US1699754A - Telephone system - Google Patents

Description

Jan. 22, 1929. 1,699,754

A. J. RAY

TELEPHONE SYSTEM Sheets-Sheet 1 Filed June 25, 1924 2 MZWA HIT-H.-

Jan. 22, 1929. 1,699,754

A. J. RAY

TELEPHONE SYSTEM Filed June 23, 1924 2 Sheets-Sheet 2 HIT":

JRE L Iii) ARTHUR J. RAY, OF CHICAGO, ILLINOIS,

AUTOMATIC ELECTRIC INCL, OF CHICAGO, ILLINOIS,

AWARE.

Application filed June 23,

The present invention relates in general to telephone systems, but is concerned more particularly with non-numerical trunking arrangements as applied to telephone systems.

The main object of the invention is the provision of new and improved circuit arrangements for distributing the trat'fic amongst the various trunks accessible to a group of non-numerical switches oi the type that have no normal position, in order that two successive calls handled by the same nonnumerical switch do not take the same trunk. This avoids the possibility of a detective trunk being used repeatedly by the same nounumerical switch with the result that all calls coming into such non-numerical switch duringthis period are lost on account of the deitective trunk.

The applicant is aware of the fact that the foregoing is not broadly new, arrangements being known in which a non-numerical s titch is automatically advancedone or more steps upon the release of a connection. This arrangement, however, while in most cases satisfactory from an operating standpoint, is in many cases very ditlicult to carry out on account of the somewhat complicated cir cuit arrangement required. it is, therefore, one object of the invention to provide new and improved circuit arrangements whereby a non-numerical switch advanced one or more steps automatically upon being taken for use, rather than. upon being freed. Other objects have to do with the necessary circuit details as will appear hereinafter.

lte'terring now to the accompanying drawinu's comprising F 1, 2, and 3, they show by means of the usual circuit diagrams, a

sufficient amount of apparatus involved in a telephone system embodying the principles of the invention, to enahlethe invention to be understood and its utility appreciated.

Fig. 1 shows the line switcn LE5 individual. to the line or substatioii A. and having access to the selector S; Fig. 2 shows the secondary line switch SL555, which is accessible to the sclector S, Fig. l, and which has access to the repeater R which is associated with a trunk outgoing to a distant ofiicc; and Fig. 3 shows a desirable modification of the secondary line switch SL3, Fig. 2-. l f

Regarding the equipment shown, the sub-' station A is an. ordinary automatic substation or. the two-wire type and has theusual talking and signalling instriimeutalities, as

ASSIGNOR, BY MESNE ASSIGNMENTS, TO

A CORPORATION OF DEL- IELZEPHONE SYSTEM.

192a. Serial 110,721,615.

well as a calling devicetor controlling the automatic switches; the line switch LS is mechanically of the well known rotary type in which the wipers have no normal position and are advanced in a forward direction only,

being advanced upon the backward stroke of the associated stepping magnet, rather than upon the forward stroke, and has suitlevels; the secondary line switch SLS is pro-,

vided for the purpose of increasing the efiiciency of the trunks in the associated outgoing group and, aside from its somewhat different circuit arrangements necessitated by the different condition under which it operates, is similar to the line switch LS mechanically and also in that it is always advanced automatically when seized; and the repeater R is an ordinary two-wire repeater and is provided primarily in order to permit the use of a two conductor inter-ofiice trunk, and it accordingly supplies ground, when seized, to the associated release trunk conductor to hold up the connection.

The detailed description of the operation of the apparatus shown will now be given. For this purpose, it will be assumed that the subscriber at substation A,desiring to make a call, removes his receiver. is removed at substation A, line relay 13 of the line switch LS energizes over conductors ll and 12 and closes atarmature 16 a circuit for the slow-to-pull up relay 14, and at armature 17 closes a circuit for stepping magnet 28 through the jumper 27. This circuit in cludes armature 19 of relay 1% and its resting contact, but relay 14. being slow-to-pull up,

permits this circuit to remain closed long and opens the circuitoif stepping magnet 28 When the receiver at armature 19, whereupon stepping magnet lil the banks of the connector switches having access to it, and closing a circuit for switching relay and stepping magnet 28 in series, At the same time, relay 14 connects test wiper 30 to the junction of switching relay 15 and stepping magnet 28. In case the trunk upon which the wipers of the line switch are standing is idle, however, this latter operation is of no particular utility at this time, and switching relay 15, not being short circuited energizes, seizing the trunk.

