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. With that in mind I need to wire up the electrics (there's already a CU there, currently supplying lighting and a single socket for the garage).
Given the 'workshop' element, I want to fit one ring of surface-mounted metal-clad sockets (probably these:
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and was going to use surface-mounted PVC conduit (it's a single-thickness block-building). Thing is, although I've done plenty of wiring before I've never used conduit and am not entirely sure how to go about it: I could really use an on-line how-to-do-it guide but can't find one - is there such a resource around?
To be honest I have no intention of taking this to Building Control but still want the work to be up to standard. Is PVC conduit considered acceptable in this sort of environment? (We're talking a very low-key, domestic, end-of-garage-type workshop, not one with lots of massive machine tools etc).
Do you have to use single-core wires; ie, will two 2.5mm2 T&E cables not fit down a standard 20mm PVC conduit? And/or does that present potential overheating problems? I'd rather not have to use single-core stuff if I can help it, as I've got plenty of T&E, and you can only buy the singles in 100m lengths AFAICS.
How do the couplers, male and female adaptors etc work in connecting up conduit boxes and socket boxes etc? Probably be obvious when I've got them in my hands, but I'm putting together an on-line shopping list...
As I say - a simple Noddy guide is probably what I need!
I've used it for three phase in a factory environment, although I always bought heavy grade, rather than standard, conduit.
It will be a struggle, particularly if you use elbows. I would use 25mm conduit if I had to run T&E. If you decide to use single core wire, try to get a trade discount from your local electrical wholesaler - I always got 65% off list on wire and cable.
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Male couplers - push thread into hole in box from outside and do up nut. Female couplers - put male threaded part through hole from inside and screw into female part on end of conduit.
If you areny going to be pulling huge amounts of current why not use suitable armoured cable and surface mount it using the proper clips ? Might look a little less pretty, but the end result will be the same if you aren't taking it that far. Otherwise pop into a local "shed" and have a play with the conduit and connectors, all will be revealed once you get to handling it. T & E through conduit is a bit overkill on the mechanical protection front and can be quite challenging at corners/bends when pushing it through, but for shortish runs (Say under 3m to a join) then I have done it with some success using a squirt of silicon spray (NOT WD40!) to help it through. Boxes and CUs willl need to have the corect size holes in preferably with push out blanks ot alternatively the relevant size hole saw to make the apertures.
Are you wanting the cable in conduit in all the workshop or just for the drops down to switches and sockets? If it is all conduit then you need to use single cables not T&E. I would not attempt to pull T&E down anything other than straight runs.
The adaptors eg
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are used for connecting up to socket backboxes etc. Undo the nut on the adaptor, fit into the hole and screw the nut back on. The conduit then just pushes into the adaptor. You do not use these adaptors for connecting the conduit to conduit boxes and bends, the conduit just shoves into those without the need for adaptors.
I often just run a big piece of trunking around the garage between the ceiling and wall and just use conduit for the drops (a 20mm hole cutter is needed). That way I can use T&E and any additions later are easy. It is a damn site easier and faster than using conduit all over the place.
You now have the choice of pulling T+E *or* singles through it - but for the record 2.5mm2 T+E will pull round 2 90 deg hand-bent sections over a
5m length with fishwire - I know because I've tried.
I prefer female couplers - just because they leave a smooth bore in the socket box but you can use male too.
In either case, knock out the knockout, insert adaptor, apply male or female nut from inside - done. PVC conduit cuts very nicely with a pair of JG Speedfit type hand shears - quicker than a hacksaw, square cut no burr. There are these too:
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the tube to the adaptors with solvent weld a la waste pipe.
If you can a low section hanging of conduit it is worth drilling a 1mm hole in the bottom at the lowest point (before cabling!) to act a a drain hole for condensate.
Bends - for one or two in a section, hand bend with a pipe spring over knee or use a pre formed solvent bend with or without inspection cover. Or use a round box. Good idea to make sur eyou get the gastkets - sometimes sold sepeartely.
