US1727592A

US1727592A - Automatic telephone system

Info

Publication number: US1727592A
Application number: US582159A
Authority: US
Inventors: John E Gardner
Original assignee: Automatic Electric Inc
Current assignee: Automatic Electric Inc
Priority date: 1922-01-27
Filing date: 1922-01-27
Publication date: 1929-09-10
Anticipated expiration: 1946-09-10
Also published as: USRE18686E; US1727593A

Description

Sept. 10, 1929' I JIE. GARDNER r 1,727,592

AUTOMATIC TELEPHONE SYSTEM Original Filed Jan. 27. 1922 3 Sheets-Sheet l TUJETZIU Jul-Ln E.Earu nsr Sept. 10, 1929. J. E. GARDNER 1,727,592

AUTOMATIC TELEPHONE SYSTEM Original Filed Jan. 27. 1922 3 Sheets-Sheet 2 I1wE-m?- Jul-m E.Eard n1ar HIT y:

' p 1929' J. E. GARDNER 1,727,592

AUTOMATIC TELEPHONE SYSTEM Original Filed Jan. 27. 1922 s Shets-Sheet s IfiTfilEf- Jul-m EEardnsr Z- Many.-

Patented Sept. 10, 1929.

unites stares rarsnr orrics.

Jenn GARDNER, on 6310.55.60, runners, .essrenon, BY Mnsnn Assremvrnnrs, To

AUTOMATIC ELECTEZO INC, 0E OHIOAGQ,

VIARE.

ILLINOIS, A CORPORATION OF DELA- AUTOMATIC TELEEHONE s'rsrnrir.

Application filed January 27, 1922, Serial No. 532,159. Renewed December 3,1928.

The present invention relates in general to automatic telephone systems but'is more particularly concerned with small exchanges of the type which are commonly used for giving telephone service in factories, commercial establishments andthelike; and the object of the invention, broadly stated, is the provision of a private automatic exchange system embodying new features and novel circuit arrangements which are better adaptedto meet the service requirements of systems of this character. I I I According to' the invention an attendant operator is employed at the private automatic exchange to complete all connections from the main to the branch exchange. All connections in the other direction from the private automatic to the main exchange are completed automatically though if need be the operator may complete the connection.

A feature 01 the invention relates to the provision of an improved large capacity connector switch which has access to trunk lines extending to private automatic exchanges.

Another feature of the invention concerns itself with the provision of a novel trunk circuit extending iromthe main to the branch exchange so that it a trunk becomes open or grounded it is automatically made busy in both exchanges.

A further feature of the invention relates to the provision of a novel cord circuit at the attendant operators position provided with improved means for giving supervision.

Still another featureof the invention provides means for automatically rendering the trunk line accessible in either the main or branch exchange for a call in either direction when the calling subscriber at the main exchange replaces his receiver, notwithstanding that the operator may have the plug of a cord circuit in the associated'jack. f

Uther features of the invention relate to the provision of means whereby when a call is extended from the main to a branch exchange subscriber through an operators cord circuit at the branch exchange the replacement of the receiver at the called substation causes the release 01": the connection both in the main and branch exchanges and renders the trunk line connecting theseeXchang-es accessible for calls in either'direction; and to the novel ar rangement whe'rebywhen a connection is extended by the operator in the" branch X- change to a subscriber in the main exchange the replacement of the receiver at the called substation in the main exchange causes the release of the connection and the trunk line "from the main to the branch exchange rendered accessible for calls in either direc tion eventhough the attendant operators cord circuit remains in thc'jaclr associated with this trunk'line.

There are other objects of the invention not now specifically mentionedwhich together with the foregoing will be described fully hereinafter referencebeing had to the accompanying drawings forming a part of this specification. s

Reterring now to the drawings comprising Figs. 1, 2, and there is shown by means of the conventional circuit diagrams enough of the apparatus to fully illustrate the invention. This apparatus includes a large capacity rotary connector switch H,

Fig. l, in the main exchange, a trunk line comprising conductors 14.0 and 14; extend ing to the private automatic exchange, a cord circuit 0, Fig. 2, a connector switch H, Fig; 3, and a subscribers station A in the privateibranch exchange. i

Referring now more particularly to Fig. l, the connector switch H is of the samegeneral mechanical construction as that of the a well known Strowger switches, but differs from them inasmuch as it is provided with an extra set of wipers and associated hank contacts; thus the'co'nnector H, which has twenty levels, has access to 200 lines and is capable of testing,'aiter selecting a group of lines, for an idleline in two levels simultaneously. One of the trunk lines extending to a private automatic exchange to which the connector switch H has access is shown in the drawings terminating in the bank contacts 106-108, inclusive.

' This trunk line is of the two way type, that p is, it is adapted to beused for calls from the main to the branch exchange or from the branch to themain exchange. in order to enable a call to be extended from the branch to the main exchange the trunk line comprising conductors 1 and Ill is provided with a line switch C in the main exchange. This line switch is the usual rotary type of mechanical construction the circuits of which have been modified in accordance with teatures of the invention and has access to trunk linesextending to first selectorswitches in say that the conductorslGQ-ll' 1, inclusive,

associated with the trunk line comprising conductors 140 and 1 11 entendto the, local connector selector repeater switches and'are multipled therein in the usualinanner;

At 0, Fig. 2,is shown a cord circuit-at the attendant operators position in the private automatic exchange. This cord circuit is one of a plurality located at the attendant operators position which isused for extending incoming calls from a main exchange to a branch exchange subscriber..

The jack J is the terminal of a trunk line extending toan incoming connector switch which is shown at H, Fig. 3.

The connector H is of the usual Strowger type having access tolocal' subscribers lines such as that of the, substation A.

The substation A is of the well lrnown automatic type having the usual talking instrumentalities and impulse sending device, the associated line of which termi, ates at the exchange in the line switch C.

The line switch C is similar to the line switch C, Fig. 1, already described;

Having briefly described the apparatus shown in the drawings a detailed descr ption of its operation will now be given; For this purpose it will be assumed that a subscriber in the main exchange desires to ezste d a conection to a subscriber A in the private automatic eirchangef It will be assumed further that the subscriber in'the main exchange has removed his receiver and operated his calling device in order to cause the operation of his individual line l AAAAU sw tcn and the neces ary 'numbero'f selector switches in the main e:;

subscribers line in series and, upon op rat ing, closes the circuit ot'its associated slow acting relay 17. Relay 17, upon energizing, at its armature 37 places ground upon conoi times in response thereto.

ductor 51 in the connector H in order to provide a locking circuit for certain relays which become operated subsequently, at its armature 39 opens a point in the circuit of the release magnet 102, at the front contact P of this armature prepares the impulsing circuits of the connector H and at armature 38 places ground upon the release trunk conductor 11 thereby establishing in the usual manner a holding circuit for the previously operated switches The calling subscriber may now operate his calling device for the next digit of the desired number thereby producing a series of interruptions in the circuit of the line relay 16 which retracts its armature. a plurality At the first retraction of its armature an impulse of current is sent over circuit extending from ground by way oi 'armature 52 and its baclr cont-act armature 39 and its front Contact, off normal springs 11 and 10, through the winding of the slow acting low resistance relay 18, and thence through the winding of the vertical magnet 101 tobattery. The above is the circuit over which the first impulse to the vertical magnet is transmitted. However, upon the first vertical'step of the switch the 011 normal springs are shifted and the remaining vertical impulses traverse a different circuit which is the same as the one previously traced except that it includes the off normal springs ll and 4:2 and armature 43 and its front contact, relaylS being new in an operated position. The vertical magnet 101 operatesto raise the switch'sha'ft carrying the two sets of wipers 103-105, inclusive, and 1091l1, inclusive, step by step until these wipers stand opposite the levels of bank contacts corresponding to the digit dialled. The slow acting relay 18 is energized in series with the vertical ,magneuinaintains its armature attracted throughout the vertical operation of the switch and at the termination thereof deenergizes thereby transferring the impulsing circuit to the rotary magnet 98.

