On Dec 7, 11:56*pm, Lobster wrote:
I think the time has finally come when I may get to convert the "storage
room" at the end of the garage into a "workshop" as was intended when
the building was erected about 10 years ago.

I've got a garage as a "storage room" (for cars) on the end of my
workshop. Just cabled some of it in the same way you describe, T&E in
20mm (and some 25mm), but I'll probably do the rest in singles in
20mm. I can easily use 100m reels, but for a small job I'd struggle
with the T&E.

I would really have benefitted from a "Guide to goood workmanship in
PVC conduit" It's not all obvious from the first, particularly in
terms of which type of bend to use. One for the DIY wiki?

Do you have to use single-core wires; ie, will two 2.5mm2 T&E cables not
fit down a standard 20mm PVC conduit?

You can get two 2.5mm^2 T&E _and_ a 1mm^2 down there, but that's just
about the limit.

In practical terms you can get two 2.5s down there "easily" so long as
you do the following:

* The cables are straight and unkinked. You need a reel stand.
* You push (or pull) both from the same end
* You're only pulling through straight conduit, i.e each length is a
separate pull and you cable as you install the conduit.
* If it won't push, try pulling it.
* You never want to replace cables!

So you can see that it's workable for a small one-off, but if you're
in someone like Adam's position and time is money, then it's a crazy
way to do it. Singles are certainly easier.

And/or does that present potential
overheating problems?

The numbers change (in your OSG), but it's no big deal. Bundled cables
are bundled cables, and there's less de-rating due to heat from
surface conduit than under loft insulation.

How do the couplers, male and female adaptors etc work in connecting up
conduit boxes and socket boxes etc? *

I bought a sackful of round conduit boxes, then hardly used them. You
need lots of bends, a few tees, very few round boxes. You need more
female & male adaptors than you expect. Female adaptors _should_ allow
you to slip lengths of conduit in between boxes, then insert the
screwed bush from inside the box. In practice they don't, because
you've got the other end in a moulded socket and it's not that bendy.
I mostly used males, as I find them easier to tighten inside the box.

Bends come in many shapes and about three different radii. The CED
ones (from TLC?) with a screwed lid are a bit ugly, but their two
radii are neat for multiple fan outs from a CU. I preferred the clip
lid sort from discount-electrical, which have a fixed base and the
whole lid and sides clips off. Easy access when open and they look
cleaner installed too. You can pull cable through a nice bend or
elbow, but not through a round box (take the lid off and treat as two
pulls).

You need a bending spring (and a hot air gun), because many odd
corners in an existing old building just aren't straight or square.
It's also handy for dog-legging over other conduits or services.

Conduit clips vary. Two-piece saddle clips screw beneath the conduit,
so need to be installed early. I like the single-sided P clips from
discount-electrical from horizontal runs in the roofspace, two screw
saddles where there's a mechanical risk, and two-piece near the ends
where I might want to dismantle it again.

Rolson's conduit cutter is crap. Cuts well enough, but really slow and
clumsy to use. Again, it'll do for a garage but you wouldn't put up
with it commercially.

25mm conduit is only useful for lighting where you have junctions in
multiple conduit boxes and a lot of separate circuits, with lots of
wires between. Otherwise you find that its adaptors into the boxes at
the ends are just the same size as 20mm, so you can't pull any more
cable than you could with 20mm conduit.

If you have racks of adjacent metalclad sockets, you need metal
conduit nipples and spare lockrings to bolt them together. There used
to be a brass thing for doing this in one piece, but no-one seems to
stock them? Remember to crop the faceplate screws to clear these, or
you'll break the screw lugs out of the back boxes. Remember to tell
your teenage assistant this, or at least "Don't force it if it won't
go, stop and ask". It's a right pain to be "finished", then find that
half your backboxes are now broken and you have to strip the whole lot
out! Don't use teenagers as labourers if they're likely to take the
"sweep it under the carpet" approach to problems, especially not if
they then repeat it on a whole row before you find out.