USRE14411E - Feind - Google Patents

Description

. n. H. BURFEIND. Raissued Dec. 18, AUTOMATIC TELEPHONE SYSTEM. I

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APPLICATION FILED nov. 13.1017.

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flTTOR/VEXE UNITED STATES PATENT OFFICE. RAYMOND H. IUltFIlINI), CHICAGO; ILLINOIS, A S SIGNOB TO AUTOIVIATIC ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

AUTOMATIC TELEPHONE SYSTEM.

Specification of Reissued Letters Patent. Rpjss ed Dec, 18, 1917 Original No. I, 2S7,998, datcd August 21, 1917, Serial No. 775,067, filed June 21, 1913. Application for reissue 7 '0 all whom it may concern: I

Be it known that I, -RAYMOND H. BUR- FEIND, a citizen of the United States of America. and resident of Chicag0,'Co0k county, Illinois, have invented certain new and useful Improvements in Automatic Telephone Systems, of which the following is aspecification.

My mventlon relates to improvements 1n automatic telephone systems, and more particularly to an improved type of switch for use in such systems which is enabled not only to select an idle contact from among a group of such contacts, but is enabled to select an idle contact in any one of a number of such groups.

Heretofore, in connection with the selector switches which have been commonly employed, these selector switches were provided with a plurality of bank contacts, usually arranged in different levels, each level constituting a group. When the selector was raised to the proper level it then rotated automatically to select an idle trunk in that As there were usually but ten such level. trunks in one level, it will be seen that this automatic selection was confined to a comparatively small group oftrunks. It often appens that it is desirable to have a larger group of trunks any one of which can be employed in extending the connection, for instance, where a connection is extended to a manual operators position. An object of m invention is, therefore, to provide a switc which, if all the trunks in one level or group are busy, will automatically step to the next level or group and then automaticall select an idle trunk in this second group. can be automatically selected in this manner,

- and after the switch has found a group in 'mongroups are busy, means are then provided for giving the subscriber the usual busy signal.

A further feature of-my invention isits adaptationto what is known as a rotary connectorthatis, a connector which, on-

certain levels, is provided with means for automatically selecting one of a plurality of trunk lines anv one of which may be employed for extendmg the 00111160131011. Heref desired, two three or more groups.

filed November 13, 1917. Serial No. 201,87 9.

tofore, as in the selectors, this automatic selection has been confined to the terminals in one group or level, but by my invention I am enabled to increase the number of terminals which can be automatically selected by having the connectorautomatically step from one level or group to the next when all the terminals in one group are busy.

These and other objects of my invention to the accompanying drawings, in which I have illustrated diagrammatically an automatic telephone system of a particular type embodying the novel features of my invention. 7

Figure 1 is -a diagrammatic layout of a telephone system in connection with which I have chosen to illustrate my invention.

Figs. 2 and 3taken together show a complete connection established through automatic switches embodying the principles of my invention, with a trunk line leading to a manual or private branch exchange such as shown at WV in Fig. 1.

Fig; 4 is a detail view showing a. portion of the selector auxiliary bank of contacts.

'Fig. 5 is a' sectional view taken on the line 5-5 in Fig. 4.

Fig. 6 is a detail view of a portion of the connector bank contacts.

The telephone system illustrated in- Fig. 1 comprises an automatic exchange M and a manual exchange or exchanges \V. The manual exchanges are represented by manual 'switchboards W and W and are provided with suitable cord circuits N and N for establishing connection between said manual exchanges W and the automatic exchange M. It is thought unnecessary to explain in detail the operations of the manual apparatus used in this system, as they are generally well known. The automatic exchange M is of a well-known type, comprising subscribers individual switchcs,.first selector switches, second selector switches and connector switches. Inaddition to the usual connectors, the system is also provided with a plurality of connectors which are adapted to select trunks leading to the manual exchangcs W. In the drawings there are represented, on a scale of three to ten, two of the thousands of an exchange of ten'thousand lines capacity. The automatic subscribers substations are divided into groupswill be more clearly understood by reference are multipled together. .All of the tenf 1, A, etc., usually of one hundred lines each. On a scale of three to ten, therefore,

i the three groups A, A and A represent one complete iousand and the groups A, A and A represent another thousand.

The selector and. connector switches represented herein comprise banks of contactsarranged in horizontal rows or levels, usually tenin number. These levels are represented byh'oriiontal lines which extend beneath all the switches of a group to indicate that the corresponding contacts of all of the switches bank levels of the first selectors are represented," while the'banks of the second selectors and connectors are shown on a scale of such as the" selectors E.

three to ten. All of the line switches belonging to one group of subscribers lines (the line switches C, for'example) have common access to a group of first selectors,

,The bank con- 3 tacts of the. first'selectors E, E", etc., of

corresponding groups or hundreds are multi led throughout. the different thousands. The first levels 'of'these first selectors are connected to trunk lines. leading to second selector switches associated with the first thousand, the second levels of the first selectors arerconnected to-trunk lines leading to the second selectors associated with the second thousand, and the third level is connected to trunk'lines leading to the third thousand (not shown).

As'shown in the drawings, the fourth, fifth, sixth and seventh levels are'multipled together and 'extend to a plurality of connector switches shown at, H. The connectors H in turn have access to the trunk lines leading to the manual board W. 8, 9 and 10 are also multipled together and extend to a plurality of connectors shown at H, which connectors have access to trunk lines leading to the manual board W. It will be understood, of course, that the number of levels that I show connected to the manual board is arbitrary and may be changed to suit the requirements. The. bank contacts of all the second selectors associated with a given thousand are multipled together and the first'level is connected to trunk'lines leading to the connector switches which haveaccess to'the subscribers lines of the first hundred of'that'thousand. The

second level is connected to trunk lines leading to connectors which have, access to the lines of the second hundred of that thousand, etc.

The automatic substation AtFig. 2),- which we Wlll assume is in the group A,

comprises the usual receiver 2, transmitter 3,

I ringer 4 and condenser 5. Being an automatic substation it is also provided with a j suitable impulse-transmitting mechanism for controlling the automatic switches, which mechanism is represented diagrammatically The first selector 1 levels 7 by a pair of impulse springs and 7 and an impulse wheel 8, which latter may be controlled in a well-known manner, through the medium of a dial provided with' finger holes, in such a way that the impulse 5 rings may be momentarily separated a num er of times correspondin of the number of the called subscriber.