The calling subscriber, upon operating his calling device for the next and final digit of the desired number, causes the linerelay 16 to retract its armature a number of times corresponding to the digit dialled. At each retraction of its armature 52 an impulse of current is sent over the following path: from ground through the said armature and its back contact, armature 39 and its front contact, oil normal springs 41 and 4:2, armature 413 and its back contact, baclr contact and armature 66, through the winding of the slow acting relay 27, armature 91 and its back con tact, and through the winding of the rotary nagnet 98 to battery. The rotary magnet 98 operates to rotate the switch, shaft carrying the'two sets of wipers into engagement with the proper sets of bank contacts in which terminate the first two trunk lines extending to the desired private automatic exchange which We will assume are the bank contacts 106-108, inclu e, and 112-134-. wire. 1 ihe slow acti .ay 271s energ' Z011 series l with the rotaly'n'laggnet and 72 closes the circuit of the slow 29, at its armature 71 short circu ture 86 am its hack contacts on the l arrow 1' usy test armatures and Q op c. .1 p l the automatic rotary t circuit WfilQll will he described fully later. slow acting relay 29, upon opcratioe at its armature T. he

28, at its arinaturefl) opens point in the circuit of the upper winding of switching relay 30, at the trout contact of this ar1nature connects the test wiper 104: associated with the upper seto'l bunk contacts the test relay 20, at its armature 78 opens apoint in the circuit of relay and ts armature 77 prepares a point in the testing circuit of the test wiper 110 associated. .vith the second set of wipers. The relay 28, upon eneie'izing, at its armature Y6 opens a point in the busy signalling circuit, at armature TS opens a point in. a circuit of relay E20 and at its arniatures Y4: and prepai points in the automatic rotary testing circuits.

At this point it will be convenient to e plain how the lines of a group are onnected in the bank contacts of the rotary connector switches so as to enable these switches to select idle triuilt lines in the group after h avinc; connected therewith. (in all ll eve 1 which it is desired that the connector switchrotate ii the line is busy the connection of the normal conductors extending from the line switch to the connector banks are reversed. T his be seen by referring to the connection oi the normal conductors erdendii 1 from the line switch 0 to the bank contacts 108 108, inclusive. That is the conductor 1 which extends from ,irroundin the sw ch C is connected to hank contact 106 instead of haul: contact 108 and the conductor 1410 which is connected to battery in the line switch C etitends to contact 108 instead of contact 106. The line switches associated with all thelines which are the end o1 1e group in'the rotary connector changed so that resistance ppears in the private uorinal conductor as may be seen with reference to the line switch C, that is the cormcctien between the terminals and, lsfiwhich normally short circuits the resistance and also the connection which normally short circl. s he rcwist ancc R are reinovcc. ilhese re mces are of about 300 ohms each and are included in the circuit so that should this so be making acall ground will app on the private nor mal conductor through this resistance and if a rotary connector switch is rotated into engagement with the bank, contacts associated with this line the rotation of the witch will cease and a busy tonewill be given to the calling subscriber.

Adverting; now to the operation of the connector H when engagement was made with the bank contacts 100-108, inclusive, it will be as uned that the trunk line of the gl'OIilP which the trunk line now associates with the first set of wipers 103105, inclusive, is busy there will be a ground potential on the test contact 10'? and the test relay 26 will he energized over-the following circuit Ground ed, contact 107, test wiper 104i, armature 79 and its front contact, armature audits back contact, andthence through the winding of the test relay 2Gto battery; Relay 26, upon energizing, at its armature 65 prepares a point in its locking circuit which is estab lished immediately upon the deenergization of the slow acting; relay 29, at arn'iati re 66 opens a point in the circuit of the rotary magnet, at armature G? prepares a point in the circuit of, tcl'iingg' relay 31, at armature68 prepares a point in the busy signalling lead, at its armature G4 switches the connection of the test relay 520 from the first set of wipers to the secouc set for a purpose which will appear later and at its armature 63 closes a point in the circuit of the test relay 25. 11 511111111 that the second trunk line of the group is busy a ground potential will be present on the test contact 113. A circuit for the testing relay 251nay now be traced from grounded test contact 113, test wiper-110, armature 77 and its front contact, armature (33 and its front contact and through the winding ofrelay 25 to battery. Relay 25, upon energizr e, at its U armature 59 preparesapoint in its locking circuit which is completed immediately upon the deenergization oftho slow acting relay 29, at its armatureGz?) opens a point in the circuit of vitching relay 31, st arinatureQSQC transit'ers the circuit of the slow acting relay 1? to ground at armature 283 for a purpose which will be explained later, and at ar1natending from grounded test contact 113, test wiper 110, armature 74 and its front contact, arniatiu'e 69 audits back contact, armature 60 and its front contact, armature 99 and its back contact and through i the winding of the coil 23 and resistance R to battery. The

1,51 relay 21 may be traced, the circuit 1 relay 21 is'energized over this circuit and, upon operating, at its armatures 56 and 5'? establishes locking circuit-s for both its wind ings 23 and 24, at armature 58 closes the circuit of the rotary magnet 98. Magnet 98 operates to rotate the switch shaft carrying the two sets of switch wipers into engagement with the next two sets of bank contacts and at its armatures 99 and 100 opens the circuits of the coils 23 and 24 of the stepping relay 21. Relay 21 deenergizes thereby opening the energizing circuit of the rotary magnet which deenergizes also. It will be noted that when an impulse of current is sent to the rotary magnet 98 the slow acting relay 29 will receivean impulse of current. Therefore, the slow acting relays 29 and 28 will remain energized to preserve the continuity of the testing circuits.

Atthis point it is convenient to describe the operation and construction'oi the stepping relay 21. Relay 21 is a relay of the so called shunt field type, that is, it does not attract its armature with only one coil energized as the relay armature is short circuited by the soft iron core of the other coil. However, it willbe apparent that when both coils 23 and 2 1 areenergized magnetic flux must flow in a path which includes the relay armature which will thus be attracted. The windings 23 and 24 of the coil 21 are or" very low resistance (about 5 ohms) and are in series with resistance coil B which is or somewhat higher resistance (about 50 ohms). The relay is wound in this mannerso that it there happens to be a ground potential upon the test contacts through a fairly high resistance say of about 300 ohms, which is the case when the connector wipers engage a busy line which is the last trunk line of the group, it will not be ener ized. That 18 the rela 21, does not attract its armature with one 0011 energized by atest contact which is directly grounded and the other coil isenergized over a circuit which includes a test contact grounded through a resistance of about 300 ohms. It will be observed that under these conditions the windingot the coil energized through 800 ohms is practically short circuited by direct ground through one of the low resistance windings of the relay 21. There is practically no margin to the adjustment of the relay 21 inasmuch as under these conditions which are the most adverse encountered the coil energized through 300 ohms generates practically no magnetic flux and the flux generated by the other coil is'short circuited from the relay armature'so that it does not operate.

Returning now to the trunk selecting operation of the connector switch H, it the next two trunk lines, which are now associated with both sets 6f wipers, are rotary trunks and busy, the

relays

25 and 26 will'be maintained energized and the stepping relay 21 will again operate to close the circuit of the appear fully later.

rotary magnet 98. The alternate operation of the stepping relay 21 and the rotary magnet- 98 continues until the switch wipers are rotated into engagement with an idle trunk line or a busy trunk line which is the last one of a group. It will be noted that each impulse sent to the rotary magnet 98 also keeps the slow acting relay 29 energized so that the test wipers are maintained connected to their respective testing relays.

Assuming'that the upper set of wipers engage a trunk line which is thelast of a. group ground will be connected to the test contact engaged by the test wiper 104: through a resistance of 360 ohms. This resistance being included in the private normal circuit as will Relay 26 will be maintained energized but the stepping relay 21 will not operate for the reasons stated above and the rotation of the connector switch will cease. The slow acting relays 28 and 29 deenergize and a busy tone is given to the calling subscriber over a circuit extending from the busy machine, back contact and armature 76, front contact and armature 68 to the lower line conductor 12 and thence over the calling subscribers line. Upon hearing this signal the calling subscriber will replace his receiver thereby initiating the release of the operated switches including the connector H in a manner which will 'be described subsequently. here the last trunkline of the group terminates in a set of bank contacts engaged by the upper set of wipers 103405, inclusive, it is necessary to leave the bank contacts associated with the lower set of wipers open and to ground the testcontact of this set in order to secure proper operationof the connector H. However, where there are an even number of trunk lines in the group the last trunk line will terminate in a set of contacts accessible to the lower set of wipersand in this case no special provision is necessary. That is, it is unnecessary to leave any set of bank contacts disconnected from a trunk line. In order to describe the operation in this case it will be assumed that the connector I-I rotates its wipers 109111, inclusive, into engagement with the trunk line which is the last of a group. The operation in this case is similar to that above described, that is, the relay 26 remains energized as'does the relay 25, the

relay 21 remaining inoperative. As relay 21 does not energize the rotation of the switch ceases and a busy signal is given to the calling subscriber.

