Why does a USA/Canada surge-protected extension lead (110V) trip the circuit breakers in the UK (220V)

circuit breakerextension-cord

I moved from Canada to the UK and for convenience I would like to use some of my Canadian aquired extension leads (for light power items such as ethernet switches).

Problem is that the surge-protected extension leads seem to always trip my circuit breaker, so this pretty much means I cannot use them.

However I am not satisfied to just accept this fact without knowing why.

So I'd appreciate if some knowledgeable electrician would be able to explain to me why a surge-protected extension lead designed for the USA/Canada (110V) trips my UK circuit breakers on 220V.

Best Answer

The surge suppression in most consumer grade power strips includes a metal oxide varistor (MOV) placed across the line at the supply side of the power strip:

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These devices suppress voltage spikes by conducting energy across the line when the incoming voltage exceeds a preset threshold determined by the manufacturer. Wikipedia has a good description of varistors here:

https://en.wikipedia.org/wiki/Varistor

MOVs in a surge suppressor designed for 120v are selected to conduct at roughly 200v. This ensures the MOVs do not interfere with normal operating conditions, which include peak voltages up to 55% greater than the nominal line voltage. If you connect one of these across 220VRMS where the nominal peak voltage is 310v, far into the conduction region of the device, then the MOV conducts during normal operating conditions shorting out your extension lead.