Protective method and circuit arrangement for appliance incorporating sheathed heating element

DETAILED DESCRIPTION Briefly stated and in accordance with one aspect of the invention, there is provided a protective control arrangement for heating units of the type comprising the concentric assembly of a resistance heating element embedded in an insulating material and enclosed within a metallic sheath.
The control arrangement comprises switch means operatively connected to the heating element for selectively coupling the heating element to an external power supply.
Control means operatively connected to the switch means is effective to periodically interrupt power to the heating element by opening the switch means for interrupt periods of predetermined duration.
The time between successive ones of these interrupt periods is determined such that extinction of any arc which may develop at a discontinuity in the heating element occurs before any resultant separation can propagate along a substantial portion of the sheath; and the duration of each of these interrupt periods is at least approximately equal to the nominal recovery time for the insulating material required to allow the insulating material to return from its relatively low resistance molten and plasma state to its relatively high resistance state.
By periodically interrupting energization of the heating unit in this manner, any arc which occurs is extinguished by the next occurring interrupt period.