Abstract: The required electrical connections between the ends of the windings on an electrical motor, the switch terminals for the motor, and the motor protector are made by means of an electrical connector which comprises a housing having a plurality of cavities. Each of the cavities has a double-ended terminal therein to which the winding ends are connected. Each terminal also has a receptacle portion which receives a tab extending from either the motor protector or the switch. The connector, the motor protector, and the switch are clustered adjacent to each other with the protector against or adjacent to the coil windings of the motor. The shape of the connector housing, the protector, and the switch, and the location of the cavities in the connector and the terminals on the switch is such that when the parts are assembled to each other on the motor, all of the required electrical connections will be made correctly.

Abstract: A sealed thermostatic electric switch has a heat responsive thermostatic element disposed in good heat transfer relationship with the closed end of a heat conductive cup shaped member. The side wall of the cup shaped member extends upwardly from the closed end and is spaced a selected distance from the housing of the switch. A plastic sleeve has one end tightly received over the side wall and adhesively secured thereto and another end closed except for a tubular portion extending therefrom with electrical leads of the switch extending from the switch through and beyond the tubular portion. The tubular portion has opposed wall portions which are in contact and coalesced with each other and with the aligned plastic insulation of the leads to effectively seal the tubular portion of the sleeve.A mounting plate is welded to the bottom outer surface of the cup shaped member which interfits with a strap or clip for attachment to a surface whose temperature is to be monitored.

Abstract: In a hermetic compressor there is provided a resilient retainer member adapted to removably secure a thermal overload protector relative to the compressor casing. The overload protector is arranged in a housing which is adapted to engage the upper wall of the casing. The retainer member includes one end portion dimensioned to engage the housing whereby downward pressure on the retainer member secures the overload protector relative to the casing. The overload protector housing is formed to include a pair outwardly projecting leg members. A slot formed on one of the legs aligns with an opening in the other leg are engageable by a tool which is employed to exert an external force on the housing sufficient to allow removal and replacement of the thermal protector housing relative to the retainer member.

Abstract: A generator having stator windings which are water cooled includes a plurality of sensors each for measuring the temperature of cooling water as it is discharged from respective sections of the stator windings and prior to its collection in a common manifold. The outputs of the sensors are combined to obtain an average reading and during an initialization process, each sensor reading is subtracted from the average to derive a correction factor for that particular sensor, for that particular average. The generator is operated so that other averages are selected for the calculation of other sensor correction factors. When operating on line, the correction factors are utilized to obtain a value for a percent of average coil temperature in accordance with the relationship: ##EQU1## where T is the temperature indication provided by the sensor, AVG is the average of all of the sensor readings, and CF is the appropriate correction factor for that sensor for that average.

Abstract: Apparatus and system for terminating the winding wires of a dynamoelectric machine (e.g., a fractional horsepower electric motor) is disclosed in which wires (referred to as magnet wires) constituting the coils of the windings of the dynamoelectric machine are terminated in an electrically insulative block fixedly secured to the core of the motor. The magnet wires from the windings of the motor are fitted into respective receptacles of the terminal block and magnet wire terminals are forceably inserted into the receptacles so as to make electrical contact with the magnet wires and so as to securely hold the magnet wires within the terminal block.

Abstract: A variable output generator for supplying electrical power to a specific load is cooled by a plurality of motor driven fans 112, 113, 114, 115 disposed in a generator pit 2. An appropriate number of motor driven fans for providing cooling air for the generator are energized in response to the instantaneous generator output, to thereby avoid wasteful power consumption.

Abstract: Difficulties in sensing the temperature of end turns in dynamoelectric machines are avoided through the use of an envelope containing a temperature sensor disposed between abutting sets of end turns in such machine. The envelope has two insulating plies formed of insulating material sandwiching a ply formed of metal having excellent thermal conductivity. The latter is bonded to the former such that an exposed edge of the insulating plies exists by which the envelope may be closed to totally encapsulate the metal ply.

Abstract: In a hermetic compressor there is provided a resilient retainer member adapted to removably secure a terminal receptacle block assembly and a thermal overload protector relative to the compressor casing. The receptacle block assembly is adapted to engage conductor pins of an electrical terminal secured to the upper wall of the casing while the overload protector is adapted to engage the upper wall of the casing. The retainer member includes a first leg portion dimensioned to engage the thermal overload protector and a second leg portion dimensioned to engage the terminal receptacle block whereby downward pressure on the retainer member secures both the overload protector and terminal receptacle block relative to the casing.

