an alternative circuit for its own winding, while at contact 308 it prepares a circuit to the permanent lock out alarm; its other contacts perform no useful function at this time.

Returning to the operation ofswitching relay 360 in the finder switch, it will be seen that this, at contacts 35I and 362 extends the line conductors to the line relay 310 of the selector switch. Thereupon, relay 310 operates (or, if it was preenergized as shown in the patent to Lomax et al., the preenergizing circuit now is interrupted, and

- 325 operated. The holding circuit for relay 366 extends from earth over contacts 1 8| and 364,

winding of relay 365 and battery to earth. The holding circuit for relay 32.5 extends from earth over contacts 38! and 353, finder switch wiper 336, bank contact 333, contact 321, winding of.

relay325, and battery to earth.

It will be recognized that the link 3411 hashee'n' conditioned to receive the call-directing impulses will operate the manual key 2|-5 momentarily in order "to clear the line of the attachment represented 'by relay 320 being connected to th line conductors over contacts 324 and 326. The operation-of the key completes a circuit extending from earth, over resistance 2 l3, contact 2 |6,.con-

which, in the case of a bona fide call, would now.

be transmitted from the substation300 by the subscribers operation of the dial. Since-no impulses are received within a certain time, relay 4.00 is operated in the wellknown way, which, by

opening contact 4M, causes relay 380 to release.

In consequence thereof, contact 38| is opened.

andicauses relays 360 and .325 to release.

Relay 3.63. upon restoring opens its contacts and initiates therelease of the link 346, whereby the finder switch wipers v334i, 33.5 and 336 are. restored to normal and the link 3 30 is made. free to handle calls over other lines. Relay 32.5 upon restoring reconnects relay 320 to. the line conductors by closing contacts 324 and 326; opens its own circuit atcontact .321; opens the circuit for relay 30.5 at

contact 366; and, at con-tactBfl'l, completes a.

circuit over contact .368. andconductor .3.09' to the permanent lockout alarm. Due to its slow-to-r'elease characteristic, relay .305 willnot at once restore; meanwhile relay 320.reoperates;o er the following path: battery, earth, upper winding ofrelay 32!], contact 324, conductor 3I5, jumper 3J3, conductor 3| l, and earth at Y. The operation of relay. 32o prevents relay 305 from restoring-by completing the following circuit: .earth,.conta.ct

323, contact 303, windingof relay 305, battery and earth. Contact 322 is closed but has. no .efiect since contact 302 is open, andit will be. seen that earth again is applied to conductor 319 oyer' contact 329. Line-3M now is locked out.

Let it lie/assumed. that the line. 30| is thus locked out at the time the test operator extends his connection thereto over the test switchtrain. After the final Setting of the test connector wipers upon bank contacts 291, 298 and 293, relay 250 releases and the usual test is. thereupon made to determine whether the line is lousyv or idle; this test results in the operation of test relay. 24!) over the following circuit: earth, battery, winding of relay 240, contacts 25| and 26.3, wiper2:1.3.of

thetest distributor, Wiper 293 of the test. con

nector, bank contact-299, conductor 3|.9, contact ductor 2', contact 22|, contact 23L wiper 2'|| of the 'test distributor, wiper 23| of thetest connector, bank contact 297, conductor 3|1, conductor '3:|fi,contact 32.4, upper winding of relay 1320, and battery to earth, it also completes the following -circuit: earth, booster battery, resistor 21-9, ciontact2| l, conductor 2| 2, contact .2 22, contact 2.62., wiper 212 of the test distributor, wiper 2920f the test connector, bank contact .298, conductor; Sit, contact 326, lower winding of relay 3.2.0, andearth The first .of these two circuits invsurenxthat currentwill continue to flow over the upperwinding of relay I10 inythe samedirection as it-did'beforc switch key 2|5-was'operated, while the latter circuit causes current to how through -.the1ower windingof relay 32cm sucha direction asto neutralize the effect of. the. upper winding, Accordingly, relay 320' will restore. .At contact 2 the-circuit for relay 240 is opened, and at 9t-. 323; the circuit for the slow relay its is opened. Relay 240 releases before relay .305, and

