US2303460A - Electric heating apparatus - Google Patents

Description

4 Sheets-Sheet l ENVENTOR Char/55 H. Hadghns. G I

ATTO

- C. H. HODGKINS ELECTRIC HEATING APPARATUS Filed Nov. 29, 1939 Dec. 1, 1942 WITNESSES:

Dec. 1, 1942. c. H. HODGKINS 2,303,460

ELECTRIC HEATING APPARATUS Filed Nov. 29,

Ill 38 INVENTOR BY I g f ATTORNEY WITNESSES:

Patented Dec. 1, 1942 2,303,460 ELECTRIC HEATING APPARATUS I Charles H. Hodgkins, Fairficld, Conn., assignor-to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application November 29, 1939, Serial No. 306,656

5 Claims.

My invention relates in general to electric heating apparatus, and more particularly to apparatus of this type having a control circuit adapted to provide a plurality of different degrees of heat from the heating elements employed.

This type of electric heating apparatus finds one application in heaters for cooking purposes, such as ranges, ovens and the like, and various embodiments of my novel apparatus will be disclosed particularly for applications of this type, although it should be understood that my invention is applicable to any desired application of electric heating apparatus.

One object of my invention is to provide new and improved electric heating apparatus of the above-mentioned type.

Another object of my invention is to provide a novel arrangement of electrical heating apparatus wherein a single control member is adapted to provide a pluralityof different degrees of heat fromsaid apparatus.

Another object of my invention is to provide a novel arrangement of electrical heating apparatus wherein a single control member is adapted to connect the heating elements to a plurality of different voltage values in a plurality of different relations thereto.

A further object of my invention is to provide simplified apparatus of this type which is efllcient in operation.

A still further object of my invention is to provide a single control for heating apparatus capable of connecting the apparatus in different circuits to obtain different degrees of heat from the apparatus, while confining the arcs formed by interruption of said circuits to a predetermined arcing zone.

These and other objects of my invention will become more apparent upon consideration of the following detailed specification of preferred embodiments of my invention, and taken in connection with the attached drawings, in which:

Figure l is a perspective view of a control switch for controlling electrical heating apparatus.

Fig. 2 is a plan view of the switch shown in Fig. l with the handle and cover plate removed, and a portion of the arcing shield broken away;

Fig. 3 is a bottom plan View of the switch shown in Fig. l;

Fig. 4 is a plan view of the interior of the switch similar to Fig. 2, but with the contact operating member and its indexing means removed;

another embodiment of my invention; and

Fig. 8 is a view similar to Figs-6 and 7 but showing still another embodiment of my invention and,

Fig. 9 is a diagrammatic view illustrating another arrangement of heating apparatus.

The switch per se disclosed herein is particularly claimed in my copending application, Serial No. 306,655, filed November 29, 1939, and assigned to the Bryant Electric Company.

The switch hown in Figs. 1 to 5, generally is of the multi-position type and two methods of making contact are employed; (1) in which movable, normally spring closed contacts are operated by cams to cause these contacts to engage or disengage from stationary contacts, and (2') in which pairs of stationary segmental contacts are bridged by a sliding shoe carried by the cam which operates the spring contacts.

The connection relation of this.. switch with respect to the circuit which it controls is such that the circuit is always madejor interrupted by the cam operated spring contacts engaging with or separating from their cooperating stationary contacts. Therefore, arcing occurs at these contacts only.

The relation of the segmental contacts and the sliding shoe to the cams which operate the spring contacts is such that there is a definite timing in the functioning of all contacts. When switch ing from one position to another, the sequence is as follows: The spring contacts are first opened by the cam. The sliding shoe moves from one set of segmental contacts to another set and the spring contacts are then closed, thereby completing the circuit. The sliding shoe and seemental contacts can, therefore, be considered as set-up contacts or circuit selecting contacts, and no arcing can occur at this point.

Referring to the drawings, I have illustrated a switch which is mounted in an insulating casing 2, which may be of any desired heat resistant insulating material such, for example, as a moulded insulating material such as Bakelite. The insulating casing 2 includes a bottom wall 4, opposed side walls 6, and end walls 8. The bottom Wal 4 of the casing is provided with a central aperture I for receiving a reduced end portion I2 of the switch operating shaft. Concentric with the aperture I0 in the bottom wall of the casing, there is provided concentric annular grooves I4 and I6. In the outer groove I4 there is mounted spaced arcuate contact segments I8, 20, and 22 maintained in spaced relation by the arcuate insulating segments 28. These segments may be maintained in the groove I4 in any desired manner, preferably by friction. The contact segments may be of any desired conducting material such, for example, as copper or the like. The inner groove I6 is likewise provided with spaced arcuate contact segments 24 and 26 maintained in spaced relation by the arcuate insulating segments 28. The segments are preferably slightly raised above the adjacent surface of the bottom wall 4 of the switch casing as shown in Fig. 5.

