Electric cooking apparatus with safety control

The improved operating-safety control uses an operating contactor and a safety contactor each having normally open switch contacts and means connect these switch contacts on opposite sides of and in main power series circuits with the electric heating elements of the cooking apparatus effective for controlling electric input to same. An actuating coil is effective for closing each contactor switch contacts, and the control includes an operating thermostat and a safety thermostat each having a heat sensor in the cooking environment and each having a heat sensor in the cooking environment and each having normally closed contacts opened responsive to a set sensed high temperature. The control connects main on and off switch means operatively in series with a parallel hookup connection of the safety contactor actuating coil as one leg and the serially connected operator contactor actuating coil and operating thermostat controlled contacts as the other leg. Thus actuation of said main on and off switch means effectively opens and/or closes the switch contacts of both contactors. The control further connects the safety thermostat controlled contacts operatively with a power series connection through said mentioned parallel hookup connection and in series with the main on and off switch means and operates responsive to the opening of said contacts for deenergizing the actuating coils of both contactors, and means hold the safety thermostat controlled contacts open until reset means is actuated. A signal device is hooked across the main power input lines at locations between the safety contactor switch contacts and heating elements effective to indicate both a power on condition and a faulted closed condition of the operating and/or safety contactor switch contacts.

.Iadd.BACKGROUND OF INVENTION .Iaddend. 
This invention relates to a control circuit for automatically deenergizing 
electric heating elements operating in a cooking environment, such as in 
an electric deep fat fryer or in an electric oven, responsive to an over 
temperature condition. 
In restaurant cooking equipment, such as deep fat fryers for example, there 
is normally a container filled with cooking fat heated to a set cooking 
temperature, most often in excess of 250.degree. F, and an operating 
thermostat sensing the cooking fat temperature cycles the heating means on 
and off to maintain the set temperature. In an electric deep fat fryer, 
power to the electric heating elements is controlled by a contactor having 
a set of high capacity contacts opened and/or closed by a coil connected 
in a low power control circuit with a set of switch contacts actuated by 
the operating thermostat. Most safety regulations further require a high 
temperature safety control which functions if the operating control fails 
and which is designed to terminate input power only if high unsafe 
temperatures are sensed. 
U.S. Pat. No. 3,824,373 issued July 16, 1974, to Clarence H. Napier 
illustrates a safety control circuit for a deep fat fryer which 
incorporates two control contactors each having high-current contacts 
connected in series with the heating elements, and the operating coils for 
the separate contactors are controlled, respectively by the operating 
thermostat and by a high temperature safety thermostat. However, since the 
safety contactor contacts are never shifted except responsive to an over 
temperature condition, if the contacts should become fused together, the 
fact that the safety thermostat signalled an unsafe condition would not 
necessarily assure that input power to the heating elements had been 
terminated. 
.Iadd.SUMMARY OF INVENTION .Iaddend. 
This invention represents not only a more reliable safety control but also 
a control that during normal use is continuously being checked as to its 
workability, and this confidently assures the users that the same is 
operating satisfactorily. 
The disclosed safety control uses a safety contactor having high-current 
contacts in a series power connection with the heating elements and 
further provides that these contactor contacts are shifted responsive to 
an over temperature condition and moreover everytime the main power 
control switch is opened. Moreover a signal device is connected across the 
main power lines between the safety contactor high-current contacts and 
the heating elements operable to detect the "on" power input condition to 
the heating elements and further to detect malfunctioning fused closed 
contacts of the safety contactor. This allows for continuous appraisal of 
the proper working condition of the safety contactor even though it might 
never have been activated responsive to a non-safe condition. 
One embodiment of the subject invention provides a safety thermostat of the 
manual reset type, so that once it has been triggered responsive to an 
over temperature condition it must be manually reset in order to have 
input power to the heating elements. 
Another embodiment of the subject invention has operating and safety relays 
in the control circuit and manually actuated start and stop control 
buttons connected respectively to normally open start switch contacts and 
normally closed stop switch contacts. These control buttons can be located 
on a front panel of the fryer unit forward of the cooking fat container 
holding the normally high temperature fat. Further, the energized safety 
relay holds the fryer unit in a power off inoperative condition responsive 
to a sensed over temperature condition, and the stop button must first be 
manually shifted to release this activated safety relay and the start 
switch button must then be shifted before subsequent use of the fryer can 
be started, and only then if the cooking fat as sensed by the safety 
thermostat has sufficiently cooled.

.Iadd.DETAILED DESCRIPTION OF THE INVENTION .Iaddend. 
