US 3848111 A
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 a single set 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 (OCR text may contain errors)
United States Patent 1 Brouneus 1 Nov. 12, 1974  ELECTRICAL HEATING UNIT 3,496,336 2/1970 Hingorany c1 a1. 219/464 3,668,367 6/1972 W'llizn 219/212  Inventor: Harold A. Brouneus, Painted Post, 3'754'118 8/1973 l 4 p v v 219/528 X N.Y. 3,757,087 9/1973 Bernard.... 219/549 Assigneez Corning Glass w g 3,758,747 9/1973 R0111 219/212 N.Y. Primary ExaminerVolodymyr Y. Mayewsky 122] Flledi Sept- 1973 Attorney, Agent, or FirmCharles W. Gregg; Clarence [211 App]. No.: 400,217 R. Patty, Jr.
152 US. Cl 219/543, 219/452, 219/464,  ABSTRACT 219/522, 174/685, 338/61, 338/308 An electrical heating unit including a plate or panel of  Int. Cl. 1105b 3/16, HOSb 3/74 a glassy material having in intimate physical contact  Field of Search 219/203, 212,213, 435, with a surface of the plate, in a selected area of the 219/436, 441, 451, 452, 453, 464, 494, 522, plate surface, a 240 volt heating element comprising a 528, 543, 549; 338/61, 62, 63, 212, 308, pair of electrical resistance conductors extending in 309; 174/685 sinuous parallel paths over the contacted area of the panel surface, and circuit means for normally connect-  References Cited ing the conductors across opposite terminals of a 240 TED STATES PATENTS volt source of electrical energy with a single set of 2 H4 396 4,1938 McFarlan et al 219549 X temperature responsive contacts included in the cir- 227771930 1 1957 Nathanson 219 543 means for interrupting electrical energy to the 29,15,130 7/1960 Parke, A 338/61 X conductors when the temperature of the heating unit 2,976,386 3/1961 Salton 219 543 x reaches a pr s l cted maximum temperature. 3,067,315 12/1962 Hurko 219/543 6C] l 3,130,289 4/1964 Katzman et al 219/528 D'awmg I5 B I4 I 1 I +105 \+75: +45 +|5 I -105 -1s; -15 L z r a 3 I l I l l l l eee eeele zeeeeee ae ieesaaa aeaassaa g 1 1 J l I 2 +5) 6 O 9o i so 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 at times present the possibility of an electrical shock. For example, kitchen ranges having smooth continuous cooktops made of a glassy material, such as a glass-ceramic 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 defining 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 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 in- 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 11 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. 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 l4 and 15 need not necessarily be a conductive film or foil but may be electrical resistance 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 or circuit means comprising wires 16 and 17, is provided for connecting first corresponding ends 14a and 15a of conductors 14 and 15, respectively, to fixed and movable members a and b, respectively, of a set of normally closed temperature actuated or responsive contacts of a thermostat or thermally sensitive switch T. Thus, such first electrical circuit or circuit means connects conductors l4 and 15 in series with each other when the set of contacts a-b are in their closed or circuit closing condition. Second and third electrical circuits or circuit means, comprising wires or leads l8 and 19 are provided for connecting second corresponding ends 14b and 15b of conductors 14 and 15, respectively, to the altematingly positive and negative terminals, respectively, of a commercial 240 volt source PS of alternating electrical current, the neutral or grounded terminal of such source being designated N.
The above mentioned thermostat or thermally actuated 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 thermally actuated switches which include a set of temperature actuated contacts, such as contacts a-b in the drawing, which normally occupy or are in a closed position or condition 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 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 contacts a-b to an open condition when the temperature of area 12 of surface 11 of panel 10, 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 potentials 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 l4 and 15 as discussed below.
OPERATIONAL EXAMPLE OF THE INVENTION A brief operational example of the manner in which the invention disclosed reduces the possibility of electrical shock if and when electrical leakage occurs through the material of a panel such as will now be set forth.
Referring to the drawing, it will be assumed that ends 1412 and b of conductors 14 and 15 are connected across power source PS as shown and as previously discussed, and that ends 14a and 15a of the conductors are connected to each other through the set of contacts a-b of switch or thermostat T as also shown in the drawing and previously discussed. If, for example, electrical leakage occurs in area 12 of panel 10 in the region designated by the letter L in the drawing, such leakage, assuming for the purposes of the present example that the leakage path has an electrical resistance of one megohm, for example, may be at approximately a 105 volt potential or higher. Such a voltage potential could present the possibility of an electrical shock to a housewife handling an electrically conductive vessel as previously discussed. By the parallel arrangement of conductors l4 and 15 as shown in the drawings, some of said electrical leakage would probably flow between adjacent points on the closely parallel conductors l4 and 15 in said region L and thus be cancelled out. However, that part of the leakage which is not so cancelled 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 electric shock to said housewife is said parallel arrangement of conductors were not used. That is to say, said parallel arrangement of conductors provides for said part of the electric leakage to flow between adjacent points on the bottom of said vessel and thus be effectively cancelled to reduce the possibility of electric shock to said housewife. This is, of course, similarly true throughout the lengths of conductors 14 and 15, that is, in any of the regions of the area 12 over surface 11 of which conductors l4 and 15 extend.
It is pointed out that ends 14a and 15a of conductors l4 and 15 could be directly connected with each other if contacts of switch or thermostat T were interposed in the circuitry connecting ends 14b and 15b of conductors l4 and 15 across power source PS. However, in such case, if only a single set of contacts such as set a-b of switch T are interposed in one of the wires 18 or 19, when such set of contacts are in their open or circuit interrupting condition, the above discussed protection against electrical shock would not be provided, because both conductors 14 and 15 would be at the same instantaneous polarity with respect to the grounded terminal N of power source PS. Therefore, if ends 14a and 15a of conductors l4 and 15 were in direct connection with each other as mentioned, a set of contacts such as a-b of thermostat or switch T must be interposed in each of the wires 18 and 19 to attain the desired protection against electrical shock such discussed above.
It is also desired to here make reference to the copending US. Pat. application of James P. Hooker and entitled Electrical Heating Unit," such application being filed on even date herewith and assigned to the same assignee as the present application. Such copcnding 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 a pair of 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,
C. first circuit means including a single set of normally closed and thermally actuated contacts for connecting first adjacent ends of said conductors with each other, and
D. second circuit means for connecting the second adjacent ends of said first and second conductors with first and second opposite terminals, respectively, of a commercial 240 volt source of altemating current.
2. A heating unit as in claim 1 and in which said eonductors 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.