The subscribers individual switch C is of the general type of 'subscribers switch shown in British patent to R. W. James 'No'. 26,301 of 1906, being, however, of the particular type disclosed in British patent to T. G. Martin No. 1419 of 1910. This line switchcomprises, among other'details,

a plunger (not shown) attached to the end of a so-called plunger arm 9 which is controlled by the magnet 10. The magnet 10 comprises four windings, namely, a pull down winding 11, cut-o fi or holding winding 12, linewinding 13 and auxiliary winding 14. The core of the'magnet 10 is-so con structed that-the magnetic circuit of the windings 11 and 12 is separatesfrom that of the windin l3 and 14. The winding 11 operates both the plunger arm 9 and the armature 15, while the winding 12 is only strong enough to operate the cut-ofi armature 15 and to hold the plunger arm 9 in' its operated position after it has been opto the respective digits erated. When the plunger arm 9 is operated, the plunger is forcedinto the bank of contact springs, forcing the springs 16, 17, 18 and 19 into engagement, respectively, with the springs 20, 21, 22 and 23. Al-

1 though only one set of springs (16 to23) is shown, each line switch is providedwith a plurality of such sets, each set forming the terminal of a trunk line leading to a first selector switch E. Each trunk line is connected in multiple to the corresponding springs of all the line switches of the group which are controlled by the master switch D. The switch C is controlled by the subscriber through the medium of the line relay 13, as will be hereinafter more fully explained.

The masterswitch D is'of the same eneral type as that disclosed in British atent No. 26,301 of 1906, referred to above,

being, however, ofthe particular type disclosed in the above-mentioned British Patent No. 141901? 1910. The function of the master switch, as is well known, is to maintain the plungers of all the idle line switches .in position to engage the terminals of an idle trunk line.

p The first selectorswitch E. is of the general type of selector switch disclosed in United States Letters Patent No. 815,321, issued March 13, 1906, to Keith, Erickson and Erickson, the circuits being modified, however, to operate in a system embodying the principles of my invention. 'Among otherdetaals, theselector E comprises e bank of line contacts arranged in horizontal rows or levels,which contacts are adapted to be engaged by a set of wipers 25 and 27 carried upon a shaft, (not shown) which has a vertical movement controlled bythe vertical magnet 28 and a rotary movement controlled by the rotary magnet 29; There is also a bank of private contacts engaged by the private wiper 26 and a further or extra bank engaged by the extra wiper .72. The operations of the switch are controlled through the medium of thedouble-wound line relay 30. Means for. permitting the switchto be returned to normal position are provided in the release magnet 31, which,

upon energizing, withdraws the retaining pawls from the shaft, which is instantly returned to normal in the well-known manner. Normally open contact springs 32 and 33 are provided, which close only when the switch shaft has been raised one or more steps from its lowest position. The relays 34 and 35 are slow actmg-that is, they deenergize slowly after their energized circuits are broken. .Means for automatically interrupting the circuit of the vertical magnet 28 is provided in the relay 105, as will be hereinafter explained. In addition to the regular line bank contacts and the private bank contacts, together with the usual line and private wipers, the selector E is provided with an extra shaft wiper 71 and an extra set of bank contacts a, as shown in Fig. 2. .This extra bank of contacts consists of ten groups or levels, the same as the line and private banks, each group comprising;

ten pairs of contacts. The shaft wiper 71 rovided with a pair of wiping arms which engage with the two contacts of each pair and thus connect them together. In order to enable the switch to automatically step from one level to another, the corre-' w spending levels in this extra bank of contacts are wired in a particular manner. This conslsts in electrlcally connecting the bottom contact" of one set of bank contacts with the top contact of the next adjacent set, and so on, the bottom contact of the tenth or last set being grounded. When,

as in .the' present instance, it is desired to select an idle trunk from either the fourth, fifth, sixth or seventh levels, 'then the fourth fifth and'sixth levels of the extra set ofbank contacts would be wired in this 5 5 manner.

I also provide a series of contacts 71 (Fig. 2), there being one of these contacts for each of the levels 4, 5 and 6 that is, one for each level above which the wipers may be automatically raised, which contacts are adapted to be engaged bythe wiper 72 carried by the switch shaft. If it were desired to have not only the fourth, fifth andsixth levels so arranged, but also the' first, second and third, the contacts 71 would be adapted to be engaged by the wiper '72 after the switch shaft is operated vertically one step, the first rotary step disengaging said contacts. However, since only levels 4, 5 and 6 are so arranged, the contacts 71? are not engaged until the fourth level is reached. The wiper 71 is a short-circuiting wipcr that is, a wiper the function of which is to electrically connect the upper and lower contacts of any set in the extra bank upon which it may stop in the fourth, fifth and sixth levels. Therefore, it will be seen that if all the bank contacts of the fourth level,

for example, are in use, a ground potential willbe placed on the contact 71 opposite the .fourth level, said potential extending from ground G through the short-circuiting wipers 71 of different first selector switches which are resting on the fourth level, and through the connections between the lower contact of one, set to the upper contact of the next set, and thence to the contact 71. As shown in the diagrammatic drawing Fig. 1,the fourth, fifth, sixth and seventh levels ofthe first selector banks are multipled throughout the exchange and thence lead to the manual oflice connectors H.

. With the selectors constructed in this manner, they are enabled not only to auto matically select anidle trunk in the fourth level, but if all the trunks in. that level are busy, to automatically move upto the next or fifth level and find an idle trunk there, or if all the trunks inthe fifth level are busy, to automatically pass to the sixth level, etc. The connector switch H (Fig. 3) is of the same general type of connector switch as that disclosed in United States Letters Pat out No. 8 5,176, issued March 13, 1906, to Keith, Erickson and Erickson, the circuits,

however, being modified to adapt the switch to operate in a system in which the central office apparatus is controlled by impulses delivered over the 4 two sides of the line in series. The circuits are also modified to adapt the switch to operate in a system embodying the principles of my invention. Like the selectors, the connector is provided with a shaft (not shown) carryin the wipers 36, 37 -and 38. Being a so-calle rotary connector and of a partlculartype used to illustrate my invention, it'also carrie the extra wipers 37", 71" and 72.

rotary magnet 40, and the usual side switch comprising the wipers 41, 42, 43 and 44 is p The mag?- net 46' is the usual release magnet. The line relay 47 is connected to the line throu h the reversing springs of a so-called backridge relay 48. The ringingrelay 49 is the means by which ringing current is applied to the called trunk or line, as the case may be. At' 0 there is shown a busy signaling machine- The shaft is controlled by the vertical magnet 39 and the controlled by' the private magnet 45 in the, usual and well-known manner.