In FIG. 1, frying apparatus 10 is shown having a structurally rigid housing 
including side walls 11 and an upper panel 12 with an opening for 
receiving and holding open top fat container 13 at the upper peripheral 
lip portion thereof. A box-like control head 14 is located at the rear of 
the upper panel hinged at pins 15 to be swung between the operating 
position as shown and a tilted back position (shown in phantom). 
Electric heating elements 17, 18, and 19 are mounted structurally from the 
control head and are bent downwardly to extend toward the bottom of the 
fat container 13 and forwardly to traverse the container for heating 
cooking oil contained therein. The tilted back support of the control head 
allows for the removal of the otherwise rigid heating elements from within 
the container, and the removal of the container completely from the 
housing for changing the fat or otherwise cleaning or servicing the fryer. 
The heating elements shown are typically of a sheathed type, and the 
general practice is to use three such elements for ready use of the fryer 
on three phase power electrical inputs and to stagger them side by side 
for compact arrangement. 
There also is a thermostat control typically of the sealed hydraulic type 
having a sensing bulb strapped to the heating element in a manner to sense 
both the temperature of the fat in the container and the temperature of 
the heating element should there accidentally be no fat covering the 
heating element. A capillary tube connects the bulb to an actuating 
bellows which expands and contracts as the temperature of the bulb varies, 
and the bellows movement opens and closes a set of switch contacts which 
is used to control the power input to the heating elements. The bellows 
and switch contacts are mounted in the control head and the sensing bulb 
is mounted on a heating element, and such location is typical with a 
thermobulb type thermostat to minimize repeated flexture of the connecting 
capillary tube. In the subject disclosure .Iadd.and referring both to 
FIGS. 1 and 2.Iaddend., one thermostat control with its bulb 20, 
connecting capillary tube 21, bellows 22 and operated switch contacts 23 
is associated with the normal operating on-off cycling of the heating 
elements whereby the temperature can be adjustably set as required to 
within the operating range of 250.degree. F to 400.degree. F, for 
example, whereas a second thermostat control and its bulb 25, connecting 
capillary tube 26, bellows 27 and operated switch contacts 28 is used only 
to sense over temperature conditions which are deemed unsafe for 
consistant use, and this high limit should not exceed 475.degree. F. 
Referring to FIG. 2, the heating elements 17, 18, and 19 are shown in 
.[.an.]. appropriate power series circuits with three-phase power lines X, 
Y, and Z and spaced contactors 30 and 34 having separate operating high 
capacity contacts (31, 32, and 33) and (35, 36, and 37) respectively. The 
three-phase power .[.circuit.]. has full voltage for example 208, 240, or 
480 volts depending on power requirements of the heating elements across 
any two lines XY, ZY, or XZ. The series power .[.circuit.]. .Iadd.circuits 
.Iaddend.through contactors 30 and 34 and the heating elements 17, 18, and 
19, provide that the opening of the contacts of either contactor 
terminates the energy input from the power lines X, Y, Z to and through 
the heating elements. .Iadd.The power series circuits through the heating 
elements and the closed contacts of the contactors 30 and 34 are 
independent of one another. .Iaddend. 
In the subject disclosure, there are two embodiments and where appropriate 
like components shown in the respective embodiments are illustrated with 
identical numbers. Each contactor has an actuating coil which is connected 
in the control system and which upon being energized closes the contacts 
of the respective contactor. In this regard, coil 46 is operatively 
associated with the contactor .[.30.]. .Iadd., hereinafter referred to as 
the operate or operating contactor, .Iaddend.and coil 48 is operatively 
associated with the contactor .[.34.]. .Iadd., hereinafter referred to as 
the safety contactor. .Iaddend.Also in connection with the common 
components, an indicator light 49 of amber color is connected in parallel 
across the coil 48 of the operating contactor 34, and an indicator light 
52 of green color is connected across .Iadd.two of .Iaddend.the power 
.[.input.]. .Iadd.circuits between .Iaddend.lines X and Y as shown at a 
location between the heating elements 17 and 18 and the operating contacts 
31 and 32 of the safety contactor 30. 
Referring first to FIG. 2 for a more detailed description of the first 
operating circuit, there is provided a main on/off switch 50 having 
separable contacts which can be permanently held closed or permanently 
held open, and the switch is in a series circuit from power line L1 
through the contacts 28 of the safety thermostat control to junction point 
53, where the circuit breaks into two parallel legs to power line L2, one 
leg including the actuating coil 46 to the safety contactor 30 and the 
other leg including the series connection of the operated switch contacts 
23 of the operating thermostat and the coil 48 of the operating contactor 
34. .Iadd.The switch 50 can be located on the front wall of the fryer as 
shown in FIG. 1. .Iaddend. 
