US2762896A

US2762896A - Electrically-operated heatgenerating devices

Info

Publication number: US2762896A
Application number: US444735A
Authority: US
Inventors: Louis B Pendleton
Original assignee: Individual
Current assignee: Individual
Priority date: 1954-07-21
Filing date: 1954-07-21
Publication date: 1956-09-11
Anticipated expiration: 1973-09-11

Description

United States Patent ELECTRICALLY-OPERATED HEAT- GENERATING DEVICES Louis B. Pendleton, St. Louis, Mo. Application July 21, 1954, Serial No. 444,735 Claims. (Cl. 219-19) This invention relates to improvements in electricallyoperated heat-generating devices. More particularly this invention relates to electrically-operated heat-generating devices which can be releasably placed within a structure to heat the area within that structure.

It is therefore an object of the present invention to provide an improved electrically-operated heat-generating device that can be releasably placed in a structure for heating the area within same.

The present invention provides an electrically-operated heat-generating device which can be releasably placed within the structure for the purposes of heating the area. within the structure. This device can be installed simply and easily and can be removed with equal ease and simplicity. As a result, there is virtually no installation cost, and the cost of repairs is limited largely to replacement of parts and not to the expenditure of labor. As a result, the overall cost of the electrically-operated heat-generating device provided by the present invention is small. It is therefore an object of the present invention to provide an electrically-operated heat-generating device which can .be readily installed within or removed from a structure.

The electrically-operated heat-generating device provided by the present invention can be placed on the floor of the structure and suitably connected to a source of electric current. Heat is readily transferred to the area above the device and will heat that area. This, in turn, will lead to the heating of the rest of the space within the structure. The electrically-operated heat-generating device is merely laid on the floor and need not be perma nently associated with that floor. Consequently, the device can be removed readily, either for replacement or for repair. It is therefore an object of the present invention to provide an electrically-operated heat-generating device that can be laid loosely on the floor of a structure and which can be connected to an outlet for electric current.

The electrically-operated heat-generating device provided by the present invention is made in a number of sections. Each of these sections contains a heat-generating element of electrical resistance material and that element can be connected to a suitable source of electricity. Each of the sections can be mechanically interlocked into one large overall electrically-operated heat-generating device. However, by being made in sections, the device can be packaged very conveniently and can be assembled into various sizes. In this way, a standard section can be established and the interlocking of a number of sections can accommodate structures of different sizes. The proper selection and interconnection of the required sections will enable the purchaser to provide full heating of any given structure. It is therefore an object of the present invention to provide a section of an electricallyoperated heat-generating device which can be connected with other similar sections to assure full heating of a structure.

2,762,896 Patented Sept. 11, 1956 The sections of the electrically-operated heat-generating device provided by the present invention have inter locking surfaces. These surfaces permit ready assembly and disassembly of the sections, and they automatically orient the sections relative to each other. In this way, the interlocking surfaces prevent improper assembly of the sections.

The electrically-operated heat-generating device of the present invention is equipped with connecting strips which interconnect the various sections of the device in parallel. In that way, the various sections are assured of substantially the same voltage throughout and the overall heat can be controlled quite readily. The connecting strip is suitably connected to the individual sections by interlocking surfaces so that the connecting strip will coact with the sections to provide a suitably integrated electrically-operated heat-generating device. It is therefore an object of the present invention to provide connecting strips which can be suitably interlocked with the sections of the electrically-operated heat-generating device to provide full electrical voltage for the resistance elements of the sections.

The various sections of the electrically-operated heatgenerating device provided by the present invention will have the same thickness. Similarly, the connecting strips for the electrically-operated heat-generating device of the present invention will have the same thickness as do the sections of that device. Consequently, the various sections can be interlocked together and can be interlocked with the connecting strips and still provide a uniform flat surface for the users of the structure. As a part of that fiat uniform surface, there will be tabs which are resilient and which can be bent upwardly to facilitate the interconnection of the electrical components of the sections and of the strips. These resilient tabs will then be returned to their normal fiat position where they will overlie those terminals and will complete the plane of the top of the electrically-operated heat-generating device.

