US2100517A - Automatic telephone switch - Google Patents

Description

Nov. 30, 1937. lR. G. RlcHARDsoN 29100517 AUTOMATIC TELEPHONE SWITCH 3 Sheets-Sheet 2 Filed May l, 1936 INVENTOR. PODNE-Y G. IQICHARDSON ATTORNEY.

NOV. 30, 1937. R RgCg- zARDgQN 2,19%5117 AUTOMATIC TBLEPHONE swITCH Filed May 1, 1936 3 Sheets-Sheet 5 FINDER INVENTOR. RODNEY G. DICHAIQDSON ATTORNEY.

Patented Nov. 30, 1937 UNITED STATES PATENT OFFICE AUTOMATIC TELEPHONE SWITCH Delaware Application May 1, 1936, Serial No. 77,361

15 Claims.

The present invention relates in general to automatic telephone systems, and more in particular to the Strowger type of system using vertical and rotary switches. The object of the invention, generally speaking, is to reduce the cost of such systems.

A major item infiuencing the cost of the Strowger system is the multiple banks. Although efforts have been made to improve manufacturing methods so as to make the banks less expensive, the economics effected have not been great, and the present invention therefore proceeds along different lines. In brief, the saving is accomplished by arranging matters so that two groups of switches may use the same set of multiple banks. This results in reducing the number of banks in an exchange by one half and also saves a considerable number of multiple cables that are otherwise required.

The invention Will be described hereinafter With reference to the accompanying drawings, in which- Fig. 1 is a front view showing parts of a connector switch and a finder switch using the same banks;

Fig. 2 is a side view of the same parts as shown in Fig. 1;

Fig. 3 is a section on the line 3--3, Fg. 1;

Fig. 4 is a section through one bank on the line 4-4, Fig 3;

Figs. 5 and 6 are details of the guiding and supporting means for the finder wipers;

Fig. 7 shows a modified arrangement for selectors; and

Fig 8 is a circuit diagram of a link circuit comprisng a connector switch and a finder switch.

Referring to the drawings, the reference character Il] indicates a part of the frame of a Strowger connector and Il indicates part of the frame of a Strowger finder. These switches are of well known mechanical construction and hence are not shown, except for parts of the frames and the ends of the shafts carrying the wipers. In a one-hundred line switchboard there may be ten connectors mounted one above the Vother on suitable uprights and ten nders similarly mounted, making two vertical rows of Switches. These two rows are spaced apart and between them is a 50 single set of multiple banks, which are used in common by the connectors and nders. Since the switches are mounted with their shafts in a horizont-al position gravity cannot be used for restoring purposes and each switch is provided 55 with restoring mechanism of the type shown in the` pending application of Mahoney, S. N. 18,774, filed April 29, 1935.

Between frames IU and l l extend two bank rods |2 and 13, on which are mounted in the usual manner two banks 14 and l5. These banks are 5 in part indicated diagrammatically in Figs. 1 and 2, but are shown in detail in Figs. 3 and 4. They are of the usual construction, except for modifications that Will be explained. The banks shown are multipled with similar banks in a 10 vertical direction.

The shaft IB of the connector carries two pairs of wipers I'l l8 and |9-20, which may be of the usual construction. In the so-called vertical movement of the connector the shaft 16 is moved 15 step by step in a horizontal direction to the left and thus the wipers may be positioned opposite any desired level of bank contacts. In the rotary movement of the connector the shaft is rotated step by step in a clockwise direction, Fig. 3, and 20 the wipers are thus positioned on any desired set of contacts in the selected level. These operations are well understood.

The finder shaft 34 is in axial alignment with the connector shaft 16 and is operated in pre- 25 cisely the same manner, except that since the two shafts point in opposite directions the directions of movement are opposite With respect to the bank. That is, the finder shaft moves to the right as seen in Fig. 1 during the vertical movement of 30 the switch and the wipers rotate in a counterclockwise direction as seen in Fig. 3.

