Active safety circuit operated by temperature of solid state relay with crowbar circuit

Controller 4 monitors the temperature of solid state relays 1, 2, 3, using a sensor 10 and if a temperature anomaly such as overheating is detected firstly opens the relays 1, 2, 3. If the temperature anomaly persists for a time period controller 4 then operates safety switch 9 to ground the supply at node 8 and thereby operate current breaker 5. Current breaker 5 may comprise a fuse, solid state relays 1, 2, 3 may comprise a field effect transistor (FET) and safety switch 9 may comprise a relay or a FET. Temperature sensor 10 may comprise a separate sensor (fig 2: 10, 10a and 10b) for each solid state relay 1, 2, 3.