The breaking current of a circuit breaker is

A. Less than its making current

B. More than its making current

C. Equal to its making current

D. None of the other options

Answer

A. Less than its making current

Explanation 

Making current of a circuit breaker is the peak value of maximum current loop during sub transient conditions including DC component when breaker closes.

The breaking current of a circuit breaker depends on the instant on the current wave where the contacts of the breaker start separating.

Making current is more than breaking current and the relation between them is,

Symmetrical making current = 2.55 × symmetrical breaking current

The circuit breaker is used for switching on and off the circuit and also for the isolation of the faulty section in case of a fault. The Making and Breaking Current of circuit breaker both these terms are very important for selection of circuit breaker for any electrical installation. The making and breaking current capacity parameter of circuit breaker has prime importance when the circuit breaker opens at the time of fault and also when the circuit breaker closes at fault.

The braking current capacity of the circuit breaker is the maximum fault current that can flow through the circuit breaker for a short period of time from the time of occurring short circuit till the clearing of the fault without any permanent damage. The breaking current capacity or short circuit breaking current of the breaker is expressed in KA(RMS). The circuit breaker of 40 KA short circuit interrupting capacity can break the 40 KA current without getting damaged. 

The making current of the circuit breaker is the maximum peak value of the current that the breaker can interrupt without any damage if the breaker is closed at fault.

The making current of the circuit breaker is always more than the breaking current. To understand why making current capacity of the breaker should be more than its breaking current capacity, let’s discuss how fault current behaves, what is the characteristics of the fault current.

When the fault occurs in the electrical network, the AC and DC current is present. The DC current magnitude is about 60 to 80 % of the AC current.

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