Abstract: A heating device, such as a heating coil for use in apparatus to be heated, has a removable flexible strip carrier which enables the coil, already supported on ceramic insulators and carried by brackets, to be readily installed in the apparatus. The disposable or reusable strip carrier is notched for supporting the insulators and is easily removed after installation of the device.

Abstract: A vacuum furnace has a heating chamber heated by metal strip electric heater elements. The elements have insulated mechanical support between their ends to hold them in position in the furnace. Support is provided by assemblies having spaced apart mounting assemblies with a rigid bridge compliantly mounted therebetween. The heater strip is compliantly connected to the bridge. Each mounting assembly has a metal post connected to the furnace heating chamber and surrounded by a ceramic sleeve. The ceramic sleeve is surrounded by two ceramic tubes which hold an end of the bridge therebetween.

Abstract: A duct heater includes end brackets by frame bars. The end brackets are formed into a geometric shape whereby only corners of the bracket engage an inner suface of the duct. Assembly is facilitated by providing the end bracket as thin, flat strips having narrower and wider sections. The frame bars are attached to the wider sections, and when the strips are bent to form a closed geometric form, the thinner sections are curved to form duct-engaging corners while the wider sections remain substantially straight. Insulating supports are attached to the frame bars, and a heater coil is attached to the insulating supports. The structure may be easily slid into a duct because only the corners of the end brackets contact the duct. Thus, a method for forming the heater brackets and attaching heater elements is set forth.

Abstract: An electric resistance heater array having an open metal frame with multiple heater wires of heavy gauge, U-shaped Nichrome wire that are vertically spaced across the panel. The lower vertical portions of the heater wire are encased in ceramic sleeves which insulate the wire from the small apertures in the metal frame that support the wire by its constraints upon side to side and fore to aft movement.

Abstract: The invention relates to a support frame for a resistor element in a heating furnace for glass sheets, said flame providing a substantially continuously extending, elongated rest surface for a resistor element. The support frame elements consist of trough-like castings and are fastened to each other in an articulated manner. The short frame elements are easy to cast and can be assembled into long continuous support frames for resistor elements, the thermal stresses of said frames not passing over the link points. A long continuous support frame structure makes it accordingly possible to employ resistor elements that are long and continuous and thus readily replaceable.

Abstract: A heater and limit switch assembly, particularly useful for installation in the conditioned air duct of a rooftop air conditioner. The loop of a rigid-loop heater, mounted on a vertical plate by two parallel legs, is modified to provide an inward offset portion leading to the second leg. Radiation, from the offset portion and its bend into the second leg, is received at close range by a simple disk-type limit switch, positioned on the plate outward of the second leg and facing the offset, inducing prompt response to any increase over design temperature.

Abstract: An electric heater employs plate-shaped heating elements, each consisting of a core of semiconductor material whose opposing faces are coated with conductive material and having a multiplicity of apertures to permit passage of air. The heater includes a housing with a rear air inlet and a forward air outlet. A fan having a fan venturi causes air flows forwardly through the housing. A two-piece, ceramic holder maintains a number of the plate-shaped heating elements in generally coplanar, spaced-apart relationship, in front of a forward venturi opening. The holder has a large recess positioned over the forward venturi opening which receives substantially all air flow from the venturi, and a number of passages, one associated with each heating element, which direct air from the recess through the cores towards the forward air outlet.

Abstract: An electric heater incorporating simple support structure therefor. A frame is insulated from an electric resistance heater coil by insulator supports mounted within beam members of the frame. The supports incorporate structural features enabling the use of simplified supporting beams. The support insulators include additional structural features for retaining the resistance wire in place and for simplified engagement therewith. The insulators may project on both sides of the support beams and retain heater wires in two planes. The support insulators further provide an integrated structure easily fabricated and simply assembled to the frame.

Abstract: An insulator for an electric heater employs a central elongated slot and two guide surfaces. Below each guide surface is a notch for receiving an outer convolution of a heater coil, while the central slot terminates in a notch for receiving an intermediate convolution of the heater coil. The slot engages the central convolution of the heater coil before outer convolutions engage the guide surfaces to facilitate installation of the insulator. As the insulator is inserted into the heater coil, the guide surfaces engage the outer convolutions and direct them to respective notches for securely holding the heater coil. The insulator may support a single pass of the heater coil or may be arranged to have these surfaces and notches on opposite ends to support two passes of the heater coil.

