US1265228A - Telephone-exchange trunking system. - Google Patents

Description

Fig. 1

E. A. mmmaim- TELEPHONE EXCHANGE TRUNKING SYSTEM, APPLICATION FILED 06T- UYWIO. flENEWED MAY HI. Hill.

Patented May7, 1918.

8 SHEETS-SHEET I- -IIIIIIIIIIIIIHI 'q d E. A. MELLINGER.

TELEPHONE EXCHANGE TRUNKING SYSTEM.

APPLICATION FILED out. n. 1910. nzuzwso MAY 18. m1.

E. A. mmmsen. TELHHGNE EXCHANGE TRUNKING SYSTEM. APPLICATKON. FILED UCT. H, I910. RENEWED MAY I8. 911.

1,265,228. PatentedMayZlSB. l

3 SHEETS-HIE? I.

WITNESS a fivmzvroxa 197: TOR/vine.

UNITED STATES PATENT OFFICE.

EDWARD A. MELLINGER, OF CHICAGO, ILLINOIS, ASSIGNOR T0 AUTOMrQTIG ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

TELEPHONE-EXCHANGE TRUNKING SYSTEM.

Specification of Letters Patent.

Patented May '7, 1918.

Application filed Octoberll, 1910, Serial No. 586.531. Renewed May 18, 1917. Serial No. 189,578.

[0 all when; it may comma:

ie it known that l, Euwann A. MELLIN- onn, va citizen of the United Slates of America, and resident of Chicago, Cook county, Illinois, have invented a certain new and useful Improvement in 'lclephonc-Exchange Trunking Systems, of which the following is a specification].

My invention relates to telephone exchange systems of that kind in which automatic switches are employed for selecting trunks or other lines. It relates more particularly to systems in which non-numerical trunking switches, sometimes called line switches, are employed between first and second selectors, whereby the said switches are greater in number than the trunks lead ing therefrom. In such case it frequently happens that the trunks are all busy, and that a number of the switches, although id le, are for this reason not available for use. Suppose, for example, that all of the trunks leading from a certain switchboard become busy, there will then be a certain number of switches thereon that are idle, but which are not available for use, because they,oan-

not find any trunks which are idle. It becomes desirable. therefore, that some provision be made' for preventing selection of an idle switch that is temporarily precluded from finding an idle trunk or other line.

The object of my invention is, therefore, to provide an improved arrang ment wle e by, in a system in which certaii switches re greater in number than the tru, "s leaning therefrom, the idle switches cannot be setlected, and in which no connection therewith can be made after and while the trunks leading therefrom. are all in use.

It is also an object to provide an improved construction and arrangement whereby the simultaneous use of all the trunks leading from a certain switchboard, leayin a certain number of switches that are idle but incapable ogt use, willserve automatically to prevent. connection with any of Another object isato provide'a system in which a. ,j urality: of trunking switches are bya jmaster switch, and in which from said switches are'already in use, the said master switch thereby being incapable of operation except when one or more of the trunks are idle.

A further object is to providea novel arrangement whereby' a guarding potential will b established for one or more idle switches to prevent connection therewith whenever it shall occur that all of the trunks or lines leading from said switches are in use, as in such case a switch, although itself not in use, is incapable of finding a trunk orlinc which is idle,-and its actuation will accomplish no useful purpose.

Another object is to provide a system in which non-numerical trunking switches or employed. between the first and second selectors, so that the second selectors are common to all of the subscribers, and in which the simultaneous use of all the trunks leading from a certain group of non-numerical trunking switches will serve automatically to temporarily prevent all further connection with that group, and to divert the pre- ;vented connection to some other group, as "will hereinafter more fully appear.

It is also an object to provide certain details and features of improvement and eethbinations tending to increase the general efliciency and serviceability of a telephone exchange system of this particular char acter.

In the accompanying drawings Figs. 1 and 2 taken together show diagrammatically a. complete circuit connection established between two substations A, and A of ditferent exchanges in a system involving the principles ofm invention.

At A (Fig. 1 thereis shown a subscribei"s three-wire automatic substation. By three-wire t e is meant; thatwtypa -in which a groan connection'isf used at the substationfor operatin p ,Thepiid substation is connected means of tw'ciline co ductorstothefirst; ector 0. The first sl ector O has access-Ito terminals-of trunks &

Fig. '2. The trunk lines leading from each level of the selector bank contacts are distributcd among a number of groups of these non-numerical switches, and these groups of non-nu1ne1icul switches are common to a number of diil'crent groups of selector S\\ltlfll(fS.

Fig. 3 is a diagram showing how the trunk lines leading from one level of a number of dillercnt groups of first selectors may be distributed among a number of groups of sec ondary line switches, and showing how there may be a larger number of secondary switches in each group than trunk lines leading therefrom.

The plunger-s of the non-n1nnerical trunking switches such as the one shown at; I) (Fig. 1) are all normally in locking engagewent with a plunger shaft. (not shown) which is controlled by the mechanism shown at 1 1, usually called a master switch. This master switch E controls the plungcrs of tin; trunking; switches of the group of which the sir ch D is a nien'il'ier in such a manner hat the are normally held directly opposinan idle trunlr line leading to a repeater sot-l1 as the repeater F.

The selector switch shown at H (Fig. 2) is similar to the selector (1 (Fig. l). The selector H has access to trunks leading to connectors. one of which is the connector shown at 'I. At A. and C there are shown a substation and first selector similar to those shown at A and C, respectively. As herein represented, there are but two bat teries. with their positive terminals preferably grounded; but it will be understood, of course, that there may be any number, depending upon the conditions to be met.

The substations may be of any suitable or approved type. As shown, the substation A comprises the usual receiver 2, switch hook 3, transmitter l, induction coil 5,1ingcr l, condenser '7 and release springs 8, 9 and it). which springs are momentarily forced into contact by the cam arm 11 on the downward movement; of the switch book 3. Like the cam 11, there are also secured to the hook 3 thcicarn arms 12 and 13, When the hook is in its lowest position the cam 12 serves to press the spring 14 into engagement with the spring 15 and to allow the spring 16 to disengage the-spring 17. When the hook is in its lowest position the cam 13 holds the around spring 18 away from the spring 19. The locking cam 20 serves to prevent the rlial hnot shown) from being rotated as long as tho receiver is on the hook, and also prc vents the. springJB from engaging spring 19, afterthemeceivcr is removed from the hook, untilthe dial is turned. The impulse wheel 21. carrying; the so-called vertical teeth 22 and rotary tooth 23. and the cam 24- are so curcly fastened to the shalt 25, to which is also secured a dial (not; shown) provided.

with finger holes. As soon as the dial is rotated, the ram it permits spring 17 to disengage spring ltf.

On the backward movement of the impulse wheel the \crtical teeth 22 force the spring 26 into engagement with the spring 27. Following the last engagement of springs 2|; and ill, the rotary tooth 23 forces the spring 255 into engagement with spring The substation it. also supplied with a push button 30.

The substation A is connected to the selector U by means of the line conductors 3i and 3'2. The selector (J of the general type disclosed in United States Letters lat (:Ilt #815,321, granted March 13, 1906, to Keith, Erickson ct Erickson. In general, it; conu'n'ises the Ha'uul ahal't (not shown) carrying the wipers fill, ill and 35. This shaft has a vertical motion controlled by the vertical magnet .J-tl and a rotary motion con trolled by the rotary magnet 37. The private magnet 38 controls the aide switch carry-- ing the wipers it), i ll and lid in the usual and well ltnonn manrnrr. The release oi the snitch mechanism is provided for in the release magnet 43. The cut'oll relay 44 is for the innnine of cutting oil the two line relays iii and i from battery.

The non-numerioal trunking switch shown at l) is of the general type disclosed in British Patent No. 26,301 of 1906, and in the American Telephone Journal of New York, N. Y., of June 6, I908, but is slightly modified to operate in a system en'ibodying the principles of my invention. it comrises the usual plunger (not shown) attached to the plunger arm 47. This plnn ger arm is at racted upon the energization of the magnet 48 to force the said plunger into a bank of trunk terminals consisting of a. plurality of sets of springs. The said plunger lltlt'th the springs 49, 51, {ti'lfllld 55 into itllilitfl ilositi' with the springs 50, :32, 5 and be, respectively. As the plunger is attracted the epring 535 is shifted out. of engagement with the sprinc 57 and into engagement with the spring 5%).

