US3281730A - Polarized relay having a pushbutton resetting means - Google Patents

Description

Oct. 25, 1966 M. R. MAROT 3,281,730

POLARIZED RELAY HAVING A PUSHBUTTON RESETTING MEANS Filed- March 10, 1965 5 Sheets-Sheet l Oct. 25, 1966 M. R. MAROT 3,

POLARIZED RELAY HAVING A PUSHBUTTON RESETTING MEANS Filed March 10, 1965 5 Sheets-Sheet 2 Oct. 25, 1966 M. R. MAROT 3,231,730

POLARIZED RELAY HAUNG A PUSHBUTTON RESETTING MEANS Filed March 10, 1965 5 Sheets-Sheet 5 United States Patent 3,281,730 POLARIZED RELAY HAVING A PUSHBUTTON RESETTING MEANS Maurice Ren Marot, Dunvegan, Edenvale, Transvaal,

Republic of South Africa, assignor to Electrical Protection Company (Proprietary) Limited, Transvaal, Republic of South Africa, a South African private limitedliability company Filed Mar. 10, 1965, Ser. No. 438,581 Claims priority, application Republic of South Africa, Mar. 17, 1964, 64/1,262, 64/ 1,263, 64/1,264 Claims. ,(Cl. 335-86) The present invention relates to electrical relay mechanisms which, in this specification, means a mechanism which, on receiving an input electrical signal, is electromagnetically energised and tripped so as to close a circuit which relays a response electrical signal or signals.

More particularly this invention relates to a resetting device for electrical relay mechanism-s by means of which a relay may be externally, e.g. manually reset after it has tripped or been energised to be rendered receptive to a further tripping operation.

This invention is applicable to electromagnetically operated electrical relays of the type which are not automatically resetting.

The invention furthermore makes provision for the combination of the resetting device with a relay, to result in electrical relay mechanisms which, when electromagnetically energised, are adapted to close the contacts of a relay circuit to provide a relayed electrical signal. Certain features of the invention are specifically designed to allow a quick response of such relay mechanisms.

In addition the invention provides for an indicating means in an electrical relay mechanism as aforesaid, which in such combination offers special advantages.

An electrical relay mechanism resetting device for relays which are not automatically resetting in accordance with the present invention comprises an externally operable resetting component which is linked to an internal resetting member in such a way that external operation of this resetting component allows the internal resetting member to mechanically reset the tripped relay under the influence of a force whose magnitude is independent of the operation of the external resetting component; (in the above context externally operable means operable by an agency independent of the relay mechanism); the internal resetting member being adapted to reset the relay in such a manner that the relayed electrical signal is maintained by this resetting operation for as long as the externally operable resetting component is in the resetting position.

In accordance with a preferred embodiment of the invention the resetting device is adapted to be incorporated in an electrical relay mechanism in which the armature normally rests against the relay pole pieces and moves away from the pole pieces when the relay is tripped.

In accordance with a preferred embodiment of the invention, the resetting device is adapted to be used in conjunction with a magnetic shunt polarised relay of a recent type of construction, which is constituted by a permanent magnet including two pole pieces co-operating with the armature of the relay, at least one electric winding and a magnetic shunt inserted between the pole pieces, the characteristic feature of said relay consisting in that a shunt is constituted by two polar masses separated by a gap of a reduced breadth and having a large area, while the relay winding surrounds one or both pole pieces between the magnetic shunt and the armature. This relay is of the type in which the armature is normally in con-' tact with the pole pieces held in place by the attractive force induced by the magnetic flux of the permanent magnet against spring force. On being energised the magice netic flux is reduced and spring force exceeds that due to the flux, tripping the relay, so that the armature moves away from the pole pieces, closing the contacts of the relay circuit.

The relay mechanism resulting from the aforementioned combination of the resetting device and the said magnetic shunt polarised relay is also considered as falling Within the scope of the present invention.

