A few rewiring queries

Am currently doing a rewire and have a few questions please...
1. (the main question!). I'm proposing the following circuits - does this plan sound sensible? BTW total floor area is 70m2; CU is a Volex split-load item: http://tinyurl.com/7fe6m (Screwfix 82204). So:
Non-RCD protected: a) upstairs lights, 6A MCB, 1.5mm T&E cable b) downstairs lights, 6A MCB, 1.5mm T&E c) linked smoke alarms, 6A MCB, 1.5mm T&E d) downstairs ringmain feeding specifically the oven, fridge-freezer and gas combi boiler, 32A MCD, 2.5mm T&E cable
RCD protected: e) upstairs ringmain, 32A MCB, 2.5mm T&E f) downstairs ringmain - all sockets other than those in circuit (d) 32A MCB, 2.5mm T&E g) electric shower, 40A MCB, 10mm T&E
I expect circuit (d) to cause most comment?! I don't see the need for a dedicated cooker circuit because I'll be fitting a built-in single oven with 13A plug (plus gas hob), which could be plugged into an ordinary ringmain. OK?
2. I've got some spare 1.0mm red/black cable which I'd like to use up - would there be any issue with me mixing-and-matching 1.0mm and 1.5mm cable within one installation (I don't have enough 1.0mm do do the whole house)?
3. CU is under the stairs, which means that the route for all cables will be running under the stairs, in a straight line, at ~45deg, in the space created behind plasterboard attached to battens on the bottom of the stairs (clear?!.) Now, if the plasterboard were 'ceiling', that arrangement would unequivocably be perfectly OK; however if it were 'wall', it would definitely be unacceptable because the cables would be well within 50mm of the surface. What I'm unclear about is what does a 45-deg-mounted surface count as - ceiling or wall? I think it's ceiling, but I'd like reassurance that some future inspector isn't going to throw a wobbler at it! Not sure what to do if it's unacceptable as it is.
Thanks a lot David
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I'd certainly have a separate ring for the kitchen - and also look carefully at the load on that before running the oven from that. Because it's all too easy to exceed the loading. A washing machine can take 13 amps when heating. Also a dishwasher. Drier? A kettle perhaps 10 amps. Already, you're over the nominal 30 amps. Add in a toaster and say grill - let alone your oven, and it's easy to see a possible problem.

None. I'd use 1.5mm for the feeds and the spare 1.0mm for the switch drops. But for 6 amp circuits, 1.0mm is fine anyway.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Dave Plowman (News) wrote:

Thanks to you (and Christian) for this advice. I take your point, but do you not think that by pulling the oven out of the downstairs circuit, I've pretty well done the same thing? I mean, all the high-load items you describe above will be on the kitchen circuit, just that I'm calling it a 'downstairs' circuit(!) - in addition to the (dining) kitchen, it will only cover the living room and hall, and I can't see any high-load appliances being used there. Just TV/table lights/hifi/vacuum cleaner, that sort of thing (there will be a gas fire plus gas CH, so really see no likelihood of any electric heaters.) When I looked at having another kitchen circuit, it seemed like overkill having 3 downstairs ringmains for such a small house.
Or maybe I should incorporate the living-room and hall circuits into the upstairs ringmain, releasing the 'downstairs' ring just for the kitchen. What do you think?
Thanks David
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Lobster wrote:

You could consider splitting the rings front and back rather than upstairs/downstairs. That way the kitchen shares with the back bedrooms, the lounge with the front bedrooms. As well as giving you two circuits on every floor (so you still have power on every floor without having to run an extension lead up the stairs) it means that the kitchen is shared with rooms which are probably lightly used during the day.
If people are in the lounge (and you have eg temporary electric heaters plugged in) they're less likely to be in the bedrooms, but lounge and kitchen/oven use is likely to coincide.
Owain
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Sorry to come in so slow on this. I've been away for a week.
One of the main reasons for the area limits on socket circuits is the fact that they should be designed to provide emergency electric heating requirements. Fixed electric heating should have its own circuits, whilst socket circuits should be capable of running enough thermostatically controlled fan heaters to heat the area, in case the main heating system fails.
Christian.
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You haven't said what type of earthing your system is.