It will now be assumed that the connector H is rotated until its upper set of wipers are associated with an idle trunk line in the group. Under these conditions there will be no ground potential present upon the test contact engaged by the test wiper 104,-. Relay 26 deenergizes and opens the circuit of the test relay 25. Then immediately up on the cleenergization of the slow'acting relay 29 a ing of the switching relay 30, back contact and armature 96, back contact and armature 7 9,

test wiper 104, test contact associated with it,

and thence over the private normal conductor thereof through the winding oi the switching relay in the associated line switch and motor he relay 30 is energized magnet to battery. over this circuit, and, upon operating, establishes a locking circuit for itself at its an mature 88, opens a point in the circuit of the testing relay 26 at armature *90, opens the rotary magnet circuit at armature 91, at armature 89 places direct ground uponthe test wiper 10st, at armature 87 prepares a circuit for giving the calling subscriber the so called ringing induction and at armatures 86 and 92 completes the ringing circuit. Ringing cur rent is now projected out on the trunk line until a response is obtained. Other results of the energization of relay 30 are that at ar mature 283 groundis' removed from armature 284 for a purpose which will be described, and at armature 285 a locking circuit is prepared for the relay 25.

The above is the operation of the connector H when an idle rotary line is connected with.

. However, it the idle line engaged by the upper set of wipers is the last tr unl'r line in the group the operation is slightly diii rat. his will now be briefly described. It will be noted that upon the decnergization of the slowact ing relay 29, whena circuit is completed for the switching; relay 30, a circuit is prepared which extends from battery tnrough the winding of relay 20, noru' allyclosed springs controlled by armature l8, armature 6e and its back contact, armature 78 and its bacl: contact, back contact and armature 92,2Hll121'tl116 97 and its back contact, to wiper 105. lthas been described. before how the normal conductors extending from the line switch are reversed in case the line is rotary line and how it the line is straight they are connected in the usual manne As it'is a sinned that the upperset' oi wipers arenow :rnengagement with a trunk line which is the last of the group there will be ground on the bank con. tact engaged by the wiper 105 from the back contact of an. armature in the associated line switch such as the armature in the line switch C. The relay 20 is therefore energized,

and upon operating", at its arn'iature l8 estal l shes a. locking circuit for itself, at its arma ture 419 removes direct ground from the arma ture 89 on the switchin rela 80 and at its aruiatures 4t? ant 50 reverses the connections between the wipers of the connector and the connections to the ring out olt and back bridge relays 19 and 15, res mctively. Upon the ener- 1 gization of the switching relay 30 which oc-' ours in the same manner as before described, ground is placed upon the test contact engag-ed by the test Wiper IO l, through the resistance R which is of about 300 ohms. The

other circuit changes broughtabout by the energization of the switchlng relay 30 are the,

same as before described except that ringing current is now sent out over the wipers ot the connector H in the opposite direction. This is for a purpose which will appear fully later. I

Should the lower set of wipers of the connector'll have been the first to engage an idle trunk line the operation of the connector dit? 'lers from that above described'in the following manner: The .test relay 26 associated with the upper, set of wipers remains energized while the test relay 25 deenergizes. Under lay 81, back contact and armature T l, test wiper 110 associated with the lower set of wipers, test contact engaged thereby and thence over the private normal conductor through the switching; relay and motor inagnet or the associated line switch to battery. The switching relay 31 is energized over this circuit anchupon operating, establishes a lockingcircuit -for itselfat rinature 94, at this same armature closes a circuit for the lower winding; of the switching relay 80 at armature places ground upon the test contact engaged by the test wiper110, at arma-' ture 96 opens a point inthe circuit ofthe upper winding of relay 30 and at armatures'93 and 97 disconnects thefirst set ofwipers and connects up the second set. The energization of the switching relay 30 produces the same results as before except that ground is disconnected from the armature 89 so that the wiper 104 will remain disconnected from the switch. in the above operation, upon the deenergization of the slow acting relay 28 the discriminating relay 20 is connected with the wiper 111 of thelower set of wipers in order to test whether or nottheassociated line is the last one or agroup. It the associated line is the last one of a group, relay 20 is energized and operates as before described, that is, upon the ,energization oi the sw1tching' relays 30 and 81 ringing current will be projected in the opposite direction from the" wipers of the connector and ground willbe supplied by the test contact, engagedby the test wiper through the resistance B so that it another connector is rotated into engagement with this line its rotation will be stopped and a signal given to the calling subscriber.

Returning now to the description of the ex tension of the connection 1t Wlll be assumed that whenthe connector H was operated 1I1lOr en age nent with the bank contacts 106-108,

switching relay 30 is closed at armature 79. i

As the bank contacts 106-108, inclusive, are associated with the first line of a group extending to the private automaticexchange the connector switch must rotate over it when it is busy and therefor, the normal conductors will be connected in the reverse manner and the, discriminating relay 20 will not be ener gized as the contact 108 is connected to battery in the line switch C. Switching relay 30 is energized over the following circuit:

ground on release trunk conductor 11, armature 65 and its back contact, through't-he upper winding of switching relay 30, back'contact and armature 96, back contact and armature 79, test wiper 101, test contact 107, through the winding of the switching relay 121 and the motor magnet 125 of theline switch C to battery. Relay 121, is energized over this circuit. However, its operation at this time is. only efiective to open its back contacts but not to close its working contacts on accountof a mechanical interlocking device controlledby the armature of the line relay 123 which is now normal. The operation of relay 121 disconnects the normal battery and ground connections in the line switch 0 from the trunk conductors 1 10 and 141.

In theconnector H relay 30, upon operating, makes certain circuit changes in a manner which has already been described, these being among others: Ground is placed upon the test contact 107 and the ringing circuit is closed. Ringing current is now intermittently projected over the trunk line comprising conductors 1 10 and 141 extending to the private automatic exchange. that ringing current leaves the wiper 103 and returns to the wiper 105. The operation of the relay 121 in the line switch C, as before stated, removes the normal battery connection from the trunk line comprising conductors and 141. Since the conductors 140 and 141 are reversed in the bank contacts of the connector H the battery supplied by the connector H superimposed on the ringing current is of the opposite polarity to that normally supplied by the line switch C when the trunk line is not in use. The relay 152 in the trunk circuit associated with this trunk line at the private automatic exchange is a high resistancepolarized relay normally energized by battery on the trunk in series with the windings of the line relay 123 and the relay 122 and consequently it will retract its armature 165 whenever battery is removed from the trunk or reversed thereover. soon as the trunk line is seized by the connector H the relay 152 will retract its armature.

It will be noted Thus as Upon deenergizing, relay 152 completes a circuit extending from ground by way of back contact and armature 162, armature 165 and its resting contacts and thence through the winding of the slow acting relay 153 to battery. Upon energizing, this latter relay at armature 167 places ground upon the release trunk conductor 170 extending to multiple test contacts associated with this trunk line in the outgoing level of the local connector switches thereby making this trunk line busy to any outgoing calls and at armature 173' prepares a point in its locking circuit. The relay in this trunk circuit is bridged across the conductors 1&0 and 1&1 in series with a condenser and is operated by the ringing current from the connector H. Relay 150, upon energizing, establishes a locking circuit for itself at its armature 161 and at its armature closes the circuit of the line lamp T Upon noting this signal, the attendant operator will insert the plug of an idle cord circuit, which we will assume is the plug P of the cord circuit 0, into the jack J. By this operation a circuit is completedextending from ground through the winding of the low resistance relay 175, normally closed springs controlled by armature 181, sleeve of plug 1?, sleeve of jack J and through the winding of relay 151 to battery. The relays 17 5 and 151 are energized over this circuit. Relay 151, upon operating, at its armature 163 opens the locking circuit of the ring up relay 150, at its armature 16 1 removes the polarized relay 152 as well as the lower winding of the ring up relay 150 from bridge of the trunk conductors 140 and 1 11 and at its armature 162 removes one ground connection from the armature 165 of the polarized rela This latter operation is ineffective at the present time as ground has been connected to the armature 165 by the operation of spring 155 of jack J. The visual signal 168 is energized in multiple with relay 151. However, its operation is with-out function at the present time. In the cord circuit 0, relay at its armature closes the circuit of the polarizing winding of the electrop-olarized relay 177 and also the circuits for the supervisory lamps L and L It will be noted that the lower winding of the polarized relay 17 7 is bridged directly across the cord circuit and consequently across the trunk line comprising conductors 140 and 141. The ring out ofi' relay 19 in the connector H is therefore energized in series with the lower winding of relay 177. Upon operating, relay 19 establishes a locking circuit for itself at armature as, at armatures er and 46 opens the ringing circuit and at. the front contacts of these armatures connects up the back bridge relay 15. Back bridge relay 15 is also energized over the trunk lineand upon operating, reverses the normal current flow over the incoming trunk lines comprising conductors 10 and 12 for supervisory or metering purposes. Another result of the energization of relay 15 is that a circuit is closed at armature 82 vfor the slow acting rela 38. 7 Upon operating, the latter relay at armature 3a prepares a circuit for the relay 25 in order to prepare a release circuit for the connector which will be explained.