The operating shaft is provided with an enlarged cylindrical portion 30 adjacent the re duced portion I2, and forming a shoulder 32 which is adapted to abut against the bottom wall of the switch casing to limit movement of the operating shaft into the switch casing. The operating shaft is also provided with an intermediate hexagonal portion 84, forming a shoulder 86 at its juncture with the portion 30, and an outer reduced portion 38 forming a shoulder 40 at its juncture with the hexagonal portion 34. The outer end of the operating shaft is reduced as at 42 to receive an operating handle I48.

A contact operating member 44 of any desired insulating material such, for example, as a moulded insulating material such as Bakelite, is slipped over the reduced end of the operating shaft I2 until the shoulder provided in the aperture through the operating member 44, engages the shoulder 36 on the operating shaft. The enlarged portion of the aperture through the operating member 44 is made hexagonal in shape to correspond with the hexagonal portion 34 of the operating shaft, to lock the operating member 44 for movement with the operating shaft. The contact operating member 44 is formed on its lower side with integral annular concentric projections 46 positioned to be received in spaced annular depressions 48 provided in the bottom wall 4 of the swi-teh-=casi ng. These'projections 46 are provided between the sets of contact segments, and between the operating shaft and the inner set of contact segments, respectively, to reduce the creepage distance between these parts. The contact operating member 44 is provided with an opening 50 which opens toward the bottom wall 4 of the switch casing, and has an enlarged openendportion 52 in which is received the contact segment bridging contact 54, which is elongated in shape and has an outwardly extending integral projecting portion 56, extending into the.

inner portion of the aperture 50 and telescoping into one end of a coil compression spring 58,

which bears against the bridging contact 54 at one end thereof, and engages the closed end of the aperture 50 at its other end. The coil spring 58 acts to continuously urge the bridging contact 54 into engagement with the contact segments.

Mounted'in the two corners of the switch casing at one end thereof, are fixed contact supports 60 and I4 carrying the contact portion 62 and I6, respectively. The contact supports may be made of any suitable conducting material such as brass, copper, or the like, but the contacting portions thereof are preferably made of a metal capable of withstanding repeated arcing, such as silver or a silver alloy. Cooperating with the contacting portions 62 and 16 are the resilient contact carrying arms 64 and 18, respectively, secured in the opposite corners of the switch casing, on conducting supporting members 66 and 60, respectively. The resilient contact carrying arms carry at their free ends contacting portions 10 and 64 for cooperation with the contact portions 62 and I6, respectively, and are formed of a like material. The resilient contact carrying arms 64 and 16 are stressed so as to normally engage their contacting portions with the fixed contacts 62 and T5. Each of the resilient contact carrying arms 64 and 18 is provided at substantially its mid-portion with'a struck-out part I2 and 86, respectively.

As viewed in Figs. 2 and 4, the struck-out portion 86 of the resilient contact carrying arm 16 is struck out of the upper edge of this contact carrying arm, whereas, the struck-out portion 12 of the other arm 64 is struck out adjacent the lower edge of that contact carrying arm, all for a purpose hereinafter to be described. The contact carrying arms 64 and I8 are secured to the supports 66 and 80, respectively, by any suitable means such, for example, as by rivets 68 and 82, respectively. Also secured-to the support 66 by the rivets 68 is a .-fixed contact strip 00, having an angularly extending contact portion 90. A substantially U -shaped resilient conducting member 92 integral with a supporting member 94 secured in the switch casing in any desired manner, has one leg 96 thereof extended for cooperation with the fixed contact 90. An intermediate portion of the leg 96 is struck out as at 98 for a purpose to be hereinafter described.

The contact operating member 44 is provided with peripheral cam surfaces, as shown especially in Fig. 2. These cam surfaces are provided for cooperation with the struck-out portions 12, 86 and 98 of the three resilient contact bearing arms. As shown in Fig. 2, the periphery of the Contact operating member is provided with outer indented portions I00, IN and I02 for cooperation only with the outer struck-out portion 06 of the resilient contact carrying arm "I0. These indented portions I00, MI and I02 are provided only in the outer portion of the peripheral surface of the contact operating member 44 as is apparent from Fig. 2. The contact operating member 44 is also provided with indentations I04 and I06 which extend throughout the width of the periphery of the contact operating member 44, so as to operate, or engage with both of the indented portions 86 and 12 of the resilient contact carrying arms. The contact operating member 44 is further provided with an outwardly offset protuberance I00 for engagement only with the resilient contact arm 96.

