There are different essential parameters of the circuit breakers which necessary to understand. Furthermore, These parameters we often see marked on circuit breakers.

The characteristics of circuit breakers mainly include: rated voltage Ue; rated current In; overload protection (Ir or Irth) and short-circuit protection (Im) trip current setting range; rated short-circuit breaking current (industrial circuit breaker Icu; household circuit breaker Icn) )

Operating Voltage (Ue)

It is the voltage at which any circuit breaker is designed under normal conditions.

Rated current (In)

This is the maximum value of current that a circuit-breaker, can carry indefinitely at an ambient temperature designed by the manufacturer, without any interruption.

Read Also: How to Read Nameplate of MCB (Miniature Circuit Breaker)?

However, These are the parameters which need to understand by every electrical engineer.

Overload Trip (Ir) Setting:

It is used for the continuous ampere rating according to current. Moreover, It has different set of multiples in the adjustable knob ranging from 0.4 to 1 of nominal or rated current of circuit breaker which can be represented by In.

Figure 1: Parameters setting knobs
Figure 1: Parameters setting knobs


Ir= multiple *In.


Let suppose we have a circuit breaker having rating of 2000 A which has a current load of 1000A so we will set it 1000A by moving the knob at 0.5 which means

Ir= 0.5*2000
Ir = 1000A

Hence, After exceeding 1000A of load it will trip the Circuit Breaker and will disconnect the load.

Short-circuit relay trip current setting value (Im):

The short-circuit trip relay (instantaneous or short delay) is used to quickly trip the circuit breaker when a high fault current value occurs, and its trip limit Im.

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