hereinafter. In the cord circuit G the elcctropolarized relay lllis energized in series with the ring cut oil relay 19 as the current flow from the connector H is in the proper direction to operate it. Upon operating, relay 177 at its armature'18ti opens the circuit of the supervisory lamp L and at its armature 187 closes the circuit of the slow acting relay 178. Relay 178, uponjoperating, pro-- pares a circuit for the relay 176 at armature 188. the listening hey K thereby associating her head set with the cord circuit and enabling her to ascertain what number the calling subscriber in the main exchange desires. Should the attendant operator plug into the jack J with the listening key K thrown she would likely get a ring in the car were not special provisions made to prevent this. It rin ig current is being impressed on the trunk line when the operator plugs in the jack 5 with the key K operated the alternating current relay 192 associated with her head set would be energized. Upon operating, relay 192 at armature 193 short circuits the right hand winding of the repeating coil through the r sistance 19 1. This prevents any disagreeable noises in the operators head set due the ring ing current. Wlienthe attendant operator finds out what number is desired she will in sert the plug P into an idle jack which we will assume is the jack J extending to the incoming connector switch H, Fig. 3. By this operation a circuit is completed. for the line relay 210 of the connector H over the "following path: from ground by way of nor mally closed springs controlled 'byarniature 191, impulse springs of the calling device GD, springs 01" the release key K spring 196 and its working contact, sleeve of plug, P, sleeve of jack J, springs 198 and 199, conductor 201 and through the winding of the line relay 210 of the connector H to battery.

The relay 210 is energized over this circuit and, upon operating, closes the circuittor its associated slow acting release relay 1211. Upon operating, the latter relay opens the release magnet circuit at armature 229, at the front contact otthis armatureprepares the operating circuits otthe connector l1 and at armatures 227 and 228 prepares certain circuits for other relays in the switch.

It will be noted that the'line relay 210 is not connected directly to the sleeve of the jack J but is connected through the springs 198 and 199. The connection is made in this man-. ner so that there Will be no so called preliminary impulse sent to the line relay 210 due to The attendant operator will now throw a contact bein made between the tip or the interruptions in the above traced circuitot line. relay 210 which dcenergizes a plurality of times in response thereto. traction of its armatureQ-QG a circuit is completed extending from ground by Way of the said armature and its back contact, armature 229 and its front contact, otl'

normal springs

231 and 230 through the winding of the vertical magnet 219 and then through the wind ing of the slow acting relay 213 to battery. The above is the circuit over which the first impulse to the vertical magnet is transmitted.

Uponthe first vertical step of the shaft the off normal springs are shifted and the remainvertlcal magnet impulses are sent over a circuit which is different from the one pre viously traced inasmuch as it includes the oil normal springs E231 and 232 and armature 236 and its front contact, relay 213 being now in an operated position, Magnet 219 operates At the first reto raise the switch wipers 258-261,inclusive,

step by step until they are placed opposite the level of bank contacts in which is located the 7 terminals of the substation A. The slow acting relay 213 which is energized in serieswith the vertical magnet maintains its armature attracted throughout the vertical movement of the switch and at its termination retracts its armatures and transfers the impulsing circuit to the rotary magnet 220. i

The private automatic.eirchange operator may now operate her calling device in accordanrjze with the final d'git of the called SlllJSCl'llQ8-1S number. As h ore, a of interruptions is produced in the circuit of line relay 216 which deencrgizes a plurality of times in responsetheroto. Uponeach de-' energization, a circuit completed extending 7' .1 (on from ground by Way or armature 241.40 and its a a; c nuns, arina .41. i 1 s o 1- bd oa t 9 dtt tci tact, ott normal springs 931 and 232, arniiature 236 aiul its baclr contact, haclrcontact and armature 246, through the winding of the slow acting low resistance relay 216, armature fiotland its back contact, and hence through the winding of the rotary magnet ry. hrlagnet 220 operatesto rotate the wipers 2584261, inclusive, int-o enlit) gagement with the hanl: contacts associated w :h the line of the desired called suhstation A which we will assume are the bank contacts 262-:265, inclusive. l"heslow acting relay the, deenergiztact by way of testwiper 250, armature 250 and its front contact and through the winding of the test relay 215 to battery. Relay energizes over this circuit and operates to establish a point in its locking circuit at armature 245, this being completed upon the deenergization of the slow acting relay 216, at armature 246 opens the circuit of the rotary magne at armature 24-? prepares an automatic testing circuit which will be described later and at armature 2&8 places a busy tone on the lower heavy talking conductor 202. This tone will be audible to the attendant operator and the calling subscriber and will serve to inform them that thedesired-line is busy. Should the calling subscriber in the main exchange new desire connection with another subscriber in the privateautoinatic exchange he may inform the attendant of illlS- fact. The attendantoperator will then operate the release key K thereby opening the circuitof the line relay 2100f the connector It When this relay deenergizes the slow acting release relay 211 deenergizes shortly after and the connector H is released in the well known manner. The operator may now by operating her calling device for the digits oft-he desired subscriber s number, cause the connector 1 to connect with the desired lines. tion in this case is similar to that just described and will be readilyapparent. However, should the calling subscriber in the main exchange replace his receiver upon hearing the audible busy signal the connection will be released in a manner which will be described hereinafter.

It will new is assumed that the line of the substation A is idle when the wipers of the connector H are rotated into engagement with the bank contacts 262-265, inclusive.

Under these conditions there will be no ground on the test contact 264- and the est relay 215 is not operated. Then, following tion of the slow acting relay 216, a circuitis completed extending from ground by way of front contact and armature 228, normally closed springs controlled by armature 235, armature 2&5 and its 1 oaclrcontact, through the lower winding of the switching relay 217, back contact and armature 250, test wiper 260, test contact 26%, through the winding of the switching relay 266 and motor magnet 26'? of the line switchC to battery. The

relays

217 and 266 operate over this circuit.- However, due to a mechanical interlocking device controlled by the armature of the line relay 268 which has not been enthis time a The opera-' ergized, the switching relay 256 only attracts its arinatures enough to disconnect the line of the substation A froinits normal battery and ground connections in the line switch G.

In the connector H, the switching relay 217, upon energizing, establishes a locking ,ture 197 of relay 176 and its back contact for purpose which will appear subsequently. in the connector H, ringing current is-now intermittently applied to the line of the substation fl unti an answer is obtained. When this occurs a circuit is completed over the called subscribers line for the ring cut- 05 relay 214. Upon energizing, this relay establishes a locking circuit for itself at arinature 238, at arniatures 23? and 239 opens the ringing circuit and at the front contact of these armatures finally completes the talking connection.

lVhen the ring out off relay 214 energizes adirect nietalliccircuit extends from the back bridge relay of theconnector H in the main exchange. to the substation A. The current flowing over this circuit serves to energize the relay 1? 9 in the cord circuit 0. Relay 1Y9, upon energizing, opens the circuit of the called supervisory lamp L. thereby notifying the attendant'operator that the called subscriber has answered and closes the circuit of the slow acting relay 280 at armature 282. Upon operating relay 280 prepares a circuit for relay 176 at armature 281. The conversation may now be carried on over the heavy talking conductors between the subscriber in the main exchange and the subscriber at substation A, battery being supplied to the subscriber in the main exchange from the windings of the line relay 16 of the connector H and to the called subscriber at substation A in the private automatic exchange from the windings of the back bridge relay 15 of the connector H.

