A heavy-duty switch designed to automatically interrupt power when it detects an overload or short circuit. Unlike a fuse that melts and must be replaced, a circuit breaker uses magnetic or thermal mechanisms to trip open the contacts and can be reset once the fault is cleared. In power systems, they range from small molded-case units to massive high-voltage gas-insulated tanks that extinguish arcs using SF6 or a vacuum.
The main circuit breaker tripped on overcurrent, so we need to test the downstream cables before resetting it.
Also heard as
- CB
- breaker
Related terms
Fuse
A sacrificial protection device containing a conductive element that melts to safely break a circuit during an overcurrent event.
Switchgear
Assemblies of breakers, switches, fuses, busbars and enclosures that control and protect power circuits.
Trip
To open a circuit breaker automatically through its protection, or to order a breaker open by command.
SF6
Sulphur hexafluoride: a dense, highly insulating gas used to quench arcs in high-voltage switchgear.
Breaking capacity
Highest fault current a circuit breaker or fuse can interrupt safely at its rated voltage.