On the other hand, assuming the trunk to be busy, switching relay 15 is short circuited by the ground potential encountered upon the busy test contact by test wiper 30 and does not energize, and, stepping magnet 28 is energized from this same ground potential and, being seltinterrupting, operates the wipers 29, 30, and 31 step by step in search of an idle trunk. 'When an idle trunk is reached, for example, the trunk comprising conductors 3234, inclusive, switching relay 15, being no longer short circuited, energizes in series with stepping magnet 28. Stepping magnet 28, however, does not energize at this time on account of the high resistance of switching relay 15. Upon energizing, switching relay 15 closes a locking circuit for itself through the resistance 36 at armature 22, at the same time, opening its initial circuit through stepping magnet 28; opens the test circuit and prepares the holding circuit at armature 21; and at armatures QO and 23 disconnects conductors 11 and12 from the winding otline relay 13 and ground and extends them by way of wipers 29 and 31, the bank contact with which they are now in engagement, conductors 32 and 34, and armatures 57 and and their resting contacts to the upper and lower windings, respectively, of the double wound line relay 41 of the selector S.

Line relay 41 now energizes over the calling line, its upper winding being connected directly to battery and its lower winding bein connected to ground through the left hand winding of the common dial tone trans former, and closes at armature 51 a circuit for release relay 42 which energizes and prepares thevertical magnet circuit at armature 53, at thesame time places ground upon the release trunk conductor33 at armature 52, thereby closing the usual holding circuit for switching relay 15 of the line switch LS before the slow acting line relay13 and relay 14 have had time to deenergize.

he calling subscriber now hears the dial tone placed on his line through the common dial tone transformer and through the lower winding of line relay 41 and knows that he may now dial the first digit. When he does so, line relay 41 is deenergized a corresponding number of times. Upon each deenergization, line relay41 closes at armature 51 a circuit througharmature 53 and its working contact and series relay 43 for vertical mag net 48. By the operation of vertical magnet 48, the wipers 51-53, inclusive, of the selector S are raised step by step and come to rest opposite the desired level of bank contacts. Relay 43 is energized in series with vertical magnet 48 and, bein slow acting, maintains its armature attracted throughout the vertical movement. At armature 54, relay 43 closes, in conjunction with the oil normal contacts 49 which close upon the first vertical step, a circuit through the interrupter contacts 50 for stepping relay 44 which thereupon energizes and closes a locking circuit for itself at armature 55, and at armature 56 prepares a circuit for the rotary magnet 48.

At the end of the vertical movement, the slow acting series relay 43 deenergizcs and closes a circuit for the rotary magnet 48 at armature 54, whereupon rotary magnet 48 energizes and advances the wipers 61463, inclusive, into engagement with the first set of bank contacts in the selected level, and, near the end of its stroke, opens the circuit of stepping relay 44 at the interrupter contacts 50. Stepping relay 44 now deencrgizes and opens the circuit of rotary magnet 48 at armature 56, whereupon rotary magnet 48 deenergizes also and again closes its interrupter contacts. From this point, the operation depends upon whether the trunk terminating in the first set of bank contacts is busy or idle. If it is idle, switching relay 45 energizes and seizes it. On the'other hand, if the trunk is busy, switching relay 45 is short circuited by the ground potential encoun tered on the busy test contact by test wiper 62 and does not energize, and stepping relay 44 is energized through test wiper 62 and closes at armature 56 a circuit for rotary n1agnet'48 which again energizes and advances the wipers 61-63, inclusive, another step. This alternate operation oi stepping relay 44 and rotary magnet 48 continues as described until an idle trunk is reached, for example, the trunk conn'nrising cmnluctm's 64436, inclusive. hen this occurs, swilching relay 4-5, being no longer short ciriuiitcd, energizes in series with stepping relay 44 from the grounded release trunkconductor 33 and through the 011' normal contacts 49 and the il'ltcrrupter contacts 50. Stepping relay 44, hmvever, does not ener ize at this time on account of the 1 1 il irely h resist ance ol switching relay 4-5. llptfit(:Iltlfiflwing, switching relay 45 disconnech-i ground from armature 51 of line relay 4-1 atarinature 59. so as to prevent the release of the selector after the connection has been switchedthrough and. after relays 41 and 42 deenergized. Incidentally, this operation opens the circuit of release relay 42 without waiting for line relay 4] to deenergize and open itat armature 51. As a further result of the energization of relay 45, it opens the test circuit and prepares the holding cir- LEI) cui t at armature 58, thereby grounding release trunk conductor 65; and at armatures 57 and 60 disconnects conductors 32 and 34 from line relay 41 and extends them by way 01 wipers 61 and 63, conductors 64 and 66, and armatures 112 and 116 to the winding of line relay 101 of the secondary line switch SLS and ground, respectively. This results in a circuit being closed for the slow-to-pull up line relay 101 over the calling subscribers line. This relay does not pull up in stantly upon its circuit being closed but hesitates just a trifle, so as to give time for stepping magnet 103 to energize responsive to the release trunk conductor 65 being grounded by the. selector S as pointed out above. The circuit of stepping magnet 103 at this time includes the normally closed contacts controlled by armature 113, armature 109 and its resting contact, terminal 105, jumper 108, and the terminal 107, as well as the common conductor 125 which is connected to battery at armature 124 of the common relay 123. Upon energizing, steppingmagnet 103 makes ready to operate the wipers 117-119, inclusive, when it subsequently deenergizes. 1