The master switch l) is of the general type disclosed in the aforesaid British patent and Telephone Journal. The master switch I) comprises the ratchet wheel 60 to the shaft of which there is also secured the notched wheel 61. This notched wheel is usually constructed of fiber or some good insulating material. The ratchet wheelifitl is capable of being rotated upon the attraction of the armature 62 by the motor magnet (33. The switch also comprises the bank a consisting; of the individual segments 64. 126, etc, and the. common segment 65. There is also a wiper 66 secured to the pin ger shaft which is used to always keep som *one of the individual contacts in electrical conncetion with the common segment 65. There names are a number of relays 67, 68 and 69, one of which is connected to each of the individual segments of the master switch bank. There are also the operating relays 70, 71 and 72 and lamp 73 used in connection with the master switch.

The repeater shown at F, as before stated,

exchange. It consists essentially of the two line relays 74 and 75 and the differentiallywound double-wound relay 76. There is also a relay 77, the function of which will be explained later.

The selector shown at H. Fig. 2, is quite similar to that shown at C. Fig. 1, but unlike selector C it has no cut-oil" relay.

The connector shown at I is of the general type disclosed in United States Letters Patout No. 815,176, granted March .13, 1906, to Keith, Erickson & Erickson. It, like the selectors l and H, comprises a shaft and shaft wipers 78, 79 and 80, the vertical motion of the shaft being controlled by the vertical magnet 81 and the rotary motion by the rotary magnet 82. v The private magnet 83 controls the side switch carrying the wipers 84, 85, 86 and 87. The release of the connector is provided for in the release magnet 88. The operation of the switch is controlled by the calling subscriber through the medium of the two line relays 89 and 90.

he connector is also provided with a ringer relay 91 and two double-wound relays 92 and 93. 1

As before stated, the substation A and first selector C are like substation A and selector C in Fig. 1.

Having given a general description of the apparatus involved in the system, I will now describe the operations of the apparatus when a subscriber at substation A, f stance, calls a subscriber in another exchange, subscriber at substation A, for example, whose number we will assume to be 2220. In making the call the subscriber at substation A removes the receiver from the hook, which permits the springs 14 and 15 to disengage and springs 16 and 17 to engage. The disengagement of 5 rings 14 and 15 opens the circuit of the he] s 6. The engagement of springs 16 and 17 has no particular function at this time. The subscriber, after having removed the receiver, rotates the dial, and consequently the impulse wheel 21 and cam arm 24, forward in the usual manner. As the cam arm is rotated upon the forward movement of the dial, it strikes the cam 20, which then allows the spring 1 8 to engage spring 19. The cam 24 also breaks the engagement of springs 16 and 17.

s the subscriber wishes to call the digit 2,112 rotates the dial until two of the vertical teeth 22 and the rotary tooth 23 are carried 22 strike the cam 9.

,rotary magnet 37.

past the cams 94 and 95 on the springs 26 and 28. As soon as the dial is released, the impulse wheel rotates backward.

and force the spring 26 into contact with the spring 27. The engagement of these two springs closes an energizing circuit through the vertical line rclay -l5 of the selector (J. This circuit extends from ground G through springs 18 and 19, springs 27 and 26, conductor 31, side switch wiper 40, line relay 4:) and springs 96 and 97 to battery lead 98, thence through battery B to ground G. The relay 45 energizes over The teeth this circuit tr-close a circuit through the vertical magnet 36. This Cll'Cllll; extends from ground G through springs 99 and 100, 101 and 102 and 98. As the springs 27 and 26 engage twice momentarily, the vertical magnet energizes twice to raise the shaft and shaft wipers two steps opposite the second level of bank contacts. After the shaft has been raised one or more steps, the arm 114 is lifted from spring 112, permitting it to engage spring 113, which puts a guarding ground onto the connector private bank contact of the calling line in the banks of all of the connectors that have access to said line. This is to prevent the substation A from being called while it is making a call. A moment after the vertical impulses are sent in, the rota tooth 23 strikes the cam 95 on spring 28 and forces said spring against the ground spring 27. This closes a circuit extending from ground G through springs 18 and 19, springs 27 and 28, line conductor 32, side switch wi er 39, line rela 46 and springs 103 and 97 to battery lead 98. The rotary line relay 46 energizes once over this circuit and closes a circuit through the private mag net 38. This circuit extends from ground G through s. rings 99 and magnet 38 to attery lead 98, thence through battery B to ground G. The private magnet thereupon energizes and denergizes, permitting the side switch to pass to second position. As soon as wiper 41 reaches second position a circuit is closed through the through wiper 41, interand rotary magnet 37 to attery lead 98. The rotar magnet energizcs once to rotate the sllaft and shaft wipers one step onto the terminals of a trunk leading to the switch D. The rotary magnet also presses down the private ma net armature and breaks its own circuit. f the first contact upon which the wipers are rotated is idle, the private magnet armature will be released when the rotary ma t armature falls back,'and the side switc V will thereby be allowed to pass to third position. If, however, the first; trunk is busy, theprivate from ground G rupter springs 105 bank'contact upon which the private wiper 34 is rotated will have upon it a. guarding This circuit extends magnet 36 to battery lead 104 and private 38 to the battery lead 98. The relay 220 does not energize over this circuit, but the private magnet does energize, thereby locking the side switch in the second position, and as soon as the rotary magnet dei nergizes, it is energized again and thus acts in the manner .of a buzzer to rotate the shaft, carrying wipers 33, 34 and 35 to a contact that is not busy, at. which time the side switch 15 permitted to pass to the tlnrd posltlon. As soon as the side switch wipers 39 and 40 reach the .third position, the line conductors are extended to the switch 1). wiper 1-3 to the third position puts a guardin; ground on the private bank contact of the trunk leading; to the switch D in the hanks of all of the first selectors that have access to the switch D. This circuit. extends from ground (11 through side switch wiper l2, relay 22!) to wiper 3t, thence. to all of said private bank contacts. A circuit also extends over the circuit just traced to the wiper Ill, thence through magnet 48, springs 58 and 57, armature 10G, contact point. 107, armature 108, contact 109 and coil 71 to bat-- tery. The lnagi'tet 48 is energized over this circuit and attracts the danger arm 4:7. As the spring 58 is shifted from spring 57 to spring fill-upon the attraction of the plunger arm, the holding circuit for magnet 48 is shifted through resistance 111 to battery, As before stated, the plunger being thrust into the bank of springs 49 56 forces springs 49, 51. 53 and into engagement with springs 50, 52, 54.- and 56, respectively, T he engagement of the springs 4-9, 51. and 551 with springs 50, 52 and 56 completes the trunk conductors to the repeater H. The engagement of springs 53 and 54 closes a circult through the relays 67 and 70 in multiple. The circuit through relay 70 extends from ground G through armature 115, contact point 116, relay 70, common segment (35 of master switch bank a, wiper 66, individual segment 64 and springs5-.lr and 53 to battery lead 98. The other circuit extends from ground Gr through relay 6? and springs 5-1 and 53 to battery lead 98. The energization of relay 67 places ground potential upon the oint 117 by means of armature 118 engagmg point 119. The function of this ground potential will he explained more fully later.

' magnet 63.