There are two pairs of finder wipers 23-24 and 25-26. These wipers are curved in shape to conform to the shape of the bank, as seen in Fig. 3. 35 The wipers are mounted as shown in Fig. 1 on a wiper carriage 22 which may be of right angle section for the sake of lightness and rigidity. This wiper carriage is in turn supported on a member 2! which is secured to shaft 34. 40

Due to the length of the finder wipers it is desirable to provide supporting means for the ends, as otherwise vibration would be apt to occur during the vertlcal movement and the wipers might not enter the banks properly on the ensuing rotary movement. To avoid any diflicultyon this account, the arrangement about to be described is provided. On the shaft 34 there is mounted an arm 26, as shown in Fig. 1, which partakes in the vertical or longitudinal movement of the shaft but not in the rotary movement. The arm 26 carries a horizontal member 21, also seen in Fig.

1, and more in detail in Fig. 5. The right-hand clamping member 28 of bank H is made With an extension 29, Figs. 1 and 6, which is bent as shown in Fig. 1 and les parallel to the member 21. The latter has a pin or stud 33 which lies in the slot 36 of extension 29. It Will be seen that with this arrangement the member 21 will move longitudinally to the right during the primary movement of shaft 34, but when the shaft is rotated the member v27 will remain stationary due to the stud 33 engaging the side of slot 30. The member 21 carries two insulated pins 3! and 32 which lie between the wipers of wiper pairs 2% 24 and 25 26, respectively, and against Which the wipers are tensioned. It will be seen that the pins 31 and 32 serve to steady the wipersand prevent vibration thereof during the primary movement of the finder and insure that the wipers will enter the banks properly at the beginning of the rotary movement. i i i The clamping member 35 of bank 14 has an extension 36 and there is a similar extension on' the clamping member 31 of bank 15. To these extensions there is secured a member 38 on Which is mounted the usual vertical bank 39. This bank 39 comprises the level test Contacts for the finder. The level test wiper 40 is mounted on a bracket M which is secured to the carriage 22. i

The banks are of the Vusual construction except for the modifications required to adapt them for use by two sets of wipers simultaneously. To this end the bank Contacts are made somewhat longer than in the standard bank, and the wipers H-ZG of the connector, which operate on the bank contactsclose to the ends thereof, are made slightly shorter than usual. This leaves a portion of each contact set outside the arcs described by the connector wipers l'-l-ZU which can be engaged by the finder wipers 23-28. It Will be seen, therefore, that although the finder and Vconnector use the same banks the connector wipers and finder wipers may be operated entirely independent of each other without interference. That is, the finder wipers may be positioned on any desired Set of VContacts and while the finder remains in operated position theV connector wipers may be positioned on any desired set of Contacts, even on the same set that is engaged by the finder wipers.

i Fig. 4 shows the construction of the bank and also shows the relative position of a pair of connectorwipers and a pair of finder wipers when engaging the same pair of contacts. It may be pointed out that the insulators, such as 45 and 46, extend within the arc described by the outer edge of finder wipers such as 23, as is shown clearly in Figs. 3 and 4. The reason for thisconstruction is to obviate any danger of accidental touching of Contacts by the finder wipers. These wipers are rather long and if not perfectly adjusted there might be some danger of touching other'contacts than the ones selected, particularly at times when the wipersare rotated far into the banks. V' i Referring now to Fig. 8 an explanation will be made of the operation of a system in which the nvention is applied. It will be assumed that the system comprises one hundred subscribersf lines and that connections areestablished by means of finderconnector links of which one is shown in the drawings. Two subscribers' stations A and B are also shown, with their associated lines and linecircuits. The numbering of the subscribers' lines is, of course, determined by considering the banks from the standpoint of the connector wipers, as the connector is the switch which is directively controlled by'digit impulses in accordance'with called numbers. The bank contact sets shown in the drawings are the first COIlfit Sets of the ten levels, that is, the first contact sets engaged by the connector wipers in their rotary motion. Now, the line of station A is connected to the first set of contacts in the sixth level, the levels being numbered in their order of access from the connector wipers, and the line of station B is connected to the first set of contacts in the eighth level. Hence the telephone number of station A is GI and the number of station B is l It will now be assumed that the subscriber at Station A desires to call the subscriber at Station B. Upon the removal o-f the receiver at station A a bridge is closed across the line in the usual manner, which operates the line relay 58. On energizing, the line relay places a low resistance shunt Varound the cut-off relay 5! and 52, which has the effect ofrmarking the line as calling in the banks of the finders such as F, and at 53 grounds the group .or level start conductcr IH. The latter operation places a ground on the level test contact ll2 and operates the common start re lay Hil. i