Power lines L1 and L2 can be identical to any two of power lines X, Y, or 
Z; or can be at a lower voltage resulting from a step down transformer 
(not shown), connection with these lines, depending on the local code 
requirements or on the preference of the installer. .Iadd.The power lines 
are brought into the interior control section of the fryer in any typical 
manner and are therefore not shown other than in the schematic. 
.Iaddend.Red indicator light 54 is connected in a parallel hookup across 
the controlled switch contacts 28 of the safety thermostat control and the 
same is of such high resistance so that in the normal contacts closed 
condition there is insufficient current draw to light the indicator light, 
whereas with the switch contacts 28 open there is sufficient draw to light 
the indicator light 54 but not enough to energize either actuating coil 46 
or 48. 
The safety thermostat bellows arrangement is preferably of the type that 
actuation of the bellows 27 in a manner to open the switch contacts 28 
throws an overcenter toggle or the like (not shown) to preclude back 
movement or closing of the contacts 28 incident to a cool down of the 
sensed temperature, instead the contacts must be manually shifted such as 
by actuation of control button 56 for instituting a restart condition of 
the circuit. 
In normal operation of the control circuit indicated in FIG. 2, it will be 
appreciated that the safety contacts 28 are closed as are normally the 
operating thermostat contacts 23. Consequently with power in the lines X, 
Y, and Z, and L1 and L2, closing the main on-off switch 50 simultaneously 
energizes the actuating coils 46 and 48 of the respective safety and 
operating contactors 30 and 34 to bring main-line power through the 
heating elements 17, 18, and 19. At this time the amber indicator light 49 
glows indicating that the operating contactor 34 is closed, and the green 
indicator light 52 glows indicating that likewise the safety contactor 30 
is closed. Power is thus carried to the heating elements until the time 
that the operating thermostat bulb 20 senses the set high temperature and 
actuates bellows 22 to open the contacts 23 and thereby deenergize the 
actuating coil 48 and indicator light 49, and thereby open the contactor 
.[.switches.]. .Iadd.contacts .Iaddend.35, 36, and 37 to deenergize the 
heating elements. The green indicator light 52 remains on since the safety 
contactor 30 through energized actuating coil 46 is still closed. 
Under normal use the operating thermostat thus cycles to energize and 
deenergize the heating elements sufficient to satisfy the demand. Should 
however the contactor 34 or the operating thermostat fail and an over 
temperature condition be reached, the safety thermostat is activated to 
open the safety thermostat control contacts 28 to cut power to both 
actuating coils 46 and 48 of the respective contactors. 
When the contacts 31, 32, and 33 open, main power to the heating elements 
is cut off to stop further heating of the cooking oil. Opening of contacts 
28 turns red signal light 54 on indicating an over temperature condition 
of the cooking oil. 
In as much as under normal operation an over temperature condition will not 
be reached except by the malfunction of the operating contactor 34, the 
green signal light 52 shall still remain on because of leakage current 
through closed contacts 35 and 36 and the heating elements 17 and 18. This 
indicates that main power to the unit is still on; however, this leakage 
current is insufficient for significant operation of the heating elements 
and the oil thus cools down. 
Power can only be restored by manually resetting the safety control, by 
depressing the button 56, but this is only after sufficient cool down of 
the cooking oil, and this closes the safety thermostat control contacts 28 
and reenergizes the actuating coils 46 and 48 of the respective safety and 
operating contactors 30 and 34. If the subsequent operation results in 
another over temperature condition, the operator is clearly appraised of 
malfunctioning equipment and can arrange for service of same. 
Of significance in the subject invention is the fact that the main on-off 
switch 50 and the .Iadd.contacts 28 of the .Iaddend. safety control 
.[.thermostats 28.]. .Iadd.thermostat .Iaddend.are effectively in series 
and each is effectively in a parallel hookup with the actuating coils 46 
and 48 .[.and.]. .Iadd.of .Iaddend.contactors. This means that each of the 
contactors is actuated responsive to the operator opening the on-off 
switch 50 such as at the end of the cooking day. Consequently both 
contactors should open and should take power away from the heating 
elements, and the green light 52 should thus turn off. If the safety 
contactor 50 should malfunction fused closed, then a circuit is 
established from lines X and Y through the closed contacts 31 and 32 to 
the indicator 52, and the illuminated indicator warns the operator that 
such a malfunction exists and repair of same is in order. It should be 
appreciated that the contactors are of such physical construction that 
should any pair of separate contacts become fused together none of the 
contacts can be separated since the operating mechanism of the contacts 
acts in unison responsive to the single pull of the actuating coil and/or 
of a return spring not shown. 