As shown in Figs. 2 and 4, I have provided an insulating barrier I64 integral with the switch casing and positioned between the fixed contacts 62 and 16. The insulating barrier I64 is provided with arcuate extensions I66 to substantially isolate the contacts 62 and I6 from the contact segments. A cover I is suitably secured to the open side of the switch casing, for example, as by the machine screws I5I. Secured between the cover and the casing is an arcing shield I52 of insulating material such, for example, as fiber or the like, which, together with the switch casing and the insulating barrier I64, I66, completes the ..siibstantial enclosureor segregation of the contests 62 and I6 from each other and from the contact operating member, and contact segments provided in the bottom of the switch casing.

For indexing the contact operating member in the desired operating positions, I have provided resilient rod elements I54 and I56, on opposite sides of the hexagonal portion 34 of the operating shaft with corresponding ends of the resilient rods received in notches I58 provided in one side wall of the switch casing, and with the opposite ends of the resilient rods received in notches I60 provided in the opposite side wall of the insulating casing, which latter notches are elongated to receive the coil compression spring I62 engaging between the resilient rods I54 and I56, respectively, and the outer ends of the notches I60.- The springs I62 act to maintain the resilient rods I54 and I56 in engagement with the opposed flat sides of the hexagonal portion 34 of the switch operating shaft. Thus, in turning the shaft, it is necessary to slightly separate the resilient rods I54 and I56 by a cam action of the hexagonal portion 34 of the switch operating shaft, until another set of opposite fiat surfaces on the shaft are brought into flush engagement with the resilient rods.

' This will clearly indicate to the manipulator when an operating position of the switch has been reached, and the resilient rods I54 and I56 under the influence of the springs I62 will tend to maintain the switch in its operative positions. A handle I48 is frictionally fit on the outer end of the switch operating shaft and is provided with suitable indicia, which will be hereinafter referred to.

The various switch connections which I have provided in this embodiment of my invention will have use primarily in the circuit shown in Fig. 6. s

The switch proper is provided with a terminal I I which has portions extending through the casing spection of Figs. 5 and 6. All the switch terminals are provided with screws I28 for attach ing lead wires thereto.

Referring now particularly to Fig. 6 I have illustrated in schematic form, one embodiment of volts between the positive and negative conductors of the supply circuit and one-half that value, or 125 volts between either the positive or negative conductors and the grounded neutral conbottom wall and connected with the contact segment I8 and the conducting support 66, respec- '-tively, which in turn connects this terminal with the resilient contact arm 64 and its contact portion I0 and with the fixed contact 88 and its contacting portion 90. The terminal I I2 of the switch is electrically connected through the bottom wall of the switch casing with the support 80, thus connecting this terminal with the resilient contact arm 18 and its contacting portion 64. A terminal H4 is provided on the back of the switch and, as shown in Fig. 5, includes an inner angular portion II 6 extending through the bottom wall of the casing and connected with one leg of the U- shaped resilient contact 92 shown in the upper end of the switch casing in Fig. 4. The terminal I I8, also provided on the back of the switch casing on one side thereof, is provided with an integral extension I20, extending through the bottom wall of the switch casing, as shown in Fig. 5, which is in turn, integral with the contact segment 24. The switch terminal I 22 at the back of the switch casing is connected through the bottom wall of the casing to the fixed contact support l4, and has an extension I23 for connection with a portion extending through the bottom wall of the switch casing for connection with the contact segment 22. The switch terminal I26 also mounted on the back of the switch casing is connected to the fixed contact support 60 through the bottom wall of the casing, and is provided with an extension I21 for connection through the bottom wall of the casing with the contact segment 26. The terminal E24 of the switch casing is provided with a connection through the bottom wall of the casing to the contact segment 20. These connections of the switch terminals with the corresponding contacts or contact segments are readily apparent from an inductor. H2 is connected by a conductor I30 to the posi tive conductor of the supply circuit. A conductor I32 connects the neutral conductor of the supply circuit with the switch terminal I24, and a conductor I34 connects the switch terminal IIO with the negative conductor of the supply source. The terminal II4 of the switch is connected to the neutral conductor of the supply circuit through a pilot lamp I 36. One end of the resistance heater element I38 is connected by conductor I42 to the switch terminal I22. One end of the resistance heater element I is connected by the conductor I46 to the switch terminal H8, and a conductor I44 connects the switch terminal I26 to the other ends of the resistance heater elements I38 and I40.