The relay 70 energizes over the circuit leeiore traced to close thecircuit'of the motor This circuit extends from ground Gr through contact 120, armature 108, contact 121, springs 122 and 123 and motor magnet 63 to battery lead 98. The

The pa ssing oil.

motor magnet attracts its armature, which rotates the ratchet wheel one step. As soon as the ratchet wheel is rotated one step the spring! 12+ which normally rests in a notch in the wheel (31 is forced. against the spring 1'35 and held in this engaged position until the spring 12% again engages a notch in the wheel 61. The attraction of the motor armature also breaks its own. circuit at springs 12-2 and 1523 and the armature falls back, but as the circuit is now closed at springs 121 and 125, it in'nnediately attracted again. Thus it operates in the manner of a. buzzer to rotate the ratchet wheel until the spring 12% engages the next notch. By means of a suitable mechanical arrangement the rotary motion of the ratchet wheel is imparted to the plunger shaft, giving said plunger shaft an oscillatory motion to move the plungers which are in locking engagement therewith back and forth in front of the banks of trunk terminals. The notched wheel 61 is so constructwlv that every time the spring 121 et'tg'ages a. notch the pioneers stand directly opposite the terminals of a trunk conductor leading to a repeater l Had the next t'runlr after the one last put in use been busy, the Contact; 126 would have guarding potential upon it, which, when the wiper 6S engaged said contact, would complete a circuit through the relay 70, which would energize the motor n'iagnet again and thus would more the plungers to the next trunk.

In case all of the trunks leading from the roop of switches of which the switch D is a member are lousy, the relays 67, G8, 69, etc, will all be energized in the manner before described, at which time a circuit will he closed through. the relay 72. This circuit extends from ground G through contact point 119, armature 118, contact. 117, arinature 128, etc,, through the armatures of all relays 67, 68, G9, etc., consecutively, through. the armature of the relay individual to the last trunk, thence through relay 72 to battery.' The relay 72 remains energized long as the trunks are all busy, The energization of the relay 72 opens the circuit of the relay 70 at armature 115 and contact 116,

which in turn deenergizes and opens the motor magnet circuit, thereby stopping the operation of the master switch. The energize,- tion of the relay 72 also closes a circuit through the lamp 73, and puts a guarding potential on the selector private bank contacts of all of the trunk lines leading to the switches that are controlled by the master switch E that are not in use. This circuit extends from ground G through contact point 127, armature 106, thence through springs 57 and 58 of all of the idle switches D, through magnet 48 and back over conductor 130 to said private bank contacts. Thus when all the trunk lines leading from a group of non numerical switches I) become .16 nection with a trunk leading to a different he operation of the repeater 1 bus i s master switch E is prevented from magnet 151, thereby stepping the side switch usel ess y rotating, even though all its bank to second position, wh ch closes the circuit contacts are provided with a guarding poof the rotor magnet 152 to rotate the shaft tential, and at the same time a guarding p and shaft wipers to the first idle trunk as- 5 tential is provided forall trunk lines leadln sumed'to be the trunk leading to the coninto t is group of non-numerical switches, neetor I. The side switch wipers pass to even though some of said trunks are not the third position and thus connect the trunk actually in use. This a calling line is prelines 132 and 146 directly from the repeater vented from beingextended into connec- F to the connector I. The energization of 10 tion with a non-numerical switch D from relay 76 of the repeater F, as the lines are which no idle trunks are available to extend grounded at the substation A, serves to 0 en t e connection farther. When the selector t e circuit of the relay 77 to prevent the wipersencounter a trunk line which is thus ground impulse from going to the connector guarded, they are rotated past it into oonover both sides of the line. f I

Or he 80 group of non-n imerica'l switches. last two digits is the same as it was for the he foregoing is the operation of the censecond digit. 2. The connector I, upon retral oiiice.mechiinism upon the operation of ceiving the round impulses over the verti- 2. he subcal line as t 9 third digit is called, operates 20 member at substation A now rotates the dial y means of magnet 81 to raise the shaft and 85 and 28. T dial is now released and perhe rotary impulse l1 iewise operates to 26 mitted to rotate backward, forcing spring step the side switch to second position. The 26 twice against the ground spring 27. The side switch wiper 87, in passing to the secthese two, springs sends two end position, shifts the connection of the imground impulses through the vertical line pulse spring 110 from the vertical magnet rain 74 of the repeater F. Thisrcircuit ex- 81 to the rotary ma net 82. The switch is 30 ten s from ground G throu 'h springs 18 now in position for the fourth and last di it and 19, springs 27 and 26, conductor 31, O. The subscriber at substation A turns the wiper 40, shaft wiper 33, springs 49 and 50 dial until ten vertical teeth on the impulse 0 switch 1). line relay 74 of repeater F and wheel have passed the impulse springs 26. upper winding of relay 76 to battery lead 98, The dial, upon being released, rotates back- 35 thencethrough batteryBto groundG; The ward, as before described, grounding the relays 74 and 76 both energize twice over vertical line ten times and the rotary line is circuit, thereby sending two ground imonce. Therepeater repeats the impulses the pulses over trunk conductor'132 to the secsame as before to close the circuit of the 0nd selector H. is circuit extends from connector line relay 89. The relay 89 now 40 ground G through springs 133 and 134, operates to close the circuit extending from springs 135 and 136, conductor 132, side ground G" through springs 153 and 110,

switch wiper 137 and line relay 138 of sesprings 154 and 155, wiper 87 and rotary lector H to battery lead 139, thence through magnet82 to battery lead 139. The rotary 45 crates in the same manner as the seieetor the shaft wipers 78. 79 and 80 ten steps onto to raise the shaft and shaft wipers 140. 141 the lineof the called subscriber. I

and 142 opposite. the second level of bank ow comes the one rotary impiilse,'as contacts. As the rotary tooth 23 of the imheretofore explained, which energizes the pulse wheel 21 passes the cam 90 on spring rotary relay 90. The energization of this .50 28 1t forges said spring into engagement relay again closesthecircuit of the private with spring 27, which closes a circuit magnet 83. This circuit extends from through the rotary line relay 75 of the reground G,through springs 153 and 156, pester. This circuit extends from ground magnet 83 and springs 157 and 158 to batthrough springs 18 and 19. springs 27 tery'lead 139. The private magnet energizes 65 and 28, rotary line conductor 32, wipers 39 and de 'e'nergizes, permitting theside switch and 35, bank springs 55 and'56, relay .75, to pass to third position. The wipers 84 lower winding of relay 76 and springs 113' and 85, in the third position, connect the and 144 to battery lead 98, thence to batcalling subscriber with the called siib- V B- scriber. T e wiper 86, in third position,

60 The relay 75 energizes to close a circuit closes a circuit from ground G through extending from ground G through springs wiper 86,-shiift wi er 80, private bank eon- 33 and 134, springs 185 and145, springs 149 tact.159, ofl'-norma springs 160 and 161 and M14150, conductor 146, wiper 147 and relay cut-ofi relay 162 to battery. The cut-off 1- to battery-lead 13.9. :The relay 148 enrelay is energized, thereby disconnectin $5 ergizes to close a circuit through the private battery ,froin' the line relays 163 and 10 which prevents substation A from calling while another substation has connection with its line.

A circuit also extends from the contact 159 to the. corre.-'spondinc contacts in the banks of all of the connectors that have ac cess to the called line, thus putting a guarding potential on the private bank contacts, which prevents a third party from calling substation A while said substation is being called.