V which supplies a busy signal to the calling I having been line through the medium of the busy relay 120 in case the called line is in use. At B a battery is shown which is for the purpose of supplying battery current foroperating and talking urposes. The'connector is also provided w1th a special contact bank d, shown in Figs. 3 and 6, similar' to the bank a of the selectors. a j

A general description of the apparatus 'ven, 1t will be explained how a connection is extended from a calling substation A,the line of which we will assume terminates in the main exchange, to a called substation A, the line of which terminates in the manual exchange W. \Ve' will assume thenumber of the manual exchange to be 441. 'Upon the removal of the receiver from theswitch hook at the substation A preparatory to makin a call, an energizing circuit isclosed t rou h the line'winding 13 of the individual switch C, thereby attracting the line armature 51. upon being attracted, closes a circuit through the pull-down coil 11 in series with the auxiliary winding 14. The pull-down coil, upon energizing, attracts the plunger arm 9, therebyoperating to close circuits throu h the bank of springs 16' to 23, inclusive. t also operates the cut-off armature 15, thereby disconnecting the line winding13 from the line. The armature 51 does not fall back im: mediately, however, owing to the fact that the winding. 14 is still in series with the.

pull-down winding 11. Upon the plunger arm 9 being attracted, the springs 10 and l2 are brought together to short-ci'rcuitthe auxqiliary winding 14, thus permitting the armature 51 to fall back. This slow action of the armature 51 allows sufiicient time for a holdingcircuitto be closed in the switch ahead for the cut-ofl or holding winding 12., The engagement of the springs 16 and 19 with the springs 20 and 23, respectively, extends the subscribers lines to the line relay 30 of the selector E. The line relay 30 of the selector switch E is thereupon energized, closing a circuit through the relay 34. The relay 34, upon energizlng, closes the above: mentioned holding circuit 1 through the cutoil winding 12 of the 'line switch 0. This circuit extends from ground G through the springs 52, bank sprin 21 and'17, cutoil winding 12 to battery p unger arm 9 in their operated positions after the circuit of the pull-down winding ing ground potential is supplied to the conmotor or normal private bank contacts of the calling line by way of the conductor 24' as soon as therelay 34 is energized. This circuit extends over the circuit just traced to The armature,

thence through battery B to ground G. The winding 12, u on energizing, holds the armature l5 and the bank spring 17 thence over the normal conductor 24 to said private bank contact.

The energization of the relay 34 also pre-- pares a circuit for the vertical magnet by' bringing into engagement the springs 53 and 54 and opens the clrcuit of the release magnet 31 at the spring 55.

The calling subscriber now calling device for the first digit 4 ofthe called number, whereby the substation imoperates his pulse springs 6 and 7 are separated four times momentarily, each time breaking the' circuit of the selector line relay 30. The

relay 34 of the selector being slow] acting does not deenergize during the momentary interruptions of its circuit by the .line relay 30, and consequently each time the latter relay denergizes, an impulse is transmitted j over the circuit extending from ground G through the contact of springs 182 and 183, springs 57 and 56 of the relay 58, springs- 53 and 54 of the relay 34, through the relay 35 and the vertical magnet 28 to battery'B.

The vertical magnet receives four impulses;

over this circult and operates to raise the switch shaft and wipers four steps to a positionoppositethe fourth row or level of bank contacts. engages the contact. point 71 of the ourth level. The slow acting relay 35 is maintained in its energized condition while im% pulses are being sent'through the vertlcal' magnet, and in its energized condition this relay closes a. circuit .f-ronr ground G through the springs 68 and '67 and relay At the same time the wi er 7 2 66 to battery B. The relay 66. upon ener switch shaft is raised at least. one step, i

which 'is also true of the off-normal springs 32 and 33 that control the circuit of the release magnet131. This relay 66 controls in part the circuit of the rotary magnet 29 and is locked in energized position at the stage of the operation for the purpose of preparing the circuit over which the rotary magnet 29 is subsequently to be operated. As a result of the pause that follows the sending of the four impulses frointhe telephone, the

relay 35deenergizesand upon so doing 'permits the springslO! and 108 to close in contact, thereby closing a new circ u1t through the vertical magnet 28 for causing therswitch shaft to be automatically raised above the fourth level if all the trunks in that level are busy. These springs 107 and 108 maybe adjusted, if necessary,so that the springs 52, rotary magnet 67 and 69 come into contact. For example,

if all of the the trunks leadingfrom the fourth level are busy, a circuit will be found closed from ground G through the series of bank contacts, (the upper and lower contacts of each set being connected together by the wiper 71 of the switch using that particular trunk), contact 71, through the spring wiper-.72, springs 103 and 104, relays 105 and 106, springs 108 and 107 and the vertical magnet 28 vto battery B. The relays 105 and 106 and the vertical magnet 28 energize over the circuit just traced. The vertical magnet, upon energizing, operates to step the shaft and shaft wipers one step that is, to a point opposite the fifth level of bank contacts. The relay 105, upon'ener 'gizing, interrupts its own circuit at the springs 104, thereby allowing the vertical magnet to denergize. If the fifth level trunks are all in use, the spring 72 will again engage a grounded contact and the foregolngoperations will be repeated to step the shaft wipers to a point opposite the sixth level of bank contacts; Likewise, if the trunks leading from the sixth level are also busy, the shaft will be raised still another step. As the fourth, fifth, sixth and seventh levels were the only ones assigned to the connectors H which have access to the manual board W' the seventh level bank contact 71 will not be connected Therefore this contact will have no guarding ground potential, whereupon the relays 105 and 106 and the magnet 28 will all deenergize. During the rate, in order to insure against the relay 66 unlocking when the rotary armature separates the interrupter springs 59 should it do so before the private Wiper 26 has been rotated sufliciently to engage the first private bank contact. This circuit extends from ground G through the springs 52, 60 and 59, 61 and 62, 64 and 63, 67 and 69, 69 and 67", interrupter springs 70 and the rota ry magnet 29 to battery B. The rotarymagnet, upon energizing, rotates the wipers one step and by opening the springs 70 and the springs 59 and 00 disconnects the ground G from itself and the relay 66. If the first.

