US2186163A - Fire alarm system - Google Patents

Description

Jan. 9, 1940. F` R. BRIDGES ET AL FIRE ALARM SYSTEM Filed July 5, 1936 3 Sheets-Sheet 1 w n i E wx MNA www j mmm NN u Q E n m. WN WN QN NM. Nw WN f uw@ mwxmw ||L m zJan'. 9, 1940. F. R. BRIDGES AL FIRE ALARM SYSTEM Filed July 5, 1936 5 Sheets-Sheet 2 Jan. 9, 1940. F, R BRlDGES ET AL 2,186,163

FIRE ALARM SYSTEM Filed July 3, 1936 sheets-sheet 5 6 S T32 illy RECTIFIER. 140/ \/13 .AMIIIIMIIL Patented Jan. 9, 1940 UNITED STATES PATENT OFFICE FIRE ALARM SYSTEM Frank R. Bridges, Needham, and Folter E. Wold, Newton, Mass., asslgno'rs to The Ganeweil. Coin# pany, Newton Upper Falls, Mall., a

l Probably the greatest difllculty involved iny normally closed une containing a number of si@ l0 nghting mes m a Smau community arises from nal formulating devices X "in series, comprising the fact that the force must be largely, if not boxes of any mail or preferred type with oro wholly, composed of call men. Under such condivision however or 'connecting to grouod during a tions the need for adequate alarm equipment' is code signaling operation The particular method Y l greatest, but systems formerly available have of connecting to oround' not important and a l5 not been entirely suitable for small town use, not Simple construction is shown in mg 1 ,Itho box only because of their cost, but also because of the has the normally olosod codo4 oontaots 2 3 com necessity for more or less constant personal superoeoted in the une and o grounding Contact vision.

With the above object in view, one of the prinmagg.; von; vogllgcggt 2l' cipal features of the present invention comprises is automatically. moveo noot-o the Contact 2 a system in which automatic supervisory and When the code leveroi'.the box drops into a emergency signaling devices are provided to take tooth the line is broken at! I and the ground care of practically au adverse conditions which connection is broken at! l At the completion are likely to arise. Attention may be directed to of a signal the grouodmgoootaot is restored to 25 two of the most common faults which may occur inactive position They grounding Contact does on the alarm System namely 9' break in the box not enter into a signaling operation through the circuit, and failure of the local battery through normal closed loop .mover-ts transmission of inattention. For the first of these faults the signals through if the une is broken invention provides automatic means for establish- The system' hoopromioo ox-'i automatically con; 30

ing an emergency circuit which affords adequate dmomng the une following .o break to permit protection until the line can be repaired. To code signaling throu'gh round avoid the necessity for constant attention to the The une is oonoected at no onds through loca] battery, there is provided an automatic charge remy and sigoojuno eqmpmeot to the terminals control which assures that the battery-tis main- 35 of Massachusetts Application July 3, 1936, Serial No. 88,8.

1 Claim. (Ci. 177-387) The present invention relates to nre alarm systems.

The principal object of the present invention is to provide a tire alarm system which is particularly suitable for small town use, and which therefore should be inexpensive to install and maintain, and should be reliable in operation while requiring only a minimum of personal attentlon.

tained in readiness for any demands that may be placed on it. Furthermore, the line and battery, as well as the central oi'ilce equipment are placed under the constant supervision of automatic alarms.

The central equipment is particularly compact and may be conveniently housed in a small tamper prooi' cabinet. This is an important feature, since 4in those cases where space is at a premium or where the department does not have the services of lull time members, the equipment may be installed as an adjunct to some other municipal office.

The present invention also involves other features of construction and certain combinations and arrangements of parts hereinafter described and particularly defined in the claim.

In the accompanying drawings illustrating what is now considered the preferred form of the invention, Fig. 1 is a diagram of the complete system; Fig. 2 is a diagram showing the operation of the relays duxlnga signaling operation;v Fig. 3 is a diagram showing the operation o! the automatic grounding or conditioning relay; Fig. 4 is a diagram o! the station transmitter; and Fig. 5 5 is a diagram o1' the battery charging connections.

General The system shown in the drawings comprises a of a battery 8i At44 the connection between the station equipment and the line suitable lightning arresters 8 and fuses l0 may be included.

