I am about to empty (This will take some time!) strip out, insulate, ply line and rewire my workshop/shed. Currently, all the wiring is surface clipped (Taken back to a small consumer unit). I would like to run it all in 20mm plastic conduit, as I think it will look neater.
I have a few questions about this as I have not used it before... Do I have to use T&E in this, or can I run singles? Can I mix different circuits in the same conduit (Sockets and lighting for example) When joining the pipes to the connectors, do I solvent weld them, or just push them in? I have a small bulkhead light outside, this has a knockout, I assume I will need to solvent weld the pipe to the connector here - Do I also need an O ring/PTFE tape between the adaptor
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and the side of the light to seal it?
Do I really need a special cutter
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or will the trusty hacksaw do the job?
It looks like I will need a new CU, as the current one does not have the
20mm knockouts, and cant accept them (the top cover covered the whole lot, right back to the wall) I guess a plastic CU would be best, so I can drill additional 20mm holes easier? any recommendations (Currently I have an 9 way CU in there)
I don't really think I need a split load CU in here as I have an emergency light. (If I did get a split load, would I need a 100mA RCD protecting the lot? (Earth is exported from the house, which is connected to the supply cable armour.
You can use either, but the conduit space soon goes if using T&E. Provided all the wiring will be fully enclosed it's best to use singles (and get stranded 2.5 mm^2, not solid, as it's much easier to work with in conduit).
You might want to think about using a trunking and conduit system. Run a ring of (say) 50 x 50 mm trunking right round the building walls at a suitable height (e.g. above door height) and then run conduit 'drops' up and down to switches, lights, sockets, etc. This makes it very easy to make changes and move things around, which in a workshop you will tend to want to do.
Yes. The wiring for each final circuit must be _electrically_ separate (apart from CPCs) - so no common neutrals! - but the enclosure system may be shared.
IME push-fit is usually quite OK indoors, provided everything is well secured.
Where is the wiring to enter the light: at the back, or at one end? It's not usual to try to make a conduit system waterproof - you arrange for any water that might enter locally to be able to drain freely. One approach would to mount the light on a round conduit box with a drain hole drilled in the bottom, with the conduit approaching from the top, so that water will drain and won't be able to get back into the indoor conduit. Alternatively connect to the light using a waterproof cable gland and a suitable round cable such as Hi-Tuf taken thro' the wall and then into the indoor wiring system via another gland on a small adaptable box.
A hacksaw is fine, together with files, etc. for deburring. (You can use a plumber's deburring tool or a taper reamer for internal deburring.)
Metal ones usually have lots of 20 mm knockouts and would be OK if you stick with the TN-S earthing. Plastic simplifies things though if you decide to convert to TT earthing and 20 mm holes are easily drilled with a holesaw. All the mainstream makes are OK - MK, Crabtree, Wylex, MEM, Merlin Gerin, etc. Much opinion suggests avoiding the cheaper own brands though. It's not a good idea to mix component parts from different manufacturers.
No separate motor circuits for fixed workshop machinery? - Bench drill, grinder, lathe, planer thicknesser...? Do provide separate circuits (with Type C MCBs) if you have such items.
Well with TN-S earthing you only need to RCD-protect the sockets, so you could have a non-RCD / 30 mA RCD split, provide that sufficiently low earth fault loop impedance values can be achieved. How is this lot being fed? - device type & rating in the house, submain cable type and size, and length of run?
Converting to TT earthing (i.e. earthing to a local rod electrode) is another option to consider. The advantage of this is that it avoids the risk of any local rise in the voltage of the installation earths, relative to the actual local ground. If this installation is ever to be extended to a metal greenhouse, or if you're likely to be using any Class 1 (earthed) equipment outdoors, the TT option should be considered. Clearly with TT all final circuits would need to be RCD-protected, but whether to use one 30 mA RCD or two is a matter of judgement about the safety and convenience implications of losing the whole supply if the RCD were to trip.
Actually, singles are preferred, although you can use T&E if you have some lying about and do some careful planning.
Yes.
I just left mine.
No need to seal, provided you route the conduit to drain away. I used "female" adapters.
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Do I really need a special cutter
Hacksaw is just fine. Then use a Stanley knife to clear up the edges. You can do this in a second or two by chamfering the inside and outside edge with some practice.
Also, if there is TT earthing, you must use plastic anyway.
Personally I would, as if you are using power tools, you don't want the lights going out at the precise moment you cut through the power cord.
You don't need 100mA protecting the lot, as you have an exported earth.
However, I would be wary of relying on a supply cable armour earth and consider using an earth spike and TT earthing anyway. It is difficult to use the armour earthing reliably, as the armour steel rusts. Personally, I would use TT earthing, or use 3 core SWA cable to the house and export the earth down a copper conductor.
At the moment it is in the side, so I guess i will have to keep it there really, or I will have to block the exisitng 20mm knockout with somthing!
Thought as much...
It is only a small wooden building, mainly for PC type and electronics stuff, no room for any big stuff...yet...
The workshop is fed from the house, from a 32A MCB in my non-RCD consumer unit It starts off as 6mm T&E for about 15m this terminates in a IP65 plastic box on the side of the house (Fed from behind) From there, I have about 7m of 6mm SWA (three core) to a metal box in the workshop. Form here, there is about .5m of 6mm T&E to the CU. Also from this metal box, another length of SWA (about 35m) goes up to the garage.