I have illustrated in Fig. 6 the six positions of the switch used with this particular circuit. This is capable of providing five different degrees of heat from the heating elements I30 and I40. At the extreme right in Fig. 6, I have illustrated the off position of the switch wherein all contacts are open and the circuit through the pilot lamp I36 is broken. To the left of this, I have illustrated the first or lowest heat position, labeled the simmer position, wherein the circuit through the switch extends from the positive conductor of the supply source through conducill) tor I30, terminal II2, resilient contact arm 18, fixed contact '14, terminal I22, conductor I42, resistance elements I38 and I 40, conductor I46, switch terminal II8 contact segment 24, bridg ing contact 54, contact segment 20, switch terminal I24, and conductor I32 to the neutral conductor of the supply circuit. This provides volts across the two resistance elements I38 and 440 connected in series, thus providing, for example, with a resistance of approximately 62.5 ohms, and assuming unity power factor, substantially 125 watts of heating effort. The other four heating positions of my switch are illustrated to the left of the "simmer position with progres sively higher heating effects provided by successive positions of the switch. Thus, in'the position marked low, the heating element I36 alone is subjected to 125 volts, and at the low medium" position the heating elements in series are connected. across 250 volts. In the medium" position, the heating element I38 alone is connected across 250 volts, and in high position, each of the heating elements I38 and I40 is individually connected, or connected in parallel across 250 volts. each of the positions shown in Fig. 6.

The sequence of operation of the contacts of the switch are as follows. 1 The switch, as shown Figs. 1 to 5 is in the of! position, corresponding to the off position shown in Fig. 6. It will be noted that in this position; referring As shown in Fig. 6, the switch terminal Ehe voltage and wattage are marked (or.

particularly to Figs. 2, 4 and 6, the resilient contact arms 84 and I8 are maintained by the contacu operating member 44 out of engagement with their cooperating fixed contacts 52 and "I6, respectively. Also, the switch operating member 44 is in a position such that the segment brid'ging member 54 engages only the segment 24. Also, the projection I08 on the contact operating member is in engagement with the struck-out portion 98 on the leg 96 of the U-shaped resilient contact controlling the pilot lamp I36, to maintain the resilient contact out of engagement with its cooperating fixed contact 90. Upon move ment of the switching handle from the off position in a counterclockwise direction, as viewed in Figs. 1, 2 and 4, to the next or simmer position, it is obvious that the resilient cont-act bearing arms 64 and I8 will remain open until the bridging contact 54 is in a position to bridge the contacts 24 and 20, after which the struck-out portion 86 of the resilient contact carrying arm I8 registers with the indentation l04 provided on the switch operating member 44, to permit the contacts 84 and IE to close to complete the circuit to the heating element I38. It is thus apparent that the circuit is first set up by the bridging contact 54 and the contact segments, and then the circuit is closed by the arcing contacts I6 and 84.

In moving the switch operating member from the simmer position to the next or low position, it is obvious that the first thing that takes place is engagement of the struck-out portion 86 of the resilient contact carrying arm I8 with the protuberance below I08 on the contact operating member 44 to open the contacts 16 and 84 prior to disengagement of the bridging contact 54 with the contact segments 20 and 24. The bridging contact 54 then moves from engagement with the contact segments 20 and 24 into engagement with the contact segments 20 and 26, and thereafter, the indentation I06 on the contact operating member 44 registers with the struck-out portion 86 on the resilient contact carrying arm 18, to permit the contacts I6 and 84 to close.

This same sequence of operations of the switch contacts takes place upon movement of the switch to all of its six positions. In other words, the arcing contacts 16 and 84, and 62 and ID are first opened upon movement of the switch from one position to another before the bridging contact 54 leaves one set of contact segments to engage with another set of contact segments. These arcing contacts remain open until the bridging contact 54 has engaged with the next set of contact segments, whereupon one or both of the arcing contacts may be closed depending upon whether the resistance elements are to be connected between one of the live conductors of the supply circuit and the neutral conductor, or whether they are to be connected between the two live conductors of the supply circuit. It is thus obvious that no arcing can occur at the small contact segments where the circuits through the switch are selected, and that all arcing is done at one or both of the heavy arcing contacts I6, 84 and 62, I0, in especially provided arcing chambers which are substantially insulated from the contact segments and the contact operating member 44.

This type of switching arrangement makes it possible to reduce the number of contacts requiring special arcing metals, and also permits the provision of special arcing chambers to prevent distress due to fiash-over from one arcing contact to another. The small space required by the segmental contacts, and sliding bridging contact, lends itself readily to a device of small dimension and permits great flexibilit since a variety of arrangements of segmental contacts may be employed for the control of difierent circuits.