Purchasers can select the desired number of sections and those sections will be neatly packaged in numbers appropriate to standard sizes of rooms. Those sections can then be taken to the home or to other structures and placed in juxtaposition so that the interlocking surfaces thereof interact to releasably secure the sections together. This placing of the individual sections can be done by unskilled labor. Moreover, these sections need not be cemented to or embedded within the floor, but need only be placed on the surface of the floor. The electrical connections can readily be made by unskilled labor and the resilient tabs which normally overlie those connections can be restored into the plane of the upper surface of the electrically-operated heat-generating device. Once this had been done, a connection can be made to a suitable source of current and the heat will begin to generate.

Other and further objects and advantages of the present invention should become apparent from an examination of the drawing and accompanying description.

In the drawing and accompanying description a preferred embodiment of the present invention is shown and described but it is to be understood that the drawing and accompanying description are for the purpose of illustration only and do not limit the invention and that the invention will be defined by the appended claims.

In the drawing Fig. l is a plan view, that is partially broken away, of an integrated electrically-operated heatgenerating device composed of a number of sections and of a number of connecting strips,

Fig. 2 is a cross sectional view of the electricallyoperated heat-generating device of Fig. l, and it is taken along the plane indicated by the line 2-2 in Fig. 1,

Fig. 3 is an enlarged plan view of one of the sections of the electrically-operated heat-generating device of Figs. 1 and 2,

Fig. 4 is an enlarged view of one of the connecting strips of the electrically-operated heat-generating device of Figs. 1 and 2,

Fig. 5 is an enlarged cross sectional view of a portion of the interconnecting surfaces of one strip and one section, and

Fig. 6'is an enlarged view in plan of a portion of the connecting surface of the strip of Fig. 4.

Referring to the drawing in detail, the numeral 10 generally denotes a section of an electrically-operated heatgenerating device that is made in accordance with the principles and teachings of the present invention. The section 10 consists of two layers and a heat-generating element. The numeral 12 denotes the lower layer of material which forms the bottom of the section In. This material is intended to resist the passage of heat through it. Consequently, this material will tend to prevent the loss of heat from the electric heating element to the floor of the structure in which the electrically-operated heatgenerating device is installed. This material should be relatively stiff and rigid, and two such materials that meet these limitations are composition boards sold under the trade names Masonite and Celotex. Another such material would be asbestos board. The upper surfaces of the layer 12 should be heat reflecting, as by being glazed with a white enamel, a light colored paint or a metallic paint. The combination of the heat-resisting nature of the material itself, together with the heatrefiecting nature of the coating on its upper surface, will enable the layer 12 to minimize the transfer of heat through it to the floor.

"Disposed on the upper surface of the layer 12 is an elongated heat-generating element 14 of electric resistance material. The element 14 is formed in serpentine fashion so that it covers a considerable area while lying flat on the upper surface of the lower layer 12. This heatgenerating element 14 will be suitably encased by electrical insulation of standard and usual type. That insulation will, of course, be designed to resist the heat generated whenever current flows through the element 14. Nichrome or other resistance wire can be used for the element 14.

An upper layer 16 of material is provided to overlie the heat-generating element 14; and it is cemented or otherwise secured to the element 14. The layer 16 can be formed with a series of channels to receive and accommodate the element 14, or that layer can be molded around the heat-generating element 14. This upper layer should be of a material that readily transmits heat and which will have a yieldable surface. One such material isrubber that is designed to have a good heat transferring capacity. Another material is plastic with good heat transferring ability. Where the electrically-operated heatgenerating device is to be disposed beneath a rug or other floor covering, the upper layer 16 can be of any neutral color and of any smooth appearance. However, where the electrically-operated heat-generating device is to be exposed, the upper surface of the layer 16 should be suitably ornamented and colored. A number of patterns or designs can be imprinted upon the upper surface of the layer 16, and a number of different color schemes can be used. In this way, the electrically-operated heat-generating device can be made attractive and pleasing in appearance.