Upon energizing,rrelay HG closes the finder start circuit which, on the assumption that the link circuit shown in the drawings is idle, extends through to the start relay IM of the finder F.

The circuit extends from ground by way of iil,

IZZ, and winding of relay le! to battery. On energizing, relay lfll connects up' the level test wiper 40 at IZI, grounds therelease trunk conductor' 132 at 120, and closes a circuit for the vertical magnet IM at HS. The latter circuit extends from ground by way of HB, lie, lz, :26, and winding of magnet Hill to battery. Upon energizing, magnet IM operates the finder shaft carrying wipers 23-25 one step, the direction of movement being downward as indicated in the circuit drawing, Fig. 8, and to the right as seen in Fig. l. The vertical magnet also closes a circuit for the interrupter relay lll2. On energizing, the interrupter relay closes the level test circuit through at l25, and at lZll breaks the circuit of the vertical magnet. The vertical magnet accordingly deenergizes'and breaks the circuit, of the interrupter relay, which thereupon falls back and again closes the vertical magnetV circuit. It Will be seen, therefore, that the vertical magnet and interrupter relay operate alternately, the former advancing the finder shaft and wipers step by step past the levels 0, 9, 8, 7, ete.

On the fifth step Vthe wipers will be moved opposite the sixth level of bank Contacts, and the level test wiper @30 will be brought into engagement with the level test contact I! 2. When the interrupter relay N32 energizes, therefore, following the fifth operation of the vertical magnet, a circuit will be completed for the level test relay l. This circuit includes the lower winding of the interrupter relay N32, thus'preventing it from falling back for the time being. On energizing, relay N33 transfers the- Operating circuit from the vertical magnet HM to the rotary magnet l at l26, at l2'i prepares a circuit for the line test or switch-through relay! ili), and closes Va locking circuit for itself at l28. At the same time that the looking circuit of relay Hl is closed at lZ, the initial energizing circuit o-f this relay is broken and accordingly the interrupter relay lilZ is permitted to fall back. The deenergization of the interrupter relay at this time closes a circuit for the rotary magnet i05 at l24.

