In August of 1974, a Federal safety standard went into effect that required that all microwave ovens be equipped with an interlock monitoring system. Generally speaking, the normal sequence of switch operation when the door is opened is as follows. First the primary switch opens its contacts. Finally, the interlock monitor switch closes its contacts. All this happens before the door can be opened far enough to allow any dangerous levels of microwave radiation to escape.
All switches have a voltage and current rating.
A typical door-interlock switch is rated at 15 amps with 125 or 250 VAC applied. When replacing an interlock switch, these ratings must be met or exceeded, otherwise premature switch failure will result. Another replacement consideration is the operating and release force. This is the relative amount of pressure needed to actuate the switch. Various applications call for differing amounts of operating pressure.