In Fig. 7 I have shown another schematic form illustrating an arrangement of a switch similar to that shown in Figs. 1 to 6 for controlling a pair of heating elements I55 and IBI of unequal resistance, and having six positions as in Fig. 6 which includes an "ofi position and five heating positions. The switch used in this embodiment of my invention is the same as that shown in detail in Figs. 1 to 5 with the exception of a slightly difierent arrangement of contact segments, and hence like reference numerals are used to designate like parts.

As shown in Fig. "I the heating elements or resistors I59 and NH are supplied from a three wire source of electrical energy similar to that described in Fig. 6.

Referring in particular to the off position shown in Fig. 7, Ihave shown a conductor I 48 connecting the positive wire of the supply circuit with the switch terminal I53, which in turn is connected with the resilient contact arm I8 of the switch. A conductor I63 also connects the positive conductor of the supply circuit with a terminal I61 of the switch which is connected with the resilient contact arm 96, cooperable with the fixed contact 90, which in turn is connected with the switch terminal I66 for controlling a pilot lamp I36 in series with the conductor I60 connecting the switch terminal I66 with the neutral conductor of the supply circuit. A conductor I10 connects the neutral conductor of the supply circuit with the switch terminal I12, which is connected with the resilient contact arm 64 of the switch. The contact segment I is electrically connected by the conductor I65 with the contact arm 64. The resistor I59 which has a greater resistance than the resistor I 6|, ha one end thereof connected by the conductor II4 to the switch terminal I16, which is connected with the inner annular switch contact segment I18. The resistor I6I has one end thereof connected by a conductor I80 with a switch terminal I82, which is connected to the fixed switch contact 80. The other ends of the resistors are connected by a common conductor I51 to the switch terminal I 55, which in turn is connected with the fixed switch contact "I4. The negative conductor of the supply circuit is connected as by the ,conduc tor I84 with the switch terminal [86, which is in turn connected with the switch contact segment Assuming that the supply circuit is capable of supplying the same voltages as in Fig. 6, that is, for example, 250 volts between the positive and negative conductors and volts between the neutral conductor and either of the other two conductors, and further assuming by way of illustration that the resistor I59 consumes 1400 watts when connected across 250 volts and the resistor I6 I consumes 600 watts when connected across 125 volts, the several positions illustrated in Fig. '7 will give the several wattages marked thereon. The switch used in Fig. 7, of course, has a single controller like the switch shown in Figs. 1 to 6 and the positions marked on Fig. 7 will correspond to those provided on the controller in the In the next position to the left of the on? position or the position marked super, the connections are as follows: One circuit extends from the negative conductor of the supply circuit through conductor I84, switch terminal I86, contact segment I88, bridging contact 54, contact segment I18, switch terminal I16, conductor I14, to one end of the resistor I59, to the conductor I51, switch terminal I55, switch contact 14, resi1 ient contact arm I8, switch terminal I53, conductor I49 to the positive conductor of the supply circuit, thus providing for the voltage values given above, 250 volts supplied to the resistor I59. The circuit for the other resistor I6I extends from the conductor I51 and the positive conductor of the supply circuit in the manner stated above through the resistor I6I, conductor I80, switch terminal I82, switch contact 60, resilient switch contact arm 64, switch terminal I12, conductor I10 to the neutral conductor of the supply circuit, thus providing 125 volts supply for the resistor IBI, thus with the values given above, providing a total of 2,000 watts for the two resistors in the position marked super of Fig. 7.

In th next position marked simmer the two resistors are connected in series across a pair of supply conductors supplyin 125 volts. In the next position marked high the resistor I59 alone is connected across 250 volts; in the next or medium position the resistor IBI is connected across 125 volts, and in the final or low position the resistor I59 alone is supplied with 125 volts. It is also to be noted that in each position excepting the off position the circuit through the pilot lamp I36 is closed bythe movable contact 96.

It should be noted in connection with this embodiment of my invention that I have provided one position, th simmer position which is the lowest heat position, in between the two highest heat positions. This is advantageous when it is desired to heat a relatively large mass quickly up to a certain temperature by use of either of the two higher heat positions, and then maintain it at that temperature by supplying a relatively small quantity of heat thereto for a relatively long period of time, which can be readily accomplished by merely turning the control to the adjacent simmer position, conveniently located intermediate the higher and super positions of the switch.