The garage is up the top of the garden, approxamatly 35M of the same 6mm SWA. This terminates in a 5 way CU
At the moment this is also all on the house earth, but I expect it should be a TT here. It was origanally a 2.5mm T&E overhead cable from the house to an older shed, then 2.5mm T&E from there, buiried in a mixture of clay drain pipe and hose pipe! I have gradually been upgrading it as and when I can.
You can get blanking plugs for that purpose (although in this case you probably don't need to).
That's about 0.18 ohm contribution to Zs (R1 + R2 from OSG Table 9A, corrected for (say) 50 deg. conductor temperature).
So 7.5 m to the workshop board: that's another 0.05 ohm [1], so the max Zs seen at the input to that board is about 1.03 ohm (0.8 max Ze at origin + 0.18 + 0.05). Provided the house MCB is a Type B, that should be OK for protection of the submain cables to that point. Your largest circuit in the 'shop is 20 A and if that were a Type C, Zs max would be
1.2 ohm, leaving you only 0.17 ohm for the R1 + R2 of the 'shop wiring. That would only allow you about 10 m circuit length, using 2.5/2.5 mm^2 wires before needing to resort to RCD protection on grounds of Zs. (No such restrictions with a 20 A Type B, where Zs max is 2.4 ohm.)
Just to be clear, this is in parallel with the feed to the workshop, the metal box being a T-junction?
Which adds another 0.24 ohm, so the worst-case Zs at the incoming side of the garage board is getting on for 1.3 ohm. Again OK provided the house MCB is a Type B, but this is pretty marginal design - 10 mm^2 would have been better for the SWA sections.
[1] You said the SWA was 3-core, so I've assumed the CPC is 6 mm^2 and ignored the effect of the parallel armour wire.
All the MCB's in the workshop are type B, I dont have any big motors in there. The biggist thing is a 2HP compressor.
Yes, this is correct, the workshop Tees into the SWA on its route to the top of the garden. so the only protection devices downstream of the CU in the garage are the
32A MCB in the house and then the company fuse.
All my MCB's are type B, I dont have any others.
I was going to go for 10mm origanally, but the bloke wo was doing some of our hard lanscaping decided to chage the order of things he was doing, wich ment I had to go and get the SWA with a few hours notice, unfoutunatly I couln't get and 10mm that day :-( In the end, it has been layed so removal is possible without too much destruction, but as there is very little demand in the garage, it will probably stay as is until somthing major happens in the garage (maybe never!)
The short run of SWA from the house to the workshop is under the patio, so replacement of this isn't going to happen any time soon!
Would changing the 20A MCB in the garage for a 16A one make it better, there are only two double socets up there after all? The sockets are only used for the odd battery charge and maybe the pressure washer very very occasionally (Normally that is used on the drive, as the ouside tap is on the house, 30 odd meters from the garage) I can also run a seperate earth from the CU to the IP65 box, if that would improve things (I am sure I ran two seperate 10mm earth's to the kitchen, one for the gas, and one for the water, so I could utilise one of these and just use one cable for both water and gas (can't I?)?
That's correct, the armour is connected to the house earth at it's start point, but not connected to anythiung at the far end, and not used as an earth for any thing other than the cable protection.
On Mon, 19 Jun 2006 18:32:54 +0100, Sparks wrote (in article ):
Along these lines, I used three-compartment trunking run around three walls of the workshop. This will take 13A outlets and other wiring accessories with the normal single and double faceplate sizes in the centre section. These can be moved around and supplemented very easily.
I have conduit drops connected to it in a number of places where I have EN60309 16 and 32A outlets for woodworking machinery, dust extractor, compressor etc.. Each has an isolator associated with it and a radial circuit to the CU.
In a few places where a lot of conductors were required (e.g. lighting system) 20mm conduit was not enough and 25mm was used instead.
I welded all mine. If you do do this, then it is a good idea to leave the tube alone for several hours for the solvent to completely evaporate before feeding (PVC) wires through.
No, they're your main equipotential bonding conductors and if you 'borrow' one you'll have to joint the other between gas and water, and AIUI joints aren't allowed in main equi bonding condrs.
You only need to isolate the armour at the distant end if you're separating the house earth (typically PME) from the shed earth (typically TT). If you're exporting the earth you can connect the armour at both ends.
That wouldn't be a problem, as the gas one goes right past the strap around the water pipe anyway! Origanally the gas was going to go a different route, but it ended up next to the rising main.
I have a funny feeling there is a third spare 10mm earth in the kitchen loft too!
The reason I only connected one end was because I was planning on making the garage a TT system, but it looks like it doesn't need to be going by what Andy Wade has said :-)
And if there are long runs of conduit, to leave sliding expansion joints in places or it all goes wavy in the summertime (mine does, but it wasn't me that installed it)
No need for that - the critical point was the protection of the submain cabling in the event of an earth fault on the cable close to the garage end. This requires the house MCB to trip promptly and now that we know that that is Type B you should be OK. After the garage board you've got smaller MCBs and an RCD, so it's fine in there.
Oh - you ought to connect the armour at both ends (and at the T-junction in the middle) as that will help lower the Zs values. Only isolate it, and the earthed 3rd core, where you go into a TT part of the installation (if any).
Hmm, nothing in BS 7671 itself says that joints aren't allowed. If looping-in (daisy chaining) it's good practice, mentioned in the OSG, not to break the conductor at intermediate points. This is so that earth clamps can be temporarily removed without disturbing the bonding to the other services.
Agreed - and indeed you _should_ connect [...] at both ends.
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