The ends of the heat-generating element 14 terminate in electrical terminals 18. As indicated particularly in Fig. 5, the terminals 18 have a generally cylindrical portion to receive the ends of the heat-generating element 14 and they have a flat portion with an opening therethrough'to receive the screw 20. The screws 2% and the terminals 18 are of standard form anddesign and can be manipulated readily by unskilled persons.

The section 10 has two generally trapezoidal tongues 22 at one side thereof. The section 10 also has two generally trapezoidal recesses 24 at the opposite side thereof. The tongues 22 and the recesses 24 are in register with each other, and they interact with the recesses and tongues of other sections 10 and with

end sections

11 and 13. The end sections 11 are equipped only with recesses 24, while the end sections 13 are equipped only with tongues 22. The particular advantage of the

end sections

11 and 13 is that they complete the shape and form of the electrically-operated heat-generating device and do not leave any projections or recesses which could be unsightly. Electrically speaking, the operation of the

sections

10, 11 and 13 is identical.

The tongues 22 of one section will fit readily into the recesses 24 of adjacent sections, and the tongues and re cesses will interact to releasably lock the sections together. However, forces applied to the tongues 22 or to the areas defining the recesses 24 in a vertical direction can readily separate the tongues from the recesses. Hence, it is possible to separate one or more sections if replacement or repair is indicated. Moreover, that separation can readily be effected in the event the user of the structure has to move to still another structure. In this way, ready assembly and disassembly of the sections of the electrically-operated heat-generating device can be effected.

The numeral 26 denotes a section of a connecting strip. This particular section is shown as being disposed between two aligned rows of sections 10, but if desired a connecting strip could be provided that was usable with just one row of sections it). Such a connecting strip would be desirable in a long narrow room or area. The connecting strip 26 is desirable for a room which is long and wide. The strip 26 has two spaced conductors 28 and 3t), and those conductors are electrically isolated from each other. The section 26 is made of two layers, as indicated particularly in Fig. 2. The bottom layer will be generally of the same height as the layer 12 of the sections 10 and the upper layer of the strip 26 will be of the same general thickness as the layer 16 of the sections 10. The overall height of the section 26 will, therefore, be substantially the same as the overall height of the sections 10. Consequently, the strip 26 will coact with the sections 10 to provide a uniform, flat upper surface to the feet of the users of the structure.

Terminals 32 and 34 are provided at the ends of the

conductors

28 and 30 of the strip 26. These terminals will be of the same type shown particularly in Fig. 5. As indicated previously, those terminals will have a cylindrical portion to receive the wire or conductor; and will.

have a. flat, perforated portion to receive the screw 20. These terminals 32 and 34 are disposed immediately adacent a recess 36 in one end of the strip 26. These terminals will coact with terminals on the connector strip 38 to supply current to the conductors 2% and 30 of the connector strip 26. The connector strip 38 has two spaced

electrical conductors

28 and 30, and those conductors will be appropriately connected to the

conductors

28 and 30 of the connector strip 26. The terminals of

theconductors

28 and 30 of the connecting strip 38 will be carried by the tongue 40 of that strip. This tongue will fit within the recess 36 of the connector strip 26 and will releasably maintain the two

strips

26 and 38 in assembled relation. A resilient flap 42 will be provided on the upper surface of the connector strip 38, and that resilient flap will overlie the screws 20 and the fiat portions of the terminals carried by the connector strips 26 and 38. The connector strip 26 will have a recess to accommodate the resilient flap 42 as well as the screws 24) and the fiat portions of the terminals of the

wires

28 and 30 of the connector strips 26 and 38. In this way, aflat uniform surface is assured for the electricallyoperated heat-generating device, while ready access to the screws and terminals is assured. The connector strips 26 and 38 are similar; the principal difference being that st rip 26 mustbe connected to the connector strip 38. In

the event t-he electrically-operated heat-generating devicev of the present invention was materially longer than indicated in Fig. 1 as would be the case in anunusually long room, a third type of connector strip would beprovided.