trunk line of this level is idle,jt he relay 66 dcenergizes-as soon asthe springs 70 are opened. If this trunk hne is busy, however,

the private wiper 26 finds the contact with which it engages provided with a guarding ground potential which is transmitted to the relay 66 through the springs 63 and 64, thereby preventing it from deenergizing. The rotary magnet, however, deiinergizes when the springs 70 disengage regardless of whether the relay 66 remains energized or not. If the relay 66 remains energized, the circuit of the rotary magnet will be again closedas soon as the armature drops back far enough to close the springs '70. The rotary magnet will, therefore, operate intermittently to advance the wipers step by step over the contacts until a non-grounded contact of an idle trunk line is reached by the wiper 26, whereupon the relay 66 deenergizes. The relay 66, upon deenergizing,

whether after one or several operations of the rotary magnet, permanently breaks the circuitflof the'magnet 29 and closes the circuit of the switching relay 58. The circuit through said relay 58 extends from ground Gr through the springs 52, 60 and 59 61 and 62, 64 and 65 and the relay 58 to battery B. The relay 58, upon energizing, disconnects the line relay 30 from the line and extends the line connection over the heavy conductors through the wipers 25 and 27 to the connector H. 1

' When the connection is completed to the connector H, the circuit of the line relay 47 is closed. The relay 47, upon energizing, closes an energizin circuit through the slow relay 100.- The re ay 100, upon energizing, supplies a new holding ground G to the relay 58 of the selector E, the original circuit havlng been broken by the denergization of the relay 34 of the selector E. The energization of the relay 100 also prepares a circuit for the vertical magnet 39 andopens the circuit I of the release magnet 46. When the substa:

tion calling device is operated for the se nd digit 4, the circuit of the line relay 47 is momentarily broken four.times. Since the relay 100 is slow acting, it does not deenergize during the momentar interruptions of its circuit by the relay 4 so that each time the latter relay deenergizes, a circuit is closed extending from ground Gr through theback. contact springs 117 and 117 of the relay 47, springs 75 of the relay 100, relay 74, vertical magnet 39 and the side switch wiper 42 to the battery B. The vertical magnet 39 receives four impulses over this circuit and operates to step the'wipers 36,37, 37*,38, 72 and 71 to a position opposite the fourth level of bank contacts. The relay 74, whichwas included in series with the vertical magnet, remains in its energized position during the entire time that impulses are being transmitted and operates to close the circuit of the private magnet 45 in series with the slow relay 101. It will be assumed that the fourth, fifth, sixth and seventh levels'of the connector banks are the levels from which the trunks leading to the Q manual board W are taken. If the fourth level bank contacts are all in use, the contact'71, which correspond to the fourth bank level, will have a ground potential-upon it extendmg from ground G through the short-circuiting wipers 71 (which are on the contacts of the fourth level) and thence to the contact 71. The wip'er 72, upon com-- ing in contact with the grounded contact71", closes a circuit extending from said ground through the wiper 72, springs 109 and 110,

relay 108 to the battery B. The relay 108,

upon energizing, completes a circuit extenda ing from ground G through the springs 111 and 112, interrupter springs 113 and the relay 114 to the spring 115, and after the re a ten s through the springs 115 and 116 to the vertical magnet 39 and the wiper 42 to the battery B. The relay 108, upon energizing, also closes a circuit through the private magnet extending from ground Gr through the springs 111 and 112, relay 101 and the private magnet 45 to the battery B, Thus the private magnet is held in an energized position even after the rela 74 vdeenergizes and until the spring 72 is raised to'an i'dlecontact, whereupon it"falls back and sends the side switch tosecond position. The vertical magnet and the relay 114 operate in the same manner asdescribed'for the selector E to raise the shaft wipers step by step until the wiper 7 2 finds a non-grounded contact, at which time the relay 108 denergizes, thereby breaking the circuit of the private magnet 45, thereby allowing the side switch to pass to second position, as stated. The side switch, upon passing to second position, causesthe wlper 42 to transfer the battery connection from the vertical magnet to the rotary magnet 40, leaving the apparatus in readiness for the last digit 1.

After the second pause the calling device is o erated for the digit 1, thereby momentari y denergizing the relay 47 once, which relay then closes an energizing circuit through the rotary magnet 40. This circuit extends from ground Gr through the back contact of the spring 117, springs 75, relay 74, springs 118 and 119, magnet 40' and the wiper 42 to the battery B. The relay 74 energizes as before to open the circuit of, the relay 114' and the busy relay 120 and to again close the circuit of the private magnet 74 deiinergizes, the circuit then ex-V '45. The rotarv magnet energizes over the circuit above traced and steps the shaft wipers on the first contactof the bank level in which there is an idle contact. If it is the first contact that is idle. therelay 121 will not pull up, and slnce the relay 74 deenergizes after the impulse is transmitted, the

side switch wipers to pas to third position.

,2 private magnet will deenergize and allow the j acircuit extending from If, however, the trunk terminating on the first contact is busy, the private wiper 37 will find the first bank contact grounded and the relay 121 will be held u over a circuit extending from saidgroun at the private wiper through the side switch wiper 44 (in second position) and the relay 121 to bat tery B. The relay 121, upon energizing,

closes another circuit for the private mag- 4 net 45vextending from ground G9 through the springs 122 and 123, thence over 2161?- cuit heretofore traced throu h the'magnets 101 and 45 to battery B. T e energization' of therrelay 121 also closes an energizing circuit for therotary magnet 40, the relay.

74 having denergized, as stated, said circuit extending from ground G through the springs 125 and 126, 127 and'128, 129 and 130, 119 and 118, magnet40 and the wiper 42 to battery B., The rotary magnet, upon venergizing, operates to rotate the shaft wipers one step onto the next trunk line and also operates to close the circuit of the relay 131 by the closure of the springs 124. The relay 131, upon energizing, opens'the circuit of the rotary magnet at the springs 127 and, 128, causing the rotary armature to 4 fall back, as well as the relay131; If the second trunk line is also in use, the wiper 37 will still engage a grounded contact and the relay 121 will remain energized,]whereupon the operations of the rotary magnet and the-relay 131 will be repeated to rotate the shaftwipers onto an idle trunk line and the relay 121 will deenergize and break the circuits of the rotary magnet 40 and also of the cut-off and private magnets 101 and 45, respectively, whereupon the private magnet will permit the side switch to pass to third position and the'cut-ofi' magnet 101 willcut the talking circuit through to the line wipers 36 and 38. The wiper 44,,upon passing to third position, supplies a guarding ground potential from ground G to the private bank contact of the called line in the banks of all the connectors which have access to said line, and also closes anenergizin circuit through the windin 143 of the in ividual switch C of the cal ed line. The winding 143, upon becomin energized, attracts the armature 144, w ich brings the so disconnects the line win ing 147 from the line. The side switch wipers 41 and 43, upon passlng to third position, complete the springs 145 and 146 into en agement and a connection from the ,callingvline through to the called manual board as shown by the heavy conductors. The side switch -wiper 42, upon passing to third position,

