The first characteristic is the overload which is intended to prevent the accidental overloading of the cable in a no fault situation. The speed of the MCB tripping will vary with the degree of the overload. This is usually achieved by the use of a thermal device in the MCB. The second characteristic is the magnetic fault protection, which is intended to operate when the fault reaches a predetermined level and to trip the MCB within one tenth of a second. The level of this magnetic trip gives the MCB its type characteristic as follows

MCB its type characteristic

Type Tripping Current Operating Time
Type B 3 To 5 time full load current 0.04 To 13 Sec
Type C 5 To 10 times full load current 0.04 To 5 Sec
Type D 10 To 20 times full load current 0.04 To 3 Sec

The third characteristic is the short circuit protection, which is intended to protect against heavy faults maybe in thousands of amps caused by short circuit faults. The capability of the MCB to operate under these conditions gives its short circuit rating in Kilo amps (KA). In general for consumer units a 6KA fault level is adequate whereas for industrial boards 10KA fault capabilities or above may be required.

ELCB (Earth Leakage Circuit Breaker):

Salient Features