Electrics Upgrade Advice

Notwithstanding BAS's points (most of which are valid), I think that you proposal is conceptually reasonable, and certainly a good/adequate basis for your up-front discussions with the electrician who will be involved.

John, thanks for the general comment. Equally, while I accept the validity of BAS’s points, I have tried to explain the reasons for asking for ‘advice’ as suggested in the title of this thread from the outset. While somewhat tangential to this thread, the following quote from the article link is somewhat reflective of my situation:

http://www.govyou.co.uk/part-p-of-the-building-regulations-scrapped/
"However there are other issues as well from a non-qualified but intelligent sensible DIYer. My daughter has a 50′s house with botched electrics from previous owners. We have had qualified electricians look at it and they say they can’t put right or improve obvious faults and can only rewire the whole house. My daughter is very poor and can’t afford the astronomical quotes and required disruption. The result is I repair the dangerous elements (e.g wires that were joined with insulation tape etc) probably to part P standard but certainly to a much safer level. As far as I’m concerned my first priority is to make it safe, regulations or not."


Your electrician will undoubtedly have views on details of your proposal. In particular, (s)he may well feel that all your proposed cable sizes represent 'overkill' - not just the 6mm² cable for hob and oven circuits that we've already discussed, but also the 6mm² for sockets circuit and 1.5mm² for the lighting circuit.

I did take onboard your previous advice about cable size. I also read up a little on ring versus radial circuits and compared the price of 6mm versus 4mm cable. Overall, I thought a radial design might be more sensible in this case, requiring the larger cable size indicated, and the cost difference between 4-6mm appears to only be a few £’s. However, there may be good reasons not to 'overkill' on the cable sizes.

(S)he will probably also have views on the optimum ways to distribute the circuits between the two RCDs in the new CU.

Based on early advice on this matter, I tried to balance the loading between the 2 RCD’s as being suggested by the attached diagram. Again, this is only a proposal for discussion not a statement of intent.

BAS's suggestion that enough spare cable be utilised so that the definitive connections to the new CU can be made without the need for joins in JBs is a good one.

Agreed. Truly I am listening to this advice and it is much appreciated.
 
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John, thanks for the general comment. Equally, while I accept the validity of BAS’s points, I have tried to explain the reasons for asking for ‘advice’ as suggested in the title of this thread from the outset. While somewhat tangential to this thread, the following quote from the article link is somewhat reflective of my situation:
I don't disagree with any of what that says, but just wanted to 'keep out' of BAS's exchanges with you!
I did take onboard your previous advice about cable size. I also read up a little on ring versus radial circuits and compared the price of 6mm versus 4mm cable. Overall, I thought a radial design might be more sensible in this case, requiring the larger cable size indicated, and the cost difference between 4-6mm appears to only be a few £’s. However, there may be good reasons not to 'overkill' on the cable sizes.
There's nothing wrong with radials - many people actually favour them over rings. It obviously depends upon 'installation method', but 4mm² will often/usually be plenty adequate for 32A sockets circuits. As you say, the cost differentials are not large, but one practical issue is that playing with two 6mm² cables in a back box is not necessarily the easiest of tasks. Probably the main argument, particularly given the considerable 'margins of safety' which are undoubtedly built into the 'maximum current' figures we work with, is that there will generally be no advantage at all in using an unnecessarily large cable on a sockets circuit. Similarly 1.0mm² cable is more than adequate for a modest lighting circuit such as you have.
Based on early advice on this matter, I tried to balance the loading between the 2 RCD’s as being suggested by the attached diagram. Again, this is only a proposal for discussion not a statement of intent.
That looks very reasonable, and a good basis for discussion with your electrician. As you probably understand, it'snot just a question of 'balancing loads' (current-wise) between the two RCDs, but also to minimise the inconvenience/risks if one RCD trips and takes out half of the circuits.

Kind Regards, John
 
There's nothing wrong with radials - many people actually favour them over rings. It obviously depends upon 'installation method', but 4mm² will often/usually be plenty adequate for 32A sockets circuits. As you say, the cost differentials are not large, but one practical issue is that playing with two 6mm² cables in a back box is not necessarily the easiest of tasks. Probably the main argument, particularly given the considerable 'margins of safety' which are undoubtedly built into the 'maximum current' figures we work with, is that there will generally be no advantage at all in using an unnecessarily large cable on a sockets circuit. Similarly 1.0mm² cable is more than adequate for a modest lighting circuit such as you have.

John, I certainly agree with you on the 1mm cable for the lighting circuit being proposed, but I was simply over-spec’ing everything to be on the cautious side, as cost did not seem to be a big issue. However, I have been slightly confused by the various sources discussing the current rating of different cables sizes, especially 4mm and 6mm. For example, the DIYnot site seems to suggest that 4mm is only good for 25A, while the MCB on this circuit would be 32A. Possibly this single figure is just for method A, see 2nd link for details. So, if I assume that all cables are installed as either methods B or C, would 4mm cover the current rating of the 32A MCB and be adequate for certification, which is the main concern at the end of the day. Sorry to belabor this point as I know you have advised on this issue several times.

//www.diynot.com/pages/el/el004.php
http://www.lightwiring.co.uk/lighti...-cables/twin-and-earth-cable-current-ratings/

That looks very reasonable, and a good basis for discussion with your electrician. As you probably understand, it's not just a question of 'balancing loads' (current-wise) between the two RCDs, but also to minimise the inconvenience/risks if one RCD trips and takes out half of the circuits.