The finder F now begins to operate in its rotary movement, moving the wipers 23-25 in onto the bank Contacts of the sixth level in search of the callingline. The rotary magnet l and interrupter relay 102 cooperate' during the rotary movement the same as the vertical magnet and interrupter relay did during the vertical movement. The test relay I00 is marginal and will not operate in series with cut-off relays such as 5 I, as these relays are of relatively high resistance. The relay I 00 Will, however, operate in series with any cut-off relay which has been shunted by a resistance through the operation of the associated line relay. It follows, therefore, that the finder continues to rotate its wipers step by step until ten consecutive steps have been taken, bringing the wipers 23-25 into engagement with the first set of contacts in the sixth level. This is the set of Contacts in which the line of station A terminates, and since the line is now in oalling condition, test contact II3 will be found to be marked with a heavy battery potential, due to the shunting of cut-off relay 5I at 52, as previously explained. It follows that when the test wiper 25 engages test contact Ii3 test relay I00 Will be energized, the circuit extending from ground at [21 by way of the lower winding of relay Iilil, test wiper 25, test contact I I3, and thence to battery through the cut-off relay 5I and the resistance connected in parallel therewith. On energizing, relay [00 stopsthe operation of the rotary magnet by opening the Operating circuit at I IB, locks itself to the release trunk conductor at I I G, connects the release trunk conductor through to test wiper 25-at i il, breaks the circuit of level test relay I03 at II5, opens the circuit of start relay I OI at I22, and closesr through the heavy talking conductors of the link to the line wipers 23 and 24. By the latter operation the calling line is extended through over wipers 23 and 24 and link talking conductors I3I and I3-3 to the line relay 55 of the connector C. On energizing, the line relay closes a circuit for the slow-acting release relay 56 at 66. The release relay accordingly energizes and grounds the release trunk conductor I32 at 61. When the circuit of the start relay I GI is broken at I22 it falls back, but is sufliciently slow-acting so that ground is not removed from the release trunk condflctor at IZS until it has been connected at 61. The deenergization of relay IOI prepares a circuit for the release magnet I 06 at II9 and also transfers the start circuit to the next finder at I23. The deenergization of relay N53 is of no consequence at this time.

When the test circuit is closed through the lower winding of the test relay I00, cut-off relay 5I energizes in series with the test relay and is subsequently maintained energized by ground on the release trunk oonductor via I I'l and the test wiper 25. On energizing, relay 5I clears the line of its normal battery and ground connections, resulting in the deenergizing of the line relay 50. This relay removes the resistance from in shunt of cut-off relay 5I, and also breaks the starting circuit at 53. Relay 51 energizes promptly and line relay 50 falls back quickly so that the common start relay IIO will be deenergized in time to prevent the starting of another finder upon the transfer of the start circuit by the deenergization of start relay I0l.

The calling line has now been extended to the connector C and the link is ready for the calling subscriber to start dialling the number of the called subscriber.

When the calling device is operated in accordance with the first digit 8 of the called number, eight interruptions are produced in the circuit of line relay 55, and this relay accordingly deenergizes eight times, transmitting eight impulses to the vertical magnet 63 in series with the change-over relay 57. The vertical magnet responds to these impulses and operates the connector shaft eight steps in an upward direction as seen in Fig. 8, and to the left as seen in Fig. 1. The ofi-normal springs ON are shifted on the first step of the shaft, but the Operating circuit of the vertical magnet is maintained throughout the series of impulses by change-over relay 51, which energizes on the first impulse of the vertical magnet and stays energized until the series is finished.

When the impulses for the first digit 8 have all been transmitted the change-over relay 51 falls back and transfers the Operating circuit to the rotary magnet 64. The subscriber may now dial the second digit 1 of the called number. The line relay 55 accordingly has its circuit interrupted once, and falls back once to deliver a single impulse to the rotary magnet 64. On energizing responsive to this impulse the rotary magnet rotates the shaft of the connector and brings the wipers I'I-IS into engagement with the first set of Contacts in the eighth level, being the set of Contacts in which the line of station B is terminated. The slow-acting relay 50 is operated in parallel with the rotary magnet and closes a circuit for the slow-acting relay GI. These two relays, therefore, are energizecl throughout the rotary movement of the switch, whether one or more rotary steps are taken. In energized position relay 60 connects the test Wiper I9 with the upper winding of the busy test relay 59 by way of 'iQ and "II, and thus when the wiper I9 is brought into engagement with test contact II4 of the called line a test is made to ascertain if it is busy or idle.

