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 currents associated with lightning induced voltage surges....http://www.google.co.uk/patents/US4168514?utm_source=gb-gplus-sharePatent US4168514 - Combination circuit breaker-lightning arrestor