The equipment included in series with the line at the station for signaling and supervisory purposes comprises a marginal'excess current relay K. a supervisory or low current relay S, a main relay M, a gong B and a -station transmitter` ST. The excess current. relay K indicates an abnormal increase in line current and is useful in connection wtlh the establishment of telephone connections over the line, but does not enter into the normal nre alarm operation and will not be further described herein.

The supervisory relay S controls a trouble bell P which is operated from alternating current. It is sumcient tosay at this time that opening of the line or diminution ot line current below a predetermined value operates the trouble bell, and the particular connections involving the u supervisory relay will be later described in more detail.

The relay M is the principal means by which the public alarms and the local registering and signaling equipment are operated.

The station transmitter ST which is shown in detail in Fig. 4 provides for sounding of the public alarms according to any desired code from the central ofce.

It will be noted that the negative side of the battery is connected with the negative line through a pair of normally closed contacts of a' conditioning or grounding relay G which is automatically operated if the line is held open longer than a predetermined time, to convert the normally closed loop into two open ended lines whereby signaling may be accomplished through ground. When the line "is unbroken, however, the signals are transmitted through the closed loop and the relay G does not enter into the operation.

The local operating equipment which is under the primary control of the main relay M is actuated from the battery 8. To avoid complicating the diagram, the actual connections from the battery to the various station equipment are omitted and are merely indicated on the drawings by appropriate plus and minus signs. The supervisory equipment which includes the trouble bell is operated from low voltage alternating current from the transformer I2, and on the drawings the alternating current connections to the secondary transformer are merly indicated by the symbols +AC and -AC.

The battery is connected with automatic charging controls arranged to give a trickle charge continuously, and to give a high rate charge following use of the system.

Main relay and associated circuits The main relay M has the contacts designated I3 to Il inclusive. The movable contact I4 is normally closed on I3, but is adapted to close on I5 when the relay is de-energized. The contacts I8, I1 are normally open, but are adapted to close when the relay is de-energized. The contacts I3, I4 and I5 are included in control circuits of a cut-off relay C which has the contacts designated I8 to 28 inclusive. Contact I3 of the relay M and contact I 8 of the relay C are connected to the positive terminal and contacts I4 and I9 of the relays are connected together by a wire 28. l'I'he cut-oir relay C is connected at one side toits own contact I9 by a wire 30 and at the other side through a wire 32 and a resistance 34 to the negative terminal. When the main relay M is energized a circuit is therefore established from the positive terminal through contacts I3, I4 of relay M, wires 28 and 30, relay C, wire 32 and resistance 34 to the negative terminal. The relay C being thus energized, a holding circuit is established through its own contacts I8, I8.

A slow release circuit for the relay C is provided vby a resistance 38 which is included between the wire 32 and contact I5 of the relay M, so that upon de-energization of the relay M and closure of its contacts I4, I5 the relay C is shunted by the resistance 38. 'I'he relay C then drops its contacts, but because of the shunt through the resistance 38, the release is slow and there is a short interval in which the contacts of M are down while the contacts of C are still up. It is in this interval that the public alarms and certain of the station equipment are operated.

Contact I8 of the relay M is connected to the positive terminal and contact I I is connected by a lead 38 with the fixed contact 28 and the movable contact 23 of the cut-oil.' relay C. The movable contact 2| of relay C which is normally closed on contact 28 is connected by a wire 40 with a register magnet R which in turn is connected to the negative terminal. The energization of the register magnet acts to punch a. hole in the register tape. It also serves as the relay coil of a time relay T. Connected to the wire 40 is a wire 42 which leads to certain of the public alarm equipment as will be hereinafter described.

The time relay T has the contacts 43 to 50 in elusive, oi which the contacts 45, 48 and 43 are.

-the cut-off relay C is connected by a wire 88 with the movable contact 48 of the time relay T, this connection forming a part of the circuit leading to the conditioning relay G to be hereinafter described.

Contacts 25 and 28 of the cut-off relay C are included in a trouble bell circuit. Contact 28 is connected to AC and contact 25 is connected by a wire 8l, shown in dotted lines, with the contacts of the supervisory relay S for the purpose of indicating trouble in the local circuits as will be later described.

The time relay T has a latch 82, which holds up the contacts 45, 48 and 48 after they have been once attracted by the register magnet, as shown in Fig. 2. The latch is adapted to be tripped by a timing mechanism indicated generally at 84 and operated by the paper feed motor. The particular construction of the timing mechanism is not shown, since such devices are in general well known, it being understood that the mechanism is reset on each impulse of the register magnet and is so arranged that the latch is tripped only after the magnet has remained de-energized continuously for a predetermined period, which is so set as to be longer than the longest open circuit interval of the boxes, usually the longest interval between rounds of any box on the system.

