US3846620A

US3846620A - Electrical heating unit

Info

Publication number: US3846620A
Application number: US00400216A
Authority: US
Inventors: J Hocker
Original assignee: Corning Glass Works
Current assignee: Corning Glass Works
Priority date: 1973-09-24
Filing date: 1973-09-24
Publication date: 1974-11-05
Anticipated expiration: 1991-11-05

Abstract

An electrical heating unit including a plate or panel of a glassy material having in intimate physical contact with a surface of the plate, in a selected area of the plate surface, a 240 volt heating element comprising a pair of electrical resistance conductors extending in sinuous parallel paths over the contacted area of the panel surface, and circuit means for normally connecting the conductors across opposite terminals of a 240 volt source of electrical energy with two sets of temperature responsive contacts included in the circuit means for interrupting electrical energy to the conductors when the temperature of the heating unit reaches a preselected maximum temperature.

Description

United States Patent [191 Hocker ELECTRICAL HEATING UNIT [75] Inventor: James P. Hocker, Corning, NY.

[73] Assignee: Corning Glass Works, Corning,

22 Filed: Sept. 24, 1973 21 Appl. No.: 400,216

[52] US. Cl 219/543, 219/452, 219/464,

219/522, 174/685, 338/61, 338/308 [51] Int. Cl. H05b 3/16, H05b 3/74 [58] Field of Search 219/230, 211, 212, 213,

3,496,336 2/1970 Hingorany et a1. 219/464 3,668,367 6/1972 Williams 219/212 3,757,087 9/1973 Bernard 219/549 3,758,747 9/1973 Rohr 219/212 Primary Examiner-Volodymyr Y. Mayewsky Attorney, Agent, or FirmCharles W. Gregg; Clarence R. Patty, Jr.

[57] ABSTRACT An electrical heating unit including a plate or panel of a glassy material having in intimate physical contact with a surface of the plate, in a selected area of the plate surface, a 240 volt heating element comprising a pair of electrical resistance conductors extending in sinuous parallel paths over the contacted area of the panel surface, and circuit means for normally connecting the conductors across opposite terminals of a 240 volt source of electrical energy with two sets of temperature responsive contacts included in the circuit means for interrupting electrical energy to the conductors when the temperature of the heating unit reaches a preselected maximum temperature.

6 Claims, 1 Drawing Figure PATENTEDHDV 5 1914 m l m mh T 1 ELECTRICAL HEATING UNIT BACKGROUND OF THE INVENTION In an electrically heated appliance employing a heating unit comprising a panel or plate of a glassy material having heating elements including narrow continuous strips of electrical resistance heating conductors in intimate physical contact with or integrally bonded to an area of one of the surfaces of the panel of the heating unit, electrical leakage can occur through the material of such a panel at certain times such as when the temperature of the panel exceeds by a selected allowed margin, a normal maximum operating temperature for such panel. Such electrical leakage can, when overly large, present the possibility of an electrical shock. For example, kitchen ranges having smooth continuous cooktops made of a glassy material, such as a glassceramic material, are becoming increasingly popular. The cooktop of such a range comprises a panel of said glassy material which may be the panel of a heating unit such as that discussed above. In actuality, such a panel usually provides for two or more of said heating units, each such unit including a selected area of the panel to be used as a heating area on the upper surface of the panel. As mentioned above, electrical leakage through the material of such a cooktop can present the possibility of an electrical shock. For example, a housewife handling an electrically conductive cooking vessel in contact or resting on a cooktop cooking surface of the type mentioned, is subject to a possible electric shock if an overly large electrical leakage such as that mentioned occurs. This is especially true, of course, if the housewife handling the vessel is also in good contact with an electrical ground such as an electrically conductive part of the cooking range itself or any other electrically conductive and electrically grounded item in the immediate environs of the range. Accordingly, it is an object of the present invention to provide electrical heating units of the class mentioned using 240 volt heating elements and which include, to the extent possible, a reduction in the possibility of an electrical shock due to an inadvertent electrical leakage occurring from overheating of the glassy material of the panels used in the heating units.