The test contact II4 may have either one of two busy potentials on it. One is a ground potenf tial, which is the potential maintained on the test contact of the line throughout the time it is busy except for a short period when the line is calling extending from the time the receiver is raised up to the time the line is located by a finder. For instance, during the explanation of the call made from station A it was pointed out how a heavy battery potential Was applied to the test contact I I3 by the line relay 50. This potential remained on the contact until the line Was found, when it Was replaced by a ground potential upon the energizng of the test relay I00 of the finder. The connector C first tests for a ground potential. Assuming that there is ground potential on test contact i 54, the busy test relay 59 Will be energized in an obvious manner, and when slow-acting relay l falls back at the end of the rotary movement the relay 59 will become locked over a circuit which extends from ground at 58 by way of 76, 69, "II, and the upper winding of relay 55 to battery. In energized position relay 55 opens the Operating circuit of the rotary magnet and connects a busy tone circuit to the calling line. This notifies the calling party that the desired line is busy and he will hang up his receiver.

It will be assumed now that when the test contact IM is tested for ground potential no ground potential is found and accordingly the busy test relay 59 will not energize. When relay 50 falls back at the end of the rotary movement, therefore, relay 50 not having energized, another test circuit is completed over which the test contact lI4 is tested for a heavy battery potential, which will be present if the associated line is calling Vin series with cut-off relay BI' alone.

and Vhas not been located by a finder switch. This second test circuit extends from test wiper IS by way of'lO, 12, lower winding of busy test relay 59, 76,' and 68 to ground. Relay 59 is marginal and will not operate in the above circuit unless a heavy battery potential is found on test contact IM. That is, relay 59 Vwill not operate Assuming, however, that station B is calling, the line relay 50' will be in energized position and cut-off relay l' will be shunted by a resistance. Under this condition the requisite heavy battery potential will be present on test contact ll4, and test relay 59 will operate. On energizing, relay 59 locks itself at 69 and breaks the test circuit at 16. Otherwise the test relay functions as before and gives the calling subscriber a busy signal.

It will be assumed now that the line of station B is idle when called. Under these circumstances there will be no busy potential, neither ground nor battery, on the test contact I hi, and test relay 59 will not energize in either of the two successive tests Vthat are made. The deenergization of relay 60 is followed after a short interval by the deenergization of relay ESI, which opens its Contacts 12 and thus removes'the short circuit from the lower winding of sWitching-through relay 62. Relay 62 is adapted to energize in series with a cut-off relay such as l', and accordingly pulls up over a circuit which extends from ground at 58 by way of 16, lower winding of 58, lower winding of 52, lil, test wiper l9, test contact Hil, and winding of cut-off relay l' to battery. The cutoif relay 51' energizes in series with relay 62 and clears the line of station B in the usual manner.

At connector C the energization of relay 62 connects up the two line wipers Il and IS in the usual manner. Relay 62 also locks itself at 14, places a ground on test wiper IB at 13, and breaks the circuit of the rotary magnet Gll at 15.

V V Upon the operation of the switching-through relay 52, as previously explained, the called lineV is signalled in the usual manner, ringing current being transmitted through the lower winding ofV ring-cut-off relay 53. When the called party responds by removing his receiver the rring-cut off relay 58 operates and locks itself to ground at 57. The ring-cut-oif relay also opens the ringing circuit and completes the talking circuit through the connector. The calling and called subscribers are now connected for conversation. Station A is supplied with transmitter battery through the winding of relay 55, While station B is supplied with transmitter battery through the winding of the back bridge relay 50. I The latter 1 may be arranged to reverse the direction of current flow in the calling line as shown in the drawings.

When thesubscribers are through talking they will hang up their receivers. The release of the connection is brought about by the replacement of the receiver at the calling Station A, which opens the bridge across the calling line and breaks the circuit of the line relay 55. On falling back,

' relay 55 opens the circuit of the release relay and When this relay deenergizes a circuit is closed for the connector release magnet 55. Release magnet accordingly operates and restores the connector in the usual manner. tion of relay also removes ground from the release trunk conductor 132, which breaks the looking circuits of relays 58 andV 52 and allows them to deenergize. At the finder F theremoval of ground from the release trunk conductor 32 allowsrelay i Vto fall back, .whereupon The deenergizaa circuit is closed for the. release magnet l06. Magnet l energizes and restores the finder in the usual manner. The removal of ground from the release trunk conductor 132 also permits the cut-off relay 51 to fall back, restoring the calling line to normal condition. Cut-oif relay 55' on the called line is, of course, allowed to deenergize when relay 62 of theconnector falis back. Thus the equipment involved in the connection is restored to normal.