When the time relay contacts are first attracted by the energization of the magnet R, contact 45 closes on 43 and lifts the latter away from 44. Contact 45 is connected with the positive terminal and thus a circuit is traced direct to the paper feed motor and the take-up motor, this circuit being maintained closed so long as the time relay is latched up. Contacts 48 and 4l of the time relay are opened. 'I'he contact 48 is the one which is connected by the wire with contact 24 of the cut-oir relay C, and the contact 4l is connected with the grounding relay G through a lead 88. The lead 88 cannot be energized when either the relay M or the relay C is energized or when the time relay contacts are up. The grounding relay is therefore entirely inactive under normal conditions in the system.

Contact 48 of the time relay is connected with the positive terminal and is normally closed on the contact 50 which connects through a lead 81 with a temperature compensated voltage relay TVR. The relay TVR constitutes the means whereby the battery charging rate is controlled as will be hereinafter explained.

Contact 48, which is closed on 43 when the time relay is up, connects by a wire 66 to a siren circuit forming a part of the public alarm equipment to be later described.

The connection to the take-up motor 63 includes a switch 63 by which the motor may be operated under manual control to take up the paper following examination of a previous record.

Boa: signaling Upon opening of the line by a pulled box, the gong B strikes and the supervisory relay S is deenergized to operate the trouble bell. cipal actions occur, however, in the circuits associated with the relays M, C and T. First, the main relay is de-energized, thus closing the shunt release circuit of the cut-oil? relay C through the resistance 36. Before the cut-off relay drops its contacts, however, the register magnet is momentarily energized by a circuit from the positive terminal through contacts I6, I1 of relay M, wire 38, contacts 20, 2| of relay C and Wire 40. The public alarm line 42 is also momentarily energized. The starting circuit for the paper feed and take-up motors is also established through contacts I6, l1 of relay M, Wire 38, contacts 23, 22 of relay C, Wire 62, contacts 44, 43 of relay T and wire 54.

'I'he register magnet R., by its momentary energization, not only serves to punch a hole in the register tape, but also lifts the contacts of the time relay T which are thereafter latched. 'I'he circuit is then established to the paper feed and take-up motors through contacts 45, 43 of the time relay T, and the motors continue to operato even though the register magnet is immediately thereafter de-,energized by the release of the cut-off relay. The operation of the time relay opens its contacts 46, 41 and therefore breaks the circuit 66 to the conditioning relay G before the contacts 23, 24 of the cut-off relay are permitted to close. V

The cut-off relay contacts then drop and the relays M, C and T are as shown in Fig. 2.

It is to be noted that contacts 25 and 26 of the cut-off relay C which lead to the trouble bell are also closed, but they are now ineffective since the trouble bell is already operated by the release of the supervisory relay S following the opening of the circuit.

Upon closing of the line by the code wheel of the active box, the contacts of relay M are attracted and the cut-off relay C is immediately reenergized through contacts I3, I4 of the relay M.

vRelays M and C. are thus restored to their original positions, but the time relay contacts remain latche'd. Upon the next opening of the line by the box, the relay M is again de-energized and the relay C is released through the same slow release circuit as before. The register magnet R and the public alarm line 42 are again energized in the short interval during which the relay M is down and the relay C is up. `There is no further effect on the time relay T which remains latched. In this manner, the whole signaling operation continues its normal course according to the code of the pulled box. When the signal is completed and the line is finally closed, relays M and C come up but the time relay contacts are held up until they are unlatched by the operation of the timing train. When th-e relay T is unlatched the motors 56 and 56 stop and the whole system is restored to normal.

Public alarms The public alarm line 42, which as previously described, is momentarily energized in the short interval when the main relay is down and the cut-off relay C is still up, is connected with an alarm circuit 10 designated Horni A blast on the horn is thus given in each interval duringl which the line 42 is energized. 'Ihe horn therefore gives the code signal of the pulled box. The horn circuit is established through a switch 12 having a manually operated contact to connect with the circuit lil whereby a signal may be transmitted manually over the alarm. It is understood that a suitable alarm such as a bell or whistle may be used in place of a horn.