That connector strip would have a tongue similar to the tongue 40 of the connector strip 38 but would have a recess 36 similar to the recess 36 of the connector strip 26. By suitable multiplication of the number of this third type of strip, the electrically-operated heat-generating device of the present invention can be made to accommodate extremely long rooms. The

conductors

28 and 30 will be of low resistance material, such as copper. Moreover, the cross section of the

conductors

28 and 30 will be great enough that no appreciable line drop occurs in the operation of theelectrically-operated heatgenerating device of the present invention.

The center strips 26 and 38 have a number of tongues 44 projecting outwardly from the sides thereof. These tongues are disposed opposite each other and extend outwardly from the opposite faces of those strips. These tongues willbe placed in register with similar'recesses 46 in the sections lfl, 11 and 13. The tongues 44 will interact with the recesses 46 to releasably lock the sections 10,

. 11 and 13 to the center. strips.26 and 38. The tongues 44.and.the.recesses.46 will thus coact with the tongues 22 and. the recesses24 to .provide an integrated, but readily separable, .series of individual parts. These individual parts will, when interlocked, as shown in Fig. 1, serve as an integrated unit.

.Theconnecting strips 26 and 38 are equipped with .transversely directed taps .48. and.50. The taps 48 are .connected to the conductor 28 while the taps .50 are connected to the conductor 30. These taps are placed in register with thetongues44, and they extend into register with, and they are supported by, .those tongues. The taps 48 and 50 extend parallel to each other until they reachthe tongues 44 and then. they diverge from each other and extend to opposite ends of the tongues 44.

This is desirablesince it minimizes any possibility of the creation of short circuits between the terminals of e the taps48 and;50 and of the heat-generating elements- 14. The terminals for the taps 48 are denoted by the numerals 52 and the, terminals for the taps 50 are denoted by the numerals 54. These terminals will be in register with theterminals ;18 of the heat-generating elements 14, and theywill be releasably secured to them by the screws 20.

To connect. the terminals 52 .and 54 with the terminals .18, it is, only necessary to remove the screwsZO and to place the

terminals

52 or 54 in register with the terminals 18 and then replace the screws 20. This is a simple process and is one which can be carried out by unskilled individuals.

.When theterminals .are tobe connected or separated, the resilient flap .56 on the upper surface of the tongues T44.of.the connecting

strips

26 and 38 will be bent upwardly to expose the screws 20 and the

terminals

18 and 52 m, 54. .Once the connecting or separating operation has been completed, the resilient flaps 56 can be restored tov their normal flat position. Thus, these flaps 56 will carry ou t th e' plane eifect of the upper surface of the electricallyoper ated, heat-generating device. provided by a the. present invention.

-The sections 10 will be made of a size which is a uniform fraction ofstandard areas within homes and other structures. ,For example, in one. preferred embodiment of'the present invention, thesections .10 can. be two feet fourif eet .or can be two feet by six feet. Where the sectionsl were two feet by four feet, it would be possible to: have those sections heat rooms as small as eight feet by eight feet and to heat rooms that are roughly eight to ,,ten .feetj wide and are of limitless length. Where the sections are made to be two feet by six feet, they can .heat rooms that are from twelve to fourteen feet in width than one set of sections in a room, it ispossible to heat extremely largerooms. Moreover, by using connecting strips that cansupply just one aligned row of sections, it is possible to heat extremely narrow rooms. The length of the room will determine the number of sections used and will also determine the kind of connecting strip used. In an extremely short room, the connecting strip 38 would be modifiedby eliminating the tongue 40. In that event, the conductors 28 and would terminate short of the upper end of the connecting strip 38. By using various combinations of

sections

10, 11 and 13, and by usingvarious combinations of connecting

strips

26 and 38, the present invention makes it possible to heat rooms of many different sizes and shapes. Moreover, bybeing able. to use several groups of electrically-operated heat-generating devices which in turn consist of sections and connecting strips, the present invention makes it possible. to heat rooms of even great size and area.