It's fine. Shower probably doesn't need to be RCD protected. Smoke alarm circuits are often 3A MCBs if they're available for your CU.

No problem mixing them providing all your cable is red and black. (Whilst an installation can be mixed, you can't mix old and new colours in the same job.)

I don't have the regs on me to confirm, but I don't think it makes any difference from the point of view of depth of burying.
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Andrew Gabriel

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Andrew Gabriel wrote:

Thanks for the replies.

At the risk of provoking a "what-the-hell-are-doing-rewiring-for-if-you-don't-know-this-for-chrissakes-get-a-pro-in"-type response, what significance does the earthing system have on the circuit design? In mine, it's provided by the armoured sheath of the main supply cable; have to say I don't know any more than that. Do I need to find out?
Thanks David
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"what-the-hell-are-doing-rewiring-for-if-you-don't-know-this-for-chrissakes-get-a-pro-in"-type

If the system was a TT system with your own earth rod, the use of RCD's would have to be different.
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Andrew Gabriel

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Lobster wrote:

Lots.
If you don't understand the difference between TT, TN-C, TN-C-S, etc then you really should not be doing the job.

If you intend to do the re-cabling yourself then your follow-up certificate which will be required may prove to be very expensive. If you've hot-wired the earthing within the installation wrong then it will need to be ripped out and started over. It will be cheaper and easier to do the wiring correctly the first time.
Andrew
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Andrew McKay wrote:

OK, I'm listening...
What do you mean, hot-wiring the earthing? Of course I'll be doing it properly, and getting it certified afterwards, which is why I posted my circuit design here first for feedback, which I'm pleased to have received. [It's my third full rewire, and my previous checks by a pro came up (1) with very small easily remedied errors and (2)100% OK. Previously I had run my wiring diagram past my pro first, who OK'ed it; I assume that because my earthing plans were OK there was no need for him to go into all the ins and outs of different earthing systems?]
Anyway - given the presence of an earthing block next to the CU, connected to the CU, a clamp on the armoured cable, and (now) the incoming gas/water pipes, what influence does this have on the wiring of the ring mains and lighting circuits? They will all be T&E cable, with CPCs wired in to the CU - how would this be affected by different earth systems? Under what circumstances would all the wiring need to be 'ripped out and started over'?
Thanks David
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Lobster wrote:

I regret that I can't give you details - this is a DIY group after all. I just know from having got my C&G2381 that earthing (and bonding) is a complex subject. Making assumptions is not a good idea.
Andrew
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Andrew McKay wrote:

That seems to be a bit of a "cop out" having made the first statement IMHO...
What has this being a DIY group got to do with it either?
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John.

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John Rumm wrote:

I'm sorry you feel that way. The fact is that if you followed advice given to you on this newsgroup and it resulted in casualty or fiscal loss then you might choose to pursue a claim against the person that offered the advice.
My advice was simply to suggest that you might not understand this well enough to continue. If you disagree with that then fine.

See above. We live in a litigious society these days, and messing around with electrics is an area where there could feasibly be legal challenges made against those who offer advice. Many people these days jump on passing bandwagons.
Andrew
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The thing is that as far as I can tell, Part P does not specifically exclude DIY work any more than Parts A through N (generally) exclude DIY work. What it *does* exclude is *unchecked* DIY work. In the same manner that you should involve Building Control before (for example) knocking down a supporting wall and inserting a lintel, Part P requires either a notice to BC and a full inspection of subsequent electrical work by a suitably qualified person who is willing to take on responsibility for the work, or the work to be done by a self certifying company/person. It doesn't require even this for some sorts of work ("non-notifiable"), though obviously a complete rewire doesn't come under this category.
Note that this is a lot less strict than the situation for working with gas or with pressurised hot water systems.
So one has to make a judgement here. Since DIY isn't outlawed, why should we stop giving advice in how to do it correctly? There are several highly knowledgeable electricians in this ng who give consistently accurate and well-reasoned answers, even if they don't always come up with exactly the same solutions as each other. Some are (I believe) even working under self certifying schemes and so *should* know the answers! I have learned immense amounts from them. The only reason to stop giving such advice would be if we could be certain that the person asking would carry out any given advice without following the new rules.
Perhaps an update to the electrical section of the FAQ is called for, and perhaps any posts containing electrical advice should post a direct link to that section before any advice.
Hwyl!
M.
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Nonsense. A DIYer can do any amount of work on a gas installation system as long as he doesn't charge for his work. He has to deem himself to be competent in the art to comply with the law. This is a common misconception propagated by the likes of Corgi which you have fallen for. The act is very clear and the relevant section has been posted to this newsgroup before.
Welcome to the Nanny state.
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[...]
Yes, I've heard that too. Perhaps it wasn't the best place to make the analogy. You're not the first person to state this in this ng and I dare say you won't be the last. There are, AIUI, differences however, particularly with regard to certain types of electrical work, and the rules about "competent persons" when it comes to companies undertaking such work.
Hwyl!
M.
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DIY
with
system as

