In article ,
pm writes:
A couple of q's on boiler wiring:

The boiler manual says to run the pump live, earth & neutral from three
terminals on the boiler.
I must also run live, neutral and earth to the wiring box for the
controls. This needs to be fed from the same switch as the boiler so it
is not possible to switch part of the system of and have the rest live.

I also need a switched live from the wiring box to the boiler.

I plan to put the wiring box and pump in the airing cupboard. The boiler
will be in the kitchen.

First q - the boiler wiring must be 90deg heat resistant, I can only
find flex that is high temp rated and I understand that flex mustn't be
buried in walls. Why is this? For a fixed installation, can I run the
flex in conduit that is buried? I would rather do this than surface mount.

Flex isn't normally buried in walls, but there's nothing in the
wiring regulations which forbids it. 90deg T&E is available; it
has a white sheath with the new wiring colours (white sheath with
old wiring colours doesn't mean 90deg). You would probably have
to go to an electrical wholesaler or other specialist supplier
though.

Second q - ignoring the permanent L/N/E from the switch to the wiring
box, according to the instructions I need four conductors going from the
boiler to the airing cupboard - pump live, pump neutral, pump earth and
switched live. All the heat resistant flex I've seen is three core. Can
I get away with using the earth cable in the flex as the switched live
and take the pump earth from the wiring box if I tag (or sleeve) the
cable appropriately? To me this is similar to using the black connector
for switched live in a lighting circuit.

No, the cable needs an earth conductor in it even if it isn't
used at the other end.

I suggest you go along to a wholesaler and see if you can get a
small reel of 90deg triple and earth. You will probably have
difficuly buying it by the metre.

--
Andrew Gabriel