A second embodiment of the invention is disclosed in FIG. 3, and this 
embodiment uses a thermostat of the automatic resetting type and the 
control itself acts to maintain the thermostat disabled until a reset 
device is manually actuated. Thus there is provided normally opened start 
switch 60 and normally closed stop switch 62; and there further is 
provided an operate relay 54 and the safety relay 56. The relays are 
.Iadd.of .Iaddend.typical construction and have a pair of movable leaf 
switches each which can be connected across opposing contacts for 
completing or breaking circuits through the moving leaf, and an actuating 
coil is used to shift the movable leaf. Specifically, the operate relay 
has actuating coil 70 and a pair of moving leafs 71 and 72; whereas the 
safety relay has actuating coil 74 and a pair of moving leafs 75 and 76. 
The start and stop switches can be located on the front wall of the fryer 
forward of the fat container to allow an operator to actuate them without 
reaching over the fat container. 
The control circuit is completed, upon a momentary closing of the start 
switch 60, from the line L1 through the switch 60 to junction 78, and 
through operate relay coil 70 and closed leaf contact 76 to the line L2. 
The energized coil 70 shifts the leaf contacts 71 and 72 closed, 
.Iadd.against contacts 81 and 82, respectively, .Iaddend.whereupon a 
holding circuit is maintained through the normally closed stop switch 62 
to junction 80, and through the now closed leaf 71 to the junction 78 and 
through the energized operate relay coil 70 as noted. The power at the 
junction 78 further is carried by the now closed leaf 72 through the 
operating thermostat switch contacts 23 and the actuating coil 48 of the 
operating contactor 34 to line L2. Power is carried further from the 
common hot junction 78 and across the safety control thermostat switch 
leaf 84 and engaged contact 85 through the actuating coil 46 of the safety 
contactor 30 to line L2. Consequently upon the operate relay being 
energized, circuits are completed through the respective actuating coils 
46 and 48 to shift the contactors 30 and 34 thereby applying power through 
the heating elements 17, 18, and 19. During this power on condition the 
amber light 49 glows because of the energized coil 48; and the green 
indicator light 52 glows because of the closed safety contactor contacts. 
Also, cycling of the operating thermostat contacts 23 as dictated by 
demand cycles the heat elements on and off. 
The safety thermostat as noted includes a movable leaf 84 which.Iadd., 
.Iaddend.responsive to the sensing bulb 25 indicating the set 
.[.oversafe.]. .Iadd.overheat .Iaddend.temperature .Iadd., .Iaddend.is 
shifted from against contact 85 to against normally open contact 86 .[.and 
this.]. .Iadd.. This .Iaddend.brings power through the safety relay coil 
74 to line L2, and this further illuminates red indicator light 54 in a 
parallel hookup connection with the coil 74. Upon the safety relay coil 74 
being energized the leaf contacts 75 and 76 are shifted and the opened 
leaf 76 breaks the circuit through the operate relay coil 70 to deneergize 
the operate relay and thus allow the leaf contacts 71 and 72 to return to 
their positions as shown; and .[.secondly.]. .Iadd.the closed leaf contact 
75 .Iaddend.establishes a safety relay hold circuit through coil 74 by 
means of the closed leaf 75 .[.to junction 80 and through.]. .Iadd.and 
.Iaddend.the normally closed stop switch 62. 
The thus opened leaf contacts 71 and 72 deenergize both actuating coils 46 
and 48 of the safety and .[.operate.]. .Iadd.operating .Iaddend.contactors 
respectively and thereby terminates power input to the heating 
.[.element.]. .Iadd.elements .Iaddend.. The energized safety relay 
maintains the operate relay deenergized and the latter cannot be energized 
unless and until the safety relay is first deenergized, and this can only 
happen after the cooking oil has cooled sufficiently to allow the contact 
84 to shift back against contact 85 and then subsequent to this condition 
of manually opening stop switch 62. Thus when the safety relay coil 74 is 
energized, the unit cannot be started by closing the start switch 60, and 
likewise during the unsafe condition when the over temperature condition 
exists and contact 86 is engaged by moving leaf 84, the safety control 
cannot be deenergized merely by opening the stop switch 62 .[.. . . since 
immediately upon the same closing the stop relay will then be 
reenergized.].. The deenergized safety control relay allows the safety 
relay leafs 75 and 76 to shift to their normal positions shown, so that a 
subsequent cycle can be instigated upon momentarily closing the start 
control switch 60.