transfers the battery connection to the ringing relay 49. The relay 49 energizes over ground G through the interrupter 148, SPIIIIgS 149 and 150, relay 49and the wiper 42 to battery B. The relay 49' is intermittently energized over this circuit and operates to disconnect the a calling linefrom the called line and to interconnect the ringing current genwhereby an energizing. circuit is closed through the back-bridge relay 48 of the con,- nector II. This circuit extends from ground Gr throughthe right-hand winding of the relay 48, thence through the springs 152 and 153, ,155 and 154, conductor 152 to and through-said bridge at the board W, back over the conductor 151, springs 145 and 146,

156 and 157, 158 and 159 and the left-hand winding of the relay 48 to battery B. The relay 48, upon energizing, operates to .re-

verse the battery 'to the calling line. The

relay48, upon energizing, also operates to close the springs 160 and 161, thus closing an energizlng circuit through the ringing cut-off relay 162. This circuit extends from ground Gr through the off-normal springs 138 and 137 (closed upon the first vertical step of the switch shaft), thence through the springs 160 and 161 and the relay 162 to battery B. The relay162, upon energizing, closes a lockin circuit for itself independent of the springs 160 and 161 of the back-bridge relay, and also operates to open the circuit of the ringing relay 49, whereby the ringing current is disconnected from the called line. K

The release of the connection is brought about by the hanging up of the receiver at the calling substation as follows: The placing of the receiver on the switch hook at the calling substation opens the circuit of the connector line relay 47 at the springs 163 and 164. The relay 47, upon deenergizing, opens the circuit of the relay 100. The re-' lay 100, upon denergizing, closes an energlzing circuit through the release magnet 46 and also disconnects the holding ground from the relay 58 and the winding 12 of the switches circuit for the connector release magnet 46 extends from ground G through the back contact of spring 117, thence through the springs 75 and 166, off-normal springs 167 and 168 and the magnet 46 to battery B.

- The magnet 46, upon energizing, disengages the retaining pawls from the shaft, allowing it to return to normal position. The shaft, upon returning to normal, opens the circuitof the release magnet 46 and also opens the circuit of the ringing cut-off relay 162 at the spring 137 and 138. The relay 58 of theIselector E, upon deenergizing.

'closes a circuit through the release magnet 31.. This circuit extends from ground G" through the springs 183 and 182, 57 and 56, 53 and 55, 32 and 33 and the magnet 31 to battery B. Like the connector, the circuit 'shaft reaching its lowest position.

12 of the line switch C, upon de stance to Band C, respectively. The

of the release magnet is broken upon the The winding energizing, allows the plunger arm 9 and armature 15 to return to normal position, thereby leaving-the apparatus in readiness for another call. I r f We will now consider the operation when all of the. trunks running to the board W are busy. Under such conditions, the switch shaft will be carried from the fourth -to the seventh level automatically, and,

private bank '5 .(Fig. 6) which it will be seen are connected together.' By this arrangement, when all of the trunks running to the board W are busy, a circuit is closed through the switch wipers 37 and 3'7, said circuit extending from ground at the wiper.

37, throughthe loop 132 (Fig. 6), wiper 37, springs 133 and 134, 136 and 135,relay 120 and the wiper 42 to battery B. I The relay 120 energizes to open the rotary magnet circuit at the springs 118 and 119 and'also closes a lockin from ground 1 through the springs 137 and 138, 139 and-133, 136 and 135, thencethrough the relay 120 and the wiper 42 to battery. This ground connection also extends from the spring 139 through the springs 140 and 141, thence over the circuit heretofore traced to the private magnet 45',

therebyholding the side switch in second position The relay 101, which is in the private ma et circuit, energizes in this ineep the busy signal from the called line. energizing, o crates to close a busy signal upon the calling line in the usual and'wellknown manner. When the calling subscriber recelves the busy signal, he restores his reapparatus as before.

It will thus be seen that I have devised a"'very' eflicient telephone system and one which is much more flexible'than previous systems and one in which the percentage .of trunking can be greatly increased, as the selectors and connectors are adapted to not only select an idle trunk from a group of ten trunks, for example, but from among a much larger number of trunks.

While I have illustrated my invention in connection with a well-known form of automatic.selectors and connectors, it will, of course, be understood that my invention is of much broader 'scope and is'equally as we'll adapted for use in connection with switches of mauy'other types, my invention contemplating in its broader aspect the feature of a switch which is enabled to first The private magnet 45, upon circuit for itself extending -ceiver .tothe switchhook and releases the automatically select groupsand to then auand changes will readily suggest themincludin trunks in said first selecte exten tendin selves to those skilled intheart, and I accordingly'do notwish to belimited to the specific embodiment of my invention with which I have chosen to illustratethe same. What I claim as my invention is 1. Ina telephone system, a plurality of trunk lines divided into'groups, an auto.-

vmatic selector switch with a progressively movable element having motion in one plane to select groups and motion in a plane at right-angles thereto to .find' an idle line in the selected group, other similar selectors for the same purpose, and means including a set of test bank contacts and busy test circuits therefor for automatically controlling the movement of said element from one group to the next if all the trunks in the selected group are busy, said test circuits the progressivel movable elements 0 a plurality of said other switches. 2. In a telephone system, a subscribers line, a plurality of groups of trunk lines, a

selector switch, means controlled by said subscriber for operating said switch to select one-.ofaplurality ofsaid groups, and means for then moving-said switch automatically to select another of said (groups if all the 3. In a telephone system, a plurality of connector switches, a pluralityof roups of trunk lines extending from San? selector switches to a series i of said connector switches, a' plurality of groups of lines ex from said connectors to a called subscriber s line, means, controlled by a calling subscriber for extendin the connection, to one of saidselectors an for-then operating said selector to select one of a'plurality of groups of said trunk lines, means in said selector for then, automaticall selecting an idle group ofsaid trunks an for selectin d the connection to one of said con-. nectors, means controlled by said subscriber for then operating the connector to select the desired group of .lines extending totthe of said lines and then selecting an idle line in the :selected group? 4. In a telephone system, a \plurality'of groups-of lines, a series of switches associated therewith, having means for automatically selecting idle groups, means -.for,

making a group busy, comprising a circuit controlled directly by a plurality of said switches.