'Ihe lead 42 also connects with an alarm circuit 14 designated Tone which may, if desired, be connected with any suitable audio frequency oscillating equipment whereby coded signals may be transmitted over the line or otherwise intothe call mens houses. The tone signal circuit is provided with a switch 16 by which a signal may be transmitted manually.

The wire 68 which is connected to the positive terminal through contacts 48, 49 of the time relay is used to operate a siren which blows during the whole signaling operation. Preferably the siren is energized intermittently to give anote of increasing and decreasing pitch which has been found to cover greater distances and to provide a more striking alarm. To this end the wire 68 connects through a switch 18 which is intermittently opened and closed by a cam 80 preferably connected with the paper feed motor. The siren circuit includes a switch 62 similar to the switch 12 of the horn circuit whereby the siren may be operated manually.

Automatic Zine conditioning Provision is made, in the event the line is accidentally broken, for connecting the negative side of the battery to ground and for connecting together the positive and negative sides of the line. This converts the normally closed loop into two open ended lines, and since the boxes are arranged to connect with ground, an active box may transmit its signal notwithstanding the break.

The conditioning of the line is accomplished by the grounding relay G which is connected in the circuit of the lead 66 heretofore referred to. The lead'B runs from the contact 41 of the time relay T to a normally closed release switch 84 and thence through the grounding relay G to the negative terminal. The complete circuit of the grounding relay therefore includes the contacts I6, I1 of the main relay M, wire 38, contacts 23, 24 of the cut-oil' relay C, wire 60, contacts 46, 41 of the time relay T, lead 66 and release switch 84. When the system isv inactive the circuit of the grounding relay is open both at the contacts of the main relay M and the contacts of the cut-oif relay C, and during a code signaling operation, the circuit is open at the time relay contacts. As previously stated, the slow release circuit of relay C does not permit its contacts 23, 24 to close until after the time relay picks up, following the initial opening of the line. Under normal conditions, therefore, the grounding relay G is always inactive.

If the line breaks, all station and alarm equipment operates in the same manner as if the line had been simply opened at the iirst tooth of a pulled box. The relays M, C and T then assume the positions of Fig. 2. After the interval for which the timing train is set has elapsed, the latch 62 is tripped and the time relay is restored to normal. Since the line is open, the main relay M and the cut-off relay C remain de-energized, and therefore a closed circuit to the grounding relay G is established.

The grounding relay has the contacts designated to 93 inclusive. When the grounding relay is energized, as shown in Fig. 3, it closes its contacts 85, 86 and thereby establishes a holding circuit which runs from the positive terminal through those contacts, a connection 94, the release switch B4 and the relay coil to the negative terminal. The negative side of the battery is normally connected to the negative side of the line through contacts 89, 88, but upon energization'of the relay this connection is broken. The contact 88 closes on 81 which is connected by a wire 96 .with the positive side of the line. The negative side of the battery is connected to ground through contacts 90. 9|. The result of the energization of the relay G is therefore that both sides of the line are connected with the positive side of the battery through the main relay M, the

gong B and the transmitter ST, and the negative side of the battery is grounded.

Contacts 92 and 93 close a circuit to a warning lamp 98 operated on alternating current.

If, while the line is conditioned as described above, a box (X1) should be pulled it will transmit its signals through ground. The first action is to close the grounding contact 4 of the box on the contact 2. If the break is at the left of box X1 in Fig. l, a circuit is established from the positive side of the battery, through the right side of the line, contacts 2, 4 of the box, and through ground to the negative side of the battery. If the break is at the right of box X1, the circuit includes the other side of the line and contact 3 of the box. relay M then picks up its contacts, followed by energization of the cut-off relay C. Upon opening of the box contacts at the first tooth of the code wheel, the main relay is de-energized and the cut-oi relay and the time relay operate exactly in the same manner as in the normal signaling operation through the closed loop, as previously described. The local gong B, the register and the public alarms operate in normal fashion. It will be noted that during the signaling operation the circuit to the grounding relay through the lead 66 is broken at several points but the groundingrelay is held up by itsown holding circuit (contacts 85, 86).

The type of box above described is entirely satisfactory except that it Oilers no provision for non-interfering and succession operation on the normal loop. At some additional expense, but without change in therest of the system, boxes of the type shown in the Beach Patent 1,999,859 may be employed. These boxes are non-interfering and succession on the normal line and are arranged to connect to ground after a single test.. ing round if the line is found open.