Abstract: A particularly efficient yet inexpensive and simple heat element for such appliances as blow dryers, paint strippers, heat guns, and so forth, consists essentially of a tightly crimped corrugated wire ribbon supported on a form in such a manner that its corrugations are generally perpendicular to the surface of the form. The resulting structure, which has an end-on appearance like that of a finned tube, efficiently radiates heat to a mass of flowing gas. A particularly preferred embodiment results when the form is intersecting mica plates.

Abstract: A heater coil mounting is provided by means of a bracket having seats formed at or adjacent each axial end and into which an insulator through which the heater element passes, is adapted to be received. The bracket is mounted in position on a wall using tabs which cooperate with portions of the bracket to hold the bracket close to the wall and form a further portion of the seat to lock the insulator in position.

Abstract: A rigid frame supported resistor for dynamic braking of electric and diesel-electric locomotives has certain of the frame elements cushioned or insulated from each other and the resistance ribbon insulated and cushioned from the frame. Organic insulating material in molded or sheet form, preferably a copolymer, such as a polyester resin, protected by a metal heat shield, may be used for structural frame members, or for cushioning and insulating metal structural frame members. The organic insulating resistant is supplemented by ceramic insulating material in locations subject to high heat.

Abstract: A heater section for hair dryers utilizing spirally wound sinusoidally shaped electric resistance heating wire wound about a plurality of radially extending insulating mica boards. The mica boards are axially aligned along the external surface of a central frustoconical/cylindrical motor shroud disposed within a frustoconically shaped dryer housing and are provided with notches to hold the heating wire. A portion of the air moved by the hair dryer fan is blown past the heating wire between the interior surface of the dryer housing and the motor shroud and a portion is blown past the motor between it and the motor shroud. The apertures in the mica boards and the frustoconical/cylindrical motor shroud facilitate the circulation of heated air within the dryer housing. The frustoconical shape of the front portion of the motor shroud adjacent the hair dryer nozzle enhances turbulence within the heater section to facilitate more uniform temperature distribution at the nozzle of the hair dryer.

Abstract: An electrical radiator, particularly for fan-forced heaters, is provided which includes a resistance heating element disposed on an insulating element connected to the housing of the fan-forced heater. The coil winding of the resistance heating element is secured to the insulating element by means of clamping elements and is freely extending therefrom. A bimetallic switch in series with the resistance heating element serves as a heat protective switch and is disposed on a connector bar connected to the insulating element and carrying the electrical connectors for the coil winding. One end of the coil winding is secured on one side of the bar to a first bracket remote from the insulating element and which is rigid with the bar and connected to a first connector. The other end of the coil winding is secured to a second bracket disposed on the other side of the bar near the insulating element and which is rigid with the bar.

Abstract: An insulator for a coil-type electric resistance heater is disclosed in which the insulator has inclined side faces forming the outer end of the insulator angling inwardly toward one another with side notches in the insulator at the base of the inclined side faces and a central notch in the outer end of the insulator between the two inclined side faces. The distance between the center notch and the outer ends of the inclined side faces is less than the spacing of the adjacent convolutions of the heater element coils so that upon aligning one convolution with the central notch and upon moving the insulator inwardly toward the axis of the coil, the one convolution will be received in the center notch and the adjacent convolutions will be wedgingly engaged by the side faces of the insulator so as to resiliently spread the convolutions such that the adjacent convolutions will snap into the side notches.A method of installing an electrical resistance heater on a plurality of insulators is disclosed.

Abstract: A duct heater includes end brackets connected by frame bars. The end brackets are formed into a geometric shape whereby only corners of the bracket engage an inner surface of the duct. Assembly is facilitated by providing the end brackets as thin, flat strips having narrower and wider sections. The frame bars are attached to the wider sections, and when the strips are bent to form a closed geometric form, the thinner sections are curved to form duct-engaging corners while the wider sections remain substantially straight. Insulating supports are attached to the frame bars, and a heater coil is attached to the insulating supports. The structure may be easily slid into a duct because only the corners of the end brackets contact the duct.

Abstract: A heater assembly includes a housing which both channels air flowing around a heating element and provides support structure for the elements holding the heating element. In one embodiment, a lower U-shaped channel has recesses in opposed sidewalls to engage down-turned ends of holding elements. A second U-shaped channel is attached to form a hollow duct open at opposite ends. In a second embodiment, a U-shaped channel is made of flexible material so that the spacing between opposed sidewalls may be varied. A holding element is secured between the sidewalls by separating the sidewalls to allow insertion of the holding means.