Other objects and characteristic features of the invention will become apparent as the description proceeds.

SUMMARY OF THE INVENTION The invention is believed to be adequately summarized in the foregoing abstract of the disclosure and, therefore, for the sake of brevity and to prevent repetition and redundancy to the extent possible, no further summary of the invention will be given nor is any considered to be necessary.

BRIEF DESCRIPTION OF THE DRAWING The single drawing FIGURE comprises a bottom plan view of an electrical heating unit embodying the invention, such view including electrical circuit means for energizing such unit from a suitable source of electrical energy.

PREFERRED EMBODIMENT OF THE INVENTION Referring to single drawing FIGURE in detail, there is shown a surface 11 of an area 12 of a plate or panel 10 of a glassy material and which may, for example, be an area of the lower surface of a smooth glass-ceramic cook-top of a kitchen range such as previously discussed. A 240 volt heating element 13 comprises a pair of first and second suitable electrical resistance conductors l4 and 15 which extend parallel with or adjacent to each other in sinuous, winding, serpentine or back-and-forth parallel paths over part of surface 1] of area 12 of panel 10, such conductors l4 and 15 being in intimate physical contact or made to be integral with said part of surface 11.

Conductors

14 and 15 may, for example, comprise narrow continuous strips of a conductive film bonded to the surface of said part of area 12 as disclosed in US. Pat. No. 3,067,315, issued Dec. 4, 1962, to Bohdan Hurko, or the conductors l4 and 15 may be cut from a relatively thin foil of an electrical resistance heating material and secured to said part of surface 11 by a suitable adhesive or cement. However, it is pointed out that

conductors

14 and 15 need not necessarily be a conductive film or foil but may be electrical resistance ribbons or wires which are held against said surface 11 in any suitable manner such as being so held by a suitable backing sheet of a heat resistant and electrically non-conductive material, as is well known in the art.

A first electrical circuit arrangement or circuit means, comprising

wires

16 and 18 connects first extreme

opposite ends

14a and 15b of conductors l4 and 15, respectively, with each other and, over a wire 20, with a fixed contact member a of a set a-b of normally closed temperature actuated or responsive contacts of a thermostat or thermally sensitive switch T, the movable contact member b of said set of contacts a-b being shown connected over a wire 22 with the negative terminal of a commercial 240 source PS of alternating electrical current having a neutral terminal N connected to ground. A second electrical circuit arrangement or circuit means, comprising

wires

17 and 19, connects second extreme opposite ends 1412 and 15a of conductors l4 and 15, respectively, with each other and, over a wire 21, with a movable contact member :1 of a set c-d of normally closed temperature actuated or responsive contacts of said thermostat or thermally sensitive switch T. The fixed contact member c of said set of contacts c-d is shown connected over a wire 23 with the alternatingly positive terminal of said source PS of electrical current.

Thermostat or switch T does not, per se, form part of the present invention but such switch may, for example, be any of the well known types of thermostats or switches which include sets of temperature actuated contacts, such as contacts a-b, and c-d in the drawing, which normally occupy or are in a closed condition or position for completing an electrical circuit therethrough and which are actuated to an open or circuit interrupting position or condition when a temperature sensed by the thermostat or switch T reaches a preselected maximum temperature. It will be understood by those skilled in the art that a thermostat such as T is intended to actuate its sets of contacts a-b and c-d to open conditions when the temperature of area 12 of panel 20, for example, reaches a preselected maximum normal temperature, that is, a maximum temperature reached under normal operating conditions.

The positive and negative numerical values or designations shown on

conductors

14 and 15 represent one set of instantaneous values of voltage potentials in the approximate regions of the conductors-where the numerical values are shown, when the heating element 13 is connected with the source PS of alternating current as hereinbefore described. The values of voltage potential in the lengths of the conductors between the regions indicated by said numerical values increase or decrease in accordance with the directions of movement along said lengths, as will be readily apparent from a brief glance at the drawing by those skilled in the art. It is pointed out that electrical leakage through the material of the panels 12 is effectively cancelled out due to the opposite polarities of the parallel paths of

conductors

14 and 15 as discussed below.