The operation of the switch in this embodiment of my invention is the same as that described in the previous embodiment. In other words, the arrangement is such that the circuit is always opened or made at the contact 60 and/or I4, before the bridging contact moves from engagement with one set of segmental contacts into engagement with another set. Thus, the circuit is first set up by the bridging contact 54 engaging with the contact segments and then the segment is closed by the arcing contacts I4 and 60. Due to the different arrangement of contact segments in this embodiment of my invention, the contact operating member of this switch will necessarily be formed with a different cam portion for operating the resilient contact arms 64 and 18 than that provided for the switch shown in Figs. 1 to 5.

As in the previous embodiment of my invention this same sequence of operations of the switch contacts takes place upon movement of the switch to all or its six positions. In other words the arcing contacts 60 and 14 are first opened upon movement or the switch from one position to another before the bridging contact 54 leaves one set of contact segments to engage with another set. These arcing contacts remain open until the bridging contact 54 is in engagement with the next set of contact segments whereupon one or both of the arcing contacts may be closed depending upon which of the supply conductors are to be connected to the resistors.

In the embodiment or my invention shown in Fig. 8, I have shown a four-position switch caductor I92 connects the positive conductor of the supply circuit with a switch terminal I94, which is connected with the resilient switch contact I9. A conductor 202 also connects the positive conductor of the supply circuit with the switch contact 204 cooperable with the resilient switch contact 96 connected by a conductor 206 with the neutral conductor of the supply circuit. Included in the conductor 206 is a pilot lamp I36. A conductor 208 connects the negative conductor of the supply circuit with the switch terminal 2I0 which is connected with the resilient switch contact 64. The neutral conductor of the supply circuit is also connected by a conductor I96 with the switch terminal I98 electrically connected with the inner contact segment 200. The resistors 2 I4 and 2 I6 are connected by a common conductor 2I2 to a switch terminal 2I3, which in turn is connected with the contact segment 2I8. The other end of the resistor 2 is connected by a conductor 220 with the switch terminal 222 which in turn is connected to the fixed switch contact I4, electrically connected with the contact segment 224. The other end of resistor 2 I 6 is connected by a conductor 2 I 1 with the fixed switch contact 60. The resistors 2 and M6 in this embodiment of my invention are designed to give their greatest heating effect when con nected across a voltage corresponding to that obtained between either the positive or negative conductors of the supply circuit, and the neutral conductor.

Thus in the first or high" position shown in Fig. 8, the resistors are connected as follows: from the positive conductor of the supply circuit through conductor I92, switch terminal I94,

switch resilient contact arm I8, contact 14, switch conductor 208. Thus, for the same voltage values' given in connection with the two previously described embodiments in this position the resistors 2M and 2I6 will be connected in parallel across volts.

In the intermediate or medium position shown in Fig. 8, the resistor 2|B alone is con nected across a pair of supply conductors supplying 125 volts. In the low position shown in Fig. 8, the connections established by the switch are such as to connect the two resistors in series with a pair of supply conductors furnishing 125 volts. The switch used in Fig. 8 has a sequential operation of its several contacts the same as the switch described in connection with the other two embodiments of my invention. In other words, the switch contacts ar preferably operated in a manner so that the circuit is always made or broken at the arcing contacts 60 and/or 14, so that the bridging contact 54 is moved from one set of segments to another only when the circuit has previously been opened at the arcing contacts.

In the embodiment of my invention shown in Fig. 9, I have illustrated an eight position switch capable of providing six different degrees of heat with two off positions. The heating arrangement shown in Fig. 9 utilizes a heating element comprising two resistance elements 228 and 230 of unequal value. The switch employed in this embodiment of my invention is alsoof the same general type heretofore described, differing only from the switch shown in Figs. 1 to in the number of positions to which the switch may be moved and, of course, in the particular arrangement and number of contact segments to obtain the desired circuit connections. Accordingly, like reference numerals will be used to designate like parts.

In order to avoid complicating the drawings, it

i will be noted that I have applied reference characters in Fig. 9 as in Figs. 6 to 8, inclusive, only to those circuit connections and parts which are connected to supply conductors in the particular position involved. Thus, no numerals have been applied to the parts and connections in the two off positions. Considering the lowermost or super position shown in Fig. 9, the circuit proceeds from the negativeconductor of the supply circuit through the conductor 236 to the switch terminal 234, resilient contact arm 64, fixed contact 60, and conductor 232 to one end of the resistance heating element 228. The heating elements 228 and 230 are joined at one end by a common terminal, which is connected by a conductor 226 to switch contact I4, resilient contact arm I8, switch terminal 225, and conductor 223 to the positive conductor of the supply circuit. The other end of resistance element 230 is connected by a conductor 238 with the switch contact segment 240, by way of bridging contact 54, contact segment 242 and conductor 244 to the switch terminal 234, and conductor 226 to the negative conductor of the supply circuit. Thus, it can be seen that in this position of the switch both heating elements 230 and 228 are connected in parallel across the positive and negative conductors of this supply circuit, thus supplying, for example, 250 volts to each heating element.