Upon energizing over the subscribers line, line relay 101 opens the circuit of stepping magnet 103 at armature 109, whereupon stepping magnet 103 deenergizes and advances the associated wipers one step. Line relay 101 also places ground on release trunk con-- ductor 65 at armature 109 through the normally closed contacts controlled by armature 1.13, thereby closing the usual holdingcircuit for the switching relays of the line switch LS and the selector S before the slow acting release relay 42 of the selector S has had time to deenergize. i i

In the secondary line switch SLS, as a tru-ther result of the energization 01 line relay 101, it closes at armature 111 a circuit for switching 102 and stepping magnet 103 in series, and at armature 110 connects test wiper 113 to the junction of switching relay 102 and stepping magnet. 103. Accordingly, the secondary line switch SLS selectsan idle trunk in the same manner described for the primary line switch LE1, which. trunk, it may be assumed, is the one comprising conductors 120-122, inclusive. When thisidle trunk selected, switching relay H102 energizes in series with. stepping magnet 103; opens the test circuit and prepares the holding circuit the seizure of the switch; closes alocal loclr- 111g circuit for itself through they resistance 104 at armature 115. at the same tune disconnet-ting its lower winding terminal from the steppingmagnet 103; and at armatures112 and 116 disconnects conductors 64 and 66 from the winding of line relay 101 and ground and, extends them by way of wipers 117 and 119, the bank contacts with which these wipers are in engagement, conductors 120 and 1 22, and the upper and lower left hand windings of the repeating coil of the repeater R to the line relay 141. Linerelay 141 now energizes over the calling line and closes at armature 143 a circuit for release relay 142. Release relay 142 now energizes and places ground upon release trunk conductor 121 at armature 145, thereby establishing the usual holding circuit before the slow acting linerelay 101 of the secondary line switch SLS has had time to deenergize.

As a further result of the energization of line relay 141 of the repeater R, itcloses at armature 144 a bridge across the associated trunk conductors 147 and 148 which are as ,sumed to extend to and terminate in an in- Accord prepared coming selector in a distant ofiice. ingly, the said incoming selector is for operation in the usual manner.

The calling subscriber may now complete the remaining part of the connection in any lay 142. Release relay 142 deenergizes afteran interval and removes ground from release trunk conductor 121at armature 145, whereupon switching relay 102 of the secondary line switch SLS, switching relay 45 of the selector S, and switching relay 15 of the line i switch LS deenergize. Responsive tothe delenergization of switching relay 45 of the selector S, release magnet 46 energizes over the following circuit: From ground by way of armature 59 audits resting contact, armature 51 and its resting contact, armature 53and its resting contact, 011 normal spring 47 and its upper contact,and release magnet 46 to battery. Upon energizing, release magnet 46 restores the selector S to normal position in the usual manner, whereupon'its circuit is opened at oft normal spring 47.

It has been pointed out in the foregoing how the line switch LS is caused to take one step automatically when the receiver is removed. at substation A, whether the wipers of the line switch are, standing upon anidle trunk or not.- It will be appreciated that, with this arrangement, the subscriber at substation A will not be prevented, by a single defective first selector from establishing a connection as might well occurif the line switch LS always took the sametrunk for each call-as long as that trunk remainedidle. It has been, shown how this, same feature a has been applied to 'thesecondary line switch SLS so that in case the said secondary line switch SLS is used by the same subscriber forsuccessive calls, adiflerent outgoingtrunk will be taken in each case. This arrangement, in connection with the secondary line switch SLS, has a still furtherutility in case the secondary line switch happens to be first choice in the bank of a group of selectors, in which case, a large percentage of calls might be lost chew the secondary line switch standing on a defective trunk duringthe time when thetrafiic is comparatively light.

