What is kA rating of a circuit breaker?

What is kA rating of a circuit breaker? kA rating of a circuit breaker is the maximum current it can safely interrupt in case of short circuit. There are many types of circuit breaker, such as VCB, ACB, MCCB, MCB etc.

All circuit breaker has a kA rating. Here, kA means kilo ampere. kA rating is also known as short circuit withstand capacity or ultimate breaking capacity of a circuit breaker. If the value of short circuited current is more than the rated kA, then the circuit breaker could be damaged.

For example, if the MCCB is rated at 10kA, that means the circuit breaker can safely break the circuit during short circuit condition if the short circuited current does not exceed 10kA.

During short circuit condition, the current flow increases exponentially. That means a circuit designed for 10A can cause a current flow over a thousands of ampere. If the circuit breaker used has a very low kA rating, the circuit breaker as well as the circuit can be damaged during short circuit condition. Therefore, the kA rating of circuit breaker is most significant. The kA rating is denoted by Icu and Ics.

What’s Ultimate Breaking Capacity (Icu)

Ultimate breaking capacity of a circuit breaker is the maximum current it can safely interrupt during short circuit condition in the related circuit. It is denoted by Icu. After clearing a fault at its Icu, the circuit breaker can’t be reused.

What’s Service Breaking Capacity (Ics)

The service breaking capacity of a circuit breaker can be defined as the maximum current it can safely interrupt and yet enter back to service after fault clearance. It is denoted by Ics. After clearing a fault at its Ics, the circuit breaker can be reused.

Difference between Icu and Ics

The main difference between Icu and Ics is a circuit breaker can not be reused after clearing fault at its Icu. But it can be reused after clearing a fault at its Ics. Therefore the value is Ics is less than the value of Icu.

Importance of kA rating

The kA (kilo ampere) rating is very important factor of circuit breaker (CB). The maximum amount of current flow through a circuit in case of short circuit varies from one circuit to another. Therefore it’s necessary to pre-calculate the right size of circuit breaker (CB) to avoid danger. An incorrect kA rating CB can be a potential hazard, casing fire and sometimes it can be fatal.

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