Abstract: An internal line break assembly for a hermetic compressor is assembled in two stages. A metal protector bracket is mounted to the stator as part of the mounting procedure for the stator. At a suitable later step a thermal protector in a protector mount is snapped into place whereby it is held in a spring biased relationship by the metal protector bracket.

Abstract: An arrangement for cooling an electric rotating machine such as an alternator of an automotive vehicle by means of a fan which is intermittently driven in accordance with the cooling requirements of the electric rotating machine. A heat source is associated with the electric rotating machine which is representative of the degree of heating of the rotating machine. The heat source may be the radiator of the rectifier diodes of the alternator. A heat sensitive means in the form of a spring of "memory alloy" controls the coupling/uncoupling with respect to the shaft of the rotating machine of the fan which is mounted free for rotation coaxially of the shaft of the machine. The heat sensitive means is in heat exchange relation with the heat source. The spring, for example, operates a lever which activates a control rod passing through the hollow shaft to control the coupling or clutching of the fan with respect to the rotating shaft.

Abstract: In a hermetic compressor there is provided a resilient retainer member adapted to removably secure a terminal receptacle block assembly and a thermal overload protector relative to the compressor casing. The receptacle block assembly is adapted to engage conductor pins of an electrical terminal secured to the upper wall of the casing while the overload protector is arranged on a substantially flat portion of the upper wall of the casing. The retainer member is arcuately shaped with its downwardly diverging end portions adapted to engage the receptacle block and thermal protector respectively. A downward force on the apex of the retainer member forces its end portions to securely hold the receptacle block in electrical contact with the conductor pins and thermal protector in intimate contact with the upper wall of the compressor casing.

Abstract: A hermetic motor-compressor has a motor cover or shroud overlying the end turns of the motor windings. The motor cover is secured to a fastening device in the form of a ring held in place by the stator fastening bolts. A molded plastic holder or retainer for a motor protector is fitted on a lug formed on the ring. The retainer is adapted to hold protectors of different physical configurations. The lug projects upwardly inside the cover and in one embodiment the retainer is trapped between and held in position by the ring and the cover. The protector is of the thermally responsive electrical cutout type and is maintained in closely overlying heat conductive relationship with respect to the end turns of the motor windings by the motor cover. The parts which hold the retainer and the protector in place are movable into their holding positions by the act of moving the cover down into position, in a direction generally parallel to the axis of the motor.

Abstract: A motor protector of the type having a snap acting thermostatic element is shown particularly adapted for use with compressor motors in which a conventional three pin header is mounted on the compressor casing to allow electrical energization of the motor. An improved heat transfer path is formed between the windings of the motor and the thermostatic element of the protector by suspending the protector from one of the motor pins in optimum heat conductive relation therewith and thermally separated from the compressor casing and any component mounted on the other two pins.

Abstract: A starting relay-terminal box group for hermetic motor-driven compressors applied to cooling apparatuses, composed of a base surface secured to the outer part of the container of the motor-driven compressor, a fixed cover covering a portion of the surface and forming with it a space of limited height inside which is fitted the starting relay consisting of a positive temperature coefficient resistance (PTCR) and a removable cover covering the remaining portion of the base surface and forming with it a space, also of limited height, inside which the terminal box is fitted.

Abstract: Apparatus and system for terminating the winding wires of a dynamoelectric machine (e.g., a fractional horsepower electric motor) is disclosed in which wires (referred to as magnet wires) constituting the coils of the windings of the dynamoelectric machine are terminated in an electrically insulative block fixedly secured to the core of the motor. The magnet wires from the windings of the motor are fitted into respective receptacles of the terminal block and magnet wire terminals are forceably inserted into the receptacles so as to make electrical contact with the magnet wires and so as to securely hold the magnet wires within the terminal block.

Abstract: An electromagnetic coil construction consisting of a bobbin having a primary winding and a secondary winding, the bobbin having an end flange at either end of the hub and a central separator flange intermediately spaced between the first and second flanges, the separator flange having a through opening into which a thermal sensing device electrically, interconnected in series with the primary winding or a secondary winding is adapted to be interposed whereby the device is in physical contact with both the primary and the secondary winding to interrupt the circuit upon overheating of either or both windings.