Abstract: This duct heater assembly includes a duct section having upper and lower wall portions and opposed side portions. The upper and lower portions include end margin portions connectible to the end margins of conventional duct line section by "S" strip connectors. The side portions include C-shaped flanges connectible to the C-shaped flanges of conventional duct line sections by "C" strip connectors. One of the side portions incorporates a control box having an overhanging end spaced from the side wall of an adjacent conventional duct line section to accommodate the "C" strip connectors.

Abstract: An apparatus is disclosed for providing uniform radiant heat to a substrate by means of a plurality of parallel electroconductive heating wires which are maintained in planar relationship upon heat expansion by means of attachment to a movable bus bar attached to a tensioned spring, positioned in contact with a stationary member which limits its movement to a plane parallel to the plane of the heating wires.

Abstract: Utility model patent for a support for electrical resistances of ovens or kilns with ceramic mantle thermal insulation, used to support resistances of the kind consisting of a filament or ribbon of electrical conductor material laid in a sinuous or fretwork fashion on supports and, in this model, comprised of an isosceles-triangular end 1 which is driven into the mantle 2 and followed by a middle flange 3 which is in turn followed by a cylindrical end 4 on which rests the filament or ribbon constituting the resistance 5, the part being completed with a removable ring 8 which is placed on the free end of the end 4 and holds fast on the said end section 4 the portion of ribbon or filament constituting the resistance 5.

Abstract: An electric thermal unit is disclosed for controllably heating cylinders in plastic material extruders, rubber drawing machines, and the like apparata. The electric thermal unit is designed to provide closed circuit ventilation air circulation such as to enable the heated outlet air to be used for other applications, whether related or not to the proper operation of the cited apparata.

Abstract: An insulated electric heating element particularly suitable for use in a hot plate or electric stove is disclosed. The insulated electric heating element (11) includes a unitary two chamber housing (21). The chambers are located one above the other. A U-shaped upper chamber (22) houses a resistive electric heating element (23). A U-shaped lower chamber (24) houses thermal insulation (30). The thermal insulation reduces the heat radiated downwardly and sidewardly and correspondingly increases the heat radiation upwardly by the electric heating element.

Abstract: Resistance heating element, with a heat conductor led in meander pattern, which is fastened in the zone of the meander arches in bearing elements, characterized in that between the bearing elements there is arranged a heating conductor of at least one one-piece sheet metal stamped part strip (4) with bearing pins (25) and slide pins (27).

Abstract: An insulator for an electric heater employs a central elongated slot and two guide surfaces. Below each guide surface is a notch for receiving an outer convolution of a heater coil, while the central slot terminates in a notch for receiving an intermediate convolution of the heater coil. The slot engages the central convolution of the heater coil before outer convolutions engage the guide surfaces to facilitate installation of the insulator. As the insulator is inserted into the heater coil, the guide surfaces engage the outer convolutions and direct them to respective notches for securely holding the heater coil. The insulator may support a single pass of the heater coil or may be arranged to have these surfaces and notches on opposite ends to support two passes of the heater coil.

Abstract: An electrical resistance heating assembly having specially designed electrical insulators is disclosed. The electrical insulators have arms shaped to retain an electrical resistance heating coil which can be quickly, easily, and reliably mounted on the arms of the insulator. Top parts of the arms are generally rectangular or triangular in cross section and the arms are spaced and configured relative to each other to form a generally T-shaped opening between the arms, with the ends of the cross bar of the T-shaped opening forming electrically resistance heating coil retention surfaces. Also, cuts in side surfaces of the insulators may provide additional coil retention surfaces.

Abstract: A heater rack assembly, of the type which supports an electric heating coil in a pattern of parallel rows in a plane, utilizes double-ended stand-off insulators which are formed wafer-like in the plane. The insulators have, at each end, pairs of hook portions facing each other to provide a throat, which opens into a wire-accommodating slot behind the hook tips, the slot converging toward the center at an angle of 150.degree. or less. Adjacent turns of the coil are to be accommodated within the slot. Its convergence retains within the slot adjacent coil turns which might otherwise escape, requiring for such escape what is in effect a reverse in-plane twisting displacement.