The subscriber at substation A is now in position to ring the called subscriber. As soon. as the dial stops rotating, the subscriber at substation A presses the button 39, which forces spring 165 into engagement; with spring 166. The engagement of these two springs closes a circuit. extending from ground G through springs 18 and 19, springs 166 and 165, springs 17 and 16, con cluctor 31, wipers 1-0 and 33 springs 49 and 50 and relays 71- and 76 of repeater F to battery lead 98. The relays 7-1 and 76 encrgize as before and close a circuit through the relay 89 of the connector. This circuit ex tends from round G" through springs 137i and 134, springs 135 and 136, conductor 13:2, wipers 137 and 140, relay 89 and upper wind; ing of relay 93 to battery. The energizetion of relays 89 and 93 at this time closes a circuit through the ringer relay 91. This circuit extends from ground G through springs 153 and 11.9, springs 15-1 and 155, wiper 87, ringer relay 91 and springs 167 and. 168 to battery lead 139. The ringer rolay energizes and by so doing disconnects the calling from the called line and connects the ringing current generator with the line of the called subscriber. A circuit is now closed through the bells of the called substation extending from one side of the gen crator R through springs 169 and 179, wiper 85, shaft wiper 78, conductor 171. condenser 172, bells 173, springs 17 i and 175. conductor 176, wipers 79 and 81 and springs 177 and 178 to the other side of the generator R. The subscriber at substation A, upon hearing, the signal removes the receiver from the hook. Upon the removal of the receiver from the hook at substation A. the called 186 and 168 to battery lead 139. The relay 92 energizes over this circuit and shifts the spring 157 out; of engagement with the spring 158 and into engagement with the spring 187. This shifting ofthe springs provides an energizing circuit for the relay 77 of the repeater F, said circuit extendin from ground Gr through the side switct wiper 86, springs 187 and 157, lower winding of the relay 93 relay 90, thence over the heavy conductor to the repeater F, through the springs 189 and 190, relay 77, back over the heavy conductor to the connector relay S9 and the upper winding of the relay 93 to battery lead 139. The current; in the two windings of the relay 93 have opposite effects, thus permitting the armature to remain in its norrrial positioni The relay 77 of the repeater is energized over the circuit just traced, thereby disconnecting the rotary impulse spring 145 from the trunk 146, and also disconnecting ground G" from the spring 135 and supplying talking battery current to the calling subscriber over a circuit extending from ground G through the springs 192 and H3, lower winding of the relay 76, relay 75, thence over the heavy con ductor to substation A, through primary winding of induction coil 5, transmitter 4, push button springs 188 and 165, switch hook springs 17 and 16, back over the heavy coudoctor to repeater F, through relay 7-1 and upper winding of relay 76 to l tcry. The relay 76, like the relay 93 of the connector, is ditl'erentially wound and therefore does not energizeover the circuit just traced. Thus both subscribers may now converse, it being evident, of course, that the voice-currents flow through the condensers 193 and 194 of the repeater and condensers 195 and 196 of the connector.

The release of the apparatus used in the connection described is initiated by the hanging up of the receiver at the calling substation. As the book 3 is lowered the cam arm 11 forces springs 8. 9 and 10 momentarily into engagement, thereby groundin; both the vertical and rotary lines simul taueously. Thus the relays 74, and 76 of the repeater momentarily energize. The simultaneous energization of these three relays closes a circuit through the relays 89, 99 and 93 of the connector. The circuits thus closed are the same a's when the repeater closed the circuit of each line relay imlividually. The simultaneous energization of the relays 89, 90 and 93 closes an energizing circuit. through the release magnet 88 of the connector in series with the release relay 198 of the selector H. This circuit. extends from ground G" through side switch wiper 199, relay 198, private wiper 1-11; springs 200 and 201, magnet 88 and springs 167 and 168 to battery. The energizing of magnet 88 restores the connoctor to normal position. -The relay 198, u'pon energizing. closes a circuit extending from ground (1" through springs 202 and 202" and release magnet 203 to battery lead switch 139. The release ma net attracts its armature, but does not re ease the switch mechanism until the magnet deenergizes. turning now to the repeater, the simultaneous cnergization of the relays 74, 75 and 76 closes an energizing circuit through the release relay 220 of the selector C. This circuit extends from ground G through wiper 42, relay 220, wiper 34, springs 51 and 52, conductor 204, springs 205 and 206, resistance 207 and springs 208 and 209 to the bat- 98. The resistance 207 is low the relay 220 to be energized to close a circuit through the release magnet 43. his circuit extends from ground G throu h springs 210 and 211, and magnet 43, to attery. As soon as the release springs 8,9 and 10 at the substation real: contact the line relays of the retion where the shaft and 159. As energizes for the the private magnet energizes in manner.

' he energization of the private magnet this time, however, closes a circuit through c release ma his circuit extends ground at the private bank contact through the private wiper 80, side wi er 86 (in second position), springs 212 and 213, magnet 88 and springs 16? he battery lead 139. The energizes and restores the hanism to normal position.

0W, as \the subscriber at substation A 7 presses the button to ring, as before, the vertical magnet 81 is energized over the same circuit cover which it was energized when the third digit was called. 3 soon as the shaft is raise one or more steps the arm 215 is also raised, which allows the spring 217 to engage the spring- 216.- 'A busg signal calling subscri er over from the battery lean secondary winding" 218 of the busy 'signa chine ,springs 216*and 217,;side switch wiper 84 (m first position), ri ger springs 177 and 179, thence over the eavy ductor, including the condensers 196 and 4, to and through the substation A, back over the heavy conductor, including the more I numerical switches that are condenser 193 of the repeater, through the relays 89 and 93 to battery. Upon hearing the busy signal the subscriber receiver on the all of the apparatus used in the connection in the manner hereinbefore described.

From the foregoing it will be seen that means are provided for preventing further selection of switches on a board after and while all of the trunks leadinlg therefrom are in use, and for diverting t e incoming calls to some other switchboard. ere are as many relays of by a uarding potential is then established for al of the automatic switches which are idle, the number of automatic switches bein greater than the number of trunks leading therefrom. In other words, when the trunks are all busy there is then an excess or surplus of switches, and means are provided for preventing connection with the said excess or surplus, for diverting the connection to some other switchboard. us the second selectors are all common to the difl'erent subscribers, and at t e same time the idle nonable to find an idle trunk are removed from the sphere of use, and are caused to remain m such condition until one that after the trunks f a certain guarding is established for the maining i la switches, and the master switch prevented from operating to select a trunk-that is to sa it is so controlled that operate in any manner soon as a trunk is released, the excess 1 thenbeconie accessi 1e, and t emaster switch is again operative o select idle trunks. It wi l pbserved that the said master switch is ofthe type in which idle trunks are selected-aliead of the calls. In this way each calling subscriber obtains connection with a pres trunk, and at the sainctime causes the master switch to select anot switches cona second sellector is conher trunk for simfiar control over the connectors, which connectors are provided with means for bridging the common battery a ross the, called line. The repeaters. it will be seen, are also provided with means for bridging the talking battery across the trunk to sup ply talking battery current to the calling: su i-station. The selectors and connectors are known as numerical switches, and each one has motion first in one plane to select. a group, and then in another plane at. an angle UHEIBiLF tlIHt is to say, at an angle to the first planer-to find a line in the selected group. The selectors, of course, rotate automatical'ly to nuthmatically select an idle trunk in the prettermincd group. Each connector rotates under direct control of the subscriber to find the called line in the prc determined group.

A numerical switch is, of course, one that operates in accordance with some digit of the called number. A non-numerical switch is one that performs a trunking operation without reference to the called number. As shown. the non-numerical trunking switcl'ics are interposed between the first and second The first selector operates in ac cordanee with the first digit of the called numi'ei'. and the second selector operates in accordance with the second digit thereof.

What I claim as my invention is:--

1. In a telephone system, a plurality of trunks, a plurality of non-numerical switches for automatically connecting with idle trunks. greater in number than said trunks, first selectors for automatically selecting idle switches in accordance with the first digit of the called number, and means serving anuse.

2. In a telephone system. a pluralitv of trunks. as many relays as there are trunks. a plurality of switches for automatically selectinn idle trunks, greater in number than said trunks, means for automatically selecting idle switches, means for energizing, a relay each time a trunk is selected, and means whereby the energizing of all of said relays serves to automatically prevent. further seizure of idle switches.

3. In a tele; gone system, a plurality of trunks, a plurality of switches for automatically connecting with idle trunks. greater in number than said trunks, a set of relays for said trunks, onefor each trunk, relay mechanism adapted when energized to establish a idle switches, a

relays of the set, and means for energizing a relay of said set each time a trunk is seized by a switch.

4. In a telephone system, ,a plurality of trunks, trunking switches,-a master switch for selecting idle trunks for said switches,

switches after and elcctrically-controlled means automatica ly serving to prevent; actuation of said master switch after and while all of said trunks are in use. 4

5. in a telephone system, a plurality of truuks, uon-numerical trunking switches with which said trunks master switch for selecting idle trunks ahead of the call for said trunking, switches, and means electrically controlled only by the =ii1mltaneoi.1s use of all said trunks to tom-- porai'ily master switch.