During a signaling operation through ground the supervisory relay may or may not be intermittently energized, depending on whether the box current goes through the left or right side of the line, but as will be explained later in connection with the description of the supervisory circuits, the trouble bell, even though it may opcrate, will not ordinarily give the same code signal as the other alarms.

After the break in the line is repaired, the release switch 84 may be opened and again closed,

In any event, the main nasales thereby cle-energizing the grounding relay and restoring the line to normal. ditions, the main relay M and the cut-off relay C become energized again, and the energizing circuit for the grounding relay is broken. If, however, the release switch is opened and again closed while the line is still open, the grounding relay is again energized through the appropriate contacts of the main relay, the cut-off relay and the time relay, following which the holding circuit is re-established at contacts 85, 86.

Station transmitter When a still alarm is received'at the central ofilce it may be desirable to lsound the public alarms in the same manner as if the proper box at the location of the iire had been pulled. To this end the central ofiice is provided with the station transmitter ST having a number of code wheels which are duplicates of those on all the boxes of the system. The proper one of such wheels, indicated at |00 -in Fig. 4, is mounted on a stud which may be driven from a small direct current motor |02. 'I'he code Wheel is adapted to open and close contacts |04 and |06 which are included in the positive side of the line. 'I'he transmitter is brought into operation by a manually operated switch |08 connected in the circuit of the motor |02. The switch also carries a contact arm H0 which is connected to ground. The contact I |0 is brought up toward the contact |04 and therefore serves to transmit through ground if the line has been conditioned by the relay G. The operation of all equipment of the system by the station transmitter is identical with the operations which would result from pulling a box of the same code.

The contacts |04, |06 are normally closed so that when the station transmitter is not in use, the line remains unbroken.

Supervision The principal supervisory equipment for the system comprises the alternating current trouble bell P in conjunction with the supervisory relay S and the circuit 6I leading to contacts of the cut-off relay. The supervisory circuits are shown in dash lines.

I-The supervisory relay has a pair of normally closed contacts III and H2 which may connect with a lamp. The lamp burns continuously when the system is normal, but is extinguished under abnormal conditions. The lamp and its associated circuitsare not shown in the diagram.

The supervisory relay also has contacts H3,

H4 and H5, the movable contact H4 being normally closed on H5 but adapted to close on H3 Under "such conwhen the relay is de-energized. Contacts I I3 and H5 are connected by wires I I6 and I I8 with xed contacts |20 and |22 respectively, of a three-Way cut-out switch of which the movable contact |24 is connected to -l-AC. The movable contact H4 of the relay S is connected by a wire |26 with one side of the trouble bell, the other side of which is connnected to -AC. The Wire 6I which leads from the contact 25 of the cut-off relay C is connected to the wire H8.

Under normal conditions the trouble bell is inactive. During a code signaling operation over switch. Under these circumstances, the trouble bell sounds the proper code signal.

If the line is broken, the trouble bell rings continuously through the connections described immediately above. To avoid the annoyance of continuous ringing, the contact |24 of the trouble bell cut-out switch may be thrown to engage the contact |22, thereby breaking the bell circuit. The contact |24 is arranged to lo'ck in either position. It will be noted that if the trouble bell is silenced in this manner, the line being then conditioned by the relay G, the trouble bell will ring through contacts ||4, |5 upon subsequent energizatlon of the supervisory relay S. A code signal transmitted through the right side of the line and a grounded box will not operate the relay S, whereas a signal transmitted through the left side of the line will operate the bell on each closure of the box contacts, instead of each opening of the circuit.

The arrangement of the trouble bell in conjunction with the cut-out switch is useful for giving an audible signal for testing of the line after repair of a break. Assuming that the line has been conditioned to ground by the relay G and that the trouble bellcut-out switch has been thrown to contact |22 to silence the bell, if the line is now repaired and the grounding relay release switch 04 is opened and closed, the supervisory relay S will pick up its contacts and close the circuit to the trouble bell through its contacts ||4, H5. The ringing of the bell will then indicate that the line is normal, the cut-out switch may be thrown manually on its normal contact |20, and the bell is silenced. If, however,

the line is still open when the release switch 84- is opened and closed for testing, then the supervisory relay S is not energized and the bell does not ring.