Abstract: An insulated electric heating element particularly suitable for use in a hot plate or electric stove is disclosed. The insulated electric heating element includes an insulating member comprising a layer of ceramic insulation surrounding the sides and bottom of the housing that encloses the resistive heating element is disclosed. The ceramic insulation is mounted in the bottom and extends up the sides of a cross-sectionally U-shaped channel. The legs of the channel are formed so as to adhere to the sides of the heating element housing. The ceramic insulation reduces the heat radiated downwardly and sidewardly and, correspondingly, increases the heat radiation upwardly by the electric heating element. The upper edge of the channel legs lie below the upper surface of the heating element housing to avoid creating a gap between the bottom of a vessel (e.g., pot) to be heated and the upper surface of the heating element housing.

Abstract: A heater is disclosed having an elongate wire heating element with the heating element including at least two generally parallel runs supported on a frame by insulators with the portion of the heating element consituting the runs being formed generally in a helical coil and with the portion of the heating element between the runs being referred to as a turnaround. Specifically, the turnarounds are of non-helical coil construction and have at least one loop therein between the insulators supporting adjacent runs of the heating element thereby to permit limited movement between the adjacent runs and to permit thermal expansion and contraction of the turnarounds without applying a substantial force to the insulators.

Abstract: An electric heater incorporating simple support structure therefor. A frame is insulated from an electric resistance heater coil by insulated supports mounted within beam members of the frame. The supports incorporate structural features enabling the use of simplified supporting beams. The support insulators include additional structural features for retaining the resistance wire in place and for simplified engagement therewith. The insulators may project on both sides of the support beams and retain heater wires in two planes. The support insulators further provide an integrated structure easily fabricated and simply assembled to the frame.

Abstract: This invention relates to a spacer clip for an injection molding electric heating element. A number of clips, each formed of a continuous band, are slipped over one end of the heating element and slid along to predetermined positions. Each clip is then crimped to the heating element in that position which forms a finger which extends radially from the heating element in a predetermined orientation. The heating element with the spacer clips attached is located in a suitable mold for casting and the fingers of the clips locate each coil of the element with sufficient clearance from the mold and the other coils. The thickness of the conductive heater cast around the heating element is important to provide uniform heat transfer. The spacer clips are formed of a material such as stainless steel which has sufficient pliability to be securely crimped to the heating element, but sufficient strength to reliably retain the heating element in position.

Abstract: A film heating oven for a skin packaging machine. The oven has a metallic housing in which are supported a plurality of elongated heaters in spaced parallel relationship. The heaters are energized by a control system which raises their temperature for heating the film and lowers the temperature during other operations of the machine. The housing includes a reflector for each tube to direct the heat downwardly onto the film and further includes an outer covering of insulation to minimize the escape of heat.

Abstract: An apparatus replaceably carries an electrical resistance element for a furnace. The electrical element is of serpentine configuration having a plurality of U-shaped portions. At least one plate-shaped carrying element is mechanically fastened in a block of ceramic fibrous material. The carrying element includes a plurality of through-passages into which the U-shaped portions of the electrical element are inserted. The through-passages each include side walls and transverse walls which restrain movement of the electrical element in all directions except a direction in which the electrical element is inserted and removed. The carrying element is spaced from the adjacent curved segments of the U-shaped portions. The electrical element terminates in elongated terminals which are carried by a plug of fibrous ceramic material. The electrical element is situated within a recess of the ceramic block.

Abstract: The insulative stand-off is mounted on a frame and supports a heating coil. In the preferred embodiment the coil loops engage retention surfaces inside the inverted T-shaped opening in the end of the stand-off. The sides of the stand-off forming the opening have cam surfaces which squeeze adjacent central loops together during mounting while the loops adjacent the central loops are deflected to the outside of the stand-off. When the central loops reach the crossbar of the T they spring apart to fix the coil. Other embodiments are shown--all have retention surfaces generally parallel to the coil loops and transverse the coil axis. Cam surfaces control access to the retention surfaces to deflect the loops as they are moved to the retention surfaces and the coil resiliency biases the loops into engagement with the retention surfaces when mounting is completed.