It is an advantage of the present invention that it can be constructed such that the resetting of the relay by the interior resetting member (which exerts a force of unvarying magnitude irrespective of the exterior resetting action) resets the armature against the pole pieces with substantially the same pressure every time. It is a further advantage that damage to the relay cannot be incurred through mistreatment of the externally operable resetting component, e.g. through a person applying an unnecessarily large pressure to a manually operated resetting com ponent.

A further advantage resides in it being impossible to hold the relay in an inoperable condition by means of the external resetting mechanism in accordance with the present invention. Thus a condition commonly known in the art as trip free resetting is obtained, a very necessary condition when the relay is used in fault protection systems.

In accordance with a preferred embodiment of the invention the relay mechanism defined further above comprises the feature that the one contact of each pair of contacts which engages or is first engaged or actuated by the relay armature on tripping thereof is electrically connected to the relay armature.

Most commonly only one pair of contacts is incorporated in a relay mechanism, and the construction is such that one of these two contacts is electrically connected to the relay, e.g. through the relay body, but at least to the relay armature whilst tripping is in process.

If the contact is mounted on the armature, it is electrically connected thereto permanently. In this construction the whole relay body or at least the armature is normally insulated from the outside of the outer casing of the relay mechanism.

This construction obviates the need for electrical insulation between the relay armature and the contact or between armature and relay body. For most applications of the device it is necessary merely to insulate the armature rendered alive by the arrangement herein described against the support on which the relay is mounted, either by insulating mounting means or by making the relay body out of insulating material.

In accordance with a preferred embodiment of the invention the relay armature is made as light as possible commensurate with performance considerations, and similarly the weight of any appendant parts which move Wit-h the armature are made as light as possible, as well as the contact which is first engaged by the armature on tripping and moved against the other contact, or which is mounted on the armature.

These features of lightness in construction reduce the delay period between the initiation of the tripping action when the relay is energised and the instant when the contacts are closed by reducing the inertia effects in the above-mentioned parts. It is further explained that the elimination of insulation between the one contact and the relay armature provides a valuable saving in weight.

The resulting enhanced speed of operation of the relay has important results when, in accordance with a preferred embodiment of the invention the relay is used in earth leakage or other protection systems, in which damage to machinery to be protected which may occur due to a fault is reduced by increasing speed of operation of the relay.

In electrical relay mechanisms it is known to provide an indicating means which provides an indication of whether the relay is tripped or not. Usually this indication is a visual one and very commonly comprises a small mechanical signal of the type referred to in the art as a flag indicator.

The indicating means performs essentially a secondary operation and it is desirable that no possibility exist of it interfering with or adversely affecting the performance of the primary function of the relay, which is the relaying of a signal.

The relay mechanism in accordance with the invention lends itself particularly well to such an indicating means which, in accordance with the present invention, comprises a visual and/or auditory indicating means which, by virtue of an arresting member resting against a part of the relay which moves on tripping of the relay, being on that side of the part opposite to the direction of its movement due to a tripping action, is allowed, under action of a force independent of the tripping mechanism, to provide a perceptible indication when the relay mechanism trips.

Thus the arrangement of the arresting member is such that the part of the relay mechanism against which it rests restrains the arresting member until tripping occurs when the arresting member becomes free to move under the influence of an independent force by virtue of the movement of that part of the relay.

It is in general advantageous for the indicating means to be constructed lightly. This minimises inertia and frictional elfects of the indicating means, and thereby improves its performance.

The force independent of the tripping mechanism for actuating the indicating means may be provided by a light spring, but preferably the action of gravitational force on the indicating means is employed to actuate the indicating means.

In order to more fully describe the present invention, the following preferred embodiments are described with reference to the accompanying drawings, by way of example, but without limiting the invention thereto.