Abstract: A speed sensor (30) for an electromagnetic machine (31) such as a permanent magnet generator includes a magnetic core (44) mounted laterally outboard of the machine's stator teeth (36) and having at least one leg (48) adjacent openings (43) in slots (38) between the stator teeth (36) which extends into the alternating magnetic flux field (42) generated by the machine's rotor (34) in order to pick up a sample (42) of the rotor flux. A portion (50) of the core (44) has wrapped therearound an electrical coil (52) within which there is induced by the flux sample (42) an alternating electrical signal having a frequency proportional to the angular velocity of the rotor (34). The magnetic core (44) may consist of either one or more discrete U-shaped members (44) each having legs (46,48) immediately adjacent or extending into the slots (38) of the stator (32) or a continuous strip (44f,44g) of material extending circumferentially around the stator (32) and having a plurality of the legs (48).

Abstract: An overload protection arrangement for an electric motor, especially of a hand-held power tool, includes an electronic speed of rotation control arrangement which is, in turn, controlled by an overload circuitry which includes a positive temperature coefficient resistor situated in the winding of the electric motor and incorporated in a voltage divider. The output of the PTC-resistor is amplified by an amplifier and, when the temperature of the winding increases above an acceptable level, the maximum current which can be drawn by the electric motor is reduced to a level at which the winding cannot burn out even if the rotor of the electric motor is blocked. If the rotor can rotate freely, the speed of rotation thereof even at the reduced power input will be sufficient to assure rapid cooling of the device powered by the electric motor. A time-delay member consisting of a capacitor and a resistor is arranged in parallel with the operational amplifier.

Abstract: A circuit, safe against an overload, for incrementally varying the power to an electric blower motor used for heating, ventilating and conditioning vehicles, having a PTC resistor in series with other series resistors in the circuit.

Abstract: A thermoswitch is physically located on a portion of the current supply connector between the current source and the exciter winding of the starter motor. The portion, constructed as a simple strip with flaps holding the thermostat, influences the temperature-dependent control portion of the thermoswitch according to heating in the armature, field winding, and brushes of the starter motor. The thermoswitch turns OFF the starter system by interrupting current supply to the kick-in starter relay.

Abstract: In a squirrel cage type of induction motor, conductive strips insulated from the stator are circularly spaced, ninety degrees apart, and project 0.003 inches into the rotor-to-stator clearance space. Upon excessive lateral rotor movement, it contacts a strip, closing a low voltage circuit triggering an alarm and de-energizing the motor. A reset button must be pressed to enable starting the motor.

Abstract: An apparatus and method of drying a transformer by applying current to a winding thereof in a controlled fashion. Alternating with periods of applying the current to the winding, the electrical resistance of the winding is periodically measured using a bridge circuit. The application of the current is controlled, dependent on the results of the resistance measurements, to discontinue the application of current when the measured resistance is equal to or greater than a preset resistance. The current application is resumed when the measured resistance falls below the preset resistance. In a preferred form insulation resistance is tested by measuring leakage current after each measurement of winding resistance and when leakage resistance reaches an acceptable level the apparatus is shut down.

Abstract: A recording apparatus including a beam generator for generating a beam modulated by a modulating signal supplied thereto; a deflector for deflecting the beam generated by the beam generator repeatedly in two directions; a recording member for receiving the beam deflected by the deflector and recording the trajectory of irradiation by the beam; a recording information storage for storing information to be recorded on the recording member; the recording information read from the information storage being supplied to the beam generator as the modulating signal; a beam detector provided in the deflecting area of the beam deflected by the deflector and adapted to release a beam detection signal upon detection of arrival of the deflected beam at the detector; and a signal forming device adapted for selecting either one of two consecutive beam detection signals released from the beam detector thereby forming a reference signal for instructing the initiation of the readout from the recording information storage.

Abstract: A releasable combination of a separable starter device and a separable protector device adapted for connection in circuit relation with a dynamoelectric machine. A PTCR (positive temperature coefficient resistor) in the starter device and a switch means in the protector device are adapted for association in thermal coupling relation when the starter device and the protector device are in the releasable combination thereof. One of the starter device and the protector device includes yieldable means extending generally circumferentially about at least a major circumferential portion of a part of the other of the starter device and the protector device for releasable engagement therewith so as to releasably maintain the starter device and the protector device against separation from the releasable combination thereof.A method of assembling a releasable combination of a starter device and a protector device is also disclosed.