In many instances, the electrically-operated heat-generating device. of the present invention will not be used as the sole source of heat. This is particularly true in old structures where the source of heat is already installed but is not completely satisfactory. In such cases, the electrically-operated heat-generating device of the present invention willaugment the heat provided by the permanent heating system. If desired, a suitable thermostat can be connected between the conductors28 and 30 and a source of current. In other cases, manual control of thetemperature within the structure can be attained by installing a switch between the

conductors

28 and 30 and the source of current.

- The electrically-operated heat-generating device of the present invention is largely free of the objectionable heat lag experienced with many heating systems. For example, in the case of radiant heating systems, the heat must be used to warm the entire floor structure before that structure can radiate the heat into the area above it. This often times results in over-shooting? of temperature, and it leads to unpleasant warmth in times of sudden temperature rises of the atmosphere outside the building. With the electrically-operated heat-generating device of the present invention the response is prompt and it is subject to very close control.

In some instances the overall dimensions of the integrated sections of the electrically-operated heat-generating device will be smaller than those of the rug, Where a rug is used, or of the floor where no rug is used. For those instances, filler strips will be provided which will have the same thickness as the sections, and which can be cut to size. Those filler strips will not have electrical wires embedded within them; and hence they can be cut freely.

Whereas the drawing and accompanying description have shown and described a preferred embodiment of the present invention, it should be apparent to those skilled in the art that various changes may be made in the form of the invention without aifectinx the scope thereof.

What 1 claim is:

1. An electrically-operated, heat-generating device that has a substantially plane exposed surface and that is releasably disposable on the floor of a structure to heat the area within said structure immediately above said floor and that comprises a plurality of individual sections of prefabricated unitary construction that are selectively securable to or separable from each other, each of said sections having a layer of material that is disposable against said floor having a heat generating element of electrical resistance material that is disposed above said layer, having a layer of material that is disposed above said heat generating element and that transmits heat therethrough to the area immediately above said floor, and having terminals for said heat generating element,

fand a plurality of electrical conductors that are wholly external of said sections and'are selectively securable to or separable from the terminals of said plurality of sections and that are selectively connectible to a source of electricity, said plurality of conductors being encased within a prefabricated elongated strip of unitary construction, said strip and said sections being of substantially the same thickness, said plurality of conductors having taps that are selectively connectible to or separable from said terminals of said sections, said strip having the exposed surface thereof substantially coplanar with the exposed surfacesof said sections.

2. An electrically-operated, heat-generating device that has a substantially plane exposed surface and that is releasably disposable on the floor of a structure to heat the area within said structure immediately above said floor and that comprises a plurality of individual sections of prefabricated unitary construction that are selectively securable to or separable from each other, each of said sections having a layer of material that is disposable against said fioor, having a heat generating element of electrical resistance material that is disposed above said layer, having a layer of material that is disposed above said heat generating element and that transmits heat therethrough to the area immediately above said floor, and having terminals for said heat generating element, and pairs of interacting surfaces on at least one of said layers of said sections that selectively maintain said sections in assembled relation, one interacting surface of each pair of interacting surfaces being a cutout in one of said sections and the other interacting surface of said pair of interacting surfaces comprising a tongue with a lateral projection on another of said sections, said projection lying in back of the portion of said one section that defines said cutout.