6. In a tElQPliOl'lC system, a plurality of trunks, a plurality of switches for automatically connecting with idle trunks, greater in number than said trunks, means for automatically selecting idle switches, means serving automatically to prevent further seizure of idle switches after and While the trunks are all in use, a repeater in each trunk, and a second selector at the end of each trunk, each repeater adapted to control the two sides of its trunk to control the sccand selector thereof.

T, In a telephone system, a plurality of trunks, a plurality of non-numerical switches for automatically connecting with idle trunks, greater in number than said trunks, first selectors for automatically selecting idle switches in accordance with the first digit of the called number, means serving automatically to prevent further seizure of idle and while the trunks are all in use, a repeater in each trunk, and a second selector at the end of each trunk, each repeater adapted to control the two sides of its trunk to control the second selector thereof. H

8. In a telephone system, a plurality of trunks, as many relays as there are trunks, a plurality of switches forautomatically selectino idle trunks, greater in munbcr than said trunks. means for auton'iatically sclecb ing idle switches, means for energizing a relay each time a trunk is selected, means whereby the energizing of all. of said relays servcslto auton'iatically prevent further seiz are of idle switches, a repeater in each trunk,

and a second selector at the end of each trunk. each repeater adapted to control the two sides of its selector thereof.

9. In a telephone system, a plurality of trunks. switches for auton'iatically connecting with idle trunks, greater in number than said trunks, means for automatically selecting idle switches, means for automatically establishing a guarding potential forall idle switches after and while the trunks are all in use, a. repeater in each. trunk, and a second selector at the end of each trunk. each repeater adapted to control the two sides of its trunk to control the second selector ereof.

trunk to control the second prevent further actuation of said v Ill) ebanese 10. In a telephone system, a plurality of trunks, 3i: plurality of switches for automatically connecting with idle trunks, greater in number than said trunks, a set of relays for said trunks, one for each trunk, relay mechanism adapted when encr izcd to establish a guarding potential for a l idle switches, a circuit for said mechanism controlled by all relays of the set, means for energizing a relay of said set each time a trunk is seized by a switch, a repeater in each trunk, and a selection of second selector at the end of each trunlr, each re'peater adapted to control the two sides of its trunk to control the second selector thereof. a

11. In a telephone system, a plurality of switchboards, trunks leading therefrom, means for automatically selecting idle switches on said boards, means automati cally serving when the trunks on any board are all in use to divert the automatic selection to some other board, a repeater in each trunk, and a second selector at the end of each trunk, each repeater adapted to control the two sides of its trunk to control the second selector thereof.

12. In, a. telephone system, a plurality of switchboards, trunks leading therefrom, switches on each board than 'the trunks leading therefrom, means for automatically selecting idle switches on said boards, means for preventing further idle switches on any board when all the trunks thereof are busy, there being trunk lines leading to said boards so disposed that any attempted selection of an idle switch on a board when all the trunks leading therefrom are busy will be diverted to another board, a repeater in each trunk, and a second selector at the end of each trunk, each repeater adapted to control the two sides of its trunk to control the second selector thereof.

13. In a telephone system, a plurality of non-numerical trunking switchboards with trunks leading therefrom, means for extending calling connections to said boards, devices rendered operative only by the simultaneous use of all the trunks on any board to divert the calls to other boards, a repeater in each trunk, and a second selector at the end of e ch trunk, each repeater adapted to control the two sides of its trunk to control the second selector thereof. Y

14. In a telephone system, a lurality of non-numerical trunking switch cards, the switches on any board being greater in numher than the trunks leading therefrom, means for automatically selecting idle switches on said boards, means for preventing further selection of, idle switches on any board when the other switches and all the trunks are in use, there being trunk lines leading to said boards so arranged that the prevented selection will greater in number said trunks,

be diverted to another each trunk, and a second selector at the end of each trunk, each repeater adapted to control the two sides of its trunk to control the second selector thereof.

15. In a telephone system, a plurality of trunks, trunkin switches, a master switch for selecting id e trunks for said switches, electrically-controlled means automatically serving to prevent actuation of said master switch after and while. all of said trunks are in use, a repeater in each trunk, and a. second selector at the end of each trunk, each repeater adapted to control the two sides of its trunk to control the second selector thereof. 16. In a telephone system, a plurality of trunks, non-numerical trunking switches with which said trunks are multipled, a master switch for selecting idle trunks ahead of the calls for said trunking switches, means electrically controlled only by the simultaneous use of all said trunks to temporarily prevent further actuation of said master switch, a repeater in each trunk, and a. second selector at the end of each trunk, each repeater adapted to control the two sides of its trunk to control the second selector thereof. 7

17. In a telephone system, trunks, a plurality of switches board, a repeater in a plurality of for automatically connecting with idle trunks, greater in number than said trunks, means for automatically selecting idle switches, means servingautomatically to prevent further seizure of idle switches after and while the trunks are all in use, telephone lines, and means for controlling the two sides of a. calling telephone line to control said pwitchcs and extend the call to the called 18. In a telephone system, a plurality of trunks, a plurality of non-numerical switches for automatically connecting with idle trunks, greater in number than said trunks, first selectors for automatically selecting idle switches in acordance with the first digit of the called number, means serving automatically to prevent further seizure of idle switches are all in use, telephone lines, and means for controlling the two sides of a calling telephone line to control said switches and extend the call to the called line.

19. In a telephone system, a. plurality of frunks, as many relays as there are trunks, a plurality of switches forautomatically selecting idle trunks, greater in number than means for automatically selecting idle switches, means for energizing a relay each time a trunk is selected, means whereby the energizing of all of said relays serves to automatically prevent 'further seizure of idle switches,,telephone lines, and means for controlling the two sides of a leading therefrom are calling telephone line to control said switches and extend the call to the called line.

20. In a telephone system, a )lurality oi trunks, switches for automatically connectinc with idle trunks, greater in number than said trunks, means for automatically select ing idle switches, means for automatically establishing a guarding potential for all idle switches after and while the trunks are all in use, telephone lines, and means for controlling the two sides of a calling telephone line to control said switches and extend the call to the called line.

21. In a telephone system, a plurality of trunks. a plurality o switches for automatically connecting with idle trunks,

- greater in number than said trunks, a set of relays for said trunks,

one for.each trunk, relay mechanism adapted to be energize to establish a guarding potential for all idle switches, a circuit for said mechanism controlled by all relays of the set, means for energizing a relay of said set each time a trunk is seized by a switch, telephone lines, and means for controlling the two sides of a call ing telephone line to control said switches and extend the call to the called line.

22. In a telephone system, a plurality of switchboards, trunks leading therefrom, means for automatically selecting idle switches on said boards, means automatically serving when the trunks on any board are all in use to divert the automatic selection to some other board, telephone lines, and means for controlling the two sides of a. calling telephone line to control sai switches and extend the call to the called line.

23. In a telephone system, a plurality of switchboards, trunks leading therefrom, switches on each board greater in number than the trunks leading therefrom, means for automatically selecting idle switches on said boards, means for preventing further selection of idle switches on any board when all the trunks thereof are busy, there being trunk lines leading to said boards so disosed that any attempted selection of an idle switch on a board when all the trunks busy will be diverted to another board, telephone lines, and means for controlling the two sides of a callin telephone line to control said switches an extend the call to the called line.

24. In a telephone system, a plurality of non-numerical trunking switchboards, the switches on any board being greater in number than the trunks leading therefrom, means 'for automatically selecting idle switches on said boards. means for prcventing further selection of idle switches on any board when the other switches and all the trunks are in use, there being trunk lines leading to said boards so arranged that the prevented selection will be diverted to another board, telephone lines, and means for controlling the two sides of a calling telephone line to control said switches to extend the call to the called line.

25. In a telephone system, a plurality of trunks, trunking switches, a master switch for selecting idle trunks for said switches, electricallv-controlled means automatically serving to prevent actuation of said master switch after and while all of said trunks are in use, telephone lines, and means for controlling the two sides of a calling telephone line to control said switches to extend the call to the called line.