Abstract: In an electrical resistance heating element (1) comprising a heating conductor support (3) of insulating material and a heating conductor (4) of resistance wire wound in meander or sinuously coiled manner with loop ends or bights (6) and loop legs or runs (8), the loops of the heating conductor (4) being arranged substantially in a single plane, and the inner loop ends (6) which are directed towards the heating conductor support (3) being situated in the edge region of the heating conductor support (3), it is proposed according to the invention to construct the heating conductor support (3) as a flat plate, the flat plate to be situated substantially in the same plane as the loops of the heating conductor (4). It is also proposed that the outer loop ends or bights (5) remote from the heating conductor support (3) are to be self-supporting and not secured.

Abstract: An improved electrical heating element is constructed to increase the amount of electrical wire per unit space available for plug-type convection heating units. The heating element includes a metal frame structure with a plurality of spaced support elements and a plurality of spaced removable cross bars connected thereto. A plurality of ceramic heater support blocks, each of T-shape in plan, with spaced end faces are arranged end to end and have undercut grooves which receive a cross bar and are interposed between the support elements. A continuous electric resistance heating wire has a series of parallel spaced inverted U-shaped wire sections. The wire sections are arranged in groups. Each block has a support boss of reduced width adjacent one end face adapted to extend between the strands of a section of the heating wire. Each block has a pair of spaced bosses adjacent to its other end face which extend laterally outward of the support boss.

Abstract: An electric immersion heater of planar construction for use in industrial processes is constructed of a non-corrodable material and may be immersed at the side of a processing not containing corrosive liquids. The heater includes a thin planar polymeric support frame having side members with end sections extending beyond the end portions of the frame. An electrical resistance heating element wire shrouded with an integral layer of polymeric material is wound around the end portions of the frame to form a substantially flat heating element assembly. Imperforate polymeric cover plates are secured in spaced relationship to opposite faces of the heating element assembly by spacing and securing means engaging the side members of the frame. The peripheral edges of the cover plates are spaced apart to form a gap allowing for free flow of fluid through the heater between the plates throughout the entire extent of the heater.

Abstract: A heating device (20) is provided that may be utilized in either a film packaging machine or a thermoforming machine. Heating device (20) includes a frame (32) that carries a plurality of eyelets (36) that are utilized to suspend an elongated ribbon heating element (34) so that apart from contact with the eyelets (36), the elongated ribbon heating element (34) does not contact any other portions of the heating device (20). This construction provides for very rapid heating and cooling response times resulting in an energy savings and a simplified packaging or thermoforming device, while providing accurate heat control.

Abstract: A heating element comprising a plurality of ceramic components strung together on a heating wire to form a flexible structure, adjacent ceramic components comprising integrally formed mating projections and depressions. The element comprises ceramic components of a type each having a body defining two generally parallel passages therethrough, both passages terminating at one end in a depression, one passage terminating at the other end in a depression and the other passage terminating at the other end in a projection.

Abstract: A thermostat range control device for maintaining a thermostat temperature that has a substantially constant difference with respect to room temperature, and which allows the thermostat to respond quickly and accurately to changes in room temperature. The device includes a detachable enclosure for substantially enclosing the thermostat, a distributed heater within the enclosure having multiple openings therein for providing generally uniform heat within the enclosure, means for allowing room temperature air to enter the enclosure at a level below the thermostat, and means for allowing heated air within the enclosure to exit from the enclosure at a level above the thermostat, in a manner such that substantially only heated air passes the thermostat.

Abstract: An electrical connector assembly including an elongate resilient synthetic resin channel member for attachment to a vehicle window, the channel member having therein a longitudinally extending channel of re-entrant cross-section. An elongate electrically conductive part is arranged to be received as a snap fit in said channel, whereby one or more conductive heating elements can be trapped between said part and the wall of said channel in electrical connection with said part. The channel member has a surface which supports said part within the channel in a position spaced from the base of the channel in a direction towards the open face of the channel.

Abstract: The invention relates to electric heating elements, particularly of the open coil type, for installation in apparatus, such as room air conditioners or the like, wherein a thermostat is required and is positioned with its heat sensor in close proximity to an active heating portion of the heating element so as to be extremely sensitive to variations in heat. The invention insures that the thermostat is always properly installed, especially after service work has been performed on the air conditioner, and/or the heating element. Briefly, a tab extends from a terminal of the thermostat and is adapted to fit in only one relation within an opening in an insulator bushing. The bushing has an extending lug to fit in predetermined manner with a portion of a cross strip of a supporting frame to hold the bushing from substantial rotation.