3. An electrically-operated, heat-generating device that has a substantially plane exposed surface and that can heat the area immediately adjacent said exposed surface and that comprises a plurality of individual sections of prefabricated unitary construction that lie in a plane and that are selectively securable to or separable from each other, each of said sections having a heat generating element of electrical resistance material and having terminals for said heat generating element, and pairs of interacting surfaces on said sections that selectively maintain said sections in assembled relation, one interacting surface of each pair of interacting surfaces being physically disposed behind the other interacting surface of said pair of interacting surfaces so the shear resistance of said sections prevents separating movement of said sections While said sections lie in said plane, said one interacting surface of said pair of interacting surfaces being a lateral projection on a tongue on one of said sections, said other interacting surface of said pair of interacting surfaces being the portion of another of said sections that defines a cutout complementary to said tongue and projection, said sections coacting to provide a substantially smooth and unbroken heating surface for a structure.

4. An electrically-operated, heat-generating device that has a substantially plane exposed surface and that can heat the area immediately adjacent said exposed surface and that comprises a plurality of individual sections of prefabricated unitary construction that lie in a plane and that are disposable immediately adjacent each other, each of said sections having a heat generating element of electrical resistance material and having terminals for said heat generating element, and a plurality of electrical conductors that are wholly external of said sections and are selectively securable to or separable from the terminals of said plurality of sections and that are selectively connectible to a source of electricity, said plurality of conductors being encased within an elongated strip, and having taps that are selectively connectible to or separable from said terminals of said sections, said strip lying in said plane and said strip and said sections being conductors that are wholly external of said sections and are selectively securable to or separable from the terminals of said plurality of sections and that are selectively connectible to a source of electricity, said plurality of conductors being encased within a prefabricated elongated strip of unitary construction, and having taps that extend transversely of said strip and are selectively connectible to or separable from said terminals of said sections, said strip lying in said plane, said strip and said sections being of substantially the same thickness, said sections being disposable in side-by-side relation to define a row of aligned sections, said strip being adjacent to and being coextensive with one side of said row of aligned sections.

6. An electrically-operated, heat-generating device that has a substantially plane exposed surface and that is releasably disposable on the floor of a structure to heat the area within said structure immediately above said floor and that comprises a plurality of individual sections of prefabricated unitary construction that lie in a plane and that are selectively securable to or separable from each other, each of said sections having a heat generating element of electrical resistance material and having terminals for said heat generating element, and a plurality of electrical conductors that are wholly external of said sections and are selectively securable to or separable from the terminals of said plurality of sections and that are selectively connectible to a source of electricity, said plurality of conductors being encased within a prefabricated elongated narrow strip of unitary construction, said electrical conductors having taps that are selectively connectible to or separable from said terminals of said sections, said taps being encased Within said strip throughout the greatest portions of their lengths, said sections having flaps overlying said terminals of said heat generating elements to provide access to said terminals for the purpose of interconnecting said taps and said terminals, said strip having the exposed surface thereof substantially coplanar with the exposed surfaces of said sections, and pairs of interacting surfaces on said sections and strip that selectively maintain said sections in assembled relation With each other and with said strip, said sections being disposable in side-by-side relation to define a row of aligned sections, said strip being adjacent to and being coextensive with one side of said row of aligned sections, said heat-generating device being adapted to maintain itself as an integrated unit by the shear resistance of said interacting surfaces and to maintain itself against sideways dislodgment on said floor by gravity-induced friction.

7. An electrically-operated, heat-generating device that is releasably disposable on the floor of a structure to heat the area within said structure immediately above said floor and that comprises a plurality of sections that are selectively securable to or separable from each other, each of said sections having a layer of material that is disposable against said floor, having a heat generating element of electrical resistance material that is disposed above said layer, having a layer of material that is disposed above said heat generating element and that transmits heat therethrough to the area immediately above said floor, and having terminals for said heat generating element, and a plurality of electrical conductors that are wholly external of said sections and are selectively s'ecurable to or separable from the terminals of said sections and that are selectively connectible to a source of electricity, said plurality of conductors being encased within an elongated strip and having taps extending transversely of said strip, said taps being selectively connectible to or separable from said terminals of said sections, and interacting surfaces on at least one of said layers of said sections and said strip to selectively hold said sections in assembled relation with each other and with said strip, said heat generating device being adapted to maintain itself as an integrated unit by the shear resistance of said interacting surfaces.