OPERATIONAL EXAMPLE OF THE INVENTION There will now be set forth a brief operational example of the manner in which the invention disclosed reduces the possibility of electrical shock when electrical leakage through the material of a panel such as is overly large.

Referring to the drawing, it will be assumed that ends 140 and b of conductors l4 and 15 are connected with each other and to the alternatingly negative terminal of source PS as shown and as previously discussed, and that ends 14b and 15a of the conductors are connected with each other and to the alternatingly positive terminal of source PS as also shown in the drawing and previously discussed. Consider, for example, electrical leakage occurring in area 12 of panel 10 in the region generally designated by the letter L in the drawing, any part of such leakage which is not cancelled out by flowing generally horizontally through the material of panel 10 could flow to a conductor, such as, for example, a metal cooking vessel resting on the surface of region L, and could, of course, present the possibility of an electrical shock to a housewife handling such an electrically conductive vessel as previously discussed. This is true if the parallel arrangement of conductors l4 and 15 as shown in the drawings is not employed. However, if such parallel arrangement is employed, said part of the electrical leakage would flow between adjacent points on the vessel resting on surface 11 in said region L and thus be substantially or completely cancelled out due to voltages of equal and opposite polarities appearing throughout such region L. This effectively eliminates or cancels leakage current which could otherwise flow through a housewife connected to ground and in contact with said metal or electrically conductive vessel. This is, of course, similarly true throughout the lengths of conductors l4 and 15, that is, in any substantial regions of area 12 over which conductors l4 and 15 extend.

It is desired to here make reference to the copending United States patent application of Harold A. Brouneus entitled Electrical Heating Unit, such application being filed on even date herewith and assigned to the same assignee as the present application. Such copending application discloses another 240 volt electrical heating unit reducing the possibility of electrical shock in a manner similar to that discussed herein but using electrical resistance conductors connected in a different manner across a commercial 240 volt source of alternating current.

Although there is herein shown and described only one form of an electrical heating unit embodying the invention, it will be understood that various changes and modifications may be made therein within the purview of the appended claims without departing from the spirit and scope thereof.

What is claimed is:

1. An electrical heating unit comprising;

A. a panel of a glassy material,

B. a 240 volt heating element including first and second electrical resistance conductors in physical contact with a surface of said panel in a selected area of such panel and extending over such surface in first and second sinuous paths paralleling each other throughout the lengths thereof with the first and second ends of said first conductor being adjacent the second and first ends, respectively, of said second conductor,

C. first circuit means including a first set of normally closed and thermally actuated contacts for connecting said first ends of said conductors with each other and with one terminal of a commercial 240 volt source of alternating current, and

D. second circuit means including a second set of normally closed and thermally actuated contacts for connecting said second ends of said conductors with each other and with the opposite terminal of said current source.

2. A heating unit as in claim 1 and in which said conductors each comprise a narrow continuous strip of a metallic film.

3. A heating unit as in claim 1 and in which said conductors each comprise a narrow strip of foil.

4. A heating unit as in claim 1 and in which said glassy material is a glass-ceramic material.

5. A heating unit as in claim 2 and in which said glassy material is a glass-ceramic material.

6. A heating unit as in claim 3 and in which said glassy material is a glass-ceramic material.

Claims

1. An electrical heating unit comprising; A. a panel of a glassy material, B. a 240 volt heating element including first and second electrical resistance conductors in physical contact with a surface of said panel in a selected area of such panel and extending over such surface in first and second sinuous paths paralleling each other throughout the lengths thereof with the first and second ends of said first conductor being adjacent the second and first ends, respectively, of said second conductor, C. first circuit means including a first set of normally closed and thermally actuated contacts for connecting said first ends of said conductors with each other and with one terminal of a commercial 240 volt source of alternating current, and D. second circuit means including a second set of normally closed and thermally actuated contacts for connecting said second ends of said conductors with each other and with the opposite terminal of said current source.