MK tube is better than some no name stuff - I have noticed that one no-name is no smooth and dirties quickly - still works but will look grubby and won't wipe clean. MK is polished. Black looks very smart too.
Clips - two types - saddle or these:
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which I rather like for one screw and neatness.
Have a browse here - pretty much everything you need:
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As I say - a simple Noddy guide is probably what I need!
Go into B&Q and have a feel so to speak - it will become clearer then. Then make a list and go to the wholesalers with a printout of the TLC page to avoid rapage from either establishment!
Can be done if the bends are very gentle IME - but the bugger are any joins with straight couplers - there is always a lip the cable end snags on - can take some fiddling with pulling on a tape at one end and pushing the cable gently at the other.
I like that approach - it is what they seem to do here (Imperial College) a lot - sometimes using all plastic, sometimes galvanised trunking and steel conduit (depending on the environment) - but always that sort of layout. I would add that is for final drops - all the feeders from 32A upwards tend to be SWA.
Still some MICC around but I don't see anyone installing it new anymore.
> Perfectly satisfactory and will take several T& E cables. Best if
I would add I had to pull some ancient self adhesive trunking off a lab wall at work prior to painting the other day. Needed a jemmy from the workshop the stuff was so strongly attached! Onto a painted surface it is as strong as the paint!
When attaching the fish tape to the cable wrap a bit of tape around the square cable end and fish tape to make a rough cone. Reduces such snagging a great deal.
Extending circuits in a garage or shed or porch is non-notifiable works.
Search online for 6491X (singles) in cut lengths.
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do 1.5mm & 2.5mm 6491X at 16p & 22p per metre. I think there is another supplier out there, perhaps another on Ebay. Perhaps the sheds do a 50m reel (which would be a good length).
Plastic - no explicitly, though it could be argued as providing protection suitable for the environment.
Don't underestimate it - it's pretty tough. I'd rather a mis-aimed chisel or knife or lump of wood struck tube than T+E cable. The former might sustain some damage but you'd have to belt it pretty hard to damage what's inside.
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?
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.
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.
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.
the figures are correct the page is halfway through an update to fetch it into line with the 17th edition reference methods (I'll see if I can update it a little more tonight)
A 32A ring and 6A lighting are unlikely to cause problems when used in conduit together. It may well be possible to ignore the lighting circuit for grouping factors if it is only at 33% of it's capacity.
Do you speak from experience here? I sense a bit of ill feeling. Do tell us.
PVC has quite a significant coefficient of expansion. If you have long runs in a dry location with large temperature changes, it's a good idea not to glue all the ends, but allow some to act as expansion joins like with guttering.
Also, allow several hours from last solvent weld before drawing in any of the cable, or you may find residual solvent in the tubing ends up welding the cable to it. (Regs used to say you must finish the whole conduit/trunking installation before you start drawing in any cables.)
If you are forming your own bends, don't use a plumber's bending spring as they aren't the right size and pipe will crinkle. You need a conduit bending spring. However, a plumbers 22mm pipe bender will just about bend 20mm conduit with just a little flattening, although that may be enough to stop you using a pair of T&E. Bends have a slight tendancy to try to undo themselves, so position the clips so this can't happen.
When I cable up, I always assume the odd drip will run out of any vertical runs. Form the wires into a drip loop inside the accessory box, so this drips off rather than being directed into the back of the wiring accessory, and also drill a drain hole in the bottom of the back box (I usually go for 3-5mm). If the conduit runs through a wall to a different temperature, then condensation formation can be a very significant issue, but even temperature changes in the one location will generate some.
Thanks to all for lots of really useful advice - I feel much more confident about this now.
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Well in fact, thinking about it, that will suit my purposes really well. I was indeed intending just to install drops to sockets and switches; the workshop has a plasterboarded ceiling and there's a semi-permanent floor above sitting on the ceiling joists, so I see no reason why I can't just run 'horizontal' runs of T&E above the ceiling unprotected (ie as I would in the house) and then have 2xT&E drops down to all the accessories, within 1-metre-ish straight lengths of 20mm trunking, which pokes through the ceiling. All very much easier than I'd envisaged!
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