Abstract: The invention relates to a clamp for holding a protective device in intimate contact with the winding end turns of an electric motor. Specifically the clamp is a unitary spring member with one end secured between the motor frame and core and the other end biasing the protective device against the winding end turns.

Abstract: A heat sensing apparatus for a member requiring heat monitoring such as bearings, etc. is described. A heat conductive plate is secured to the lower end of a hollow cartridge and closes the open bottom of the cartridge. A heat sensing device is mounted on the heat conductive plate within the cartridge and has a pair of electrical wires secured thereto which extend outwardly through one end of the cartridge. A bushing is secured to one end of the bushing and has a nipple threadably mounted thereon. One end of a flexible conduit has a nut mounted thereon which is threadably secured to the nipple to provide a rodent and dust proof connection between the flexible conduit and the bushing mounted on the cartridge. An epoxy material is contained within the cartridge and at least a portion of the bushing to seal the interior of the cartridge and to protect the heat sensing device.

Abstract: The invention is directed to a disconnect and overload bypass arrangement for a hand-held portable tool equipped with an electric motor supplied from a source of electrical energy and a manually operable on-off switch for switching the tool on and off. The arrangement includes a self-reclosing disconnect switch operatively connected to the motor to temporarily disconnect the same from the energy source in response to an overload condition; and, circuit control means for supplying energy to the motor at a reduced level when the disconnect switch is open whereby the motor will continue to operate at reduced torque pending self-reclosure of the disconnect switch and thereby provide the operator of the tool with an audible and visual indication that the motor has not been deactivated by manually actuating the on-off switch.

Abstract: An end cap assembly for a direct current motor. The assembly includes a brush retainer supported by the end cap that engages spring biased brushes to maintain the brushes in a retracted position. When an armature shaft is assembled to the end cap a portion thereof engages the retainer to move it relative to the end cap to a position where the brushes now engage the commutator of the armature. The retainer becomes a part of the motor. The end cap is formed as a one-piece plastic part that carries metallic brush holders and a circuit breaker. The circuit breaker is connected to one of the brush holders and to a terminal by C-shaped clips.

Abstract: A protective circuit is provided for a brushless excitation system using a rotating rectifier assembly to supply field excitation to a synchronous generator. A thyristor is connected across the generator field winding and made conductive when the field winding voltage exceeds a preset level to shunt the field winding and protect the rectifier diodes against high reverse voltages.

Abstract: A hermetic electrical terminal construction adapted for connection to the outer housing of a hermetic motor compressor unit so that current may be carried to the compressor motor from an external source. The terminal comprises a body member welded or otherwise secured to the compressor outer housing and a plurality of conductor pins secured to and extending through the body member. Each of the conductor pins, which may be made of stainless steel, copper or other suitable material, comprises a first segment disposed within the housing, a second segment disposed outside the housing, and an intermediate segment connecting the first and second segments, the intermediate segment being disposed primarily within the body member. Electrical insulating and sealing material, such as glass or epoxy potting, surrounds the pin intermediate segment and forms a hermetic seal between the pin intermediate segment and the body member.

Abstract: Protector accommodating pocket established by a sheet of dielectric material which is folded upon itself. Includes locking flap having an accurately located entry hole for spade type terminal. Locking shoulder is established by the flap to securely lock a protector in the pocket. A solid segment, interrupted only by a lanced portion provides maximum strength against inadvertant release of the terminal. The assembled member preferably is ultrasonically spot welded and may include a reinforcing member.

Abstract: There is disclosed herein an improved motor protection assembly for a motor compressor comprising a motor cover having an opening provided on a side wall thereof adjacent the exposed end turns of the motor stator windings. A motor protection device is adjustably secured to the motor cover and projects through the opening into engagement with a portion of the stator windings so as to enable sensing of abnormal conditions existing within these windings. The motor protection device is electrically connected to the stator windings so as to de-energize the windings in response to such abnormal sensed condition. The adjustable securing arrangement allows the axial positioning of the motor protection device within the opening to be varied thereby enabling a standard motor cover to be used with stator windings of different sizes and different manufacturers.