At this point it will be convenient to describe the operation of the local connector H when it operates to select an idle line in a group of lines. In order to arrange the connector H tov give this class of service two test wipers are provided. In order to enable the switch to discriminate between private and rotary busy lines the testcontacts of the latter engaged by the two test wipers must be tied together and those of the last trunk by the test wiper 259 as well asthe test Wiper circuit is now completed extending from the grounded test contact engaged by the back test wiper 259, over said test wiper,

contact and armature 2219 armature 253 and its back contact, back contact and armature 221, armature and its front contact, through the winding of the stepping relay 212 and thence through the winding of the slow acting relay 213 to battery. 'Iherelay 212 and 213 are energized over this circuit. Relay 2153, upon energizing, again connects the test wiper 260 to the test relay 215 at arinati'ire 235. Relay212, upon energizing, establishes a lockin circuit for itself and relay 213 at armature and at armature 234 completes the circuit of the rotary magnet 220. I Magnet 220 operates to rotate the switch wipers 258 261, inclusive, into engagement with the next set of bank contacts in the selected group, and at armature 221 opens the locking circult of the relays 21.2 and 213 Upon deenergizing,

relay 212 opens a circuit ofthe rotary magnet 220 which deenergizes also. If this next trunk line is not the last one of the group and is busy the test relay 215'wi11be maintained energized and the stepping relay 212 will operate as before. The alternate operation of the stepping relay 212 and the magnet 220 continues until an idle line is found or unt l the switch wipers are rotated intoassociation' with the last trunk line of the group. If this ls'busy also test relay 215 will'be maintained energized. However. no circuit will be completed for the stepping relay 212 and as ground is not present on the test contact engaged by the upper test wiper 259 the rotation of the switch ceases and a busy tone is given to the calling sub. :ber. In casethe connector His rotated into engagement with an idle trunk line the operation proceeds as before described.

Referring back to the description of the eX-. tension of the connection, when the conversation is terminated both the subscribers will r iplace their receivers upon their respective switch hooks. leasing operation in detail it will be assumed that the called subscriber at substation A replaces his receiver before the calling subscriber in the main exchange. When the receiver is replaced at substation A the circuit of the supervisory relay 179 in the operators cord circuit 0 is opened and this relay deenergizes. Upon retracting its armatures, a circuit is closed for the lamp L in. order to notify the operator that the called subscriber has re placed his receiver and at armature 282 the circuit of the slow acting relay 280 is opened and before the deenergization of this latter In order to describe the rerelay an impulse of current is sent over a path extending from ground by way of the said armature'and its back contact, armature 281 and its front contact, and through the winding ofrelay 176 to battery. Relay 176, upon operating, at its armature 181 disconnects ground from the sleeve of the plug P, at the front contact of this armature estab-' lishes an auxiliary circuit for the sleeve re lay 175,at armature 182 establishes .a locking circuit for itself, opens the circuit of the line relayQlO of the incoming connector switch H at armature 197 and at

armatures

184 and 183 disassociates the cord circuit 0 from the jack J. a As a result of this'latter operation the circuit of'the back bridgejrelay 15 in the'connector H atthe main exchange is opened. Upon retracting its armatures relay15 restoresthe normal flow of currentover the cOnductorslO and 12 of the incoming trunk line and at armature 32 opens the circuit of the slow acting relay 33. After the deenergization' of relay 15 and before the deenergization of relay 33 an impulse of current is sent over a circuit extending from ground byway of armature 32and its back contact/front contact and armaturefit, and through the winding of the relay 25 to battery. A circuit in multiplewith the above'is completed for the'slow acting relay 29. The operation of relay 29 at this time serves merely to remove one ground connectionfrom the release trunk conductor; 11; 'Upon energizing, relay 25 at its armature 5 9 establishes a locking circuit for itself and relay 29 to ground on conductor 51 and at armature 28 1 opens the circuit of the slow acting'relay 1'1. The operation of the other armatures of relayf 25are Without function atthe present time. "Upon'the deenergization of the slow lactingrelay 17 ground is removed from the release trunk conductor 11 thereby opening a "holding circuit of the previously operated switches in the main exchange and the circuit of the re lease magnet 102 of the connector H is. pre-, pared. Immediately upon thefdeenergization ofthe relay 25 which takes place assoon as its a lockin circuit is opened bythe deenergization of the slow acting relay ITma 'net 102 operates to restore the connector F1 to its normal position in the usual manner. v

Returning now'to the description of the circuit operationsin the private automatic exchange theresults occasioned by thedisconnection of ground fromthe sleeve of the plug P will now] be considered]v When ground is disconnected from the sleeve ofplug the circuit of the relay 151 in the trunk equip ment is-opened as is the ci rcuit of the visual 168. Relay 151, upon deenergizing, at its ar mature .16 1 again bridges the lower winding of the ring up. relayv 150. and the windings of the high resistance polarized relay 152 across the trunk conductors 140 and 141.; It will be understood that when the connector H in the tery flows in the oppositedirection to that supplied by theconnector H the polarized relay 152 in the trunk circuit at the private automatic exchange is energized. Upon attracting its armature, relay 152 opens the circuit of the slow acting relay 153. Upon deenergizing, the latter relay removes ground from their associated jacks.

the release trunk conductor 170 associated with the multiples of the incoming trunk line comprising conductors 140 and 141 in the banks of the local connector switches. The two way trunkline shown in the drawings may now be used for a call in either direction eventhough the plugP remains in the jack (1 and'the operator will be given full supervision in a manner which will be described subsequently.

It will be remembered thatrelay 17 6 in the cord circuit 0 also opens the circuit of the line relay 210 of the, incoming connector H; Upon deenergizing, this latter relay opens the circuitof the associated slow'acting relay 211. Uponretracting its armatures, the latterrelay opens certain locking circuits in the connector H" and closes the circuit of the release magnet 218. The release magnet 218 operates to releasejtlie connector in the'usual manner. I

The private automatic exchange operator upon noting the lighting of the lamp L will withdrawthe'plugs of the cord circuit from Upon the plug P reaching its normal position the locking circuit of the'relay 176 is opened and this relay.

deenergizes to 'open" the circuit of'the relay 175 and restore certain other circuits in'the cord circuit tonormal.

Adverting back to the description of the extended connection it will be assumed that the calling subscriber in the main exchange is the first to replacehis receiver. WVhen the receiver is replaced at the calling substation the circuit of the line relay 16 in the connector H is opened. This relay deenergizes and in turn opens the circuit of the slow acting release relay 17. Upon retracting its armatures the latter relay removes ground from the release trunkconductor 11 thereby allowing the preceding switches to release, at armature 37 opens the locking circuit of the various relays in the connector H and at armature 39 completes the circuit of the release magnet 102. Magnet 102 operates to'restore the circuit of the slow acting relay 17 8. After the deenergization of the polarized relay 177 and before the deenergization of the slowacting relay 178'an impulse of current is sent over a circuit extending from ground by way of armature 187 and its back contact front contact and armature 188, and through the winding of the relay 176 to battery. Relay 176 operates in the same manner as before to establish a locking circuit for itself at armature 182, to open at armature 197 the circuit of the line relay 210 of the connect-or H, to

open at armature 181 the circuit of the busy visual 168 associated with the trunk circuit and also that of relay 151 and at the front contact of this armature to establish another circuit for the sleeve relay 175; Another result ofthe'energization of relay 176 is that at

armatures

183 and 184 the cord circuit is disconnected from the trunk even though the plug P remains in the jack J. As the circuit of the line relay 210 of the incoming connector H is opened the release of the connector H takes place as before described. As the circuit of the relay 151 in the trunk equipment associated with the jack J is also opened by the operation of relay 176 this relay will deenergize to again connect the lower winding of the ring up relay and the windings of the high resistance polarized relay 152 across the trunk conductors 140 and 141. The polarized relay 152 is immediately energized and operates to'open the circuit of the slow acting relay 153. The latter relay deenergizes after ashortinterval and again renders the multiples of the trunk line accessible in the local connector switches by removing ground from the release trunk conductor 17 0. The trunk line comprising conductors 140 and 141 is now free and may be used for calls in either direction even though the plug P remains in the jack J and the ordinary supervisory call signal operates just the same as if the plug P were out of the jack.

T In response to the lighting of the supervisory lamps L" and L the operator will withdraw the plugs of the cord circuit from the jacks J and J as before described. When the plug P reaches its normal posi ion the plug seat switch PS is operated and the locking conductors 140 and 141 may still be used for calls in either direction as has already been indicated. The operationunder these conditions will now be described. y

it the trunk line is again seized in the main exchange the polarized relay 152 is energized to busy the trunk line to the local switches in the private automatic exchange and the ringing current impressed upon the trunk line operates the ring up relay 150' in the same manner as before. Relay 150 looks itself energized and closes the circuit of the supervisory lamp L. Under these conditions the opera f has only to operate the listening'key K in order to answer the call. By this operation the cord circuit is associated with the BI'UILK as t e locking circuit of the relay 176 is opened and all circuits are now in the same. condition cs it the operator had answered th call by plugging into the ack.

