US3397373A

US3397373A - Fire warning cable

Info

Publication number: US3397373A
Application number: US605396A
Authority: US
Inventors: Spicer Lyndon Reginald
Original assignee: International Standard Electric Corp
Current assignee: International Standard Electric Corp
Priority date: 1965-12-31
Filing date: 1966-12-28
Publication date: 1968-08-13
Anticipated expiration: 1985-08-13
Also published as: GB1140726A; NL6618396A; DE1640501A1

Description

Aug. 13, 1968 L. R. sPlcr-:R

FIRE WARNING CABLE 2 Sheets-Sheet 1 Filed Dec. 28, 1966 Inventor L YNDON R. SP/CER 13g/Of A Morne y Aug.13,196s RSPICER 3,397,313

FIRE WARNING CABLE 'Filed nee. 2e, 196e 2 sheets-sheet 2 nveplor LYNDQN R. SPICE@ ,BOrOz/' Attorney United States Patent O 3,397,373 FIRE WARNING CABLE Lyndon Reginald Spicer, Cascades, Llandevaud, Wales,

ABSTRACT OF THE DISCLOSURE A cable for a re warning system in which a pair of conductors are covered by insulation having gaps to expose the conductors. Low melting point slugs of conductive material overlie the gaps and are encased in an elastic sleeve which when the slugs are melted force -them in-to the gaps to form a conductive path between the conductors.

Summary of invention This invention relates to cables for use in re warnin-g systems, and to methods of manufacturing such cables.

According to the present invention there is provided a cable for use in a tire warning system comprising two insulated conductors, an a plurality of slugs of material having a low melting point, said slugs being spaced apart along the length of the cable, wherein each slug is so arranged that on reaching its melting point it provides an electrically conductive path between said two conductors.

According to the present invention there is further provided a cable for use in a re warning system comprising two insulated conductors, a plurality of slugs of material having a low melting point, said slugs being spaced apart along the length of the cable, and .means individually :associated with each one of the slugs for causing the associated slug on reaching its melting point to provide an electrically conductive path between said two conductors.

According to one aspect 'of the present invention there is provided a method of manufacturing such cables.

Description of drawings FIGS. 1 and 2 are a side view and -a cross section respectively illustrating a lirst embodiment,

FIG. 3 is a cross section of a second embodiment;

FIGS. 4a and 4b are a side view and an exploded view respectively of a third embodiment;

FIG. 5 illustrates steps in the manufacture of the ythird embodiment.

Description of the preferreld embodiments The embodiment illustrated in FIGS. 1 and 2 employs a cable consisting of two parallel copperclad steel conductors 1 and 2 and a polyvinyl chloride insulating cover 3 havingtwo at surfaces. In a preferred embodiment the polyvinyl chloride cover has a height of 0.017 inch between the at surfaces, and the maximum perpendicular diameter is 0.15 inch. The conductors are exposed by gaps 4 in the polyvinyl chloride cover which occur, for example, at intervals of .three feet along the length of the cable. A Suitable width for each gap is 3/16 inch. Slugs 5 of an alloy having a low melting point bridge the gaps in the polyvinyl chloride cover, and each slug is held in place by an elastic, e.g. rubber, sleeve. Suitable examples of alloys having a low melting point are Cerrobend RTM which has a melting point in a range from 70 C. and above, and Woods metal. The composition of the latter alloy can be varied to obtain melting points in the range 117 F. to 302 F., in one form it l' 3,397,373 Ice Patented Aug. 13, 1968 consists of 50% bismuth, 13% cadmium, 25% lead and 12% tin. In one embodiment the slug has a length of 0.3 inch, a width of 0.15 inch and a thickness of 0.05 inch. The cable together with the slugs can be sheathed with out melting the alloy.

When the temperature of a slug reaches the melting point of the alloy, the rubber sleeve contracts over the now pliable slug and forces the alloy into the adjacent gap in the polyvinyl chloride cover, so that the two.

conductors are short circuited. Where less consistent action can be tolerated, the elastic sleeve may be replaced by some other retaining device and the effect of gravity on the melted slug be used to provide an electrically conductive path between the two conductors.

FIG. 3 is a cross sectional View of a second embodiment employing a coaxial cable with conductors 6 and 7. The inner conductor `6 is exposed at intervals of e.g. 3 ft. along the length of the cable 'by gaps 8 in the outer conductor 7 and any insulation between the outer and inner conductors. A suitable width for each gap is again IAG inch. Each gap is bridged by a tubular slug of alloy 9 having a length of 0.3 inch, an external diameter of 0.1 inch and an internal diameter of 0.05 inch. Copper braid 10 surrounds the external conductor together with the slugs, and rubber sleeves 11 are placed over the copper braid, one adjacent to each alloy slug. The entire arrangement is covered by a polyvinyl chloride sheath 12.