' 5. Iiii.-V a telephone system,aa, plurality of groups ovfflines, a series of switchesassociated therewith having means for, autogroup are busy.

an idle trunk in the selected group to p i matically selecting idle groups, means for making a group busy, comprising a circuit together with means common to the lines for directly controlling it.

6. In a telephone system a plurality of groups of lines, a series oi switches associated therewith, having means for automatically selecting idle groups, means for making a roup busy, comprising a circuit together withjmeans individual to a switch for directly controlling it.

7. In a telephone system, a plurality of groupsoi lines, a series of switches asso-- ciated therewith each having a progressively movable element, having means for automatically selecting idle groups, means for making a group busy,-compr1sing a circuit. controlled directly b the said progressively movable element, an means for making said switches common to the lines.

8. In a telephone system, a plurality of groups of lines, a series of switches asso ciated therewith, having means for automatically selecting idle groups, means for making a group busy, compr sing a circuit and banks for said switches, through which said circuit asses, said circuit controlled directly by said switches and means for making said switches common to the lines.

. 9. In a telephone system, a plurality of groups of lines, a series of switches associated therewith, having means for automatically selecting idle groups, means for making a group busy,- comprising a circuit and banks for said switches through'which directlyby. means individual to the switch,

said circuit passes, said circuit controlled and means for making said switch common tothe lines.

10. In a telephone system, a plurality of grougs of lines, a' series of switches associate therewith, having. means for automatically selecting idle groups, means for making a grou busy, comprising a link circuit controlle saidswitches'. a

11. In a telephone system, a plurality of directly by a plurality of ciate therewith, having means for automatically selecting idle groups, means for making a cuit toget er ,with means common to the lines for directly controlling it.

grou s of, lines, a series of switches assooup busy, comprising a link cirp 12. In a telephone system,a plurality of y of lines, a ser es of switches assogrougs therewith, each having a progresciate sively movable element, having means for automatically selecting idle groups, means for. making a oup busyycomprising a link circuit contro leddirectly by one of said or making said switches common to the of switches "assorogressively movable elements and means ciated therewith, having means for automatically selecting idle groups, means for making a group busy, comprising a link circuit and banks for said switches through which said circuit passes, said circuit controlled directly by said switches, and means for making said switches common to the lines.

a 14. In a telephone system, a plurality of,

trunk lines divided into groups, a selector switch associated therewith, means for automatically selecting an idle group, means for automatically selecting an idle trunk in the group, and means for making a group busy when all the lines therein have been seized, comprising a circuit controlled directly by a plurality of said switches.

' 1-5. In a telephone system, a plurality of trunklines divided into groups, a selector switch associated therewith,-means for automatically selecting an idle group, means for automatically selecting an idle trunk in the group, and means for making a group busy when all the lines therein have been seized, comprising a circuit together with means common to the lines for directly controlling it.

16. In a telephone system, .a plurality of trunk lines divided into groups, aselector switch associated therewith, means for automatically selecting an idle group, means for automatically selecting an 1dle trunk in the group, and means for making a group busy when all the lines therein have been seized, comprising a circuit togetherwith means individual to a switch for directly controls lin it. 1 In a telephone system, a, plurality of trunk lines divided into groups, aselector switch having a progressively movable eletrunk lines divided into groups, a selector switch associated therewith, means for automatically selecting an idle up, means for automatically selecting an 1dle trunk in the group, and means for making a group bus when all the lines therein have been seize comprising a circuit and banks for said switch through which said circuit passes,

said circuit controlled directly by said" switch, and means for making said switch' common to the lines c 19. In a telephonesystem, a plurality of trunk lines divided into groups, a selector switch associated therewith, means for automatically selecting an idle group, means for automatically selecting an idle trunk m the group, and means for making a group bu when all the lines therein have been seize comprising a circuit and banks for said switch through which said circuit passes, and means individual to the switch for directly controlling said circuit, and means for making said switch common to the lines.

20'. In a telephone system, a plurality of groups of lines, a switch associated therewith, having progressively movable means for automatically selecting an idle group, means for making a group busy, comprising a circuit controlled directly by said progressively movable means in the switch.

21. In a telephone system, a plurality of groups of lines, a switch associated therewith, having progressively movable means for automatically selecting an idle group, meansfor making'a. group busy, comprising a circuit controlled directly by said progressively movable means individual to the switch. I

22. In a telephone system, a plurality of groups of lines, a switch associated therewith having a progressively movable element, having means for automatically se- .lecting an idle group, means for making a group busy, comprising a circuit, said circuit controlled directly by said progressively movable element, and means for making said switch common to the lines.

23. In a telephone system, a plurality ofgroups of lines, a switch associated therewith, having means for automatically selecting an idle group, means for making a group busy, comprising a circuit and a bank for said switch through which said circuit passes and which is controlled directly by said switch, and means for making said switch common to the lines.-

24. In a telephone system, a plurality of groups of lines, a switch associated therewith, having means for automatically selecting an idle group, means for making a group busy, comprising a circuit and a bank for said switch through which said circuit passes, means individual toa switch,

for directly .controllin said circuit, and

means for making sai switch common to the lines.

25. In a telephone system, a plurality of trunk lines, a series of switches for connecting with said trunk lines, said trunklines divided into groups, means comprisingsaid switches for selecting an idle group and for selecting an idle line in a group and .means for making a group'busy comprising a circuit having a plurality of terminals in each switch.

26. In a telephone -system, a plurality of trunk lines, a series of switches each-having a progressively movable element for connecting with said"trunk lines, said trunk lines divided into groups, means comprislng said switches for selecting'an idle group,

means for making a line busy and for selectingan idle line 1n a rectly controlled by said progressively movable element for making a group busy in- 6 dependent of the control of the means for makin a line busy.