Should the trunk line be seized for an outgoing call from the private automatic to the main exchange ground will be placed upon the conductor 170 by the local connector selector repeater thereby energizing the relay 151 of the trunk circuit in multiple with the busy visual 168. The operation of the visual 168 serves to notify the operator that the trunk line is being used for an outgoing call. Relay 151 operates to remove the lower winding of the ringup relay 150 and the high resistance polarized relay 152 from bridge of the two trunk conductors 140 and 141. The line relay 123 of the line switch C associated with the seized trunk line in the main exchange is immediately energized via a direct current bridge in the connector selector repeater and operates to close the circuit of the switchinglrelay 121 in series with the motor magnet 125. It will be noted that the test Wiper 143, is normally connected through .a back contact on switching relay 121 to a point in the above circuit midway between the switching relay and the motor magnet. Thus it will be seen that as soon as the trunk line with which the switch wipers ot the line switch G are associated becomes busy the ground potential on the test contact engaged by test wiper 143 causes the operation of the motormagnet 125. Thus it will be seen that the wipers of the line switch are alwaysassociated with an idle trunk line or else are being operated in search of one. That is, the rotary line switch C preselects its trunks.

Returning now to the operation of the line switch C when the trunk line comprising conductors 140 and 141 was seized in the private automatic exchange the line relay 123energizes as before described and closes the circuit of the switching relay 121. The latter relay, upon operating, extends the seized trunk conductors to the line relay of the selected first selector at armatures 126 and 129, at'armature127 opens a point in the circuit of relay 124 and at armature 128' prepares a holding circuit for itself. The subsequent operations wherein the connection is extended to the desired called line in response to the digits dialled, by the calling subscriber in the private automatic exchange takes place in the usual manner. I I

The attendant operator sometimes'finds it desirable to extend connections to the main exchangefor certain subscribers in the pri vate automatic exchange In order to" enable her to do this when the plug of a cord circuit is placed in the jacket an idle trunk line a calling out key suchas key K in the cord circuitO is provided in all the cord circuits. The operation will now be briefiydescribed when the operatordesires to extend a call to a subscriber in the main exchange. i/Vhen the operator inserts the plug of an idle cord circuit into the jack of an idle trunk line, the plug P intothe jack J for example, a circuit is completed for the relay 151 over the sleeve of acord'circuit in multiple'with the Visual 168. Relay 151 operates to remove the ring up relay 150 andthe high resistance polarized relay 152 from bridge of the trunk conductors 140. and 141 as before described. Relay 152 immediately retracts its armature as its circuit is now open. However, its operation is ineffective at the present time to close a circuit of the slow acting relay 153.. ,The multiples of the trunk line comprising conductors 140 and 141 in the banks of the local connector switches are busied by ground through the winding of the low resistance relayf'l? 5 over a circuit extending from ground through the winding of relay 175, normally closed springs controlled by armature 181, sleeve of plug P, sleeve of jack J, back contact and armature 167 to release trunk conductor 170. It the operator plugs into the jack with the key K thrown the calling device CD is bridged across the conductors 140 and 141. This occurs in the following manner: When the key K is operated the relay 190, is energized.

Upon operating, this relay atits armature 191 bridges the calling device "across the trunk circuit over the circuit extending from conductor 140, tip of plug P, working contact of spring 197 and the said spring, springs of release key K impulse springsof the calling device CD, front contact and ar mature 191, right hand winding of the repeating coil associated with the operatofis head set, spring 149 of key K and its working contact, ring of fplug P, ring of jack J, to trunk conductor 141. Line relay 123 is immediately energized over this circuit and the line switch C operates to extend the connection to a preselected first selector switch. Should the operatorplug in the jack with the key K normal the linerelay 123 of the line switch G would be energized in series with the lower winding ot electropolarizing I i relay 177 of the cord circuit 0. However, the polarized relaywould not be operated at this time as the current in its polarizing winding opposes the current in its other winding it being of course understood that when the plug P was placed'in the jack J relay 17 5 operated to energize the polarized winding of'rela'y 17 7 and to light the supervisory lamps L and L In response to the digits dialled by the attendant'operator in the private automatic exchange a series of automatic switches in the main exchange are operated to extend the connection to the desired called subscribers line in a wellknown manner. when the connection is completed theattendantoperator will restore the key K to normal. When the called subscriber answers the normal current flowis reversed over the trunk conductors 140 and 141 and the electropolarized relay 177 in the cord circuit O is operated to ettace the supervisory lamp L thereby notifying the attendant that the called subscriber has answered. The attendant operator will now 7 has asked her to. establish theconnection.

The operation in the establishment of a local connection has already been described and will be readily understood. Then the subscriber in the private automatic exchange answers the attendant is informed of this fact by the effacement of the supervisory lamp L which occurs upon the 'energization of the relay17 9. If the subscriber in the private automatic exchange replaces his receiver before the called subscriber in the main office, the relay 179 is deenergized, the supervisory lamp L lighted the local incoming connector such as H released; and the trunk line freed for use as before described, Should the called subscriber in the main exchange be the first to replace his receiver the normal current flow is again restored over the trunk line comprising conductors 140 and 141 and the electropolarized relay177 will be deenergized thereby lighting the supervisory lamp L to notify the operator that the called subscriber has replaced his receiver and opening the circuit of the slow acting relay 178 and closing the circuit of the relay'17 6. As before, relay 176 operates to establish a locking circuit for itself, to remove ground from the sleeve of the ackJ and to disassociate the cord circuit from the trunk line. As there is now no bridge across thetrunk conductors 140 and 141 the operated switches in the main exchange are released in the usual manner and the two way trunk line is rendered accessible for calls in either direction in the same manner as before described. Another result of the energization of relay 176 is that the local connector switch which has been used to establish the connectionto the party in the private automatic exchange is released in the same manner ashas already been described. Upon noting the operation of the two supervisory lamps L and L the at- T tendant operator will withdraw the plugs of the cord circuit 0 from the jacks J and J.

lVhen the plug P reaches its normal position the plugseat switch PS is operated and the locking circuit of the relay 176 of the cord circuit is opened. Upon deenergizing, this relay opens the circuit of the sleeve relay 17 5 and restores certain other circuits in the cord trunk line becomes either'open or grounded it isautomatically made busy at both ends and an alarm signal given to the exchange attendant in the main exchange. It will be noted that the energizing circuit for the high resistance polarizedrelay 152 includes the line relay 123 of the line switch C associated with the trunk line in the main exchange and also the right and left hand windings of the shunt field relay 122. The construction of the relay 122, is similar to that of the relay 21 in the connector H already desClibed. The relays 122 and 152 are energized over this circuit. However the line relay 123 remains inoperative due to the high resistance of the polarized relay 152 and the shunting effect of the relay 122. Now should the trunk circuit become openedrelays 122 and 152 will deenergize. Relay 152 upon deenergizing, closes the circuit of the slow acting relay 153. The latter relay operates to place a busy potential upon the multiples of the trunk line in the banks of the local connector switches thereby preventing it being seized by a subscriber in the private automatic exchange. Relay 122 upon deenergizing opens the circuit of line relay 123 at its armature 145, and its armature 130 closes the circuit for the lower winding of the relay 124; It will be seen that the relay 124 is slow to energize but quick to deenergize as itsupper winding is normally short circuited by armature-138 and its back contact. After a short interval relay 124 energizes and, upon operating, establishes a locking circuit for itself at'armature 133 to ground on common conductor 148, places ground upon the multiple test contacts such as 107 in the banks of the rotary connector switches and at armature 132 closes the circuit for an alarm in series with the lamp L tonotify the attendant that one of the interconnecting trunk lines is in trouble. The lamp L is individual to the trunk lines extending to one private automatic exchange and serves to inform the attendant in what group of trunk lines to look for the trouble.

hen

, claims.

is now in good condition the relay 122 will now be energized'to preparethe circuit of the line relay 123 and to open the circuit of the relay 124. II" the ;trunk line should become groundedon either conductorthe left hand coil of the relay 122 will be short circuited and this relay will he ydeenergized thereby opening a circuit of the line relay 123 sothat it does not energize at thistime atarmature 145 and at armature 130 completesthe circuit for the. slow to operate relay 124. Since relay 122 is disconnected from both trunk conductors 140 and 14:1, inthe manner previously described, current fiow to the polarized relay 152 is cut oil regardless of which trunk -conductoris grounded and this relay therefore deenergizes to busy the trunk line to the local connector switches in the private branch exchange in the same manneras if the trunk were open. Otherwise the operations arethe same as have already been described. L v

Returning now to the "connector Hit will be remembered that when the connector switch automatically rotated until its wipers were associated with the last trunk line of the group and, if this trunk line is idle, the relay .20 energized. Thisr'elay operated to reverse the,connections ofthe ring cut-off and back bridgerelay with respect to the switch wipers. The reason for this will now become apparent inasmuch as the normal conductors extending from the line switch to the connector banks in the case of the last lines in a groupare not reyersedas in rotary lines therefore the wipersof the connector switch must be connected inthe opposite manner so as to properly operate the polarized relay 152 in the trunk circuits at the branch exchanges and the electropolarized relay 177 inthe cord circuit. By the operation of relay 20 this result isv secured the sameas it the normal conductors extending from the line switch to the normalconnector banks are reversed. I I

The features of the invention having been fully described what is considered to be new and desired to have protected by Letters Patent will be pointed out in the appended What I claim as y invention is In a telephone system, a twoway trunk line interconnecting two exchances, automatic changes I switches in each exchange having access to said trunk line and means operative automatically'responsive to said trunk line becoming open for rendering it inaccessible to said antomatic switches in both exchanges.

