1. Application: For protecting cables and equipments against overload and short circuit.

2. General rules for choosing MCB.

a. Technical data of the network at the point considered:The earthing systems, short-circuit current at the circuit breaker installation point, which must always be less than the breaking capacity of this device, network normal voltage.

b. There are 3 curve characteristics for magnetic operation:

B curve(3-5 In) protection and control of the circuits against length cables in TN and IT systems.

C curve (5-10 In) protection and control of the circuits against overloads and short-circuits

D curve (10-20 In) protection and control of the circuits against overloads and short-circuits; protection for circuits which supply loads with high inrush current at the circuit closing (LV/LV transformers, breakdown lamps).