Abstract: A flux sensor is provided for measuring magnetic flux in laminated cores, and especially for measuring the axial flux in the end regions of the stator cores of large generators. The sensor comprises a flat, multi-turn coil of fine wire enclosed in an insulating enclosure which includes a pressure-supporting member of greater thickness than the coil. The sensor is thin enough to be placed between the laminations of a generator core and the high clamping pressure is carried by the pressure-supporting member which protects the coil. The leads are flat conductors brought out between the laminations to the periphery of the core. Such a sensor can remain permanently embedded in the core since it does not effect the core structure.

Abstract: A permanent split capacitor induction motor rated at 460 volts AC is provided with first and second main winding parts and an auxiliary winding. The motor includes a core of magnetic material having a plurality of winding receiving slots formed in it. The main and auxiliary windings are constructed from a plurality of wire turns arranged in coil sets. The auxiliary winding is placed adjacent the first main winding part in the core slots, and is electrically connected to it. The coil sets of the auxiliary winding are separated from the coil sets defining the second main winding part by the coil sets of the first main winding part. Individual wire turns are distributed in the slots of the motor and positioned so that the voltage between coil sets forming the main winding parts and the auxiliary winding can never exceed the voltage across the capacitor.

Abstract: An electric motor of predetermined voltage rating is connected to an electric current supply source higher in voltage than the rated motor voltage in series with a voltage dropping resistor controlled by a thermal relay responsive to motor temperature. The series circuit is regulated by the relay to include or exclude the resistor thereby to maintain motor temperature at normal rated value.

Abstract: A dynamo-electric machine comprises an armature and a permanent magnet field structure including at least two permanent magnets and at least two field shoes. Each field shoe has an arcuate surface which forms one side of an air gap between the shoe and the armature, and is configured to direct magnetic flux from the permanent magnets to the arcuate surface in such a manner that the magnetic lines of force emanating from the arcuate surface and extending through the armature are of substantially uniform distribution and intensity, thereby providing a uniform magnetic field through the armature. This is accomplished by making the shoe of variable thickness to have a cross-sectional area varying substantially in proportion to the density of magnetic flux carried by the shoe at points therealong, so that the density of magnetic flux is substantially constant throughout the shoe and the shoe provides a substantially uniform distribution of magnetic flux across the arcuate surface and through the armature.

Abstract: A mechanical switch is provided which, in a first position connects a current limiting circuit to a motor and, in a second position, disconnects the current limiting circuit from the motor. Mechanical activators are provided for the mechanical switch, to switch it from the first to the second position when the tool including the motor has a predetermined relationship to the workpiece. The mechanical activators provided for the mechanical switch operate the switch either when correct positioning of the tool relative to the workpiece results in a predetermined force being applied to the activator by the workpiece or when a shaft of the tool transmits a predetermined torque.

Abstract: A stationary device for sensing the rotational speed of electric motors, comprising an impedance bridge circuit, the motor being inserted into one branch of the bridge in series with a resistive element, and a voltage proportional to the rotational speed being derived across a diagonal of the bridge, the resistive element being a winding wound directly on to the motor, in order to make it isothermic, and insensitive to the magnetic field of said motor by a form of winding of the "two wires in hand" type.

Abstract: An explosion resistant motor has a metal casing with a cluster of electrical terminals extending from a wall thereof and sealed thereto. A section of metal pipe has one end welded to the casing wall and surrounds the terminal cluster. A metal clip mounts an inherent thermal overload device in the open end of the pipe. A positive temperature coefficient resistance starting relay in the pipe is coupled between one motor terminal and one overload terminal. Electrical leads are connected to another motor terminal and another overload terminal and extend out of the pipe through a conduit welded to the wall thereof. A pipe cap is threaded on the open end of the pipe to complete an explosion resistant enclosure for the overload and starting relay, and also to secure the overload in place.

Abstract: A dynamoelectric machine having a thermal protector held in intimate thermal contact with the machine's electrical winding by a spring inserted between the machine's enclosing frame and protector. The spring is generally a V-shaped member whose one leg mates with the protector and whose other leg is divided in two with each of those divided legs being engageable with the frame. The closed end of the V-shaped spring member is progressively inserted between the protector and frame with the open end following. The frame engageable legs are sharp and thus gouge into the relatively softer frame so as to resist relative movement between the spring member and frame in the direction opposite its insertion.

