A current sensing, self-heating device for protecting equipment against abnormal current levels which is automatically resettable under mild overcurrent conditions and nonresettable under severe overcurrent conditions. The device comprises a thermostat metal assembly with a temperature compensating portion and an actuating portion which is placed adjacent a nonresettable two-position snap-acting blade electrically connected to ground. During normal operation current flows from the line source through the actuating portion of the thermostat metal assembly to the equipment. However, if an overcurrent condition occurs the heat generated in the actuating portion of the assembly will bend the assembly and cause it to make contact with the blade shorting the current from the line source to ground. As long as the overcurrent is not above a prescribed level, the assembly will bend back out of contact with the electrically grounded blade and again provide current to the equipment upon resumption of normal current levels. But if the overcurrent is above a preselected level, thermostat assembly will cause the nonresettable blade to snap to permanently electrically ground the device.
An over-current and thermal protection device adaptable for use as an electrical interrupt and in a battery environment. The protection device has a pair electrical conductors, an electrically conductive resilient switch member engageable in contact with the conductors to define an electrical conductivity pathway. The switch member is actuated by a thermally responsive shape memory alloy strip and activatable in response to a change in temperature at a predetermined level to effect a change in the metallurgical state of the shape memory alloy and position of the engagement of the switch member with one of the conductors.