27. n a. telephone system, a plurality of trunk lines divided-into groups, a switch for connecting with any one of said trunks 10 having a progressively movable element, means for enabling the switch to select an idle line, means for making a group busy and for selecting an idle group comprising an auxiliary circuit directly controlled by said element, and a releasingdevice for the switch, said device controlling the said auxiliary circuit. i r

28. In a telephone system, a plurality of trunk lines divided into groups, a switch swltch, means controllable from the calling device to carry said member to the first group and also into engagement with a terminal insaid first group, means responsive to the calling device to carry' the said member to a sub-group in the second group and if thatsub-grou is busy to automatically can;

group an into engagement with a non-busy line in a non-busy sub-group. p

30. In a telephone system, a line, a calling device therefor, a rotary connector switch, a lineleading to said switch, a group of line'terminals in said switch, a groupof trunk terminals insaid switch divided into sub-groups, a movable member in said switch for connecting the switch line with the terminals in the switch, 'means' controllableover the switch line from the callgroup of line terminals andalso into engagement with a line terminal insaid group, an

means responsive to the callin device over the switch line to carry'the said membercto a, sub-group ofthe trunk terminals, and if all the lines in that sub-group are busy to automatically and independently'of the line carry said member to asub-group, all'the-lines of which are not busy and into 05 engagement with a non-busy line therein.

oup, and means di- 7 for connecting with any one of said trunks having a progressively movable. element,

ing the. switch line with the terminals in the said mem er to a non-busy subing device to carry the said member to the 31. Ina telephone system, a line, a calling device therefor, a trunk selector switch, a group of trunk terminals in said switch, another group of trunk terminals in said switch divided into sub-groups, a movable member in said switch for connecting the line with the terminals in theswitch, means controllable .over the line from the calling device to .carry said member to the first a group, and for automatically carrying the member over the busy terminals in said group whether all the lines in the group are busy or not, and means responsive to impulses from the calling device-over the line to carry said member to a sub-group in a second group and if .all the lines in thatv sub-group are busy to automatically and independently of the line carry said member to another sub-group and into engagement with a non-busy line therein. 7 g

32. Ina telephone system, a plurality of groups of lines, a series of switches associated therewith, having means for automatically selecting'idle groups, means for making a group busy, comprising a circuit together with means common to the lines for directly controlling it, said last means involving movable contacts under the control of the switches.

.. 33. In a telephone system, a plurality of ciated therewith, having means for vautomatically selecting idle groups, means for making a' group busy, comprising a. link circuit together with means common-to the lines for directly controlling it, said last means involving movable contacts under the control of the switches. I

35. In a telephone system, a plurality of trunk lines divided into roups, a selector switch associated therewit means for auto-' matically selecting an idle group, means for automatically selecting an idle trunk in the :group, and: means for making a group busy when all the lines therein have been seized, comprising a circuit together with means common tothe linesfor irectly controlling 'it, said last means involving-movable contacts under the control of the switch.

36. In a telephonesystem, a plurality of. Q trunk lines'divided into groups,- a selector switch associated therewith, means for auto- -matically selecting an idle group, means for automatically selecting an idle trunk in the group, and means for making a group busy" .whenall thelines therein have been seized,

ciated therewith having means .for automatically selecting idle groups, means for making a group busy and means for making a group non-busy, one of said means comprising a circuit controlled directly by a plurality of said switches. p

38. In a telephone system, a plurality of groups of lines, a series of switches associated therewith having means for automaticallyselecting idle groups, mean'sfor making a group busy and means for making a group non-busy, one of said means comprising a circuit together with means com mon to the lines for directly controlling it.

39. In a telephone system, a plurality of groups of lines, a series of switches associated therewith having means for automatically selecting idle groups, means for making a group busy and means for making a group non-busy, one of said means comprising a circuit together with means individual to a switch for directly controlling it.

40. In a telephone system, a plurality of groups of lines, a series of switches assoelated therewlth havlng means for automatically selecting idle groups, means for making a group busy and means for making a group non-busy, one of said means comprising a circuit controlled directly by the switches, and means for making said switches common to the lines of the group.

41. In a telephone system, a plurality of groups of lines, a series of switches associated therewith having means for automatically selecting idle groups, means for fmaking a group busy and means for making a group non-busy, one of sand means comprising a'circuit controlled directly by one of said switches, and means for making said switch common to the lines of the group,

42. In a telephone system, a plurality of groups of lines, a series of switches asso-. ciated therewith having means for automatically selecting idle groups, means for mak ing a group busy and 'means for making a group non-busy, one of said means compris ing a circuit, banks for said switches through which said circuit passes,said circuit controlled directly by said switches, and means for making said switches common to the lines. v

43. In a telephonesystem, a plurality of trunk lines divided into groups, a selector switch associated therewith, means for-automatically selecting an idle group, means for automatlcally selecting an idletrunk in the group, means formaking a group busy and means for makinga group non-busy when all the lines therein have been seized, one

of said means comprising a circuit controlled directly by said switch.

44. In a telephone system, a plurality trunk lines divided into groups, a selector switch'associated therewith, means for autoniatlcally selecting an 1dle group, means for automatically selecting an idle trunk in the.

group, means for making a group busy and means for mak ng a group non-busy when,

all. the lines therein have been seized, one of said means comprising a circuit together with means common to the lines for directly all the lines therein have been seized, one

of said means comprising a circuit together with means individual to a switch for directly controlling it.

46. In a telephone system, a plurality of trunk lines divided into groups, a selector switch associated therewith, means for automatically selecting an idle group, means for automatically selecting an idle trunk in the group, means for making a group busy and means for making a groupnon-busy when all the lines therein have been seized, one of said means comprising a circuit controlled directly by a switch. and means for making said switch common to the lines of a group.

47. In a telephone system, a plurality of trunk lines divided into groups, a selector switch associated therewith, means for automatically selecting an idle group, means for automatically selecting an idle trunk in the group, means for making a group busy and means .for making a group non-busy when all the lines therein have been seized, one of said means comprising a circuit, banks for said switch through which said circuit passes, said circuit controlled directly 'by said switch, and means for making said switch common to the lines.

48. In a telephone system, a. plurality of trunk lines divided into groups, a selector switch associated therewith, means for automatically selecting an idle group, means for automatically selecting an idle trunk in the all the lines therein have been seized, one of said means comprising a clrcuit, banks for said switches through which said circuit passes, said circuit controlled directly by means individual to the switch and means.

for making said switch common to the lines of a group.

49. In a telephone system. a plurality of groups of lines, a series of switches associated therewith, having means for auto- -m atically selecting-idle groups, a busy test circuit for a group, means for applying a potential to said circuit to make the group busy and for removing said potential from the circuit to'make the group non-busy, comprising a circuit controlled directly by a vplurality of said switches 50. In a telephone system, a plurality of groups of lines, a. ser1es of switches associated therewith having means for automatically selectingidle groups, a busy test circuit for a group, means for applying a otential to said circuit to make the group usy and for removing said potential from the circuit to makethe group non-busy, comprising a circuit together with means common to the lines for directly controlling it.