2. In a telephone system, a two way trunk line interconnecting two exchanges, automatic switches ineach exchange having access to said trunk line and means operative automatically responsive to said trunk line becoming grounded for rendering it inaccessibleto said automatic switches in both ex- 3. Ina telephone system, a two way trunk line interconnecting two exchanges, automatic switches in each exchangehaving access to said trunk line and means operative automatically responsive to said trunk line hecoming'open vfor signalling an attendant at one of said exchanges. 1

4.. Ina telephone system, a two way trunk line interconnecting two exchanges, automatic switches in each exchange having access to said trunk line and means operative automatically responsive to said trunk line becoming grounded for signalling an attendant at one of said exchanges.

5. In a telephone system, .a two way trunk' line interconnecting two exchanges, automatic switches in each exchange having access to said trunk line and means operative automatically responsive to said trunk line becoming open or grounded for rendering it inaccessible to automatic switches in both exchanges. I i

6. In a telephone system. a twoway trunk line interconnecting two exchanges, automatic switches in each exchange having access to saidtrunk line and means operative automatically responsive to said trunk line becoming open or grounded for signalling an attendant circuit operative when said calling line is disconnected fromsaid trunk line for disconnecting the called line from said cord circuit.

9. In a telephone system, a trunk line. means for connecting a calling linewith said trunk line, means including an operators cord circuit for connecting said trunk line with a called line,and means controlled from said calling line for disconnecting sai'd called line from said cordcircuit. I

10. Ina telephone system, a trunk line, means for connecting a calling line with said trunk line, means including an operators cord circuit forconnecting said trunk line with a called line, and means including a relay controlled from said calling line for disa calling line, automatic switches controlled from said calling l ne for seizing saidv trunk line, an operators cord circuit for connecting said trunk line to a called line, andmeans controlled from said called line independent of said calling line for disconnecting said cord circuit from said called line. 7

13. In a telephone system, a trunk line,,a calling. line, automatic switches controlled from said calling line for seizing said trunk line, an operators cord circuit for connecting said trunk line to a called line, and means controlled from said calling line tordisconnecting saidcalled line'from said cord circuit.

14. In a telephone system, a calling line, a trunk line, automatic switches controlled from said calling line forconnecting with said trunk line, means including an operators cord circuit and automatic switches for connecting said trunk line with a'called line, and means controlled from said called line for releasing all of said automatic switches a trunk line, automatic switches controlled from said calling line "for, connecting with 7 said trunk line, means including an opera-v tors cord circuitand automatic switches for connectingsaid trunk linewith a called line,

meanscontrolled from said called line for{releasing all said automatic switches used in said connection, and means controlled by the release of said switches for rendering said trunk line accessible to be used for another call even though said cord circuit remains associated with said trunk line.

17. Ina telephone system, a calling'line,

.a trunk line, automatic switches controlled from said calling line for connecting. with said trunk line, an operators cord circuit for connecting said trunk line to a called line, a disconnect signal at said cord circuit, circuitconnections controlled by the release of said all automatic switches when the, calling line is disconnected for reversing the flow of current over said trunk line and a relay in said cord circuit responsive to said current reversal to control said signal.

18. In a telephone system, a calling line, a trunk line, automatic switches controlled from said calling line for connecting with said trunk line. anoperators cord circuit for connecting said trunk line to a called line, a signalling circuit, circuit connections for releasing said automatic switches and for re- Versing the flow of current over said trunk line when the receiver is replaced at the called substation and arelay in said cord circuit responsive to said current reversal to control said signal. V

19 In a telephone system, a calling line, a trunk line, an operators position, automatic switches controlled from said calling line for connecting with said trunk line, a signal at said operators position responsive to such means controlled from said called line for releasing said automatic switches to render said trunk line accessible to other calls, and means operative when said trunk line is again seized even though said .cord circuit remains asso ciated with said trunk line for operating said signal.

20. In a telephone system, .a trunk line terminating in c an automatic switch, other automatic switches accessible thereto, an operators position, means controlled by the operator at said position for seizing said trunk line and for operatingthe firstmentioned switch anda series of said other switches to extend a connection to a called line, means controlled only by said operator for releasing said switches, a calling line, means controlled from said calling line for seizing said trunk line and for operating said first mentioned switch and a series of said other switches to extend a connection to another called line, and means controlled from said other called line for releasing said connection.

21. In a telephone system, a trunk line terminating in an automatic switch, other automatic switches accessible thereto, an operators position, means controlled by the operator at said position for seizing said trunk line and for operating the first mentioned switch and a series ofsaid other switches to extend a connection to a called line, means controlled only by said operator for releasing said switches, a calling line, means controlled from said calling line for seizing said trunk line and for operating said first mentioned terminating in an automatic switch, other automatic switches accessible thereto, an op erators position, means controlled by the operator at said position for seizing said trunk line and for operating the first mentioned switch. and a series of said other switches to extend a connection to a called line, means controlled only by said operator for releasing said switches, a calling line, means controlledfrom said calling line for seizing said trunk line and for operating said first mentioned switch and a series of said other switches to extend a 'connectionto another called line, and means controlled from either the calling or said other called line for releasing said connection.

23. In a plug ending cord circuit for connecting two lines, a relay for opening the talking circuit through said cord circuit, and means responsive to the replacement oi the receiver on either connected line for energizing said relay. I

24. In a plug ending cord circuit for connecting a calling and a called line, a relay for opening the talking conductors and a sleeve conductor of said cord circuit, and means responsiveto the replacement of the receiver on the called linefor energizing said relay.

25. In a plug ending cord circuit for connecting two lines, a relay for opening the talking circuit through said cord circuit, means responsive to the replacement of the receiver on one of the connected lines for transmitting a momentary impulse to energize said relay, and a locking circuit for holding said relay energized.

26. In a plug ending cord circuit for con-,

necting two lines, a relay for opening the talking circuit through said cord circuit, means responsive to the replacement of the receiver on one of the connected lines for transmitting a momentary impulse to energize said relay, a locking circuit for holding said relay energized, and means responsive to the manual restoration of the cord to normal for opening said locking circuit.

27. In a plug ending cord circuit for connecting two lines in which each plug has a sleeve contact in addition to the two talking contacts, said cord circuit comprising circuit arrangements wherebyelectrical potentials are maintained on said sleeve contacts while the cord circuitis in use, a relay for removing said potentials, and means responsive to the replacement of the receiver on either connected line for energizing said relay. a v 28. In a plug ending cord circuit for connecting two lines in which each plug has a sleeve contact in addition to the two talking contacts, said cord" circuit comprising circuit arrangements whereby electrical potentials are maintained on'said sleeve contacts while the cord circuit is in use, a relay for removing said potentials, and means. responsive to the replacement of the receiver on one of the connected lines for energizing said relay,

' Y 29'. In a plug ending cord circuit for connecting two lines in which each plughas a sleeve contact in addition to the two talking contacts, said cord circuit comprising circuit arrangementswhereby electrical potentials are. maintained on said sleeve contacts while the cord circuit is in use, a relay for removing said potentials, means responsive to the replacement of the receiver on one of the connected linesfor transmitting a momentary impulse to energize said relay, and a locking circuit for holding saidrelaynergized. w I 30.,In a'plug ending cord'circuit for connecting two lines in which each plug has a sleeve contact in addition to the two talking contacts, said cord circuit comprising circuit arrangements whereby electrical potentials are maintained on said sleeve contacts while the cord circuit is in use, a relay for removing said potentials, means responsive to the replacement of the receiver on one of the connected lines for transmitting a momentary impulse to energize said relay, a locking circuit for holding saidrelay energized, and means responsive to the manual restoration of the cord to normal fOI'LOPGlling said locking circuit. I I I 31. In a telephone system, means including a cord circuit for connecting two lines, means outside the said cord circuit for supplying talking current to the connected lines, the talking current to the called line flowing over the two strands of said cord circuit in series, means controlled by the calling party for reversing the direction of the flow of talking current to the called line,and means in said cord circuit responsive to the saldvreversal,

for-opening the talking circuit at said cord circuit. M

32. In a telephone system, means including a cordcircuit for connecting two lines, means outside the said cord circuit for supplying talking current to the connected lines, the talking current to the called line flowingover the two strands of said cord circuit in series, means controlled by the calling party for reversing the direction of thesflow of talking current to the called line, means in said cord circuit for maintaining both connected lines in busy condition, andmeans in said cord circuit responsive to said reversal for render:- ing saidbusy means inefi'ective.

