# Difference between a double pole isolator switch and the Main Circuit Breaker?



## MikeWit8 (Sep 24, 2021)

Hi everyone,

I have a question (most likely a dumb one) regarding the double pole isolator. I would like to add an isolator between my meter and my consumer unit, so when something needs to be adjusted in the consumers unit, it would be totally safe to do so. 

What I'm trying to understand (out of curiosity) is what the differences are between a double pole isolator (linked switch) and the Main Circuit Breaker (linked switch)? Do they in essence perform the same job? Could a Main Circuit Breaker be used as an isolator to isolate the consumer unit? If not, what can an isolator do that a main breaker can't?

Many thanks in advance!
best regards,

Mike


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## paulengr (Oct 8, 2017)

An isolation switch is not meant to open or close under load.

A disconnect can open under load. A safety disconnect can open under fault conditions. Neither is designed for closing onto a load.

A circuit breaker can be used as a switch with some limitations. It is designed to open during loads or faults a LIMITED number of times. If it has the SWD rating it is designed for routine switching. But the big thing is it will automatically open if a fault or overload occurs. It is much more than a switch.

Another big difference is if the switch is visible break or not. Occasionally the contacts in any type of switch will weld themselves shut. This cannot be prevented with any known technology. At least with visible break you can see it open where with a breaker for instance you have to test to verify this (test for absence of voltage). Under UL the definition of a circuit breaker is an automatic switch with capability of opening under faults a limited number of times with both thermal and short circuit protection functions. All other breaker-like devices are “supplementary protection” used extensively in control panels and industrial plants.

None of these are designed to close into a fault. That’s what a recloser does.

These are pretty much standard IEC/ANSI terms. However a lot of European countries confuse things using the wrong terms for equipment. For instance you wouldn’t want just an isolator for your use…the tenant might have something running.

The big advantage of an external disconnect is you don’t have to have access to the distribution panel. This is why meter-mains with an integrated breaker are becoming so popular. The disadvantage is you still have to pay for a circuit breaker somewhere in the system (thus meter main popularity) so just a disconnect is extra money. Code in some areas requires an external disconnect for the fire department but makes it very convenient for burglars, too.


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