Definitions and characteristics
The main characteristics of short-circuit protection devices are:
- breaking capacity: the highest value in the estimated short-circuit current that a protection device can break at a given voltage
- closing capacity: the highest value a protection device can reach at its rated voltage in specified conditions. The closing value is k times the break capacity as shown in the table below:
Two protection devices are commonly used for this:
- Fuses, which break the circuit by melting and must be replaced
afterwards - Magnetic Circuit Breakers which automatically break the circuit and
only require to be reset - Motor Circuit Breaker: this device is a thermal and a magnetic circuit breaker in the same package