Why are circuit breakers rated MVA?

When the breaker open the contacts to eliminate the fault currents, the rated voltage appears across the circuit breaker contacts. In short, the same rated quantities do not appears continuously during the fault currents. That’s why the breaking capacity rating of a circuit breaker can’t be expressed in MVA.

Why should circuit breakers be the correct size?

In case of other (over or lower) size instead of correct sized circuit breaker, the circuit, cables and wire even the connected device may heat up or in case of short circuit, it may start to smoke and burn. That’s why a correct size circuit breaker is needed for smooth operation.

What should be the rating of the circuit breaker?

Rated voltage of circuit breaker depends upon its insulation system. For below 400 KV systems, the circuit breaker is designed to withstand 10\% above the normal system voltage. For above or equal 400 KV system the insulation of circuit breaker should be capable of withstanding 5\% above the normal system voltage.

Can I use a bigger circuit breaker?

NEVER replace a circuit breaker with a larger size. This creates the potential to overheat the circuit wiring and which could cause a house fire! The solution is to have new circuits installed for specific areas or devices which would eliminate the possibility of overloaded circuits.

How the Repturing capacity of circuit breaker is rated?

Rupturing capacity of a circuit breaker means the maximum power a circuit breaker can interrupt under a fault. It is usually expressed in Mega volt Ampere (MVA) and it is then the product of the rated breaking current in kilo amperes and rated voltage expressed in kilo volts.

What is the 80 rule in electrical?

This rule states that an OCPD can be loaded to only 80\% of its rating for continuous loads. Remember that 80\% is the inverse of 125\% (0.80 = 1 ÷ 1.25) and, as such, the rules are indeed identical in their end requirement.

Why is the resistance switching used in air blast circuit breaker?

Resistance switching is normally employed in air-blast circuit breakers. Circuit diagram for the resistance switching of circuit breaker is shown below. Resistance Switching in Circuit Breaker refers to a method adopted for dampening the over voltage transients due to current chopping, capacitive current breaking etc.