8. An electrically-operated, heat-generating device that is releasably disposable on the floor of a structure to heat the area within said structure immediately above said floor and that comprises a plurality of sections that are selectively securable to or separable from each other, each of said sections having a layer of material that is disposable against said floor and that resists the passage of heat therethrough, having a heat generating element of electrical resistance material that is disposed above said layer of heat resistance material, having a layer of material that is disposed above said heat generating element and that transmits heat therethrough to the area immediately above said floor, and having terminals for said heat generating element, and a plurality of electrical conductors that are wholly external of said sections and are selectively securable to or separable from the terminals of said sections and that are selectively connectible to a source of electricity, said plurality of conductors being encased Within an elongated strip and having taps extending transversely of said strip, said taps being selectively connectible to or separable from said terminals of said sections, and interacting surfaces on at least one of said layers of said sections and said strip to selectively hold said sections in assembled relation with each other and with said strip, said taps being in register with some of said inter-acting surfaces.

9. An electrically-operated, heat-generating device that has a substantially plane exposed surface and that can heat the area immediately adjacent said exposed surface and that comprises a plurality of individual sections of prefabricated unitary construction that lie in a plane and that are selectively securable to or separable from each other, each of said sections having a heat generating element of electrical resistance material and having terminals for said heat generating element, and a plurality of electrical conductors that are wholly external of said sections and are selectively securable to or separable from the terminals of said plurality of sections and that are selectively connectible to a source of electricity, said plurality of conductors being encased within an elongated strip, and having taps that are selectively connectible to or separable from said terminals of said sections, said strip and said sections being of substantially the same thickness, said strip being coextensive with and abutting one edge of each of said sections, said taps being encased Within said strip throughout substantially all of the lengths thereof, said sections having flaps that normally overlie said terminals of said heating elements but that are movable to expose said terminals for the interconnecting of said taps and terminals.

10. An electrically-operated, heat-generating device that has a substantially plane exposed surface and that can heat the area immediately adjacent said exposed surface and that comprises a plurality of individual sections of prefabricated unitary construction that lie in a plane and that are selectively securable to or separable from each other, each of said sections having a heat generating element of electrical resistance material and having terminals for said heat generating element, and a plurality of electrical conductors that are wholly external of said sections and are selectively securable to or separable from the terminals of said plurality of sections and that are selectively connectible to a source of electricity, said plurality of conductors being encased within an elongated strip, and having taps that are selectively connectible to or separable from said terminals of said sections, said strip and said sections being of substantially the same thickness, said strip being coextensive with and abutting one edge of said sections, said taps being encased within said strip throughout substantially all of the lengths thereof, said sections having flaps that normally overlie said terminals of said heating elements but that are movable to expose said terminals for the interconnecting of said taps and terminals, and pairs of interacting surfaces on said sections and strip that selectively maintain said sections in assembled relation with each other and with said strip, said heat-generating device being adapted to maintain itself as an integrated unit by the shear resistance of said interacting surfaces.

References Cited in the file of this patent UNITED STATES PATENTS 2,084,468 Wach June 22, 1937 2,110,660 Doczekal Mar. 8, 1938 2,502,148 Grothouse Mar. 28, 1950 2,521,540 Richardson Sept. 5, 1950 2,540,465 Tice Feb. 6, 1951 2,582,762 Tidd Jan. 15, 1952 2,609,474 Tidd Sept. 2, 1952 2,612,585 McCann Sept. 30, 1952 FOREIGN PATENTS 589,752 Great Britain June 30, 1947