26. In a telephone system, a plurality of trunks, non-numerical trunking switches with which said trunks are multipled, a master switch for selecting idle trunhs ahead of the calls for said trunking switches, means electrically controlled only by the simultaneous use of all said trunks to temporarily prevent further actuation of said master switch, telephone lines, and means for controlling the two sides of a calling telephoife line to control said switches to extend the call to the called line.

27. In a telephone system, a plurality of trunks, a p urality of non-numerical switches for automatically connecting with idle trunks, greater in number than said trunks, first selectors for automatically selecting idle switches in accordance with the first digit of the called number, means serving automatically to preventfurther seizure of idle switches after and while the trunks are all in use, telephone lines, a central source of talking and operating current, and

connectors provided with means for bridging said source of current across any called telephone line.

28. In a telephone system, a plurality of trunks, as many relays as there are trunks, a plurality of switches for automatically selecting idle trunks, reatcr in number than said trunks, means or automatically selectin;! idle switches, means for energizing a relay each time a trunk is selected, means wherebythe energizing of all of said relays serves to, automatically prevent further seizure'of idle switches, telephone lines, a central source of talking and operating current. and connectors provided with means for bridging said source of current across any called telephone line.

29. In a telephone system, a plurality of trunks, a plurality of switches for automatically connecting with idle trunks. greater in number than said trunks, a set of relays for said trunks, one for each trunk, relay mechanism adapted when energized to establish a guarding potential for all idle switches, a circuit for said mechanism controlled by all relays of the set, means for energizing a re lay of said set each time a trunk is seized by Ill image a switch, tele hone lines, a central source of talking and operating current, and conncctors provided with means for bridging said source of current across any called telephone line. i

30, In a telephone s stem, a plurality of trunks, trunking switc es, a master switch for selecting idle trunks for said switches, electrically-controlled means automatically serving to prevent actuation of said master switch after and while all of said trunks are in use, telephone lines, a central source of talking and operating current and connectors provided with means for bridging said source of current across any called telephone I line,

31. In a telephone system, a plurality of trunks, non-numerical trunking switches with which said trunks are multipled, a master switch for selecting idle trunks ahead of the calls for said trunking switches, means electrically controlled only by the simultaneous use of all said trunks to temporarily prevent further actuation of said master switch, telephone lines, a central source a of talking and operating current, and cona said trunks, means nectors provided with means for bridging said source of current across any called telephone line. I

32. In a telephone system, a plurality of trunks, a plurality of switches for automatically connecting with idle trunks, greater in number than said trunks, means for automatically selecting idle switches, means serving automatically to prevent further seizure of idle switches after and while the trunks are all in use, telephone lines, a re hater in each trunk, and a central sourceo and operating current, each repeater pro vided with means for bridging said source across the trunk thereof .to supply talking current to the calling telephone line.

33. In a telephone system, a plurality of trunks, a plurality of non-numerical switches for automatically connecting with idle trunks, greater in number than said trunks, first selectors for automatically selecting idle switches in accordance with. the first digit of the called number, means serving autoly to prevent further seizure of idle switches after and while the trunks are all in use, telephone lines, a repeater in each trunk, and a central source of talking and operating current, each repeater provided with means for bridging said source across the trunk thereof to supply talking current to the calling telephone line. 3 34. In a telephone system, a plurality of trunks, as many relays as there are trunks, a plurality of switches for automatically seecting idle trunks, greater in number than for automatically selecting idle switches, means for energizing a relay each time a trunk is selected, means whereby the energizing of all of and relays in number talking a l I 11 serves to automatically revent further seizure of idle switches, te ephone lines, a repeater in each trunk, and acentral source of talkin ando provi ed wit means for ridging said source across the trunk thereof to so ly talk' current to the calling tele hone me. 35. n a telephone system, a p urality of trunks, switches for automatically connecting with idle trunks greater in number than said trunks, means or automatically selecting idle switchesj-means for automatically establish a guarding potential for all idle switches d fter and while the trunks are all in use, telephone lines, a repeater in each and a central source of talking and operating current, each repeater provided with means for bridging said source across the trunk thereof to supply talking current to the calling telephone line.

36. Ina tele hone system, a plurality of trunks, a plum ity of switches for automaticdlly connecting with idle trunks, greater than said trunks, a set of relays for said trunks, one for each trunk, relay mechanism adapted when ener izcd to establish a guarding potential for all idle switches, a circuit for said mechanism controlled by allrelays of the set, means for ener izing a relay of said set each time a tr is seized by a switch telephone lines, a repeater in each trunk, and a central source of talking and operating current, each repeater provided with means for bridging said source across the trunk thereof to supply talking current to the calling telephone 37. In a telephone system, a plurality of switchboards, trunks leading therefrom, means for automatically selecting idle switches on said boards, means automatically serving when the trunks on any board are all in use to divert the automatic selection to some other board, telephone lines, a repeater in each trunk, and a central source of talkin and operating current, each repeater provi ed with means for bridging said source across the trunk thereof to sup ly talking current to the calling telephone line.

38 11 a telephone system, a plurality of switchhoards, trunks leading therefrom, switches on each board greater in number than the trunks leading therefrom, means for automatically selecting idle switches on said boards, means for preventing further selections of idle switches on any board when all the trunks thereof are busy, there being trunk lines leading to said boards so disposed that any attempted selection of an idle switch onie, board when all the trunks leading therefrom are busy will be diverted to another board, telephone lines, a repeater in eachtrlmk, and a central source of talking operating current each repeater provided with means for bridging said source crating current each repeater across the trunk thereof to sup ly talking current to the calling telephone inc.

39. In a telephone system, a plurality of non-numerical trunking switchboards with trunks leading therefrom, means for extending calling connections to said boards, devices rendered operative only by the simultaneous use of all the trunks on any board to divert the calls to other boards, telephone lines, a re eater in each trunk, and a central source 0 talking and operating current, each repeater provided with means for bridgin said source across the trunk thereof to supp y talking current to the calling telephone line.

40. In a telephone system, a lurality of non-numerical trunking switch cards, the switches on any board being greater in number than the trunks leading therefrom, means for automatically selecting idle switches on said boards, means for preventing further selection of idle switches on any board when the other switches and all the trunks are in use, there being trunk lines leading to said boards so arranged that the prevented selection will be diverted to another board, telephone lines, a repeater in each trunk, and a central source of talking and operating current, each repeater provided with means for bridging said source across the trunk thereof to supply talking current to the calling telephone line.

41. In a telephone system, a plurality of trunks, trunking switches, a master switch for selecting idle trunks for said switches, electrically-controlled means automatically serving to prevent actuation of said master switch after and while all of said trunks are in use, telephone lines, a repeater in each trunk, and a central source of talking and operating current, each re eater provided with means for bridging said source across the trunk thereof to supply talking current to the calling telephone line.

42. In a telephone system, a plurality of trunks, non-numerical trunking switches with which said trunks are multipled, a' master switch for selectin idle trunks ahead of the calls for said trunking switches, means electrically controlled only y the simultaneous use of all said trunks to temporarily prevent further actuation of said master switch, telephone lines, a repeater in each trunk, and a central source oi talkin and o crating current, each repeater provided wit means for bridging said source across the trunk thereof to supply talking current to the calling telephone line.

43. In a. telephone system, trunks, a plurality of non-numerical switches for automatically connecting with idle trunks, greater in number than said trunks, first selectors for automatically selecting idle switches in accordance with the first digit a plurality of of the called number means serving automatically to prevent iurther seizure of idle switches after and while the trunks are all in use, a numerical switch for each trunk, and lines leading from each numerical switch, which lines are divided into groups, each numerical switch having motion in one plane to select a grou and then in another plane at an angle to tile first plane to find a line in the selected group.

44. In a telephone system, a plurality of trunks, as many relays as there are trunks, a plurality of switches for automatically selecting idle trunks, greater in number than said trunks, means for automatically selecting idle switches, means for ener izing a. relay each time a trunk is selecte means whereby the energizing of all of said relays serves to automatically prevent further seizure of idle switches, a numerical switch for each trunk, and lines leading from each numerical switch, which lines are divided into groups, each numerical switch havin motion in one plane to select a group an then in another plane at an angle to the first plane to find a line in the selected group.