The described system may be readily converted to a two-hundred line system by suitably lengthening the bank rods such as |2 and 13 and by adding another bank for each paired finder and connector. Each switch is also provided with another pair of wipers. The wipers such as 20 and 26, not used in the one-hundred line system shown in Fig. 8, would then' be used as the test wipers for the second hundred lines.V

The circuit arrangements of two-hundred line nders and connectors are well known and hence need not be explained.

The principles of the invention are also applicable to selectors, and therefore the invention can be used in systems of any size. Considering a given group of selectors, for example, half of them may be mounted side by side on a shelf in the usual up-right or vertical position, while the other half are mounted on a similar shelf immediately below with a common set of banks between the two shelves. The switches being mounted vertically, the shafts are restored by gravity. The selectors of the upper shelf are in all respects standard selectors, except that the wipers should be slightly shorter than usual, as described in connectionV with the wipers Il-20, Fig. l. The selectors of the lower shelf are similar to standard switches but are modified in" The shafts do not extendV the following manner. belowthe switches as is the usual case, but extend upward toward the common banks and each shaft is'equipped with a special set of curved wipers mounted on an offset wiper carriage as shown in Fig. 1. In addition, the switches are arranged to rotate their shafts in the opposite direction as compared with the switches 'in the upper shelf. This amounts to a mere reversal of the parts having to do with the rotary movement.

The arrangement of the shafts and wipers of two selectors one in the upper shelf and one immediately below in the lower shelf is depicted diagrammatically in Fig. 7. This drawing indicates two banks 20! and 202 supported on bank rods 203 and 2%4 which 'extend between the switch frames. The frame of the lower switch is, of course, arranged to receive the bank rods at the top of the frame instead of at the bottom. The shaft 205 of the upper selector carries two pairs of wipers 201 and 208 and has vertical and rotary movements in the directions indicated by the arrows. The shaft 205 of the lower selector carries twoV sets of wipers 2139 and ZIG, which are similar to the wipers mounted on shaft 315 in 1. shaft 206 has a vertical movement in the same same order, and both switches can be operated i numerically to select the sameV trunk groups, as is essential. In the drawing the shaft 206 is shown partially operated as regards its vertical position, so that the wipers 209-210 will not Vobscure the wipers on shaft 205. It will be understood that normally all wipers stand just below the first bank level.

Another plan that could be adopted is to reverse the curved wipers. For instance, and referring to Fig. 3, wipers such as 23 and the wiper carrage 22 could be so constructed that the wiper tips normally lie just outside the tips of wipers such as Il and rotate in on the banks in the same direction. If this scheme is applied to the selectors indicated in Fig. '7, the Shaft 206 would be arranged to rotate in the opposite direction from the direction shown by the arro-w, or in the same direction as shaft 205. This arrangement would have the advantage that the switch operating mechanisms would be the same, instead of half the selectors having clockwise rotary movements and half counter-clockwise rotary movements. On the other hand, the selector arrangement first described has the advantage that half of the selectors search over trunk groups in the opposite directon from that in which such groups are searched by the other half, which effects a distribution of trafiic to trunk groups from the same group of Switches without any slip in the multiple between Switches.

Either of the foregoing selector arrangements can, of course, be applied to groups of finders and connectors arranged in pairs as hereinbefore described. If the second arrangement is employed, in which the wipers of both Switches of a pair move in the same direction as regards both vertical and rotary motions, each pair of Switches need not comprise a finder and a connector, but the connectors may be paired with each other and likewise the finders. Thus in an arrangement of ten connectors and ten finders for a onehundred line group, the Switches could be mounted on two spaced shelves with the banks between as descrimbed for selectors and the first five Switches in each Shelf would be connectors, while the last five Switches in each shelf would be finders.

