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joining cores of multicore cable for beter ampacity
wrote:
I imagine one issue is current sharing between the conductors. Whilst
the current share may be close to 50/50 when installed, any slightly
loose connection or corrosion of one conductor could cause one
conductor to end up carrying most of the current. not good.
Yes, that's one issue. I don't have the regs on me, but IIRC,
the conductors are required to be the same length, and without
any branches. You must show by calculation that the overload
and fault current protection will operate correctly for each conductor.
For the fault current protection, you have to consider additional
types of fault, such as one conductor shorting to ground, passing
current directly from the supply, plus that backfed from the other
end via the other conductors. Also the case where one conductor
breaks and only the backfed path is grounded, so you have a
higher earth fault loop impedance than you might otherwise
expect. For overload protection, you have to consider what
happens if one conductor breaks (without shorting). There are
probably more issues I don't recall too.
You would probably end up having to use separate but ganged
breakers for each conductor (and in the case of more than two
conductors in parallel, possibly ganged breakers at both ends of
the cable). There is simply no excuse for doing any of this in
domestic installation -- it is far cheaper to buy the correct
cable in the first place. Also, H05VV-F is flex anyway, IIRC.
--
Andrew Gabriel
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