Over-load voltage protection circuit - has thermal fuse switch that responds if first varistor fails to establish second varistor path to ground

摘要

The overload voltage protection circuit has a pair of parallel varistors (V1, V2) connected between the live phase (1) and ground (2) in parallel. The varistors connect to the live phase via a thermal fuse (3) that in the normal state connects with one of the varistors (V1). In the event that the coupled varistor overheats, the fuse switch responds and a changeover takes place to the second varistor to maintain the conductive path to ground. An optical and/or acoustic indicator alerts the operator that the first varistor (V1) must be replaced. Alternative versions to provide such failsafe operation are possible. ADVANTAGE - Includes redundant element as failsafe back up.