I'm installing some wiring in our (covered) outside passage/outbuildings viz:- an extension to the downstairs ring, (not a spur), and additionally a spur from the downstairs lighting circuit. The wiring from the house passes through the wall of the house, and I then intend to connect Hi-Tuf cable for the wiring in the passage within an adaptable box or something similar. Obviously the phase and neutral conductors for the three t&e's must remain separate in order to be a conventional ring and a separate lighting circuit. My question is though, is it acceptable to join together all 3 CPC's within the adaptable box?
Yes, provided that the circuits in question originate from the same consumer unit or dis-board, and that the CPC for the ring remains in the form of a ring.
I'm installing some wiring in our (covered) outside passage/outbuildings viz:- an extension to the downstairs ring, (not a spur), and additionally a spur from the downstairs lighting circuit. The wiring from the house passes through the wall of the house, and I then intend to connect Hi-Tuf cable for the wiring in the passage within an adaptable box or something similar. Obviously the phase and neutral conductors for the three t&e's must remain separate in order to be a conventional ring and a separate lighting circuit. My question is though, is it acceptable to join together all 3 CPC's within the adaptable box?
Andy, but therin lies the crux of my question! - If I've joined all 3 cpc's, (2 halves of the ring and the lighting circuit) then the cpc for the ring is now not a simple ring in itself.
I think that's fine. I can't quite remember exactly what the regs say, but there are cases of ring circuits where the CPC clearly isn't a ring, such as when it's provided by conduit or the outer of mineral insulated cable. I think the important point is the CPC impedance at any point must be no worse than if it was a ring, or you are going to have to do calculations to ensure you are still withing allowable earth fault loop impedance for whatever your protective devices are. No amount of extra connections between CPC's can make it worse, actually quite the opposite.
you should try and keep the cpcs separate if you intend to extend the ring main so that at no point do you end up with a figure of 8 arrangement otherwise when it is tested at the consumer unit it would appear to be continuous even if you had lost the cpc continuity in the passage way leading to the possibility that one leg could have to take the full current in the event of a fault. not really sure what the benefit of joining them together would be. I can see the hazards.
On 16 Jul 2004 12:21:16 GMT, snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) strung together this:
Although, I personally would seperate them as I have had occasions where I have done something that is within the regs but extremely uncommon and then spent more time and effort trying to convince people that it's correct than it would've taken me to do it the common method in the first place.
It has to be in the form of a ring with both ends connected to the earth bar in the CU. This does not forbid cross-connection with the CPC of another circuit - see reg. 543-02-09 (and see below re. supplementary bonding in bathrooms).
[Andrew Gabriel]
Agreed.
[Lurch]
Although I agree with the general drift of that (don't adopt unusual circuit arrangements in domestic installations) I don't agree that it applies here.
Cross-connection between the CPCs of different circuits can be expected to occur in some situations - e.g. between 'upstairs' and 'downstairs' lighting circuits where they meet at one or more 2-gang 2-way switches (one switch on each circuit) for hall and landing. Another case where cross-connection is actually _required_ by the regs is in a bathroom (within the zones) where you have some combination of shower, fused conn. unit on ring (for heater or towel rail etc.), and luminaire and/or shaver outlet. Here the CPCs of the relevant circuits must be cross connected by supplementary bonding. Since the 2001 edition of BS 7671 came into force this bonding is required whether or not the equipment connected to the said circuits has any exposed-conductive-parts - in fact the bonding is still required if all the items are Class 2.
On Sat, 17 Jul 2004 11:03:26 +0100, "Andy Wade" strung together this:
That's exactly what I mean, it would have taken 2 minutes to complete the job in the conventional method. A day and a half after the OP everyone's still trying to convince each other why the uncommon method is accepetable. I wasn't disagreeing with you, but you've proved my point, ta.
Also linking them probably increases the chance of confusing whoever next works on the installation - at least if they are doing it as DIY. Presumably a professional would take the time to figure out what was going on, not just make assumptions.
Depending on how obvious the layout is I can see some poor DIYer in a few years adding a spur socket that uses the ring live and lighting neutral.
Actually I am not keen on the whole idea of bringing two separate circuits into one box - this means two circuits need to be isolated before working in the box and what are the chances of every future DIY-novice understanding this! (Yes I know it happens in ever hall light switch...)
Quite the opposite I would have thought. A 'professional' simply doesn't have the time to waste figuring it out, if he's making his living time is, very literally, money. A D-I-Y'er on the other hand may well set about working out how something is wired almost for the sake of the intellectual exercise.
Thinking a little further through this I think I might be agreeing with Andy Wade as cross connects of CPC's in a domestic situation are fairly common as he describes. What I was intending to do was use a steel adaptable box for the task in my original post. Obviously this would need earthing, and if I just used one of the CPC's to earth the box, then at some point in the future someone could disconnect the lighting circuit, (for example), at the CU and hence leave the steel adaptable box unearthed. - Any more thoughts on THIS situation anyone ?
Sure, but do you think there may be anyone out there that ignores this rule? Just because you disapprove of their sloppyness doesn't mean you should disregard their safety!
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