. In the drawings FIG. 1 illustrates a relay mechanism in accordance with the invention in part sectional elevation, showing the resetting mechanism in accordance with the invention;

FIG. 2 illustrates an alternative arrangement of the resetting mechanism in accordance with a preferred embodiment of the invention;

FIG. 3 illustrates the incorporation in the relay of FIG. 1 or 2 of an indicating means in accordance with a preferred embodiment of the invention in front elevation with the front panel partly removed for illustration purposes;

'FIG. 4 illustrates the parts associated with the indicating means of FIG. 3 in plan view;

FIG. 5 illustrates diagrammatically a preferred application of the means illustrated in FIGS. 1 to 4.

The construction and operation of this relay is now briefly described with reference to FIG. 1.

The polarised electromagnetic relay comprises an electromagnetic release which by means of members 1 is held secure to a rigid relay body 2 constructed of a non-magnetic material. To this body 2 anelongated piece of flexible, resilient electrical conducting material 3 is rigidly fixed between 2a and 11 at one end, and the opposite end allowed to rest in its neutral position on the pin 4 securing the armature 5 of the said electromagnetic relay element to a movable shaft of non-magnetic material 6. It is explained that when the armature 5 is held hard against the pole pieces 7 of the electromagnetic relay element 1, the free end of the contact carrier 3 is barely touching the pin 4- securing the armature 5 to the movable shaft 6. A contact piece 8 having good electrical contact properties is mechanically and electrically fixed to the free end of the contact carrier 3 and positioned on the side remote from the electromagnetic relay element 1.

To the fixed side of the contact carrier 3 is electrically attached an electrical conductor 9 which forms the one connection to the device to be operated by the closing of the relay contacts 8 and 12.

A second similar conductive contact carrier 10 is fixed to a suitable piece of insulating material 11 (a non-electrical conductor) which is in turn secured to the relay body 2. This contact carrier 10 is in this manner insulated from the first-mentioned contact 8 and contact carrier 3. To the free end of the contact carrier 10 is mechanically and electrically fixed a contact piece 12 having good electrical contact properties. To the fixed side of the contact carrier is electrically fixed a second conductor 13 forming the second connection to the device to be operated by the closing of the two contacts 8 and 12.

Members 1 are two parallel magnetic plates connected each to one of the pole pieces 7 with a long narrow air gap between the plates of large surface area to provide a shunting magnetic pass on that side of winding 14 which is opposite the armature 5, in a manner known per se.

Upon energising of the electromagnetic relay by the application of an exciting current to the operating winding 14 which is insulated from the pole pieces 7 the permanent magnetisation of pole pieces 7 is opposed so that the armature 5 will release and move under the influence of the coil spring 15 which was held in compression by the armature 5. The movement of the armature will cause the contact 8 to be pushed against the contact 12 and the two contacts will complete the electrical relay circuit to the device to be operated, usually a main circuit interrupting device. The magnetic shunt provided by members 1 results in very greatly reduced energy requirements for releasing the armature 5. It is seen from the above description that only the contact carrier 10 is insulated from the relay body 2. This simplifies the construction of this type of mechanism. The electromagnetic release, the relay body 2, the first-mentioned contact 8 and carrier 3 are all in mutual electrical contact, and the whole is insulated from the outside of the mounting enclosure, which is accessible to operating personnel (not shown) by a suitable insulated mounting arrangement 16.

The resistance of the contact carrier 3 is so chosen in relation to the resistance of all other parallel paths of the current that the division of current between the conducting paths and carrier 3 is acceptable under rated operating conditions.

According to a further improvement the contacts 8 and 10 and particularly the contact 8 are represented by electroplated contact faces whereby inertia is reduced to a minimum.

Also it will be readily understood that the relay body 2 may be made of insulating material, in which case it is not necessary to provide special insulation at 16.

To reset the electromagnetic release it is necessary to restore the movable armature 5 to the pole pieces 7 against the force of the coil spring 15 and once in contact with the pole pieces 7, the flux generated by the permanent magnet is sufliciently strong to hold the armature 5 in this position against the force of the elastic coil spring 15 which is in compression.

