Combination circuit breaker-lightning arrestor

Abstract From the Canadian patent

A conventional automatic electric circuit breaker is combined with a varistor to provide both overcurrent and overvoltage circuit protection. The varistor is connected between the load end of the circuit breaker and neutral to shunt to ground the current associated with lightning induced voltage surges. As a fail-safe feature, abnormal leakage current drawn by the varistor under normal line voltage conditions directly and/or indirectly heats the thermal element of the breaker trip unit, ultimately tripping the breaker.