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Help with college formula please!


hoppy

Question

Just been doing some college work.

Was calculating if supp equip bonding was required in a bathroom. The formula given for an mcb is R < 50V / Ia.

Ia being the fault current for a particular mcb to disconnect in a certain time.

My question is, as there are likely to be various circuits in a bathroom, which mcb rating would you use as the calculation. Would it be the shower circuit mcb as this is likely to be the highest rated and thus require more fault current to disconnect within a certain time.

I know to the 17th, that supp bonding is not required if rcd protected and all that. This is a theory question and was just wondering what you guys thought.

Cheers

Craig

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I would consider using biggest MCB but there are a few points. With RCD this no longer applies and in a bathroom 12 volt is maximum voltage not 50 so should it not be:

R = 12v / Ia ? I can't find formula under 701 in 17th and both 12 and 24 volt AC are given according to zone.

Idea is of course that voltage over 12/24/50 will trip MCB and I am sure not 50 volt for bathroom?

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Thanks for the reply,

i used 50v for the example, i need to check out the touch voltage for a bathroom, i am 90% sure it is 25V, will check though.

So the largest mcb it is then.

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