Abstract: A current/flow comparator for generating an alarm signal whenever the instantaneous flow rate of a coolant fluid cooling the armature of a dynamoelectric machine falls below a predetermined percentage of a desired instantaneous flow rate, which desired flow rate varies as a function of the square of the instantaneous current flowing through the armature, is disclosed.

Abstract: An electrical insulating pocket receptacle for securing a sensing element within electrical windings of a motor includes a sheet-like flexible material having a body support portion supporting a pocket within which the element is located and having four tabs projecting from the body support portion. The tabs on the opposite side of the pocket are located within the winding and hold the pocket in place within the winding with an exposed open end for insertion and removal of the element. A wire holding tab is secured to one of the support tabs and is folded upon itself and secured against the coil end turns by the end tie cords. A third locking tab is pulled down over the spade of the sensing element to securely hold the sensing element in place. A fourth tab may be used to fold over the pocket to additionally insulate the sensing element from the windings of the motor in which the insulating pocket receptacle is inserted.

Abstract: A prime mover has a stationary assembly with a generally annular grouping of winding end turns extending therefrom, and a structural member of the prime mover is spaced from the winding end turn grouping. An overload protector device is disposed in abutting engagement with a part of the winding end turn grouping, and means is associated with both the stationary assembly and the overload protector device and arranged in biasing engagement with the structural member for positioning the overload protector device in the abutting engagement thereof with the part of the winding end turn grouping.A method of assembling a device with the prime mover is also disclosed.

Abstract: An electrical connecting means and overload protector mounting means for a motor stator comprises a housing having a plurality of terminal receiving cavities therein which receive the ends of the motor winding conductors. The cavities are dimensioned to receive electrical terminals of the type which have wire-receiving slots therein such that upon movement of the terminals into the cavities, the ends of the windings are electrically and mechanically connected to the terminals. The terminals are also connected to lead wires by means of which the control circuits to the motor are interconnected to the windings. The housing has integral supporting means for an overload protector, the arrangement being such that the protector is located adjacent to the motor windings. The electrical connections to the protector are also achieved by terminals which are inserted into cavities in the housing.

Abstract: A d.c. electric motor has a permanent magnet stator and a wound rotor both mounted within a body. An end cover is fixed to the body and carries a thermal switch which is disposed inside the body adjacent to the windings and controls the supply current to the motor.

Abstract: A metal strap is connected to a motor housing and to a metal mounting plate for a timer which carries the motor to electrically ground the motor to the timer.

Abstract: A motor protector mount formed from a preformed blank of insulation material and having a base with a pair of spaced-apart tabs extending therefrom and with each of the tabs having openings to receive a part of the motor protector for capture of the motor protector to the mount and with the mount having an opening to receive a tie strap for assembling the motor protector mount to the stator coil of a motor.

Abstract: An apparatus comprising a vessel adapted to receive a liquid, and which vessel has a drive shaft extending through the bottom of the vessel from an electric motor below the vessel to a rotary cutting or grinding blade or the like within the vessel, with a seal being provided to seal the vessel with respect to the drive shaft, has a safety device in the form of a cut-out switch which is normally held in its closed position by a plate of water-absorbent, cellulose-fibre based material disposed below the seal. Any aqueous liquid leaking from the seal will wet the plate reducing its strength and allowing the plate to bend to allow the cutout switch to move, under resilient bias to an open position, thus cutting off the supply of electrical current to the electric motor.

Abstract: A bobbin for carrying a field coil winding is made of molded plastic resin material having good electrical insulating characteristics and having an insulating channel formed in the hollow spindle portion thereof for carrying a fuse type or one-shot thermal protector. The bobbin flanges are thickened at either end of the insulating channel and sockets are formed in the flange thickened portion for carrying a quick-connect device which is generally U-shaped with slots in the legs adapted to engage coil end-wires when the device is forced into a socket. One end of the device carries a bent-over tongue adapted for locking engagement with the stripped end of an insulated lead-wire.

Abstract: A combination starting and protecting device particularly useful with split phase motors such as those used with refrigeration compressors is disclosed in which an element of material having a positive temperature coefficient (PTC) of resistivity characteristic and a thermally responsive switch are disposed in the same housing. A thermal coupling of a preselected value between the PTC element and the thermally responsive switch is provided so that a desired reset or "off" time is obtained for the thermally responsive switch without affecting the "on" time.