To facilitate main production by automatic or semiautomatic techniques, there is provided a further embodiment of the means individually associated with each one of the slugs to cause the associated slug on reaching its melting point to provide an electrically conductive path between the two conductors.

FIGS. 4a and 4b are a side view and an exploded view respectively of a fourth view of the invention. A cable 13, similar to that of FIGS. 1 and 2 is provided with gaps 14 at intervals along its length which have similar dimensions to the gaps 4 of FIG. l. Metallic, e.g. aluminium plates 15 crimped around the lgaps 14 are each provided with a punched recess 16 Iopposite the gap 14. The recesses 16 are loaded with resilient, e.g. rubber pads 17 and low melting point alloy slugs 18, the rubber pads being compressed against the slugs, and the latter bridging the gaps 14.

When the temperature of a slug reaches the melting point of the alloys, the compressed rubber pad forces the now pliable slug into the adjacent gap 14, so that the two conductors are short circuited.

FIG. 5 illustrates successive stages in the manufacture of FIG. 4. In stage (i) of the manufacture, a recess 19 is punched in an initially continuous aluminium strip 20 which is moving in lthe direction of the arrow. In stage (ii) a rubber pad 21 is blanked from a strip of rubber and drives into the recess 19. Simultaneously another recess 22 is punched on the strip at the first point of the production line. Next (stage iii) a low melting point alloy slug 23 is blanked from a strip and driven into the recess 19 over the rubber pad 21. Stages l and 2 are repeated for each recess. The assembled unit is separated from the 4strip of -aluminium stage (iv) and the aluminium surrounding the unit is preformed into a U-shaped member 24. In stage (v) a slot 14 in a cable 13 is located over the alloy slug 23 and the preformed aluminium is crimped round the cable to form a sleeve 25 so that the rubber pad is compressed against the alloy slug. Previous stages are repeated in each of stages (iv) and (v).

It is to be understood that the foregoing description of specic examples of this invention is made by way of example only and is not .to be considered as a limitation on its scope.

I claim:

1. A cable for use in a fire warning system comprising:

lat least -two conductors surrounded by insulating material having a plurality of gaps provided along the length of the insulation to periodically expose said conductors relative to each other;

ya plurality of slugs of material having a low melting point and each being positioned yto bridge said plurality of gaps;

a resilient member compressed against each of said slugs for `causing the associated slug on reaching its melting point to deform into said gap 'and provide an electrically conductive path between said two conductors; and

means surrounding and maintaining said slug and its associated resilient member in proper position with respect to the associated gap.

2. A cable according to claim 1 wherein said cable is a coaxial cable having its inner conductor exposed to the surrounding outer conductor through the gap in the insulation surrounding said inner conductor and through a gap in the outer conductor, and each of said slugs bridges one of said gaps in the outer conductor.

3. A cable according to claim 2 further including an elastic sleeve stretched over the portion of the cable which includes one of said slugs bridging one of said gaps in the -outer conductor, -and an insulating cover sur-rounding said sleeve and outer conductor.

4. A cable according to claim 1 wherein said two conductors are parallel insulated conductors which are periodically exposed by said gaps, each of said gaps is bridged by said slug and a resilient pad compressed against said slug, and means are provided at each of said gaps for locating and maintaining said slug and resilient pad in the proper position.

5. A cable according to claim 4 wherein said locating and maintaining means is a metallic plate crimped around said cable and provided with Ia recess for said resilient pad and slug.

6. A cable according to claim 5 wherein the material of said slug is an electrically conductive metal alloy.

7. A coaxial cable for use in a re warning system comprising:

an insulated inner conductor having a plurality of gaps spaced along the length of the insulation to` expose the inner conductors;

an outer conductor surrounding said insulated inner conduct-or and having coincident gaps in its surface;

a slug of material of low melting point bridging each of said gaps;

an elastic sleeve stretched over said slug for casing said slug on reaching itsrmelting kpoint tb'deform into said gap and to provide an 4electiaca'lly `con ductive path between said inner. and` outer conductor; and

van insulating cover completely surrounding said outer conductor and sleeve. l

8. A cable for use in a fire warning system comprising:

a pair of parallel conductors surrounded byf 'an insulating cover having la plurality of gaps spaced along the length of the insulation to expose said conductors;4

a slug of material having a 10W melting point bridges each of said gap;

a resilient pad is compressed against said slug causing' said slug on reaching its melting point to deform into the associated gap and provide an electrically conf References Cited UNITED STATES PATENTS 1,109,878 9/1914 Sulzbacher 200-143 1,829,149 1'0/ 1931 Mason et al. 200--143 3,294,941 12/ 1966 Mullen `200--143 3,305,625 2/1967 Ellis 200-174 3,316,343 4/1967 Sherlock 200-174 BERNARD' A. GILHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner.