wiring garage in 20mm conduit - choosing singles?

Remember that this installation has to be signed off by a trained professional such as yourselves, so it doesn't benefit me in the slightest to do anything which does not meet regulations, because it will just need to be redone. That's why I ask questions here.

I'm happy to take any (helpful) advice, and appreciate the advice received so far.

I fully intend to take it on board and make sure the installation is absolutely right.

Someone asked the quesion, I answered no. I now need to find out about it.
 
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Asking questions here can be a useful part of a learning process, but they are not a substitute for proper structured studying. The key term there is "learning process" - you cannot learn all the things you need to know just by asking questions here. It isn't structured enough - it won't provide you with a way to progress where each step builds on what you learned before.

You can't carry out a job of this magnitude by asking whatever random questions happen to occur to you. You've already shown that you have some dodgy misconceptions - what if you get something wrong because you have no idea your knowledge is wrong? It's the classic "unknown unknowns problem - what if you miss something because you simply have no idea it even exists, and just don't realise you don't know it?
 
I'll ask again - why do you think that circuits you design and install are not subject to the same constraints as those designed by professionals?
Click to expand...

What makes you think I'm trying to do something "inferior" to a professional installation? I'm not. Of course this is subject to the same constraints, anything else would be insanity. If I was trying to do a substandard job, why would I have asked the question in the original post? For that matter, why even bother with conduit at all?

Why does this have to be a battle of words? I was just asking for some simple advice. It's not rocket science...

<edit - crossed this post with your last one. I do appreciate the links, thanks >

Anyway, back to the subject in question, about making sure my installation in the conduit (bought at B&Q DIY store) meets the correct regulations for a domestic garage.

How does the fact that I'm using a 2.5mm pair of singles for a lighting circuit (6A MCB), making the cable produce LESS heat (which I think it would) than a ring main circuit, at tthe same time as taking up MORE space in the conduit than a 1.5mm pair, affect the calculations for the number of cores I can run in the 20mm plastic conduit?

<edit - fingers crossed that is covered in one of the links you sent me - thanks again>

<edit - I'm not talking about heavy welding, just doing a car restoration with a fair bit of welding, but nothing seriously heavy duty>
 
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I had a look at http://www.tlc-direct.co.uk/Book/4.5.3.htm with interest.

Looks like this has more to do with mechanical "pullability" than heat generation (assuming we are staying below the 45% fill capacity).

Anyway...

2.5mm stranded has a factor of 43.
20mm conduit has a factor of 460 (up to 3m with no bends) - there will be pull points (sockets etc) approx every 1.5 to 2m, which I think means it has capacity for around ten singles of that size.

If I have a single corner in the length (up to 3m), then this reduces the number of cores to six - which is exactly what I need. I assume this means I can have up to ten wires going into a tee, no more than six of which can exit at 90 degrees, assuming this is the only change of direction between the two nearest pull points.

On a related note, all the tee's and bends I'm using are "inspection tee's" or "inspection bends" which have a removable cover plate. Can these be used as pull points? If so, do these count as bends at all?

Do I need to consider anything else regarding this installation?
 
This website will give you examples of the type of calculations that we (you) have to do in designing circuits that involve conduit.
http://www.tlc-direct.co.uk/Book/4.5.3.htm
There are numerous ways to resolve this issue and your electrician should discuss them with you.
The separate Garage Unit or small Consumer Unit is probably your best. Don't get hung up on ring final circuits when a couple of radial circuits would be better both in terms of conduit runs but also in terms of flexibility especially if the Garage Unit or small Consumer Unit is stocked with RCBO's
For example for your garage with a small consumer unit you could have three 20Amp radial final circuits (2.5mm2 T&E) and a 6amp radial lighting circuit (1mm2 T&E) run through four RCBO's. Proper design would eleminate all the conduit cable factor issues.
But we cannot design the circuits for you that needs to be done by your electrician who can see what the design issue criteria is.
 
Thanks Riveralt. I agree that the consumer unit being in the garage is probebly the best solution. It is already there, though it's MCB's on an RCD, rather than MCBO's

I was trying to keep the garage and attached utility area on a single ring as that is what was suggested (or perhaps more correctly "specified") by the electrician. There is certainly space in the CU for more circuits if I need them, as this CU does not just power the garage, but the whole 2-storey extension (again as advised by the electrician)

He said that I needed to use conduit or trunking in the garage as I wasn't allowed to bury the t&e in the walls, with this being a two-storey extension. I don't think he mentioned using singles rather than t&e, though I "discovered" the need for that yesterday when I tried pushing T&E through the conduit.

Thanks for the link - I had actually already found it - see previous post, but I appreciate your going our of your way to source the info for me.

Incidentally, would you regard an "inspection bend" as a pull point?
 
What colour would you make the switch wire of a 2-switch setup, when wiring singles in conduit? Yellow, red? Is there a regulation for that in the new colours?
 
GCarnegi said:
What colour would you make the switch wire of a 2-switch setup, when wiring singles in conduit? Yellow, red? Is there a regulation for that in the new colours?
Click to expand...
You should use the brown, black and grey plus sleeved earth for a 2way switch setup.
You should use brown sleeving on the black and grey where appropriate.
 
GCarnegi said:
I had a look at http://www.tlc-direct.co.uk/Book/4.5.3.htm with interest.

Looks like this has more to do with mechanical "pullability" than heat generation (assuming we are staying below the 45% fill capacity).
Click to expand...
Yup.

Appendix A in Guidance Note 3 is very informative.

But you do still have to consider grouping factors.


Can these be used as pull points? If so, do these count as bends at all?
Click to expand...
Yes and no.
 
Bedroom above garage. not allowed to bury cables in walls. all to be surface mounted.
 
Must be a peculiarly Scottish Building Regulation.

But I can't believe there's not a way to make it compliant - it must be because of fire compartment rules (?), but if there were no way to do it then Scottish offices, hotels, blocks of flats etc would have surface wiring everywhere.

And they don't.

Also, given the numpty quotient your electrician has displayed before, are you sure he knows what he's talking about?

See if you can PM baldelectrician - don't see him around much these days so he might not read this topic.
 
I think its because flush sockets create paths for smoke and maybe flame to penetrate into wall cavities and maybe garages are more susceptible to fire or fumes than living spaces.
 
GCarnegi said:
Wierd thing is they're 7-strand, not solid core, but I don't suppose that matters, does it?
Click to expand...
It matters a lot.

Solid core will be incredibly difficult to pull into the conduits.
That is why stripping bits of T&E is a bad idea - even for 1.5mm
 
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