Referring now to the line switch LS, ,Fig.

1, it will be remembered that this line switch is advanced one step automatically beforeits advance is placed under the control of the test wiper 3 certain cases may be desired to arrange the line switch LS so that it will take tWO or more steps before its advance is laced under the control of its test wiper.

hen this arrangement is desired, the jumper 27 between the terminals and 26 is omitted and a jumper is connected instead between the terminals 24 and 26, with the result that up relay 14. The number of steps whic'i is l to desired for the stepping magnet 28 totake independent of the regular testing operation maybe regulated by theemount or slowness imparted to the relay 14 by adjustment in the ordinary manner. In thisw'ay, by achusti ng the relays such as 14 with varying degrees of stiffness, the condition may be obtained wherein certain of the line switches advance only one or two steps prior to the regular testing operation, while others advance three, four, or more steps prior to the regular testing operation, thus resulting in a more general mixup' of the traflic and a more even distributien of the lead amongst the various trunks concerned. y

This extra advantage however must be weighed against the increased wear and tear on the switching mechanisms.

Somewhat similarly, the secondary line switch SLS may be arranged to take two or more steps prior to the regular testing operation, as against one step, by omitting the jumper 108 which is connected. between the terminals 105 and 107 and placing a jumper between theterminals 105 and 106. The variable operation on the art of the secondary lineswitches, such as S S, is obtained with the jumperin the alternate position above pointed out by merelyadjusting the linerelays such as 101 all alike as the amount of time required for any one relayto pull up subse uent to the seizure of theswiteh is confrolled by the length of the instant calling Refierring' now again to the line switch LS, Fig.- 1, it will be noted that battery is supplied to stepping magnet 28 over the common conductor 67, which is normally connected to'battery throu h the working contact and armature 7 0 0% the normally energized relay 69. This relay 69 is normally maintained energized over the conductor 68 which is common to the group of selectors accessible to the line switch LS. For example, the particular branch of the common conductor 68 which extends to the selector 8 is normally grounded through armature 59 and ts resting contact, armature 51 and its resting cont-act, armature 53 and its resting contact, and the oil normal contacts 47. It will be appreciated, however, that as soon as the selector S is taken for use, the line and release relays 41 and 42 energize and the ground is removed at that point from the common conductor68 and is maintained disconnected from conductor 68 by off normal spring 47, which shifts to its alternate position upon the first vertical step of the shaft, until the selector S is finally restored to its normal position again. Therefore, when the last selector in the group becomes busy, the common conductor 68 is ungrounded at all points andthe all-trunks-busy relay 69 deenergizes and removes battery from the common stepping magnet supply conductor 6? so as to prevent the needless operation of the stepping magnets in case any other subscribers remove their receivers during the time when relay 69 is deenergized. The calling subscribers who are thus unable to obtain connection with first selectors are informed of this fact by the absence of the dial tone.

When a first selector becomes idle, ground is replaced on conductor 68, whereupon relay 69 energizes again and places battery on conductor 67 to permit the stepping magnets, such as the stepping magnet 28 of the line switch LS, to operate.

It may be well to point out at this time that, although the switching relay 15 is initially energized in series with stepping magnet 28 and would ordinarily be deenergized responsive to the removal of battery from stepping magnet 28, the circuit arrangement in this case is such that the switching relay 15 remains locked up through the resistance 36 and does not deenergize as when battery is removed from the stepping magnet 28 by the common relay 69 Referring now to Fig. 2, it may perhaps be advisable to explain certain arrangements hitherto not discussed. It is to be understcmd that the secondary line switch SLS is only one line switch of a single subgroup and that a number of sub-groups,say ten, taken together constitute the main group of secondary line switches accessible on one level of Ill the first selectors. Assuming that there are ten sub-groups of secondary line switches, each of the ten trunks on the level shown of the selector S extends to a secondary line switch in a different sub-group. This arrangement, as is well known, is provided so that, as one or more of the sub-groups become busy during a time of heavy trafiic, no calls need be lost but are instead diverted to the sub-groups, which, as yet, contain idle secondary line switches. A secondary trunking system of the foregoing type, but employing only two sub groups, is shown in Fig. 1, of the U. S. Patent 1,528,751, issued to Bellamy et a]. March 10, 1925. When this ar rangement is employed, it is necessary to provide means for rendering busy the remaining idle secondary line switches in a sub-group when all outgoing trunks accessible to such sub-group of line switches are busy, so that no more calls come into this sub-group at such a time, but are diverted to the other sub-group as above mentioned. To this end, the common all-trunks-busy relay 123 has been provided. Relay 123 is normally energized over the common conductor 126 which is grounded at each of the idle repeaters accessible to the secondary line switch SLS.

