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Major difference between isolator and circuit breaker is that isolator is an off-load device, whereas circuit breaker is an on-load device.
(An isolator switch is part of an electrical circuit and is most often found in industrial applications. The switch does exactly what its name suggests in that it electrically isolates the circuit or circuits that are connected to it. Such a switch is not used normally as an instrument to turn on/off the circuit in the way that a light switch does. Either the switch isolates circuits that are continually powered or is a key element which enables an electrical engineer to safely work on the protected circuit.
Isolator switches may be fitted with the ability for the switch to padlock such that inadvertent operation is not possible. In some designs the isolator switch has the additional ability to earth the isolated circuit thereby providing additional safety. Such an arrangement would apply to circuits which inter-connect power distribution systems where both end of the circuit need to be isolated.
An isolator is a switch connected after a circuit breaker. When a circuit or a busbar is taken out of service by tripping the circuit breaker, the isolator is then open circuited and the isolated line is earthed through earth switch so that the trapped line charges are safely conducted to ground.
A circuit breaker is a complex circuit -breaking device with the following duties:
Make or break both normal and abnormal currents,
Appropriately manage the high-energy arc associated with current interruption. The problem has become more acute due to interconnection of power stations resulting in very high fault levels,
Effect current interruption only when it is called upon to do so by the relay circuits. In fact they are required to trip for a minimum of the internal fault current and remain inoperative for a maximum of through fault current,
Rapid and successive automatic breaking and making to aid stable system operation,
3-pole and single pole auto-relosing arrangement.
In addition to these making and breaking capabilities, a circuit breaker is required to do so under the following typical conditions:
Short-circuit interruption
Interruption of small inductive currents
Capacitor switching,
Interruption of short-line fault,
Asynchronous switching.
Isolator is an off load device ie we can't close the isolator under load condition. If we close the isolator under load it will damage the isolator but circuit-breaker is a device having high withstand capacity(the withstand capacity is based on application) so we can open & close the breaker under both onload & offload conditions. Also while opening & closing under onload arc will appears at the contacts. The isolators have no special arrangement to extinguish that arc but in breaker we have some special arrangement to extinguish that arc.
A light switch is an on load device as it has current going through it when you break the circuit (also MCBs)
A main switch is an off load device as there is no current going through it when the circuit is broken..
In other words you have switched off the load via the load switch before you turn the isolator etc etc, the MCB switch should be turned off when the load has been removed.
Isolators will more likely be used to remove the supply to a circuit/s possibly for maintenance/repair. Because they are supposed to be operated without a load the contacts are not necessarily hardened and are not separated so quickly. If they are used as a switch it is common to see arcing (flashes) and for the contacts to be damaged.
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