Without going into detail as to the circuit connections in the next or high position, it is apparent from the conductors numbered that the heating element 230 alone, is connected across the positive and negative conductors of the supply circuit. Similarly, in the next or intermediate position, the resistance element 228 alone is connected across the positive and negative conductors of the supply circuit. The next position is an 011' position of the switch which is located intermediate the six heating positions of the switch to thereby avoid the necessity 01' turning the switch a relatively great distance when it is desired to turn the switch oif" from any one of the heating positions thereof. In the medium position, the resistance element 230 alone is connected across the positive conductor of the supply circuit and the neutral conductor to thereby obtain a reduced voltage on this resistance element, as compared to the position in which this resistance is connected across the positive and negative conductors of the supply circuit. In the next position or low position seen in Fig. 9, the resistance element 228 alone is connected across the neutral and negative conductors of the supply circuit. In the simmer" position, the two resistance elements 228 and 230 are connected in series across the neutral and negative conductors of the supply circuit. Inasmuch as this circuit involves conductors not heretofore described, it will be traced in detail. As seen in the second position from the top in Fig. 9 of the drawings, the upper end of resistor 23! is connected by the conductor 238, contact segment 240, bridging contact 54, contact segment 246, and conductor 24! to the neutral conductor of the supply circuit. The lower end oi resistance 228 is connected by a conductor 232 to the fixed switch contact 60, resilient contact arm 64, switch terminal 234 and conductor 23! to the negative conductor of the supply circuit. As shown, the common terminal of the resistors 22! and 230 is not connected to any supply conductor in this position.

Thus, progressing in a downwardly direction, the respective positions shown in Fig. 9 denote respective circuit arrangements in which the resistor elements 228 and 230 are so connected to the supply conductors as to give progressively greater heating effects, assuming, of course, that the resistor element 230 is of greater value than the resistor element 228. It will also be noted that the first three heating positions 0! the switch involve connections of the resistor elements either in series or singly between one of the live conductors of the supply circuit and the neutral conductor which, following the previous example, may supply a voltage of 125 volts. Following these three positions is an 011" position, after which the resistors are connected to the two live conductors of the supply circuit, both singly and finally in parallel relation. The voltage obtained between the supply conductors in this embodiment of my invention may be as described heretofore, by way oi example, 250 volts between the positive and negative conductors and one-half that value or 125 volts between either the positive or negative conductors and the neutral conductors.

As stated above the switch in the circuit arrangement shown in Fig. 9 operates with a sequential operation of its several contacts in the I same manner as the switch described in connection with Figs. 1 to 5. In other words, the switch contacts are operated in a manner so that the circuit is always made or broken at the arcing contacts 60 and/or 14, so that the bridging contact 54 is moved from one set of contact segments to another only when the circuit has previously been opened at the arcing contacts.

From the foregoing it should be obvious that the general type of switch described in connection with Figs. 1 to 5 of the drawings is capable of use in a plurality of diflerent novel circuit arrangements for the connection of plural elewire supply circuit be provided providing difierent voltages between different pairs of conductors, and in connection with the embodiments of Figs. 7 and 9, that a heating element be provided embodying unbalanced sections. The specific voltage, resistance or wattages are immaterial, since obviously the circuits I have shown can be used in connection with any desired voltage or any desired plural resistor heater assembly.

Having described preferred embodiments of my invention in accordance with the patent statutes, I wish it to be understood that my invention is not to be limited, to the particular embodiments disclosed herein since it will be obvious, particularly to persons skilled in the art, that many changes and modifications may be made in these particular structures without departing from the broad spirit and scope of my invention. Therefore, I desire that my invention be interpreted as broadly as possible and that it be limited only by what is set forth in the appended claims.

I claim as my invention:

1. In an electrical system for connection with a three wire supply circuit, a plurality of load devices, movable selector contact means for successively energizing a plurality of spaced selector contacts upon movement of an operating means for said selector contact means in one direction, electrical connections arranged to connect one or more of said load devices in a plurality of different relations with respect to said supply circult when difierent ones of said selector contacts are energized at difierent positions of said movable operating means and including a plurality of arcing switches each having a pair of separable contacts in certain of said connections, with certain of said selector contacts connected, respectively, to one of said supply wires and to one terminal of said load devices, and with one contact of one of said arcing switches connected to another of said supply wires and another selector contact, and the other contact thereof connected to a terminal of said load devices, the other arcing switch having one contact thereof connected to the third supply wire and its other contact connected to a third terminal of said load devices, and common operating means for said movable selector contact means and said arcing switches for energizing said spaced contacts in succession and for opening the contacts of at least one of said arcing switches prior to deenergizing a spaced contact, and for closing the contacts of at least one of said arcing switches only after energizing the next succeeding spaced contact, and operative to close said one arcing switch at least at one operative position of said switch operating means and to open said one arcing switch at least at one other operative position of said switch operating means.