For example, it is grounded at the repeater It at armature 146 of release relay 142. Relay 123, as has been pointed out hereinbefore, maintains battery connected to the common conductor 125 at armature 124 to supply battery to the stepping magnets ofall the secondary line switches in the sub-group.

When the last trunk accessible to the secondary line switch SLS becomes busy, ground is removed at all points from conductor 126 and relay 123 deenergizes and shifts the common conductor 125 from battery to ground. This immediately stops the rotation of any secondary switch in the sub-group that may happen to be'searching for a trunk at this time, and it connects ground to the release trunk conductors of all the remaining idle secondary switches. For example, if the secondary line switch SLS is at this time idle, release trunk conductor is grounded over the following circuit: From ground by way of the resting contact and armature 124 of the all-trunk busy relay 123, conductor 125, stepping magnet 103, jumper 108, resting contact and armature 109,and the normally closed contacts controlled by armature 113. From this point on, no more traffic is permitted to come into this sub-group of switches, but is diverted to the other subgroups.

When one trunk accessible to the secondary line switch SLS becomes idle, relay 123 energizes again andshifts conductor 125 from ground back to battery again, thereby rendering all idle switches in the sub-group available for use again and furnishing battery to the stepping magnets of said switches.

It will be noted that, although the switching'relay 102 of the secondary line switch SLS is initially energized in series with stepping magnet 103, it remains locked up through the resistance 10% and armature 115 and does not dcenergize responsive to the removal of battery from stepping magnet 103.

Referring now particularly to Fig. 3, the secondary line switchSLS' shown therein is a modification of the secondaryline switch SLS, F ig. 2, and the main difierence between the two circuits is that, whereas, switching relay 102 of the secondary line switch SLS is initially energized in series with stepping magnet 103 and later locks up over an inde pendent circuit, the switching relay of the secondary line switch SLS is initially ener- ,gized over a circuit which is independent of of the associated stepping magnet, thereby obviating the necessity ofproviding an armature and contacts corresponding to arma-,

ture 115 and its associated contacts of switch ing relay 102. On the other hand, however, it is necessary in the case of the secondary line switch SLS to make arrangements for connecting the test wiper to the junction of the switching relay and the associated resistance in addition to connecting it to the stepping magnet sons to prevent the energization of the switching relay during the testing operation and before an idle trunk is reached. Otherwise the circuits of the two are very much the same.

What isclaimed is: i 1. In combination, an automatic switch, trunk lines accessible to said switch, means responsive to the seizure of said switch for causing the same to hunt for an idle trunk line, and means for always advancing said switch past one of said trunk lines after it is seized and before its hunting movement starts. i

2. An automatic switch having a testwiper, means responsive to the seizure of said switch for advancing the same inde' pendent of its test wiper, and meanseflective after a predeterminedtime for continuing the advanceofthe switch under control of its test wiper. p

3.1111 automatic switch having a test wiper, means responsive to the seizure of said switch for advancing the same inde pendent of its test wiper, and delayed action means also responsive to the se1zure of said switch for placing the continued advance thereof under the control of its test wiper.

A. An automatic switch having a test.

wiper, means responsive to the taking of said switch for use for advancing the same-under control of its test wiper,and means effective each time the switch is used for preliminarily advancing the same independent of its test wiper.

5. An automatic switch having a test wiper and a motor magnet, 'a circuit for said motor magnet excluding said wiper closed when the switch is taken for use, another circuit for said motor magnet including said test wiper,and delayed action means also responsive to the taking of said switch for use for opening the first circuit and closing the second circuit.