33.; In a telephone'system, means including a cord circuit for connecting two lines, means outside the said cord circuit for supplying talking current to the connected lines, the

- talking current to the called line flowing over the two strands of said cord circuit in series, means controlled by the calling party for ,re-

versing the direction of the flow of talking current-to the called line, and means in said cord circuit responsive to the said reversal for opening the talking circuit at said cord circuit, said last means including apolarized relay bridged across the talking strands of said-cord circuit. 34. In a telephone system, means includlng a cordcircuit for connecting two lines, means outside the said cord circuit for supplying talking current to the connected lines,

the talking current to the called line flowng over the two strands of said cord circuit in series, means controlled bythe calling party for reversing the direction of the flow of talking current toithe called line, means in said cord circuit'for maintaining both connected lines in busy condition, and means in sald'cord circuit responsive to'said reversal for rendering said busying means ineffective, sa d last means including a polarized relay bridged across the talking strands of said cord circuit. 7

35. In a telephone system, a cord circuit for connecting two lines, means in said cord circuit for maintaining certain potentials on the jacks of the connected lines to make them busy, a relay in said cord circuit through which talking current is supplied to one of the connected lines from a point in thetalking connection between the cord circuit and the other connected line, and means responsive to the deenergiz'ation of 'saidvrelay for removing said busy potentials.

36. In a telephone system, a cord circuit for connecting two lines, means in said. cord circuit for maintaining Certain potentials on the jacks of the connected lines to make them busy, a relay in said cord circuit through which talking current is supplied to one of the connected lines from a point in the talking connection between thecord circuit and V the other connected line, and means responsive to the deenergiz'ation of said relay for removing said busy potentials and for opening the talking strands of said cord circuit. 37, In a telephone system, a main exchange, a branch exchange, a trunk line connecting said exchanges, means including said trunk line and a series of automatic switches in the main exchange for extending a call from a calling party in the main exchange to the branch exchange, a plug ending cord circuit in the branch exchange, means including said cord circuit and a local trunk line and automatic switch in the branch exchange tor-completingthe connection to the called line, and means under the control of either the calling or called party for releasing all said switches.

38. In a" telephone system, a main ex-, change, a branch exchange, a trunk line connecting said exchanges, means including said trunk line and a seriesfof automatic switches in the main exchange for extending ing cord circuit in the branch exchange, means including said cord circuit and a local trunk line and an automatic switch in the branch exchange for completing the connection to the called line, and mcansunder the controlof either the calling or called party for opening the talking circuit at said cord circuit.

39. In a telephone system, a main exchange, a branch exchange, a trunk lineconnecting said exchanges, means including said trunk line and a series of automatic switches in the main exchange for extending a call from a calling party in the main exchange to the'branch exchange, a plug ending cord circuit in the branch exchange, means including said cord circuit and a local trunk line and an automatic switch in the branch exchange for completing the connection to the called line, and means under the control of either the calling or called party for opening the talking circuit at said cord circuit and for restoring all of said switches to normal.

40. In a' telephone, system, a main ex-- change, a branch exchange, atrunk line connecting said exchanges, means including said trunk line and a series of automatic switches in the main exchange for extending a call from a calling party in the main exchange to the branch exchange, a plug ending cord circuit in the branch exchange, means including said cord circuit and a local trunk line and an automatic switch in the branch exchange for completing the connection to the called line, and means under the control of' the calling party for releasing all said switches. p

41. In a telephone system, a main exchange, a branch exchange, a trunk line conin the main exchange for extending a call from a calhng party in the main exchange too necting said exchanges, means including said trunk line and a series of automatic switches to the branch exchange, a plug ending cord circuit in: the branch exchange, means including said ,cord circuit and a local trunk line and an automaticswitch in the branch exchange for completing the connection to change, and means underthe control 0t either the calling or called party for releasing all said switches;

the called line, means for supplying talking current to the called line from the main ex- 42. In a telephone. system, a main ex- W change,a branch exchange, a trunk line connectingsaid exchanges, means including said trunk line'and a series ofautomatic switches in the main exchange for extendlng a call from a calling party, in the mainexchange to the branch e'xchange,a plug ending cord circuit in the, branch exchange, means including said cord circuit and a local trunk line and an automatic switch in the branch exchange for completing thevconnection to the called line, means for supplying talking curill) rent to the called line from the main exchange, and means under the control of the called party for opening the talking circuit at said cord circuit.

48. In a telephone system, a main exchange, a branch exchange, a trunk line connecting said exchanges, means including said trunk line and a series of automatic switches in the main exchange for extending a call from a calling party in the main exchange to the branch exchange, a plugending cord circuit in the branch exchange, means including said cord circuit and a local trunk line and an automatic switch in the branch exchange for completing the connection to the called line, means for supplying talking current to the called line from the main exchange, and means under the control of the calling party for opening the talking circuit at said cord circuit.

44. In a telephone system, a trunk line, means for connecting a calling line with said trunk line, means including an operators cord circuit for connecting said trunk line with a called line, and means in said cord circuit operative responsive to the hanging up of the receiver of the calling line for disconnecting the calling and called lines from said cord circuit.

45. In a telephone system, a trunk line, means for connecting a calling line with said trunk line, means including an operators cord circuit for connecting said trunk line with a called line, and means controlled from said called line independent of said calling line for disconnecting said called line from said cord circuit.

d6. In a telephone system, a trunk line, means for connecting a calling line with said trunk line, means including an operators cord circuit for connecting said trunkline with a called line, and means controlled from said called line for disconnecting said calling and called lines from said. cord circuit.

47. In a telephone system, a cord circuit for connecting two lines, means included in said cord circuit for maintaining both connected lines in busy condition, and means including a relay in said cord circuit controlled from one or said lines by current supplied to the talking connection at a point outside said cord circuit for removing the busy condition even though said cord circuit has not been disconnected.

48. In a telephone system, a cord circuit for connecting two lines, means included in said cord circuit for maintaining both connected lines in busy condition, and means included in said cord circuit controlled from either one of said lines for removing the busy condition even though said cord circuit has not been disconnected.

49. In a telephone system, a calling and 21 called line, a cord circuit, means for extending said calling line to said cord circuit, a

jack adapted when connected to said cord circuit to extend the calling line to said called line, means included in said cord circuit for maintaining the called line in busy condition, and means included in said cord circuit and controlled from said called line for removing the busy condition even though said cord circuit remains connected with said jack.

50. In a telephone system, a callingand a called line, a cord circuit, means for eXtending said calling line to said cord circuit, a jack adapted when connected to said cord circuit to extend the calling line to said called line, means included in said cord circuit for maintaining said calling and called lines in busy condition, and means included in said cord circuit controlled from either said calling line or said called line for removing said busy condition even though said jack remains connected with said cor-d circuit.

51. In a telephone system, a calling and a called line, a cord circuit, means for extending said calling line to said cord circuit, a jack adapted when connected to said cord circuit to extend the calling line to said called line, means included in said cord circuit for maintaining said calling and called lines in busy condition, and means included in said cord circuit controlled from said called line for removing said busy condition even though said jack remains connected with said cor-d circuit.

52. In a telephone system, a calling and a called line, a cord circuit, means for ext-ending said calling line to said cord circuit, a jack adapted when connected to said cord circuit to extend the calling line to said called line, means included in said cord circuit for maintaining said calling line in busy condition, and means included in said cord circuit controlled from said called line for removing said busy condition even though said jack remains connected with said cord circuit.

53. In a telephone system, a calling and a called line, a cord circuit, means for extending said calling line to said cord circuit, a jack adapted when connected to said-cord circuit to extend the calling line to said called line, means included in said cord circuit for maintaining said called line in busy condition, and means included in said cord circuit controlled from either said calling line or said called line for removing said busy condition even though said jack remains connected with said cord circuit.

54. In a telephone system, a trunk line and I a signal therefor, means for connecting a calling line with said trunk line and for operating said signal, means including an operators cord circuit for connecting said trunk line with a called line, means in said cord circuit operative responsive to the hanging up of the receiver of the calling line for disconnecting the calling and called lines from said cord cir-