Scottish Regulations (Upgrading single spur to ring main)


Postby Harvie » Fri Oct 03, 2008 7:53 pm

Hi there,

Having read the ring main page, I have a couple of queries.

Firstly, I note from the references to "Part P" that I may invalidate my house insurance by doing electrical work, but is that only in England? I live in Scotland, and as I understand it I don't have to have it inspected by an electrician up here?

Secondly, is it ok for a ring main to use a lower-rated breaker than 32 amp? I just moved into a brand new house, and the garage has one double-socket fed on a single cable from a 16 amp breaker. If I put more sockets into the garage as a ring main, must I fit a 32 amp breaker (like the rings for the upstairs & downstairs sockets) or can I continue to use the 16-amp one? It's more for the convenience of location of the sockets that I want to add more, rather than the number of high-amp devices I want to run simultaneously... I know it'll work electrically, just not whether it would be "legal".

Oh, and If anyone's wondering about my DIY competence, I learned most of my electrical wiring knowledge from my late father who was an electrical engineer and who re-wired his own garage with my help, but who is sadly no longer around to confirm it's all safe.

Thanks for any advice,

Harvie
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Postby ericmark » Sat Oct 04, 2008 4:15 pm

First although there is no Part P in Scotland there is an equivalent regulation which I think is stricter than Part P. There is a big lump of land called “England” between us so I have never studied your regulations.

2) Yes you can still use a 16 amp breaker with either a ring or radial circuit the only limit is volt drop and earth loop impedance which will likely be OK.

Not sure on your skill of course but with your father’s back ground you may have meters most DIY people only dream of so if you need more information do include that.

As to “legal” the BS 7671:2008 is not a legal document although it controls most of what we do. Electricity at work act and in Wales Part P are legal documents can’t help with law in Scotland.
Eric
ericmark

Postby Harvie » Sat Oct 04, 2008 9:22 pm

Thanks Eric,

I don't really know too much about the voltage drop etc, more the integrity of the connections. Unfortunately when you're young you don't consider asking about the complicated stuff until it's too late. I didn't clarify in my first post, the garage is part of the house (under a bedroom) and the meter, consumer unit etc are all attached to a bit of chipboard the height of the room in the garage, so it wouldn't be more than around 25 metres.

Only other thing is that to run the returning leg of the ring to the back of the consumer unit (that's the modern term for the circuit-breaker / rcd equivalent of the old fusebox isn't it?), I'd probably have to unscrew the chipboard to get the wire behind it, and I read on another topic that that's not allowed? Also, is it ok to place the new wiring in trunking rather than behind the plasterboard? And anything dangerous to prevent me sharing a bit of trunking that's currently used for the light switch cable rather than running a second section below it? (OK to answer those for England to give me an idea of what situation might be. I'm going to ask the contractor who does electrical work for my employer to check it all before I make it live).

Cheers,

Harvie
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Postby ericmark » Sun Oct 05, 2008 12:58 pm

1) It is unlikely that volt drop or earth loop impedance would be a problem but I have given answers in the past to what seemed a simple question and then found the garage is 80 meters from house the problem with DIY is people over simply things and the poor DIY guy has no idea of the size of hole he’s digging for himself and I don’t think that’s fair!
2) The board the meters fixed to is officially not to be touched but this is not such a problem with modern house where a meter cupboard is used. And often one has to remove the board it is only way it is a case of viewing the options and making a decision based on what is there and again not really something I can comment on without being on site.
3) Yes when fuse boxes started to be replaced with enclosures for MCB’s then the word “Consumer Unit” seemed a good word that included both methods or circuit protection. In the same way when it was decided neutral should be considered as a “Live” wire calling the Phase wire “Live” became a problem but plugs have for years had a L marked on them for the Phase conductor so they decided on the word “Line” which started with a “L” so would fit in and I still forget from time to time and call a “Line” wire “Live”. All jargon and does not really matter as long as the other person kens!
4) Wires of the came voltage may share the same trunking it is only where we have items like TV coax where you can’t share same partition in trunking as mains.
5) Burying cables in walls does cause problems and electrical exposed cables are safer. I do mean cables not of course wires which are found inside cables. If you look at the standard twin and earth there is no reason this can’t be just clipped up a wall only in a garage etc where you may get mechanical damage do you need to use trunking as well. On the surface everyone can see where the cable is so no danger of knocking nails through it. But once you hide behind plaster board you have to keep to permitted zones and either use special cable or RCD protection.
6) The rules as far as what or how the electrical systems are wired are the same we both use BS 7671:2008 it is only the rules on notifying work that change.
The problem with all the regulations is they are not written just for houses and have to be a little vague to cover all types so there is quite a bit of interpretation required. We tend to over simplify and come out with statements like everything has now to be RCD protected which is not strictly true and with surface wiring and Ali-tube cable only everything in a bathroom and sockets under 20 amp need RCD protection. As a result you will see conflicting reports which take you back to 1) and it is always better to get advice from someone who has seen the job. Also on here the checkers are often slow and we know there is an answer but we can't read it.
Eric
ericmark

Postby Harvie » Wed Oct 08, 2008 9:41 pm

Hi Eric,

Thanks for the advice again.

I spoke to my electrician contact, who assured me that in Scotland I could just go ahead and wire it up, no questions asked, and that voltage drop in my situation wouldn't be an issue.

He also suggested regarding wiring into the consumer unit that as it's only going to have the 16-amp breaker fitted, I just make it a radial circuit, so I've done that with the first two sockets and it's now live.

Only thing I've now found out is that apparently they've changed the colours of installed cable to match those of flex (ie brown/blue instead of red/black) and my reel was red/black from the early 90's - presumably if it's been kept dry it'll still be electrically safe - it looked in very good condition. I do need more cable to wire in the other sockets so should I just replace the old-coloured stuff with new once I get it?

One curious thing - after isolating the breaker, when checking the circuit, my multi-meter (on 250V setting) still registered a very slight potential between line and neutral, and while passing the wires through the hole in the box, when earth and neutral touched it tripped the RCD (cue wife banging through garage wall as the TV had gone off) - should I be concerned (about the electrics, not my wife)?

Cheers,

Harvie
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Postby ericmark » Thu Oct 09, 2008 6:05 am

As to cable colours where they change we should put little stickers to show two colours are used. There is something in best practice guides about the mix see http://www.esc.org.uk/business-and-comm ... uides.html sorry can’t remember which one.
As to voltage and tripping I see you have already picked up on line and neutral not live and neutral because both are considered as live but MCB only switches the Line on a PME (TN-C-S) supply then neutral and earth are bonded together but on a TN-S and TT there is likely a difference between earth and neutral and as a result connecting earth to neutral will cause an imbalance between line and neutral and so trip the RCD you should have switched off at main switch to be safe.
Also if my wife banged on the wall rather than running around to see if I was OK I would be very concerned and she would need ear plugs!!

Cheers

Eric
ericmark

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