6. An automatic switch, line and release trunk conductors terminating in said switch, means controlled over said release trunk conductor when the switch is seized toadvance theswitch, a test wiper, and means controlled over one of said line conductors for placing the continued advance of the switch under control of said test wiper. H

7. An automatic switch, line and release trunk conductors terminating in said switch, a motor :magnetcontrolled over said release conductor. to advance the switch when the same is seized, a test wiper, and a relay energized over one ofsaid line conductors for shifting the controliof said magnet from the said release conductor to the said test wiper.

8. A line switch ofthe type in which the wipers normally rest on the contacts last used,-and means for automatically advancing said switch whenever it is taken for use. 7

:9. A line switch of the type in which the wipers normally rest on the contacts last used, a test wiper in said switch, means for advancing said switch independent of control by its test wiper whenever the switch is taken for use, and means for-causing the advance of the switch to be continued under control of said test wiper. 1 i

10. A line switch of the type in which the wipers normally rest on the contacts ilast used, :a test wiper and test contacts in said switch, means for advancing said switch a definite distance independent of control by said itestlwiper whenever the switch is taken for use, and means for causing the switch to continue its advance under control \of said test wiper as long as the said wiper engages busy test contacts. i

I 11. .A line switch of the type in which the wipers restinormally on theieontacts last used, a test wiper in said switch, a motor magnet for driving said switch, means foroperating said motor magnet independent of said test wiper, and means for continuing the operationof said motor magnet by current flow through said test wiper and said magnet in series. 7

1am Iautomatic switch having a test wiper, means responsiveito the taking of said switch for use for advancingthesaine under control of its test wiper, and meansetfective eachitime the'switch is [used for preliminarily advancing the same only one step independ: ent of its Itest wiper. 1

13. An automatic swltch .having .a test wiper, means responsive to the taking ofsaid switch for use for advancing the same under control of its test w per, and means efiective each time theswitch is used for preliminarily advancing the same a plurality of steps independent of its testwiper.

14. An automatic switch having a test wiper, means responsive to the taking of said switch for use for advancing the same under control of its test wiper, and means effective each time the switch is used for preliminarily advancing the same a variable distance independent of its test wiper.

15. An automatic switch having a test wiper, means responsive to the taking ofsaid switch for use foradvanci-ng the same under contrl of its test wiper, means eflz'ective each time the switch is used itor preliminarily advancing the same a fixed distance independent ott its test wiper, and means for readily changing the switch so that it is advanced preliminanillya variable distance.

16. An automatic switch having a test wiper, means responsive to the takingof said switch for use for advancing the same under control of. its test wiper, :ITIQBJIS eftectiveeach time the switch is usedtor preliminarily advancing the same a fixed distance independent of itstest wiper, and means for readily changingthe switch soithat the fixed distance is either a singlestep or a fixed number of steps.

17. An automatic switch having a test wiper, means responsive to the taking of said switch tor useadvancing the same under control of its test wiper, means effective each time the switch is used for preliminarily advancing the same only one step independent of its test wiper, and means for readily changing the switch so that it is advanced preliminarily a plurality of steps.

18. A line switch of the type in which the wipers rest normally on the contacts last used, a test wiper in saidswitclna motorrmagnet for driving said switch, means foroperating said :motor magnetindependent ofsaid test wiper, :and means for continuing the operation of said motor imagnet by current flow through said test wiper.

i9. In a hunting switch having a driving magnet operated through the test wiper of the switch-during the hunting movement, a test conductor incoming to said switch, and

means tor placing a guarding potential on said test conductor-by altering the potential supplied to :said magnet.

.20. In an automatic switching system, :a hunting switch havingia driving magnet loperated through the "test wiper of the switch during the hunting movement of the switch, a test conductor incoming to said switch, a plurality of similar switches, a conductor for supplying operating potentialto the magnets of all said switches, and means for placing a guarding potential on the test conductors of all said switches bysaltering the potential on said supplyconductor. l

.21. In combination, a .line switclna motor magnet and a test wiper for said line switch, a relay for closing a circuit for said magnet including said wiper, a relay for energizing said first relay, and a preliminary energizing circuit for said magnet controlled by said relays jointly.

22. In combination, a line Switch, a motor magnet and a test wiper for said line switch, a relay for closing a circuit for said 10 magnet including said wiper, a relay for en ergizing said first relay, a preliminary ener gizing circuit for said magnet, contacts on the second relay for closing said preliminary energizing circuit, and contacts on said first relay for opening said preliminary energiz ing circuit.

In witness whereof, I hereunto subscribe my name this 20th day of June, A. D. 1924:.

ARTHUR Jr RAY.

Images