45. In a telephone system, a p rality of trunks, a plurality of switches for automatically connecting with idle trunks greater in number than said trunks, a set oi relays for said trunks, one for each trunk, relay mechanism adapted when energized to establish a guardin potential for all idle switches, a circuit tor said mechanism controlled by all relays of the set, means for energizing a. relay of said set each time a trunk is seized by a switch, a numerical switch for each trunk and lines leading from each numerical switch, which lines are divided into groups, each numerical switch having motion in one plane to select a grou and then in another plane at an angle to t e first plane to find a line in the selected group.

46. In a telephone systemya plurality of trunks, trunking switches, a. master switch for selecting idle trunks for said switches, clectricallycontrolled means automatically serving to prevent actuation of said master switch after andwhile all of said trunks are in use, a numerical switch for each trunk, and lines leadingfrom each numerical switch, which lines are divided into groups, each numerical switch having motion in one plane to select a group and then in another. plane at an angle to the first plane'to find a line in the selected group.

47. In a telephone stem, trunks, non-numerica with which said trunks are multip ed, a master switch for selecting idle trunks ahead of the calls for said trunking switches, means electrically c ntrolled only by the simultaneous use of a plurality of all said trunks to tem- ,porarily prevent further actuation of said trunking switches master switch, a numerical switch for each switch busy to the main switch, said means trunk, and lines leading from each numeriincluding a guarding potential circuit and cal switch, which lines are divided into a controlling magnet in said auxiliary groups, each numerical switch having moswitch. a

t on in one plane to. select a roup and then 55. In a telephone system, a main switch,

in another lane at an angle to the'first an auxiliary switch accessible thereto, a line plane to fin a line in-the selected group. accessible to said auxiliary switch, and 48. In a telephone system, a plurality of .means iormaking said line busy to the auxtrunks, as many relays as there are trunks, a iliary switch and for makin said auxiliary plurality of switches for automatically switch busy to the main switch, said means ectin'g idle trunks greater in number than including a guarding potential circuit alot-, said trunks, a master switch for automatited to said line and a controlling magnet in cally selecting idle switches, means for enersaid auxiliary switch. gizing a relay each time a trunk is selected, 56. In a telephone system, a main switch, and means whereby the energizing of all of a non-numerical auxiliary switch accessible said relays serves to automatically prevent there 0, a line accessible to said auxiliary further seizure of idle switches, and likeswitc means for making said line busy to wise prevents further operation of said masthe auxiliary switch and means for making ter switch. said auxiliary switch busy to said main 49. In a telephone system, a plurality of switch, said last means including the auxiltrunks, trunking switches, a master switch iary switch. a 86 for selectin idle trunks for said switches, a 57. In a telephone system], a main switch,

e thereto, a line trunks, means for operating one of sai reaccessible to said auxiliary switch, means for lays whenever a trunk is seized, and cans making said line busy to the auxiliary controlled by the energization of a plurality Switch and means for maklng said auxiliary 90 of said relays for preventing actuation of switch busy to the mam switch, said first said master switch. means including a guarding potential cir- 50. In a telephone system, a main switch, cuit, said last means comprlsing the auxila non-numerical auxiliary switch accessible iary switch. thereto, a line accessible to said auxiliary 58. In a telephone system, a mam switch, switch, and means for making said line busy an auxiliary switch accessible thereto, a line to the auxiliary switch and for making said accessible to said auxiliary switch, means for auxiliary switch busy to the main switch, making said line busy to the auxiliary said means including the auxiliary switch. switch and means for making said auxiliary 51. In a telephone system, a main switch, switch busy to said main switch, said first 10o plurality o relays, one for each of said an auxiliary switch accessib an auxiliary switch accessible thereto, a line means com rising a guardin potential cira cessible to said auxiliary switch, and cult allotte to said l1ne, sai last means inmeans for making said line busy to the auxcluding the auxiliary switch.

iliary switch and for making said auxiliary a 59. In a telephone system, a main switch, switch busy to the main switch, said means an auxiliary switch accessible thereto, a line including a guarding potential circuit d accessible to said auxiliary switch, means for the auxiliary switch. inking said line busy to the auxiliary 52. In a telephone system, a main switch, switch and meansfor making sa d auxiliary an auxiliary switch accessible thereto, a. line swi ch busvto said main switch, saidsecond accessible to said auxiliary switch, and means inc uding a guarding potential cm means for making said line busy to the auxcuit and the auxiliary switch. iliary switch and for making said auxiliary 60. In a telephone system a main switch, switch busy to the main switch, said means an auxiliary switch accesslb e thereto, a line including a guarding potential circuit allotaccessible to said auxillary switch, means for ted to said line and the auxiliary switch. making said line busy to the aux l ary 116 53. In atelephone system, a main switch, switch and means for makingsaid auxiliary an auxiliary switch accessible thereto, a line twitch busy to said main swatch, said first accessible, to said auxiliary switch, and and second meapscaelnnc mg aguard ng means for making said line busy to the aux-' potential circuit, the last means including iliary switch and for making said auxiliary also the auxil ary switch. switch busy to the main switch, said means 61. In a telephone system, a mam. switch, including a controlling magnet in said auxan auxiliary switch accessible thereto, a line iliary switch. I accessible to said auxiliary swltch, means for 54. In a telephone system, a main switch, making said line busy to the aux l ary an auxiliary switch accessible thereto, a line switch and means for makingsald auxlllary 126 62. In a telephone system, a main switch, an auxiliary switch accessible thereto, a line accessible to said auxiliary switch, means for making said line busy to the auxiliary switch and means for making said auxiliary switch busy to the main switch, said first means including a guarding potential circuit, said last means including a controlling magnet in said auxiliary switch 63. In a telephone system, a main switch, an auxiliary switch accessible thereto, a line accessible to said auxiliary switch, means for making said line busy to the auxiliary switch and means for making said auxiliary switch busy to said main switch, said first means including a guarding potential circuit alloted to said line, said last means including a controlling magnet in said auxiliary switch.

64. In a telephone system, a main switch, an auxiliary switch accessible thereto, a line accessible to said auxiliary switch, means or making said line busy to the auxiliary switch and means for making said auxiliary switch busy to said main switch, said second means including a guarding potential circuit and a controlling magnet in said auxiliary switch.

65. In a telephone system, a main switch, an auxiliary switch accessible thereto, line accessible to said auxiliary switch, means for making said line busy to the auxiliary switch and means for making said auxiliary switch busy to said main switch, said second means including a guarding potential cir cuit alloted to said auxiliary switch and a controlling magnet in said auxiliary switch.

66. In a telephone system, a main switch, an auxiliary switch accessible thereto, a line accessible to said auxiliary switch, means for making said line busy to the auxiliary switch and means for making said auxiliary switch busy to said main switch, said first and second means each including a guarding potential circuit, the last means including also a controlling magnet in said auxiliary switch.

67. In a telephone system, a main switch, an auxiliary switch accessible thereto, a line acessible to said auxiliary switch, means for making said line busy to the auxiliary switch and means for s itch busy to said main switch, said first means including a guarding otential circuit allotted to said line. an said second means including a guarding potential circuit allotted to said auxiliary switch and a controlling magnet in said auxiliaryswitch. 68. In a telephone system, a series of main switches, non-numerical auxiliary switches accessible thereto, lines accessible to said auxiliary switches, and means for making all of said lines busy to the auxiliary switches and for making said auxiliary switches busy making said auxiliary.

to the series of main switches, said means including the auxiliary switches.

69. In a telephone system, a series of main switches, auxiliary switches accessible thereto, lines accessible to said auxiliary switches, and means for making all ofsaid lines busy to the auxiliary switches and for making said auxiliary switches busy to the series of switches, said means including guarding potential circuits and the auxiliary switches.