Thanks, I tried to take these issues into account, but will discuss this proposal with the electrician on the basis that it is half-way sensible.
 
John, I certainly agree with you on the 1mm cable for the lighting circuit being proposed, but I was simply over-spec’ing everything to be on the cautious side, as cost did not seem to be a big issue. However, I have been slightly confused by the various sources discussing the current rating of different cables sizes, especially 4mm and 6mm. For example, the DIYnot site seems to suggest that 4mm is only good for 25A, while the MCB on this circuit would be 32A. Possibly this single figure is just for method A, see 2nd link for details. So, if I assume that all cables are installed as either methods B or C, would 4mm cover the current rating of the 32A MCB and be adequate for certification, which is the main concern at the end of the day. Sorry to belabor this point as I know you have advised on this issue several times.
You seem to be pretty well informed. Yes, the comments made have all assumed that we are talking about Method C (or E - 'in free air'), which is by far the most common. As you imply, if it were Method A or B (or any other method other than C or E), 4mm² cable on a 32A MCB would not be acceptable. However, I don't think that I have personally ever come across a 6mm² domestic sockets circuit, although I don't doubt that some probably exist.
Thanks, I tried to take these issues into account, but will discuss this proposal with the electrician on the basis that it is half-way sensible.
What you proposed (as regards distribution of circuits between the two RCDs) looked pretty sensible to me.

Kind Regards, John
 
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I won’t argue about the letter of the regulations, although I am not sure that the ‘real world’ works to such exacting requirements.
WRT to signing on the dotted line to say "I did xyz" it does.


However, presumably any electrician fitting a new CU to an existing house would not have ‘designed and constructed’ the original wiring, therefore only ‘inspects and tests’ the operation of the circuits when fitting the CU.
That is absolutely true, but the scope of the electrician's work, and therefore the scope of his EIC and his notification to Building Control would be the CU, and would not encompass all of the circuits you installed.


However, I am not sure that a professional electrician needs to channel out the walls for the cable?
No, but see above about people's experiences when they let other people do the wall-bashing. But in principle there is absolutely no reason why, if the electrician you use is happy that he has exercised enough direction and supervision over your chasing and chopping out to be able to take official responsibility for it, that you should not do that. Ditto first fix.


Again, not true. I have not decided anything, I am simply trying to understand the issues.


Surely, it is to the benefit of all parties that these issues can be understood by the customer rather than being totally reliant on the electrician, who I assume are not all born equal in terms of qualifications or experience.
Indeed they are not, and it was over 4 years ago that I first wrote this:

As ever, personal recommendation is always the best way to find a reputable tradesman, but if you're having to go ahead without much in the way of references or personal recommendation, don't put any store by registration itself - sadly it is possible to become registered with woefully inadequate qualifications and zero practical experience. You don't have to spend long here to see people cropping up who are registered and "qualified", but who are clearly seriously incompetent in reality and who should not be charging for their services.

It's your money and you have every right to ask prospective tradesmen what their qualifications are. Just being listed here is not a good enough guide. No genuinely experienced electrician, with the "full set" of C&G qualifications will mind you asking - in fact he will wish that everyone was like you.

I feel sorry for people who have been misled by training organisations and (shamefully) the Competent Person scheme organisers into thinking that a 5-day training course, a couple of trivial examples of their work and some basic understanding of how to use test equipment will make them an electrician, but not sorry enough to agree with them trying to sell their services to Joe Public.



Yeah - well - I'm afraid that as soon as I see someone referring to a "stealth tax" and claiming that a legal requirement to make reasonable provision in the design and installation of electrical installations in order to protect persons operating, maintaining or altering the installations from fire or injury is actually "a licence for unqualified inexperienced incompetent people to carry out and legally certify unsafe work" I can't help ignoring them.
 
John, I certainly agree with you on the 1mm cable for the lighting circuit being proposed,
You should; he is correct.

but I was simply over-spec’ing everything to be on the cautious side,
The regulations are already on the cautious side.
Using 50% larger than necessary for everything is wasteful.

as cost did not seem to be a big issue.
The cost is irrelevant.

However, I have been slightly confused by the various sources discussing the current rating of different cables sizes,
Hardly surprising.

The first link is, unless I have missed something, nonsense. Where did 1.25mm² T+E come from?
The second is correct.
//www.diynot.com/pages/el/el004.php
http://www.lightwiring.co.uk/lighti...-cables/twin-and-earth-cable-current-ratings/


As for your general enquiry, if you want to do it yourself (you seem as if you would be capable) then you will have to discover everything which is a bit more than DIY.
It would involve someone telling you every step and every option available.
 
The first link is, unless I have missed something, nonsense.
It's partially incorrect.

And given the photo, wholly misleading.


Where did 1.25mm² T+E come from?
Nowhere - that photo should not be there. 1.25mm² is a standard flex size, and the ratings in that table start out being the ones for 60°C thermoplastic cable, but then gradually drift off.

 
I would suggest that you get an electrician in and go through the job with him, tell him what you want and let HIM tell YOU what cabling etc you need, instead of guessing and asking random people on an internet forum who havent even seen the job

He can then set out the job for you and get to a point where you can take over if you must


It really worries me when 'apparent' electricians on this site are attempting to
Guide a DIYer through a job clearly out of his depth and the testing and inspection process to which he obviously has no real clue to what hes undertaking

Duty of care and all that
 

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