misconception
very
Sorry I didn't mean to come on strong like that. As an experienced electrical engineer with a MIEE I feel really pissed of with the nanny state that the institution I belong to insist I get a cowboy into to do the work just because he has the C&G qualification.
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No offence taken :-)
Just had a leaflet through from NICEIC which is designed for people like you - people with decent qualifications who only do a few notifiable installations a year (up to 8 IIRC); it still requires registration, but is at about half the rate of full registration.
Hwyl!
M.
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Andrew McKay wrote:

Well personally, no I would not, but I am not into this whole "blame culture" thing. You do raise an interesting point however.
I would be surprised if anyone would be able to build a case against someone for offering free advice in a public forum such as this, but I suppose it is possible. It would be easy to argue that someone injuring themselves for blindly following bad advice, without at least making attempts to verify the validity of the advice first, would be equally or more culpable.
If the issue concerns you, I would have thought that it is easy enough to add a disclaimer to any information you post along the lines of "IANAE" or even just "IMHO", but then give a reasoned answer to the question since that would be of benefit to all.
My personal preference is always to try to reduce risk by education (where reasonable) rather that opting for the "there be dragons here, you had better get a man in" approach. After all, the purpose of this forum is to support a class if like minded individual who rejects the "you have better get a man in" philosophy as a starting point.
My experience of this group is that it is very rare for poor advice to go unchallenged anyway ;-)

I agree with the principle in some cases. However I feel that it does not require that much in the way of education to get someone basically competent to the point where any electrical work they do, will be at least as good or better than much of the installed electrical work most of us live with day to day (i.e. a good proportion of the housing stock has wiring that is not actually bad - but is not to current standards).
Sometimes you can tell from the post that there is a gulf in understanding between where someone is, and where they need to be in order to not be a danger to themselves. In this case the OP had already successfully completed several house rewires in the past, and was keen to learn, so I did not get the feeling that was the situation here.

OK, I accept that is your point of view, and don't have a problem with it. My comment was more questioning the value of saying "Yup, I know the answer to your question, but I don't want to tell you in case I make a mistake and you sue me".
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Cheers,

John.

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John Rumm wrote:

Can't disagree with that. But it has to be said that I don't actually know what I am talking about (oo-err missus!) with respect to earthing arrangements. I am not a qualified spark and nor do I pretend to be.
3 years ago before I did my C&G2381 I thought I knew it all. I had been installing/repairing domestic electrical systems for 30+ years. I didn't do the course on the basis that I expected it to train me as a spark (it isn't that sort of course), but one of the things it definitely did teach me was how little I knew about things like earthing, diversity, cable sizing, you name it. Big alarm bells started clanging for me about some of the things I was previously prepared to take on - none of it unsafe in my view, but such work had always been without due respect for the regs.
From that day forward I chose to restrict any further electrical work I undertook to simple and straightforward stuff. Even though there has been lots of work that I could feasibly have taken on, I won't do so because it trips over that perimeter where I admit to "I don't actually know what I'm up to once I get to this point".
So, when I see someone who is probably at about the stage which I was at prior to me attending C&G2381 I respond as you've seen. Visions of Robbie the Robot quoting "Danger, Will Robinson, Danger!" come to mind :)
Andrew
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