Patented Oct. l5, 1946 2,409,359 UNITED STATES PATENT OFFICE 2,409,359 THERMORESPONSIVE CABLE Richard D., Kaul, Fairfield, Conn., assigner to Ther> Sealand Corporation, Southport, Conn., a cor-_ poration of ComlcQticut Application August> 17, 1943, Serial No. 499,000 5 Claims. (Cl. 200-143) _ 1 2 This invention relates t0 improvements in ther mo-responsive cable. of the apertures b. Such alarm circuits, aswell as auxiliary connectors and ñttings for use with fire detecting cable, being well known and forme ing no part of the present invention, will not; be It is the general object of the invention to pro vide an improved thermo-responsive cable for indicating fire or other high temperature con` ditions. A speciñc object of the invention is to pro vide a cable in which the certainty of response to the temperature condition to be indicated is increased. A second specific object of the invention is to further referred to. For indicating fires, a fusing temperature of about 160° F. is generally suitable, and the core A may be made of Wood’s metal or Lipperwitz’s metal. The invention, however, is not conñned provide a cable construction which reduces im- . pairment of response or dielectric strength by deterioration of the cable structure due to iiexure or other mechanical abuse. The cable of the present invention constitutes an improvement upon that disclosed in Lindsey Patent No. 2,048,271, granted July 2l, 1936, the general purposes and functions of the cable be ing similar. With the foregoing objects, as well as others to the indication of a speciñc temperature or condition but may be applied to indicating any desired temperature, an alloy Aor metal with a suitable melting point being selected. In manufacturing the cable in the preferred form, an oversize tube B is drawn down onto the core A so as to ñt the same closely or compres sively and eliminate all voids, so far as possible, with a View to compelling the alloy, when melted, 4to spurt through an aperture b. The apertures 20 b are spaced along the tube B as indicated in Figure 2, so as to weaken the tube B as little as which will appear in the following full descrip possible, and in addition are preferably made in tion in mind, the invention consists in the com the form of narrow slots, which may conven binations and arrangements of parts and details iently be formed by slitting or punching the of construction which will now first be fully de 25 metal of tube B after drawing the same down on scribed Yin connection with the accompanying the core A and then pressing the edges of the drawing and then more particularly pointed, out slit back together. While it will be understood in the appended claims. that the specific dimensions may be widely va In the drawing: ried, in the example selected for illustration, slits Figure 1 is a perspective View of a section of 30 b approximately one-quarter inch long and cable embodying the invention in a preferred form spaced longitudinally of the cable at three inch and with the elements progressively removed so intervals have been found satisfactory in a cable as to show the internal structure; having an overall outside diameter of slightly Figure 2 is a perspective View showing the cen over one-eighth inch. Before applying the in sulating layer C, a coat of insulating lacquer or -ter conductor member of the cable of Figure 1; and varnish is preferably applied to the tube B. The insulating layer C may be of any suitable in Figures 3 and 4 are typical cross sections, upon sulating material, and of any suitable form so an enlarged scale, taken at different points along the length of the cable of Figure l. long as it will permit the molten alloy to pass The cable elements, as shown in Figure l, in 40 through it; in the embodiment shown, a wrapping of beeswax-impregnated cotton or paraffin-im clude a fusible alloy core A, contained Within a pregnated cotton has been found satisfactory. seamless copper tube B, forming an inner con ductor and having apertures b to permit the. As indicated above, manufacture is completed by alloy to fiow or spurt out upon melting. The drawing down an oversize tube D so as to i'lt tube B is covered by a winding C of insulating 45 tightly upon the insulating layer C. Figure 3 of the drawing shows the completed cable struc material, and a second seamless copper tube D, ture in typical cross section passing through an which ~forms an outer conductor, is drawn onto the insulating winding C. As in the Lindsey pat aperture b, and Figure 4 is a typical cross section at a point where there is no aperture b. ent, above referred to, the cable will be located The advantages of the present invention will so as to indicate ñre or other conditions causing 50 be best understood by referring to significant temperature rises, the inner and outer conductors points of difference between the present con B and D being included in an alarm circuit which is completed upon fusing of the alloy core A struction and that of the Lindsey patent, above referred to. which connects conductors B and D by means of the fused alloy passing through one .or more 55 By employing separate apertures b, instead of a 2,409,359 4 3 continuous slot, in the inner conductor B, the ex pansive force of the melting alloy core A is con ñned and results in a more positive flow or spurt of alloy through the apertures. 2. A thermo-responsive cable comprising inner and outer tubular conductors, insulating material between said conductors and a core of fusible Secondly, the conducting material Within the inner conductor, use of a ductile and highly conductive metal, such as copper, is. made possible, as it is unneces the said inner conductor comprising a seamless tube drawn onto said core and having longitudi sary to use a steel or iron conductor B in order nally spaced apertures. to obtain the required strength, which is the case when a continuously slotted conductor is used. The ductility and continuity of the inner con ductor B make it possible for the cable to with~ stand considerable bending or other mechanical abuse without creating undue voids around the core A or otherwise impairing the cable, While, as is apparent, a continuously slotted conductor cannot be bent Without gaping and creating voids. What is claimed is: 1. A thermo-responsive cable comprising inner and outer tubular conductors, insulating ma 3. A thermo-responsive cable comprising inner and outer seamless metal tubes, insulating ma terial between said metal tubes and a core of fusible conducting material within the inner tube, the said inner tube having longitudinally spaced apertures but having an otherwise con tinuous wall. 4. A thermo-responsive cable according to claim 3, in which the said inner tube is drawn down onto said core in compressing relation thereto. 5. A thermo-responsive cable according to claim 3, in which said inner and outer tubes terial between said conductors and a core of fusi are respectively drawn down onto said core and ble conducting material within the inner con said insulating material in compressing relation ductor, the said inner conductor having longi tudinally spaced apertures but having an other wise continuous Wall. thereto. RICHARD D. KAUL.