329 and earth. Test relay 24!] upon operatin closes-contact 242 so that, when relay 2,60releases a-moment later due to the opening ofcontact'252, relay 243 is maintained energized over the following circuit: earth, battery, windingof relay 240, contacts 242 and 264, wiper 213 of the test disitrihuton wiper 293 of the test connector, bank contact 239, conductor 3|3, contact 329 and earth. v

The operation of test relay 246 willbring irr-the busy signal at the test desk, as already noted, whereupon the operator, by connecting his telephone set to the test circuit 2| 0, willascertain that no conversation is in progress. Accordingly h-e 'tory to making a test 'jductor, and means controlled at contact 2M completes the following circuit: earth, contacts-.24]; and 2,64, Wiper 213 of the'test distributor, wiper'293- of the test connector, bank contact 28-9 conductor 3|,9, contact 32l,ywinding of relay 325, batteryv and earth, .Relay. 325 opcrates responsive to its energizationover this'chcuit, and atcontact .336 it completesa circuitiior relay 305, thereby preventing the. latte relay from restoring. The opening of contact 301'npon operation of relay 325 interrupts the circuit to the permanent lockout alarm, while the opening of contacts 324 and 32 6 disconneotrelay-32c from the-conductors of line 31. The disconnection of relay 320 fromtheqline conductors has cleared I line 3M of attachments, and it now maybe tested over the test switch train from the test desk in the usual way.

45' 'sidered new and is desired to be protected by Let- -.Having described the invention, what is conters. Patent'is set forth in the following claims. What is claimed is: a

1. In a'telephone system, subscribers lines upon which faults occur at times, a test operators position, operator-controlled switching equipment for extending a connection from said position to a line upon which a fault exists, means controlled from said position .over said connection and one ofthe line conductors of said faulty line for clearing said line conductors of attachments preparaupon them, and means then effective to maintain'said line conductors cleared of attachments independently of any control over saidone line conductor.

, 2. In atelep'hone system wherein a relay is connectedto at leastone of theconductors of a tele phone line when a certain fault occurs on that line, a test operators position, operator-controlled means for completing a connection from said position to the line conductors of said faulty line, means at said positionoperated to apply a poten tial to said connection, thereby to operate said relay over said connection and said one line'conby said relay,-upon such operation, for disconnecting said relay from the line to permit said line to be tested without said relay connected thereto.

3. In a telephone system wherein a certain fault on'any-one of a group of subscribers lines causes that line to seize switching equipment common to the lines of said groups, a test operators position, operator controlled means for extending a connection from said position to said faulty line, and means in said common .equipment controlled from said position over said connection and a line conductor of said faulty line for forcibly releasing said common equipment and for clearing said line of attachments preparatory to making a test upon said line.

4. In a telephone system, subscribers lines, switching equipment common to said lines, means for causing said equipment to connect with any one of said lines, an operators position, operator controlled means for extending a connection from said position to the line conductors of said one line while said switching equipment is connected to that line, a booster battery, operator controlled means for connecting said booster battery to said connection, and means in said switching equipment controlled by said booster battery over the line conductors of said one line and said connection extended thereto from-said position for forcibly disconnecting said switching quipment from said one line responsive to said booster battery being connected to said connection.

5. In a telephone system, subscribers lines, switching equipment common to said lines, means for causing said equipment to connect with any one of said lines, a booster battery, means for connecting said booster battery to the line conductors of said one line while said common switching equipment is connected thereto, and means in said switching equipment controlled over the line conductors of saidone line by said booster battery for forcibly disconnecting said switching equipment from said one line responsive to said connection of said booster battery to said line conductors.

6. In a telephone system, subscribers lines, means for making any of said lines busy, an operators position, operator controlled means for extending a connection from said position to the line conductors of one of said busy lines, a booster battery, operator controlled means for connecting said booster battery to said connection, a device connected to the line conductors of said one line and operated, over said conductors and said connection extended thereto, by said booster battery, said first means thereupon controlled by said operation of said device to make said one line idle.