2. In electric heating apparatus having a plurality of supply conductors adapted to be connected to a plurality of conductors leading from a source of electrical energy so that difierent pairs of said supply conductors are provided with resistors: the combination of selector switch means having movable contact means adapted to successively energize a plurality of spaced contacts', means including electrical connections constructed and arranged to establish different circuits between one or more of said pairs of conductors and one or more of said resistors when said spaced contacts are energized, respectively, arcing switch means in each of said different circuits, said connections including direct connections from a pair of said supply conductors to said selector switch means and at least one direct connection between said selector switch means and at least one terminal of said resistors,

'one of said arcing switch means connected bev tween one of said last mentioned pair of supply conductors and another terminal of said resistors, another arcing switch means connected between the third supply conductor and a third terminal of said resistors and said selector switch means, and common operating means for moving said movable selector contact means to deenergize one of said spaced contacts to energize another and for opening the contacts of at least one of said arcing switches prior to movement of said movable selector contact means to deenergize said one spaced contact, and for closing the contacts or at least one of said arcing switches only after movement of said movable selector contact means to energize said other spaced contact.

3. In electrical apparatus for connection with a three-wire supply circuit, a plurality of load devices, selector switch means including movable contact means for successively energizing a plurality of spaced contacts upon movement of operating means therefor in one direction, electrical connections arranged to connect one or more of said load devices in a plurality of different relations with respect to said supply circuit corresponding to different positions of said operating means including a pair of arcing switches each having a pair of separable contacts in certain of said connections, with certain of diflerent electromotive forces and a plurality of 7 said selector contacts connected, respectively, to

one of said supply wires and to one terminal of said load devices, and with one contact of one of said arcing switches connected to another of said supply wires and another selector contact, and the other contact thereof connected to a terminal of said load devices and to still another another of said spaced contacts, and common operating means for said movable selectorcontact means and arcing switches for opening the contacts of at least one of said arcing switches prior to deenergization of a spaced contact, and

for closing the contacts ofat least one of said arcing switches only after energization of the next succeeding spaced contact.

4. In electric heating apparatus, a three wire supply circuit having a neutral conductor, a pair of resistors having a common terminal, selector switch means having movable contact means adapted to be connected to said neutral supply conductor and adapted to successively engage at least two spaced contacts upon movement oi operating means therefor in one direction, said spaced contacts connected to said common re-' sistor terminal and one other resistor terminal, respectively, a pair of arcing switches each having a pair of separable contacts, one of said areing switches connected between another supply conductor and said one other resistor terminal, the other of said arcing switches being connected between the third supply conductor and third resistor terminal, common operating means for said switches operative in three successive positions thereof to maintain said other arcing switch closed in each position, to close said one arcing switch only at the third position and to maintain said movable contact means engaged with the contact connected with said common resistor terminal at the second and third positions and engaged with the other of said spaced contacts at the first position, so that in successive positions of said movable contact means, said resistors are connected in series with said neutral and another supply conductor, one resistor is shunted across said neutral and another conductor, and both resistors are shunted across said neutral and said other conductors.

5. In electrical apparatus for connection with a three-wire supply circuit, a plurality of load devices, a selector switch means including movable contact means for successively energizing a plurality of spaced contacts upon movement of operating means for said selector switch means in one direction, electrical connections arranged to connect one or more of said load devices in a plurality of different relations with respect to said supply circuit corresponding to difierent positions of said operating means including a pair of arcing switches each having a pair of separable contacts in certain of said connections, with certain of said selector contacts connected, respectively, to one of said supply wires and to one terminal of said load devices, and with one contact of one of said arcing switches connected to another of said supply wires and another selector contact, and the other contact thereof connected to a terminal of said load devices, and to still another of said spaced contacts, the other arcing switch having one contact thereof connected to the third supply wire and its other contact connected to a third terminal of said load devices, and common operating means for said movable selector contact means and arcing switches for opening the contacts of at least one of said arcing switches prior to deenergization of a spaced contact, and for closing the contacts of at least one of said arcing switches only after energize.- tion of the next succeeding spaced contact.

CHARLES H. HODGKINS.

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