The preferred embodiment of the resetting device as applied to this relay is now described.

An interior reset member, lever 17, constructed of insulating material (a non-electrical conductor) has a central portion 18 enabling the lever to rock in a similar manner to the well known see-saw action. This central portion is pivoted on a fixed portion 19 of the relay body 2. A hairpin type of spring 20 with one or more coils is fitted over a pivot pin 21 in such a manner that the one end of the lever 17 is allowed to rest on the back of thesecond mentioned contact carrier 10. To the opposite end of the reset lever 17 in a free running hole or slot is attached by means of a collar 22 a metallic link 23 or other suitable material which is fixed in turn rigidly or pivotally to a mechanical push button 24 fitted into the external enclosure 25 of the mechanism. The metallic link 23 can also be constructed of a compressible member such as a chain link, for example. The push button 24 has built-in a coil spring 26 under compression and maintaining the said push button in the extende d position. The force exerted by the coil spring 26 is such that it overcomes the force exerted by the hairpin type elastic spring 20 fitted to the pivot pin 21 of the reset lever 17. In this way the portion of the reset lever 17 close to the contact 12 is held apart from the contact 12 and the pair of contacts 8 and 12 are therefore maintained normally apart.

When exciting current is applied to the coil 14 of the electromagnetic release, the armature is released from its pole pieces 7 and the action of the spring 1-5 in compression is to cause the pair of contacts 8 and 12 to close and complete the circuit, e.g. to the main circu t interrupting device. In order to reset the relay in readiness for a further operation, the push button 24 is depressed by the operator which allows the reset lever 17 under action of its own hairpin type elastic spring 20 to press the contact 12 on to the contact 8, which in turn presses the armature 5 against the pole pieces 7. On release of the push button 24 by the operator the spring 20 of the push button restores the reset lever 17 in opposition to the force exerted by the hairpin type elastic spring 20 to its normal position where the two contacts 8 and 1 2 are now apart and in readiness for a further operation.

The advantage claimed for this system of resetting the electromagnetic release is that the resetting force on the armature 5 is a function of the force exerted by the hairpin type elastic spring 20 and is independent of the force exerted by operating personnel when depressing the push button 24. This system further ensures that the armature will always be reset to the said pole pieces with a controlled force below the limit above which the armature can be dam-aged.

A further advantage of this system of resetting the release is that it is impossible for operating personnel, by maintaining the push button 24 depressed, to hold the relay mechanism 1 inoperative against a condition of abnormality in the main power system requiring the relay to operate. What is commonly known as a tripfree resetting device is thus obtained.

FIG. 2 illustrates an alternative method of obtaining the same means of resetting the electromagnetic release by repositioning the reset spring. Instead of incorporating a hairpin type elastic spring 20 (-FIG. 1), to exert a resetting force on reset lever 17 the reset lever 17 is allowed to pivot freely about pivot 21 which is attached to fixed portion 19 of relay body 2. This alternative arrangement now has instead an elastic coil spring 27 which is held under compression between the external enclosure 25 and the reset lever 17. The push button 24 has built-in an elastic coil spring 26 maintaining the button in the extended position. The force exerted by the latter elastic coil spring 26 is such that it overcomes the force exerted by the former elastic coil spring 27 fitted between external enclosure 25 and reset lever 17. In this way the portion of the reset lever 17 close to the contact 12 is held apart from the contact 12 and the pair of contacts 8 and 12 are therefore maintained normally apart. The operation described earlier in this specification of depressing the push button 24 now allows the reset lever 17 to depress the contact 12 on to the contact 8 which in turn restores the armature 5 to the pole piece 7.