7. In a telephone system, a subscribers line having two line conductors, a line relay having two windings connected respectively to the two conductors of said line, means for energizing said two windings over said line in such a way that they assist one another in maintaining said relay operated, means for at times reversing the direction in which one of said windings is energized and, at the same time, maintaining the other winding energized in its original direction, thereby to means for at times reversing the direction in which one of said windings is energized and, at the same time, -maintaining the other'winding energized in its original direction, therebyv to cause said relay to restore due to the differential action of its two windings, said second means controlled by said relay responsive to its restoration to make said line idle.

9. In a telephone system, a subscribers line having two line conductors, a relay having two windings connected respectively to the two conductors of said line, means for energizing at least one of said windings over said line thereby to maintain said relay. operated, a booster battery, means operated at times to connect said booster battery to one of said line conductors, said battery thereupon effective to cause current to flow in the other winding of said relay in such a direction as to oppose the effect of said one winding, thereby to restore said relay to normal, and means operated responsive to said restoration of said relay to normal for disconnecting the two windings of said relay from said line conductors. 10. In a telephone system, a subscribers line having two conductors, a relay having two windings connected respectively to the two conductors of said line, means for energizing at least one of said windings over said line thereby to maintain said relay operated, and means operated at times to cause current to flow in the other of said windings in such a direction as to oppose the eifect of said one winding, thereby to cause said relay to release.

11. In a telephone system, a subscribers line having two conductors, a relay having two windings connected respectively to the two conductors of said line, means for energizing atleast one of said windings over said line thereby to maintain said relay operated, means operated at times 40 to cause current to .fiow'in the other of said windings in such a direction as to oppose the effect of said one winding, thereby to cause said relay to release, and means responsive to the release of cause said relay to restore due to the differential said relay for maintaining it released independently of said second means.

12. In a telephone system, a subscribers line, a relay connected to at least one of the line conductors of said subscribers line, a booster battery,

sponsive to the connection of said booster battery to said conductor for disconnecting said relay from said line and maintaining it disconnected independently of said booster battery.

14. In a telephone system, subscribers lines, equipment common to said lines, means at times controlled over one of said lines for seizing said equipment, a relay in said equipment thereupon connected to the speech path of said one subscribers line, a booster battery, means for connecting said booster battery to said speech path, and means controlled by said relay responsive to said connection of said booster battery to said path for releasing said equipment.

' 15. In a telephone system, subscribers lines, equipment common to said lines, means at times controlled over one of said lines for seizing said equipment, a relay in said equipment thereupon connected to the speech path of said one subscribers line, a booster battery, means for connecting said booster battery transitorily to said speech path, means controlled by said relay responsive to said transitory connection of said booster battery to said path for releasing said equipment, and other means controlled by said relay responsive to said transitory connection of said booster battery to said path for preventing said first means from again seizing said common equipment after said booster battery has been dis connected from said path.

16. In a telephone system, a subscriber line, means for making said line busy, switching equipment operated to extend a connection to said line while same is busy, a source of booster battery potential, means for impressing said potential upon one of the line conductors of said line over said connection, a relay individual to said subscribers line connected to said one conductor and operated responsive to the connection, of said potential to that conductor, thereby to cause said line to become idle, a device in said switching equipment operated responsive to said line becoming idle, and means controlled by the operation of said device for disconnecting said relay from said line conductor.

17. In a telephone system, subscribers lines, switching equipment common to said lines, means controlled over any one of said lines for seizing said equipment and associating it individually with said one line, a relay in said equipment thereupon connected to one of the line conductors of said one subscribers line, means in said equipment for making said one line busy, other switching equipment operated to extend a connection to said one line While same is busy,'a source of booster battery potential, means for impressing said potential upon said one line conductor over said connection, said relay operated responsive to said potential beingimpressed upon said one line conductor to cause said second mean to make said line idle, means in aid first switching equipment. operated responsive to said line becoming idle for disconnecting said relay from said one line conductor, and means in, said other switching equipment operated responsive to said line becoming idle for at once making it busy again.

MORRIS E. GRIFFINS. IMRE MOLNAR.

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