Volt drop, loop impedance and micro generation?

[JohnW2]

Domestic and industrial RCD's are very different beasts.

Indeed they are, but given that this is a 'DIY' forum, I doubt that there is any great need to consider the industrial ones. I would imagine that even most of the electricians in this forum have little or no experience of the 'industrial beasts' you talk about! .... Nevertheless ....

...However these were never designed for personal safety as such. Often set with one minute delay and one amp differential to trip them.

A minute sounds like a long time. Even if the trip threshold was a 1A residual current, particularly in an industrial environment, the actual fault current which flowed for that minute could presumably be hundreds, if not thousands, of amps?

Kind Regards, John

 

[ericmark]

A minute sounds like a long time. Even if the trip threshold was a 1A residual current, particularly in an industrial environment, the actual fault current which flowed for that minute could presumably be hundreds, if not thousands, of amps?

Kind Regards, John

I would agree although not thousands of amps the moulded breaker was rarely more than 500 amp and there was no delay on the breaker only the RCD.

Also as I stated with the nail through cable all 4 devices tripped although in theory the 30 mA RCD should have tripped within 40 mS so the other three should not have tripped.

One major problem is not switching the neutral. Which is likely why all four tripped. Only the 30 mA trip switched the neutral. Over the years I have seen again and again the problems where multi-RCD's trip. With a MK 10 mA RCD metal clad socket pressing the test button always tripped the 100 mA RCD in the main board. Using a RCD tester it didn't but the test button did.