Referring now to FIGS. 3 and 4 of the drawings a nonmagnetic circular disc 28 (commonly known as a flag indicator) of light metallic material is attached by means of an arm 29 made of the same material to a spindle 30 also of non-magnetic material. The method of attaching the arm 29 to the spindle 30 is by means of an adjustable locking arrangement 31. The spindle 30 fits into a free running hole 32 in the relay body 2 and the remote end 33 of the spindle 30 is offset and allowed to rest on the extremity of the contact carrier 3. The arrangement is that the disc 28 will follow in sympathy the movement of the contact carrier 3. The complete relay mechanism is mounted in service in such a way that gravitational forces hold the extremity 33 of the offset spindle 30 against the contact carrier 3. Upon operation of the electromagnetic release the contact carrier 3 will be displaced by means of the armature 5. This displacement will allow the disc 28 to be displaced under gravitational force and made to appear in a window opening 34 in the rating plate 35. Said rating plate is so positioned relative to the complete relay mechanism enclosure that it and the window 34 are clearly visible to operating personnel through a transparent portion of the enclosure of insulating material. The advantage of this system of flag indication is that the components of the flag indicating system if proving faulty in service will not impair the operation of the relay contacts and thus interruption of the main supply is still possible if it is called upon to do so by an application of exciting current to the relay coil of the electromagnetic relay. It will be readily appreciated that for improved sensitivity the inertia of the contact set and associated parts is appropriately kept to a minimum. For example, for greater clarity the contacts 8 and 12 have been shown in the drawings much more prominently than they would appear in practice, where they are merely represented by spots of a thin layer of electroplating.

One of many applications of the relay mechanism incorporating the above embodiments is now described with reference to FIG. 5.

, A source of electrical supply having two or more supply conductors 36 is connected to the one set of terminals 37 of a circuit interrupting device 38 such as is commonly known as a circuit breaker. The remaining set of terminals 39 of the said circuit breaker has two or more conductors 40 connected to it, and the said conductors are connected to ends of windings 41 of which there are an equal number of windings as there are supply co-nductors. All of the said windings must have an equal number of turns. Linking the said windings is a magnetic core 42 of either annular shape or any other convenient configuration forming a closed magnetic loop and constructed of paramagnetic material. The remaining ends of the windings 41 are electrically connected by means of an electric cable 43 to an electrical apparatus 44 which derives its electrical energy from the said power cable. One additional winding 45 on core 42 has both extremities connected to the ends of winding 46 known as the operating coil of the electromagnetic relay element, such as described with reference to FIG. 1.

Under abnormal conditions such as a leakage of electrical current from a live portion 47 of the electrical apparatus 44 to the frame 48 of said electrical apparatus which is connected to earth will (by a process well known in the art) cause an electro-motive force to be induced in said winding 45 which will cause electrical current to pass in winding 46 to energise and so cause tripping of the electromagnetic relay element. The electrical contacts 49 of the electromagnetic relay will complete the circuit to the operating device 50 of circuit breaker and so interrupt he supply of electric current to the electrical apparatus Many variations of the described embodiment are possible. Thus the push button of the resetting device may be replaced by a foot operated control, but could also comprise a remotely controlled component, e.g. a sole noid operated component remotely controlled, which may be necessary or desirable in a particular application of the relay mechanism.

It will be readily understood that the rocker beam or reset lever 17 could be replaced by any suitable mechanical equivalent, which is preferably made of insulating material or otherwise insulated against the relay contacts.

Also whilst a visual flag indicator is found convenient,

any equivalent may be employed instead. The crank arm of the flag indicator could be replaced by a cam-like projection or any other mechanical equivalent.

In accordance with an alternative embodiment of the invention, the visual indicating means comprising an electrical light switched on or off by the action of the arresting member, which is adapted to actuate electrical contacts. In this embodiment the light may be positioned distant from the relay if this is desired or required in any particular application. Thus an elongate :arm carrying a contact may be attached to the arresting member, preferably electrically insulated therefrom. This contact may be arranged to close with a second contact when tripping occurs.

