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#211301 10/03/13 04:36 PM
Joined: Aug 2013
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Comparing the Canadian Electrical Code (CEC) with the British Wiring Regulations I can see that both documents require consideration of voltage drop and current carrying capacity when designing circuits. However within the CEC there does not seem to be any consideration of the disconnection time of the circuit breaker in the event of a fault to ground (as explained in the link below).

So my query is can anyone you tell me if when designing circuits within Canada consideration of the disconnection time of circuit breakers is part of the design process.

http://www.electrical-installation.org/enwiki/Automatic_disconnection_for_TN_systems

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I think that is among the purposes of the requirement that all equipment have CSA approval for the purpose for which it is used. Disconnection time would be dealt with in the standard for the approval of the overcurrent devices.

If you intend to export a piece of equipment to Canada, to get CSA certification, all components must be CSA approved. If certification is to be obtained after the equipment arrives in Canada, all non-approved components must be replaced. This includes fuses and breakers.

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I think the question goes deeper than this. Under serious circumstances, a German electrician would in fact calculate, whether branch circuit conductors of a certain size would actually allow an overcurrent protection device with a certain current rating and trip curve to trip within the required time based on the loop impedance/short circuit current.

This is most interesting where breakers/fuses are used as earth fault protection (which is the fact in all Canadian and US circuits that are not on a GFI). An extensive run of small wire, fed by a small transformer might actually have such a high impedance that an earth fault wouldn't be noticed as a short circuit by the breaker any more but merely as an overload.

BTW, I can't remember if we've covered this before, but do all US/Canadian breakers have both a thermal and a magnetic fast-trip? If there's only a thermal trip, trip time is likely a moot point anyway.

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From the little knowledge I have of Canadian installations circuit breakers have a magetic and thermal trip. Disconnection times can alsoe be achieved by the use of a RCD/GFCI where ground loop impedance is too high to achieve disconnection in the required time.

I have found the following in the CEC 10-500:

“The path to ground from circuits, equipment, or conductor enclosures shall be permanent and continuous, shall have ampacity to conduct safely any currents liable to be imposed on it, and shall have impedance sufficiently low to limit the voltage above ground and to facilitate the operation of the overcurrent devices in the circuit.”

And in the CEC Handbook guidance it states that this is normally achieved by a sufficiently low impedance such that the overcurrent device is presented with a fault current of 5 times it’s rating. Which in effect is the 0.4 second requirement of BS 7671.

What I would like to know is does anybody bother working this out in Canada? Are GFCIs routinely used on circuits?

Last edited by Stuart_Urban; 10/08/13 05:24 AM.

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