Mixing cales sizes on radial circuit?


Postby beaudoin_p » Sun Jul 15, 2007 1:46 pm

Hi
I am completing a Part P course and have run into a problem that is not covered anywhere I have looked: When running a radial circuit that for part of its run will go through thermal insulation. is it acceptable to run the 'normal' (2.5/1.5 mm) to the point where it enters the insulation then transit (via JB) to the required heavier cable or must the whole cable be of uniform guage?

Many thanks (hope this is not a stupid question)

Paul
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Postby sparx » Sun Jul 15, 2007 7:49 pm

Hi Paul, I think the reason u haven't met this b4 is it in reality never happens!
Presume u have 20A MCB for A3 radial, which has area limitations so as 2.5/1.5 is so overrated you can run approx 1/3rd of circuit in thermal insulation no prob.
If the loading on the circuit is too high then voltdrop figures will mean going up to 4mm2 for whole run, don't mess with changing cable size part way as will play havoc with your test sheets!!!
If this has been set as a ? on a course then they want shooting, & I don't give a toss who 'they' are, regards, best wishes & good luck with course,
SPARX
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Postby beaudoin_p » Mon Jul 16, 2007 6:55 pm

Sparx

Thanks for the advice - yes, it is a ? on an assignment but more to the point, if this is intended as a 'real life' situation, I should understand the answer. I understand what you are saying in terms of the cable being already well rated for this run but to 'do the do' I'll calculate it anyway as see if I can make it match.

Best regards

Paul
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