What I claim is:

1. A polarised electromagnetic relay of the type which is not automatically resetting which comprises:

(a) a permanent magnet including two pole pieces and an armature which in its normal position is held in such position attracted by the polarising flux of the permanent magnet;

(b) at least one electromagnetic winding adapted when energised to counteract the polarising flux to cause the release of the armature;

(c) a contact set adapted to be closed by the armature in its released position;

((1) an externally operable resetting component adapted to be operated by an agency independent of the relay;

(e) an internal resetting member, restrained in one of its extreme positions by the externally operable resetting component and biassed to return the armature to its normal position when released to move to its opposite extreme position by operation of the externally operable resetting component; and

(f) means associated with the internal resetting member adapted to maintain the contact set closed as long as the externally operable resetting component is in its resetting position.

2. A relay as claimed in claim 1 in which the externally operable resetting component and the internal resetting member are linked mechanically by a member connected to the externally operable resetting member, and provided with a stop adapted to restrain the internal resetting member against its bias and adapted to be moved to remove the restraint of the internal resetting member by actuation of the externally operable resetting component.

3. A relay as claimed in claim 2 in which the externally operable resetting component comprises a springloaded push button, the magnitude of the spring loading exceeding the said bias.

4. A relay as claimed in claim 1 which comprises a magnetic shunt inserted between the pole pieces, constituted by two polar masses separated by a gap of a reduced breadth and having a large area, the relay winding surrounding at least one of the pole pieces between the magnetic shunt and the armature, and a spring adapted to urge the armature away from the pole pieces.

5. A relay as claimed in claim 2 in which the internal resetting member comprises a biassed rocker beam comprising an arm restrained by said stop in the one extreme position of the beam and an arm adapted to hold the contact set closed and the armature in its normal position in the opposite extreme position of the beam after removal of the restraint and motivated by the bias of the beam.

6. A relay as claimed in claim 5 in which the bias of the beam is provided by a spring.

7. A relay as claimed in claim 1 in which the contact set consists of contacts, each mounted on elastic electrically conductive member provided in the path of the internal resetting intermediate between the latter and the armature and positioned for the internal resetting member when released to push one contact against the other and via the contacts and associated parts transmit a pressure to the armature in the direction of the normal position of the latter.

8. A relay as claimed in claim 1 in which the contact set comprises a pair of relay contacts, the one contact of said pair being adapted to move towards the other actuated by the relay armature on release thereof and being electrically connected to the relay armature at least Whilst 5 thus moving.

9. An externally resettable relay as claimed in claim 8 in which the contact and associated parts actuated by the armature are of light weight construction, the contact itself being a mere layer produced by electroplating.

10. A relay as claimed in claim 1 which comprises an indicator member coacting with an arresting member which rests against a part of the relay which moves on release of the relay armature, bearing on that side of the part opposite to the direction of its movement when released and which indicator member is biassed independently of the armature to provide a perceptible indication when the armature is released, the internal resetting means being adapted also to reverse said perceptible indication.

11. A relay as claimed in claim 10 in which the indicator member is biassed by gravitational force.

12. A relay as claimed in claim 10 comprising a visual indication means provided by an indicating flag, pivotally mounted, which is adapted to move into view from behind a shield when the armature is released and in which the arresting member is connected to an arm carrying the said 13. A relay as claimed in claim 12 in which the arresting member comprises a light crank shaped formation rigidly attached to the arm, carrying the flag, the eccentric part of the crank being adapted to rest against the means bearing the movable contact of the pair of contacts of the relay.

