In article ,
Martin Angove writes:
In message ,
John Rumm wrote:
Andrew Gabriel wrote:
The cable also has to be able to take the fault current (short circuit
to neutral or earth) for the time it takes the 30A fuse/MCB to trip
without overheating -- that's where a 1.5mm² cable is likely to come
unstuck (maybe literally;-) Also, it must still pass enough current to
blow the fuse within 400ms (IIRC).

Unless you are prepared to sit down and do the calculations to prove
that it's OK, stick with 2.5mm². And what are you saving anyway? peanuts.

Yup - quiet agree! I was only commenting that there is not actually a
requirement that you must not reduce cable sizes on the spur. Must admit
I tend to find very little use for 1.5mm sq cable!


For a couple of meters or less, as you say, there's not much point
skimping...

And for longer lengths, you're likely to find the impedance is too
high to meet the trip times.

but just to be pedantic, surely the fuse you have to worry
about on a (single) socket is the 13A in the plug, not the 30/32 in the
board? Now, a double...

If the short happens in the connections to the back of the socket... ?

--
Andrew Gabriel