Differences between isolator and miniature circuit breaker?

Publish Time: Author: ETEK Electric Visit: 84

Isolators are used in power systems while MCB is circuit breaker. Isolators are manually operated devices while circuit breakers are operated automatically. MCB are onload devices while isolators are offload devices. Isolator cuts out a portion of a substation when a fault occurs. The other devices operate without any interruption. The Circuit breaker is a device known as an Automatic circuit breaker (ACB) or Miniature circuit breaker (MCB), which trips the entire system if any fault occurs and thus the whole system is affected.

In low-voltage power distribution systems, isolator and circuit breakers are commonly used electrical devices. Although their purpose is very similar, in practice they are distinctly different.


Isolator: It is a switching / isolation device, intended to disconnect an equipment or electrical Load from the supply.

It is an offload device; it can be operated only when the current passing through the circuit is zero. It can be operated only during offload condition.

The basic intention behind using an isolator is to ensure safety during maintenance. Before operating an isolator, it must be ensured that the current flowing through the circuit is zero or within safety limits.

MCB (Miniature Circuit Breaker): It is a protection device. The basic function of a circuit breaker is to protect the equipment.

Circuit breakers detect such faults and interrupt the power flowing toward the equipment / circuit, and prevent further damage to the equipment. The higher the intensity of the fault, the faster will be the interruption of power.

MCB are equipped with a built-in arc quenching system. This enables them to be used during on load and fault conditions.

It works during on load as well as offload condition.


Isolator: IEC60947-3

MCB: IEC60947-2 or IEC60898-1

Number of poles

Isolators have 1, 2, 3, 4 pole.

MCBs have 1, 1+N, 2, 3, 3+N ,4 pole.

Operation method

Circuit breakers can operate automatically to disconnect the electrical circuit during unprecedented electrical surges, but they can also be operated manually. Isolator, however, can only be operated manually.

Short circuit withstanding capacity

Isolators have high short circuit withstanding capacity compared to MCBs.

Location of the circuit

The isolator is generally used upstream of the circuit breaker as the main switch to isolate the circuit in a house. Isolator is designed to provide switching under load (even inductive) in household, commercial and industrial applications. Its main function is to allow maintenance of the electric system in safe conditions. It also grants complete insulation of the downstream circuits.

MCB is generally used in circuits downstream of isolator to provide short-circuit and overload protection for electrical installations. In the event of a fault, it automatically shuts down the circuit to prevent damage to wires and avoid fire risks.


Although circuit breakers and isolating switches are common electrical devices in power distribution circuits, the application scope and functions of circuit breakers far exceed isolating switches, but in low-voltage power distribution systems, we still need to use them in a reasonable combination according to actual application scenarios. This can not only reduce the installation cost of the power distribution system but also provide safety protection.

ETEK Electric provides a series of high-quality circuit breakers and disconnectors, welcome to consult.

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