14. An earth leakage protection apparatus comprising a polarised electromagnetic relay of the type which is not automatically resetting which comprises (a) a permanent magnet including two pole pieces and an armature which in its normal position is held in such position attracted by the polarising flux of the permanent magnet;

(b) at least one electromagnet winding adapted when energised to counteract the polarising flux to cause the release of the armature;

(c) a contact set adapted to be closed by the armature in its released position,

((1) an externally operable resetting component adapted to be operated by an agency independent of the relay,

(e) an internal resetting member, restrained in one of its extreme positions by the externally operable resetting component and biassed to return the armature to its normal position when released to move to its opposite extreme position by operation of the externally operable resetting component,

(f) means associated with the internal resetting member adapted to maintain the contact set closed as long as the externally operable resetting component is in its resetting position,

(ii) a core balance transformer for monitoring a circuit and having a detector Winding connected to feed the windings of the relay; and

(iii) an electromagnetic circuit breaker adapted to interrupt a power supply being monitored on being energised by the closing of the relay contacts.

15. A polarised electromagnetic relay of the type which is not automatically resetting, comprising:

a mounting body made of non-magnetic material and mounting means, which in combination are designed to insulate all current carrying parts of the relay from a support for the relay;

a pair of flat magnetic plates mounted at their ends on said body and having a long narrow air gap therebetween,

a two-pole core and current-excitable winding thereon an armature designed to connect the poles of said core,

non-magnetic pin projecting from said body between said core poles and through said armature and extending beyond the ends of said poles,

a spring disposed around said pin and designed to exert a thrust against said armature to keep said armature out of contact with said poles,

first resilient, flexible conductive contact carrier mounted at one end on said body and having one end bearing against the end of the pin extending beyond the ends of said poles,

second resilient, flexible conductive contact carrier mounted at one end on said body beyond said first carrier and having a contact on its end disposed opposite the contact of the first carrier,

an electrical lead extending from each of said attached ends of said carriers and designed to be connected to a device to be operated by the closing of said contacts,

thrust means mounted on and within said body and having a bias to push the contact of the said second carrier against the contact of the first carrier and thereby to push the first carrier against the pin with a force designed to return said armature into contact with said poles, after an exciting winding current has demagnetised said poles and permitted said spring to force said armature out of contact with said poles,

a stop mounted within said body designed to occupy a position in which it restrains said thrust means against obeying said bias,

and an operating means exposed to the outside of said References Cited by the Examiner UNITED STATES PATENTS 3,161,802 12/1964 Gordon 317172 X BERNARD A. GILHEANY, Primary Examiner.

25 R. N. ENVALL, Assistant Examiner.

Claims (1)

1. A POLARISED ELECTROMAGNETIC RELAY OF THE TYPE WHICH IS NOT AUTOMATICALLY RESETTING WHICH COMPRISES: (A) A PERMANENT MAGNET INCLUDING TWO POLE PIECES AND AN ARMATURE WHICH IS ITS NORMAL POSITION IS HELD IN SUCH POSITION ATTRACTED BY THE POLARISING FLUX OF THE PERMANENT MAGNET; (B) AT LEAST ONE ELECTROMAGNETIC WINDING ADAPTED WHEN ENERGISED TO COUNTERACT THE POLARISING FLUX TO CAUSE THE RELEASE OF THE ARMATURE; (C) A CONTACT SET ADAPTED TO BE CLOSED BY THE ARMATURE IN ITS RELEASED POSITION; (D) AN EXTERNALLY OPERABLE RESETTING COMPONENT ADAPTED TO BE OPERATED BY AN AGENCY INDEPENDENT OF THE RELAY; (E) AN INTERNAL RESETTING MEMBER, RESTRAINED IN ONE OF ITS EXTREME POSITIONS BY THE EXTERNALLY OPERABLE RESETTING COMPONENT AND BIASSED TO RETURN THE ARMATURE TO ITS NORMAL POSITION WHEN RELEASED TO MOVE TO ITS OPPOSITE EXTREME POSITION BY OPERATION OF THE EXTERNALLY OPERABLE RESETTING COMPONENT; AND (F) MEANS ASSOCIATED WITH THE INTERNAL RESETTING MEMBER ADAPTED TO MAINTAIN THE CONTACT SET CLOSED AS LONG AS THE EXTERNALLY OPERABLE RESETTING COMPONENT IS IN ITS RESETTING POSITION.

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