What is claimed is:

1. In combination, two vertical and rotary motion Switches positioned with their shafts in alignment, a set of arcuate banks positioned concentric with the axis of said shafts, and wipers on each shaft adapted to be positioned on any set of contacts in said banks without interfering with the wipers on the other shaft.

2. In combination, a bank comprising arc Shaped rows of contacts, two Switches having primary row Selecting motion and secondary contact Selecting motion, and wipers for said Switches having common access to said bank.

3. In combination, two spaced rows of Switches, said Switches having shafts extending from the opposite Switch rows into the space between them, a row of multiple banks mounted in said space, and wipers on said shafts having common access to said banks.

4. In combination, a bank comprising contacts arranged in rows, a switch having access to said bank and having primary movement to select a row and a secondary movement to select a contact in a selected row, and a second switch having access to said bank and having primary and secondary movements which are opposite in direction to the corresponding movements of said first switch with respect to Said bank, whereby the distances moved by the second switch to reach any contact are represented by values which are complementary to the values representing the distances moved by the first switch to reach the contact.

5. In an automatic switch, a rotary Shaft, a bank having contacts disposed on the circumference of a circle the center of which lies on the rotation axis of said shaft, an arc shaped wiper positioned on a different part of the same circumference on which said contacts are disposed, said wiper having a part at one end adapted to engage said contacts successively, and a radial member connected between the other end of said \Viper and Said Shaft.

6. In an automatic switch, an arcuate bank, an arcuate wiper Subtending the Same angle as .Said bank, means for supporting said bank and wiper on a common center, and means for producing relative angular motion between the bank and wiper about said center.

7. In combination, two separate and independently operabe Switches mounted in alinement with a space between them, a bank of individual bank contacts mounted in the Space between the alined Switches, and wipers for each switch adapted to be positioned on any of said individual bank contacts of said bank without interfering with the wipers of the other Switch.

8. In combination, two separate and independently operable Switches mounted in alinement with a space between them, a shaft for each Switch extending into the Space between the alined Switches, a bank common to only said two Switches mounted in the space between said alined Switches, said bank comprising a plurality of individual bank contacts arranged in rows, and wipers on each shaft adapted to be positioned on any of said individual bank contacts of said bank without interfering with the wipers of .the other switch.

9. In combination, two separate and independently operable Switches, a bank common to only said two Switches, Said bank comprising a plurality of individual bank contacts arranged in a plurality of rows, wipers on the first switch operable in a given direction to successively engage any of said individual bank contacts in said bank, and wipers on the Second switch operable in a reverse direction to the first Switch wipers to successively engage said same individual bank contacts in reverse order without interfering with the wipers of said first switch.

10. In combination, two separate and independently operable Switches, a bank common to only said two Switches, said bank comprising a plurality of individual bank contacts arranged in a plurality of rows, and wipers for each Switch operable in directons reverse to each other to successively engage the same individual bank contacts but in reverse order without interfering with each other in case of concurrent Operations thereof.

11. In combination, two separate and independently operable Switches, a bank common to only said two Svvitches, said bank comprising a plurality of individual contacts arranged in a plurality of rows, wipers on the first Switch adapted to be positioned on any of Said individual bank contacts in said bank, and wipers on the Second switch adapted to be positioned on said same individual bank contacts in said bank as the wipers of the first switch without interference therefrom.

12. In combination, two separate and independently operable Switches, a bank common to only Said two Switches, Said bank comprising a plurality of individual bank contacts arranged in a plurality of rows, and wipers for each switch 'the other shaft.

14. In combination, a bank comprising arc shaped rows of individual contacts, two Switches having primary row Selecting motions in directions reverse to each other and secondary con- Vadapted to' engage any of said individual bank 'tact Selecting motions in 'directions'reverse to each other, and wipers for said Switches having common access to'said individual bank contacts.

15. In combination, two switches mounted in.

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