, groups of lines, 'a series of switches associated therewith, having means for automatically selecting idle grou s, a busy test potential to said circuit to make the group a '51. In a, telephone system, a plurality of circuit for a group,means or applying a busy and for removing said potentialifrom the circuit to make the group non-busy, comprising a circuit together with means individual to a switch for directly-controlling'it.

In a telephone system, a plurality of groups of'lines, a series of switches assocircuit for a group, means ciated therewith having means for automatically selecting' 'idle groups, a busy test I 7 potential to said circuit to make the group prising a circuit, banks for said switches busy and for removing said potential from the circuit to make the group non-busy, comprising a circuit controlled; directly by the switches, and means for making said switches common to the lines of a group.

53. In a telephone system, a plurality of groups of lines, a series of switches associated therewith, having means for automatically selecting idle groups, abusy test circuit for a'group, means for applying-a potential to said circuit to make the group busy and for removing said potential .from the circuit to make the group non-busy, comthrough which said circuit passes, said cir- -cuit controlled directly by said switches, and

a switch common to the lines of a group.

means for making said switches common to the lines.

54. In a telephone system, aplurality of groups of lines, a series of switches associated therewith, having means for automatically selecting idle groups, a busy test circuit for a grou means for applying a otential to sald c rcuitfto make the group usy and for removing said potential from the circuit to make the group non-busy, comprising a circuit, banks for saidswitches through which said clrcuit' passes, means individual to the switch for directly control-.

ling said circuit, and means for making said or applying a trunk lines divided intogroups, a selector switch associated therewith, means for automatically selecting an idle group, means for automatically selecting an idletrunk in the group, a busy test circuit for a group, means for applying a potential to said clrcuit to make the group busy when all the lines therein have been seized andfor removing said potential from the circuit to make the group non-busy, comprising a circuit controlled directly by said switch.

56. In a telephone system, a plurality "of trunk lines divided into groups, a selector switch associated therewith, means for automatically selecting anidle group, means for automatically selecting an idle trunk in the group, a busy test circuit for a group, means for applying a potential to said circuit to make the group busy when all the lines therein have been seized and for removing said potential from the circuit'to make the group non-busy, comprising a circuit .to-

gether with means ccm mon to the lines for directly controlling 1t.

57. In a telephone system, aplurality of trunk lines divided into groups, a selector switch associated therewith, means for automatically selecting an idle group, means for automatically selecting an idle trunk in the roup, a busy test circuit for a group, means or applying a potential to said circuit to make the group busy when all the lines therein have been seized and for removing said potential from the circuit to make the group non-busy, comprising a circuit together with means individual to a switch for directly controlling it. n V

58. In a telephone system, a pluralityof trunk linesdivided into groups, a selector switch associated therewith, means for automatically selecting an idle group, means for automatically selecting an idle trunk in the roup, a busy test circuit for a group, means or applying a potential to sald circuit to make the group busy when all the lines therein have been seized and for removing said potential from the circuit to make the group non-busy, comprising a circuit directly controlled by a switch, and means for makln said switch common to the lines.

switch associated therewith, meansfor automatically selecting an idle group, means for automatically selecting an idletrunk in the group, a busy test circuit for aygroup, means for applying a potential to said circuit to make the roup busy and ,for removing said potentia from the circuit to make the group non-busy, comprismg a circuit,

banks for said switch :through which said circuit passes, said circuit controlled directly by said switch, an means for making said I switch common to the lines. 55. In a telephone system, a plurality of GO In a telephone system, a plurality of 11:5 59. n a telephone system, a plurality of trunk lines dividedinto groups, a selector,

trunk lines divided into-groups, a selector tor applying a-potential to said circuit'tomake thegroup busy when all the lines thereinhave been seized and for removing said potential from the circuit to make the group non-bus comprising a circuit, banks for said switc through which said circuit passes, means individual to the switch for directly controlling said circuit, and means for making said switch common to the lines.

61. In a telephone system, a plurality of automatic switches, groups of lines accessible to said switches, a test circuit for each of said groups, including serially related fixed contacts in a plurality of said switches, means for operating one of said switches to close oneof said circuits to make the assoclated group busy, and means for releasing the operated switch to make the busy. 1 I

62. In a telephone system, a plurality of automatic switches, groups of lines accessible to said switches, multiple test contacts in said switches corresponding to said groups, a source of busy potential temporarily connected to one of said test contacts group nonby way of progressively movable contacts in a. plurality of operated switches, and means for releaslngany operated switch to disconnect the said source.

63. In a telephone system, a plurality of automatic switches, groups of lines accessible to said switches, multiple test contacts in said switches corresponding to said groups, means including a circuit passing through progressively movable contacts of a plurality of switches closed in the operation thereof to place a busy potential on one ofsaid test contacts, and means for releasing any operated switch to break the said circult.

64. In a telephone system, a plurality of groups of lines, a plurality of automatic .switches having access to said lines, a temprogressively movable contacts in a plurality of switches for rendering one of said groups busy, and means for releasing the movable contacts in one of said switches to break the said circuit. 7

65. In a telephone system, lines divided into groups and sub-groups,'a pluralityof automatic switches directively controllable to select desired groups of lines and automatically operable to select idle sub-groups,

a circuit temporarily closed through the medium of a plurality of operated switches to render one of said sub-groups busy, and

means in each operated switch responsive to the release thereof to break said circuit to render the'said sub-group non-busy.

66. In'a telephone system, a plurality of groups of lines, a plurality of automatic switches having access to said lines, certain of said switches being temporarily in operated position, multiple test contacts in said switches corresponding to said groups, means in another of said switches responsive to the operation thereof to place a busy potential on one. of said test contacts, and means in one .of said first operated switches responsive to the release thereof to directly remove said potential.

67. In a telephone system, a plurality of groups of lines, a plurality of automatic switches having access to said lines, certain of said switches being temporarily in operated position to connect, respectively, with the lines of one of said groups, multiple test contacts in'said switches corresponding to said groups, a source of busy potential connected to the test contacts corresponding to the connected group, and means in each operated switch responsive to the release thereof. for directly disconnecting said source from the said test contacts.

' Signed by me at Chicago, Illinois, this H. BURFEIND;

porarily closed circuit including fixed and

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