` The connection 6| leading from the contact 25 of the cut-oi relay C is used to operate the trouble bell to indicate failure of the direct current supply to the local equipment. If while the supervisory relay S remains energized the cut-off relay is de-energized, its contacts 25, 26 close an alternating current circuit through wire 6|, and contacts 5, ||4 of the supervisory relay S to the trouble bell. De-energization of the cut-oil relay may occur through breakage of the battery connections to the contacts of the main relay and the cut-off relay, through any failure of the main As previously stated in connection with the description of the time relay, contact 50 of the time relay is connected with the temperature compensated voltage control relay TVR. The relay is normally energized and has normally open l contacts |30 and |32 included in the circuit of a charge control relay CC. The charge control relay has contacts |34,'|35, |36 and |31. These parts are shown in somewhat re-arranged position in Fig. 5. Under normal conditions, contacts |36, |31 are closed to establish a connection from the negative terminal of a rectier |38 to the negative terminal of the battery through an adjustable resistance |40, thereby placing a continuous trickle charge on the battery. When the relay TVR is de-energized, the relay CC is energized, thereby bridging the contacts |34, |35 and establishing a direct connection between the rectifier and the battery for a high-rate charge. The particular construction of the relay TVR forms no part of the present invention, and it is sufficient to say that it is de-energized to close its contacts when its circuit is opened at the time relay contacts 49, 50, and it is not permitted to close its contacts again until after closure of the time relay contacts, and then only if the battery Voltage has risen to its full charge value. The relay TVR includes temperature controlled means to allow for the variation of full charge voltage with temperature.

Upon initiation of signal, resulting in attraction of the time relay contacts, the high-rate charge is applied. The high-rate charge is maintained while the time relay contacts are latched up, that is, during the whole signaling operation. This is an important feature, since it provides the necessary current for operation of the various register and alarm apparatus without appreciable drain on the battery. Even after the completion of the signal, the trickle charge is not restored until the battery comes up to full charge.

Conclusion The foregoing description relates primarily to the details of construction and operation, and although the system as described may be adapted for general purpose signaling, the advantages for small town use are to be emphasized. Although some of the operations are rather complicated, the equipment itself is of simple and compact nature and not likely to get out of order. Aside from questions of rst cost and maintenance expense, simplicity and reliability are of rst importance, particularly when the department is composed of call men who have. neither the time nor the skill to supervise and maintain systems of the usual type.

The accident most likely to occur in this or any system is a break in the box circuit. The present invention aiiords an emergency signaling circuit which is entirely effective for as long a period as may be necessary until the line can be repaired, and, what is equally important, the conditioning for emergency operation is accomplished automatically, so that immediate personal attendance is not necessary. It is to rbe noted that all public alarms, including the siren, opcrate to give a warning of the fault, and the trouble bell rings continuously until manually silenced.

Another possible source oi' trouble is the battery, which might be permitted to run down through inattention. 'I'he control of charging rate is fully automatic. Furthermore, the highrate charge is actually applied during the signaling operation, and may be adjusted to supply substantially the entire current for the line and the various alarms, so that proper operation of the system is assured even if the battery itself has been permitted to deteriorate.

Mention has been made of the fact that all oi.' the central oilice equipment may be enclosed in a small cabinet, which may be locked against tampering by unauthorized persons. Furthermore, the system contemplates the use of simple and easily operated testing devices, by which routine checks may be made to determine the condition of the system, these devices being so arranged that any operation thereof cannot possibly affect the signaling facilities of the system.

Such testing devices form no part of the present invention, but are fully disclosed in our copending application Serial'No. 88,801 `tiled of even date herewith.

Although one specific form of the invention has been shown and described, it is to be understood that the invention is not limited to this precise embodiment, but may be varied within the scope of the appended claim.

The invention having been described, what is claimed is:

A signaling system comprising a normally closed signaling circuit including a source of energy and a plurality of signal formulating means having provision for making and breaking the circuit and also for signaling through the circuit and ground, a normally energized main relay in the circuit, a normally energized cut-oi! relay controlled by the main relay, a grounding relay having provision" for conditioning the circuit for -emergency ground signaling, a, grounding relay circuit including normally open contacts of the main relay and cut-oi! relay in series, normally closed additional contacts in the grounding relay circuit, means for delaying deenergization of the cut-oil relay following deenergization of the main relay, means for opening said additional contacts upon de-energization of the main relay and in the interval of delaye'd de-energization of the cut-ofi relay, and timing means for independently closing said additional contacts after a time greater than the longest open circuit interval of the formulating means.

FRANK R. BRIDGES.

FOSTER E. WELD.

Images