Abstract: The coiled resistance heating wire is supported on electrical insulating stand-offs in a figure 8 pattern on each side of a metallic radiation panel. The radiation panel and the figure 8 arrangement of the coil each contribute to increased heat transfer to air flowing axially down the assembly in a duct and in combination result in even more efficient heat transfer.

Abstract: A heating element comprising a plurality of ceramic components strung together on a heating wire to form a flexible structure, adjacent ceramic components comprising integrally formed mating projections and depressions.

Abstract: An open coil electric heater comprising a rigid support frame composed of a pair of longitudinally extending, laterally spaced members, with cross members between and secured to the longitudinal members. The cross members carry ceramic coil supports which are detachably connected to the cross members. Each coil support has an end formed with a cross slot to pass a part of a convolution of a coil and hook-like projections are formed on opposite sides of a coil support and are cooperable with the coil convolution part to detachably hold the same to the coil support. The heating coil is secured to the coil supports in expeditious manner and without the use of tools by twisting the coil so that said convolution part is aligned sufficiently with said cross slot to enable said part to be seated within said slot. The coil is then permitted to spring back so that the convolution fits against opposite side faces of said coil support and held in position by said hook-like projections.

Abstract: Electric toaster with a toasting chamber which has heaters on at least two broad sides and is terminated by crosswise walls on two narrow sides, wherein the heaters have insulating parts supporting heater conductors and are supported by the crosswise walls. The crosswise walls have vertical slots or slits and the heaters are placed by inserting the insulating parts of the heater into the slots.

Abstract: A heating element for electrical appliances which include a meander-form winding of resistance heating wire, two or more supporting plates arranged parallel to an incident flow direction of air produced by the blower and having openings in which turns of the winding are located. Metallic spacer elements are provided for connecting the supporting plates with a voltage tap being provided on at least one of the turns of the winding. At least one of the spacer elements is provided with a prolongation which projects beyond one of the supporting plates and is deformable to constitute a sleeve engaging about a turn of the winding.

Abstract: A heating element terminal comprising a tubular conductor extending through the central bore of a two-piece insulating clamp member and an aligned aperture of the heating element frame clamped therebetween. The tubular conductor includes a flattened terminal plate at a first end projecting outwardly of the heating element and at the second opposite end includes a compression sleeve portion extending axially therefrom and projecting inwardly of the heating element. An end of the resistance wire of the heating coil is inserted into the central bore of the inwardly projecting compression sleeve portion which is crimped to secure the end of the resistance wire to the said second end of the terminal. The flattened plate formed at the first end of the terminal is drawn into abutment against the two-piece clamp member, and the second opposite end is similarly flattened at the point immediately adjacent the opposite side of the clamp member.

Abstract: A forced convection electrical heater assembly advantgeously utilizing expanded resistance alloy foil or grid in a pattern which produces a uniform temperature distribution in the existing airstream and which produces relatively little flow restriction on the airstream. The resistance grid in the form of at least one continuous strip is strung in a sinuous path to form a plurality of planar reaches spaced uniformly across the flow passage and extending longitudinally from inlet to outlet. Grid support elements at the inlet and outlet are arranged to force air to pass through the resistance grid only once to thereby achieve a minimum flow restriction. Alternation of the grain of the expanded foil in each plane and between planes and the provision of a flow deflector at the exit contribute to temperature uniformity.

Abstract: An open coil electric heater wherein the resistance conductor is supported on a frame. The resistance conductor in this instance, instead of being in the form of a single coiled wire, is composed of a plurality of strands of wire so as to reduce the cost of the resistance conductor while providing adequate surface area. The strands of fine wire or flat ribbon wire are braided into a rope which is formed into a series of reaches in customary manner. At least one of the strands is of a material which will provide strength to the wires that primarily generate the heat and thereby prevent sagging of such wires between wire supports. In a preferred form, the wires are loosely braided to form wide open spaces and insulated support members are projected through certain of the open spaces to support the strands in predetermined position.

Abstract: An electrical heater construction having a frame carrying electrical heaters and a movable drawer-like unit that is adapted to interconnect power source leads to the heaters when the unit is in one position thereof relative to the frame, the frame carrying a movable latch member that is operatively associated with the unit to latch the unit in an out position thereof when the unit is moved out of the one position thereof to the out position to disconnect the power source leads from the heaters whereby the unit cannot be moved in any direction from the out position thereof until the unit is unlatched from the latch member by the latch member being manually moved to an unlatching position thereof.