I have a Merlin Gerin board, which I need to make some changes to, and am looking for advice on a couple of points:
1) The M-G range of single-width single-pole RCBOs ( eg RS 467-9723 ) seem to all be type C tripping characteristic. Is it acceptable to use type C devices in a domestic environment where type B would normally be used?
2) Remind me what circuits require RCD protection under 17th edition?
Is it *all* power rings? Or just ones where there's a liklihood of appliances being used outside? ISTR that lighting circuits in special locations do now. Does that apply even if all the lighting in the special location ( bathroom ) is 12v?
All of them, unless the circuit is wired in its entirety in such a way that nails can't be nailed into the cable (eg steel conduit or earthed concentric wiring)
Generally speaking yes. The usual implication of using a type C in place of a type B is that the maximum earth loop impedance of the circuit is reduced. However since these are RCBOs we are talking about this is a moot point in this case.
Yes
Given the notes below, there is a fair chance even SELV circuits will end up needing RCD protection for the mains section of their supply cable. However to answer your specific question, if you can arrange things such that the circuit powering the lights never enters the zone, then it could in theory be unprotected.
[1] In addition to the specific requirements for "additional protection" in special locations etc, there is also a general requirement for the protection for buried cables. This basically means if you can't see the cable (i.e. not surface wired) then it needs to be "protected" in some way. This can be by encapsulation in a suitably earthed shield (so cables like earthshield, MICC, SWA cable, or ordinary cable in metal conduit etc are ok), or by being buried >= 50mm from the surface, or by protection with a RCD with a trip of
Pedantic point, when does cable cease to be visible? If it is enclosed in surface run trunking or conduit I'd say it was still visible and didn't need additional protection. Is this how the 17th edition would view it?
I believe it would... surface wired, or in visible trunking / conduit ought to be fairly immune to being nailed / screwed through (well at least by accident anyway!)
How is cable dangling freely in an intenal cavity wall ( say 4x2 or fatter ) considered?
Thanks for your previous answer, it's much as I suspected.
The actual reason I posted was this:
We are having major building work done, with a couple of extensions ( up and out! ) This adds some new circuits. Without asking, the electrian ripped out my '16th edition' M-G CU, ( with many spare slots ) and replaced it with a '17th edition' 'Sector' brand whole-house RCD unit. We have a big house, with many appliances, including a *lot* of computer equipment. This is nuisance-tripping up to 5 times a day. I cannot determine any particular appliance or even circuit that is causing this. It may not be an actual fault as such, just a cumulation of normal leakages.
We have just come back from a week's skiing to find a de-frosted freezer and fridge. And my Humax PVR missed Wallace and Grommit. I'm not best pleased.
There may or may not be an earth fault. It might just be the cumulation of normal earth leakages. Either way, I can't live with the whole-house approach. RCBOs would limit the damage to one circuit, and help fault-finding if a fault is indeed present.
I have a meeting with the artichoke and builder shortly, and I'm going to insist on changing the configuration away from the cheapest-way-to-achieve-17th-edition-compliance-whole-house-RCD approach.
To smooth things over, I'm going to offer to supply a new fully-populated CU myself ( I have access to M-G stuff for less than 1/4 the list price of say £70 for an RCBO ), and just ask them to shove the 'Sector' whole-house CU where the sun doesn't shine.
If it was passing through holes in the studs at their centres then you could argue it is >= 50mm from the surface and hence not in need of further protection.
A whole house RCD is not compliant with the 17th edition. In a small house with relatively few circuits you could get away with two RCDs - one protecting say downstairs power and upstairs lighting, and the other doing the inverse. On a larger install I would expect to see more RCDs or RCBOs used on the non RCD side of a multi split board.
Is it too late to get the sparks back to do the job correctly?
Won't help the fridge, but iPlayer may still have W&G (if not, I have a copy on Toppy I could stick on DVD for you!)
Indeed - I can't see how he could have fitted a single RCD and proclaim it to be compliant. It does not meet the basic requirements for discrimination.
(don't you just love spell checkers ;-)
Yup - what you have is non compliant, and also completely unsuitable for your circumstances.
Not been a great fan of the MG stuff to be honest - ever since meeting some Proteous MCBs which had a mind of their own. I hope their own label stuff is better.
Either way, Hager and Contactum both have single module RCBOs available for under £25 these days.
Thanks - but it was in HD, and I've got most of it... Just waiting for BBC-HD to repeat it. Should be along in a day or two...
I've met the sparks, and I'm not convinced he's the sharpest knife in the block. I don't want to create a fuss, but I want to provide a way to get what I want without pissing him off, so...
TBH, compared to the cost of the overall project ( >= 150K ), this is peanuts. I just want it to be done right. I get the impression that all he's done in the past is council flats. This is why I'm in d-i-y. I would honestly prefer to d-i-y.
It's just what I have to hand cheaply. If you look at list prices ( eg RS : £70 +VAT for an MG RCBO ), with a
15-way CU you are up at a grand fairly quickly. I can do the same for a couple of hundred. And the sparks can shove the twenty quid 'sector' CU where the sun don't shine.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.