70. In a telephone system, a series of main switches, auxiliary switches accessible there to, lines accessible to said auxiliary switches, and means for making all of said lines busy to the auxiliary switches and for making said auxiliary switches busy to the series of main switches, said means including guarding potential circuits allotted to said lines and the auxiliary switches.

71. In a telephone system, a series of main switches, non-numerical auxiliary switches accessible thereto, lines accessible to said auxiliary switches, and mean for making all of said lines busy to the an? iary switches and for making said auxiliar switches busy to the series of switches, sai means including magnets in said auxiliary switches.

7 2. In a telephone system, a series of main switches, auxiliary switches accessible thereto, lines accessible to said auxil y switches, and means for making all of in. lines busy to the auxiliary switches and for making said auxiliary switches busy to the series 01 main switches, said means including guarding potential circuits andcontrolling magnets in said auxiliary switches.

73. In a telephone system, switches, auxiliary switches accessible thereto, lines accessible to said auxiliary switches, and means for making all of said lines busy to the auxiliary switches and for making said auxiliary switches busy to the series of main switches, said means including guarding potential circuits allotted to said lines and controlling magnets in said auxiliary switches.

7 4. In a telephone system, a series of main switches, non-numerical auxiliary switches accessible thereto, lines accessible to said auxiliary switches, means for making all of said lines busy to the auxiliary switches and means for making said auxiliary switches busy to said series of main switches, said last means including the'auxiliaiy switches.

75. In a telephone system, a series of main switches, auxiliary switches accessible thereto, lines accessible to said auxiliary *itches,

- means for making all of said lines busyto the auxiliary switches and means for making said auxiliary switches busy to said seriesof main switches, said first means ineluding guarding potential circuits, said last means including the auxiliary switches.

7 6. In a. telephone system, a series of mai a series of main aromas switches, auxiliary switches accesible thereto, lines accessible to said auxiliary switches,

means for making all of said lines busy to the auxiliary switches and means for ma ng 1 switches.

77. In a telephone system, a series of main switches, to, lines accessible to said auxiliary switches, means for making all of said lines busy to the auxiliary said auxiliary switches busy to said se 'es 0 main switches, said second means inc tidingguarding potential circuits and the auxiliary switches.

78. In a telephone system, a series of main switches, auxiliary switches accessible thereto, lines accessible to said auxiliary switches, means for making all of said lines busy to the auxiliary switches and means for making said auxiliary switches busy to said series of main switches, said first means compris ing the guarding otential circuits, and said second means inc uding guarding potential circuits, the last means including also the auxiliary switches.

79. In a telephone system, a series of main switches, non-numerical auxiliary switches accessible thereto, lines accessible to said auxiliary switches, means for making all of said lines busy to the auxiliary switches, and

means for making said auxiliary switches busy to said series of main switches, said.

last means including controlling magnets. in said auxiliary switches. a

80. In a telephone system, a series of main switches, auxiliary switches accessible thereto, lines accessible to said auxiliary switches, means for making all of said lines busy to the auxiliary switc ass, and means for making said auxiliaryswitchesbusy to said series of main switches, said first means ineluding guarding potential circuits, said last means including controlling magnets in said auxiliary switches.

81. In a telephone system, a series of main switches, auxiliary switches accessible thereto, lines accessible to said auxiliary switches,

'means'jor making all of said lines busy to the auxiliary switches and means for making said auxiliary switches busy to said series of main switches, said first means including guarding potential circuits allotted to said lines, said last means including controlling magnets in said auxiliary switches.

$2. In a telephone system, a series of main switches, auxiliary switches accessible thereto, lines accessible to said auxiliary switches, means for making all of said lines busy to the auxiliary switches and means for making said auxiliary switches busy to said series of auxillary switches accessible thereswitches and means formakin main switches, said second means including guarding potential circuits and controlling magnets in said auxiliary switches.

83. In a telephone system, a series of main switches, auxiliary switches accessible thereto, lines accessible to said auxiliary switches, means for making all of said lines busy to the auxiliary switches and means for making said auxiliary switches busy to said series 0 main switches, said second means includin guarding potential circuits allotted to said auxiliary switches and controlling magnets in said auxiliary switches.

84. in a tele hone system, a series of main switches, auxiliary switches accessible thereto, lines accessible to said auxiliary switches, means for making all of said lines busy to the auxiliary switches and means for mak ing said auxiliar switches busy to said series of main switc es, said first means including guardin potential circuits and second means inclu ing uarding potential circuits, the last means including also controlling magnets in said auxiliary switches.

85. In a telephone system, a series of main switches, auxiliary switches accessible therc-- to, lines accessible to said auxiliary switches, means for making all of said lines busy to the auxiliary switches and means for makin said auxiliary switches busy to said series 0 main switches, said first means includin a uardin potential circuit allotted to each ine, an said second means including a guarding potential circuit allotted to cacl auxiliary switch and including also controlling magnets in said auxiliary switches.

. 86. In a telephone system, a plurality of trunks, a plurality of non-numerical switches for automatically connecting with idle trunks, greater in number than said trunks, first selectors for automatically selecting an idle one of said switches in accordance with the first digit of the called number, and electromagnets and circuits serving automatically to prevent further seizure of idle switches after and while the trunks are an in use.

87. In a telephone s trunks, a relay indivi ual to each trun a lurality of switches for automatically seacting idle trunks, reater in number than said trunks, electrica ly controlled means for automatically selecting idle switches, circuits for energizing a relay each time a trunk is selected, and electromagnets and circuits whereby the ener izing of all of said relays serves to automatically prevent fur-- ther seizure of idle swi :hes.

88. In a tale hone system, a plurality of trunks, a plum ity of switches for automatically connectin with idle trunks greater in number than sa d trunks, a set of relays for said trunks, one for each trunk and individual thereto, relay mechanism adapted when energized to establish a guarding potential for all idle switches, a circuit for said mechanism controlled by all relays of the set, and circuits for energizin a relay of said set each time a trunk is seized by a switch.

89. In a telephone system, a plurality of trunks, trunkin switches, a master switch for selecting id e trunks for said switches, a relay for each trunk and individual thereto, and electromagnetic means controlled by said relays jointly to prevent actuation of said master switch after and while all of said trunks are in use.

. 90. In a telephone system, a plurality of trunks, non-numerical trunking switches with which said trunks are multipled, a master switch for selectin idle trunks ahead of the calls for said trun ing switches, electromagneticmeans comprising a relay for each trunk and individual thereto controlled only by the simultaneous use of all of said trunks to temporarily prevent further actuation of said master switch.

91. Inv a telephone system, a plurality of groups of automatic switches, a group of trunk lines accessible to each group of switches, other automatic switches having access to said first switches, and means comprising trunk relays serving automatically when all the trunk lines in a particular group are busy to render the switches having access to such trunk lines busy also.

92. In a telephone system, .a plurality of groups of secondary automatic switches, a group of trunk lines accessible to each group of secondary switches, groups of primary switches, the switches in each primary roup having access to switches in each 0 said secondary groups, and means comprisin a, relay for each trunk serving automatica ly when all the trunk lines accessible to a particular group of secondarv switches are busy for rendering such group of secondary switches busy to said primary switches.

93. In a telephone system, a plurality of groups of trunk selecting switches, trunk lines leading into said groups, trunk lines leading out of said groups, means for selecting and seizing idle trunk lines leading into said groups, and means for preventing the seizure of an idle trunk leading into any particular group when all the trunk lines leading out of such group are busy, said last means comprising a set of chain relays for each group of outgoing trunks, and each chain comprising a relay for each trunk of the group.

94. In a telephone system, a lurality of groups of secondary switches an a group of trunk lines accessible to each group, groups of primary switches, the switches of each primary group having access to a switch in each secondary group, and means comprising trunk relays and a circuit controlled thereby serving automatically when all the trunk lines of a particular group are busy to render all the associated secondary switches busy also and to divert calls from said primary switch to another secondary switch board.

Signed by me at Chicago, Cook county, Illinois, this 30 day of Sept, 1910.

EDWARD A. MELLINGER.

Witnesses:

Eowano D. FALES, ARTHUR J. RAY.

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