Yet another wiring question.

"Malc" wrote | We are thinking of restoring an old house and obviously I will be | doing the wiring myself and getting it inspected as there is no | way that I will be able to hide the fact that I'm doing it.

If you are worried about Part P then (a) as long as you start the job this year, you are outside the scope of Part P (b) if it's a major job (any structural work, new drains, etc) you will be getting Building Regs approval anyway, so just add the wiring on to the same application.

| I was thinking that as most of the floors are likely to be ripped | up I might run steel conduit around as is done in commercial | buildings and use individual wires for L, N and E as is | done in commercial buildings. Would this be ok? I presume I'd | have to use brown, blue and green/yellow wires.

You can do this but -

(a) All conduit must be installed and complete before drawing wiring in. This might not suit if you want to get some parts of the installation finished and powered, albeit temporarily, before others.

(b) It is actually quite difficult to draw in wires into a partially occupied conduit; the conduit must be sized sufficiently for the conductors, and the conductors may have to have derating for grouping factor applied. IOW, you have to plan which conductors will go in which pipe and show this on your plans and calculations. It doesn't lend itself to as-you-go system design.

You might look at plastic conduit and trunking systems. They're much nicer to work with IMHO.

Owain

There is more to conduit wiring than just laying a length of 'pipe' for the wires, you'll probably end up with many runs of conduit (this is why most commercial buildings now use trunking) as cable size, heat built up and radiuses etc. need to be considered when working out what can be contained within each conduit run.

Unless there is a *very* [1] good reason to use conduit or you really want to lay-out a load of conduit IMO you would be better off just using normal T&E etc.

On Fri, 03 Dec 2004 21:59:27 GMT, "Malc" strung together this:

Have you ever used steel coonduit before? It's not an easy option by any means, I've done quite a bit of it on commercial and industrial jobs and wouldn't dream of wiring my house with it. Is there a particular reason why you can't use T&E?

I'd say you've never worked with conduit? It's not easy, and *very* *very* expensive. You'll also need a proper floor standing bender which also doubles as a vice for threading it. Think several hundred pounds just for that and the tools.

Careful with that. If the 'old' house is listed you won't be able to tip the floors up anyway. And if it is in a conservation area they still try to encourage you not to do so.

You can, but its not necessary.

And its expensive.

Steel conduit is there to protect wires that would otherwise be exposed

- i.e. surface trunking.

Franly, its quicker and easier to lay T & E, and simply tie wrap it loosely into bundles and hook the wraps over nails in joists etc.

Or use plastic trunking if you must.

I would agree. No point using it generally.

I have often wondered about the benefit of running the T&E through conduit in the walls to allow replacement of embedded cables without replastering/redecoration. The fact the conduit is earthed (assuming it is installed to Regs) would be an added safety feature too. The way the regulations are going, I see the exception which allows cables to be buried in walls at less than 50mm depth (Installation zones) being removed eventually anyway, as people knocking in nails without checking for cables must be one of the major causes of injury in decent installations (relatively speaking).

Never actually done this though, as chasing out is bad enough as it is.

You can normally pull replacement cables through oval conduit, and although more difficult, often under capping too.

I've seen no figures to back up your conjecture.

Had a lot of fun trying it with steel capping once - no chance. Mind you, that was mounted on uneven stone walls.

Nor me, but I am sure we will see it when they want to change the rules (especially spun for the occasion of course)

However, I have heard of people getting electric shocks from hitting buried cables even before the Jenny Tonge's daughter case. I am not convinced that fatality could not have happened if the fitters had followed regs. Does the average householder think "oh I mustn't drill/nail in the installation zones?" If the number of punctured pipes I have heard about is anything to go by, most people don't think of such things as buried services when putting up a fixture.

So given:

it doesn't take a big lap of imagination to say:

Big cause of injury generally ? Absolutely not, but since when have the regulators been concerned about relative risks? (See Part P for details).

I don't think under currents regs that you are allowed to rely on the conduit for earthing, as opposed to having it earthed.

Dave

I thought you could use the conduit as the CPC. (543-01- etc.), but it may have changed since the 16th edition first came out. Personally, I'd use a separate conductor anyway. However, the point I was trying to make was that any length of metal conduit over 150mm has to be bonded to earth regardless of whether it is used as the CPC or not.

Agreed, much better practice.

Dave

I have worked with conduit which is why I suggested it. I must admit to never having bought any however as it's always been on commercial installations. I just liked the idea of being able to run single core wires easily around the place rather than T&E.

-- Malc

OK.... so how about plastic?

This is very easy to work with and flexible enough to run through joists if you wanted to do that. It must be at least 50mm from top and bottom, though.

With any kind of conduit or trunking, you do have to be careful about both the mechanical and electrical grouping. T&E is straightforward in the sense that there are standard sizes and those for specific circuit types, well known. There are also few main installation situations in a house, e.g. being attached to masonry and in free air but supported as in joist runs. If you are going to use trunking and conduit then you do need to do the sums and be careful not to stuff them too full or exceed the allowances. The IEE On Site Guide among other publications has tables and formulae for this.

That said it seems strange, IMO, that you would ask such a question then !....

You can but the Zs must be measured to ensure that your protection operates within the required time, ie lights 5secs & "most" sockets o.2 secs.. There is a technical expression used by electricians using the installation method that you propose, it is "Oh s*it its conduit" Bob

You also have to be careful where line and neutral ain't together as in T&E. I well remember a gridswitch with fuses for lights where all the lines were routed through one conduit and all the neutrals another. Got quite hot...

You've worked with it but still don't mind the vast amount of extra work to save pennies on cable? Fine.

On Sun, 05 Dec 2004 21:03:32 GMT, "Malc" strung together this:

You mean you put a length of PVC on a wall once. I think you'll find that using galv tube everywhere is 10x harder than T&E, and PVC isn't much better, (for domestic anyway).