After getting some good advice about the current wiring in a house we are purchasing in another thread (thanks guys) I would welcome opinions on the following scheme.
Meter tails feed a 100A isolator switch (double pole DIN mounting in own enclosure).
100A isolator switch to 6 way double pole henley block (plenty of spare capactity) feeding:
(1). 12 way split load CU (80A RCD and 100A isolator) for the usual requirements and some spare.
(2). 2 way 40A RCD garage CU with 16A (sockets) and 6A (lights) MCBs
I thought like you when doing the exercise on paper, but simplified it in actuality and omitted the Henley. You can always add it later if really needed.
Settle for a 63A RCD and pick one of these up quickly if ££ is important to you.
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(2). 2 way 40A RCD garage CU with 16A (sockets) and 6A (lights) MCBs If the garage was integral then I'd just feed it from the main CU.
I wouldn't put the garage CU close to the main CU and meter, nor would I want a single RCD protecting both lights and sockets in the garage. Ass-U-ming it's a uk.d-i-y garage, i.e. place with power tools, bits of come-in-useful-one-day all over the place, the odd workbench, sockets for garden use on its outside, etc. etc., (no car in sight - when it's wet it'll make the *tools* rust, dammit!) it is both required by Regs and sensible to have the socket circuit(s) on an RCD, but neither required by Regs nor sensible for the lights to be. (When the power to your circular saw goes off 'cos someone else using the leccy lawn mower/hedge trimmer just cut through the cable or dropped it in the pond, you do NOT want to be plunged into darkness/semi-gloom as well, right?). Plus, it's just inconvenient to have to reset MCB and RCD trips in the main building.
So, smarter practice is to run a 20A or 30A feed to your garage from a non-RCD fuseway in the main CU. Put the garage CU in the garage; use either a small split-load CU there, with sockets on RCD side but lights non-RCD, or an RCBO for the sockets and a vanilla MCB for the lights. (Hell, if you want the lights on an RCD, go ahead, but use a *separate* RCBO for the lighting circuit).
Whether you use the house earth for the garage, or give it its own earth rod and take only L&N from the house, depends on how far away it is from the house, and whether you're on PME (TN-C-S) or not. Roughly, if the garage is integral to the house or just a passageway distant, exporting the house earth is the way to go. If a little further and not PME, still OK to export; if on PME and no serious structural metalwork in the garage, also OK to export; if structural metalwork, balance hassle of taking proper big-hairy-arsed equipotential bonding (unroken connector, 10mmsq minimum, no you can't get the impedance low enough using the sheath on SWA cable usually bugrit) from your main earthing terminal alongside the garage feed versus the hassle of sinking your own earth rod for and close to the garage; if substantial distance - e.g. 30 yards away at the bottom of the garden - do the garage-has-its-own-earth-rod thing. If you go the own-earth-rod (TT earthing) route, you then need a 100mA time-delay RCD as the main incomer on the garage CU (that's to give disconnection in the case of large-current-faults-to-earth quickly enough to avoid cable damage, even when your earth rod's resistance isn't low enough to make a 20A MCB or fuse blow fast enough), *plus* a 30mA RCD for the sockets (to provide better personal protection agin shock).
HTH, Stefek (summarising uk.d-i-y "earth my garage?" consensus, I hope!)
If not, will what I describe be acceptible and compliant with the regs? - (I've already bought it, if it's not ok then it was expensive and I can live with the loss - I only went to buy some wall-plugs but I got distracted.....)
"Chris" wrote | After getting some good advice about the current wiring in a house | we are purchasing in another thread (thanks guys) I would welcome | opinions on the following scheme. | Meter tails feed a 100A isolator switch (double pole DIN mounting in | own enclosure). | 100A isolator switch to 6 way double pole henley block (plenty of | spare capactity) feeding: | (1). 12 way split load CU (80A RCD and 100A isolator) for the usual | requirements and some spare.
Yes. Or a slightly bigger one.
| (2). 2 way 40A RCD garage CU with 16A (sockets) and 6A (lights) MCBs
RCBO for the sockets (but not the lights) rather than an RCD. You don't want the lights to trip off and still have a power tool spinning down.
Might be handier to have a switchfuse feeding a submain to the garage with the CU in the garage. Depends on whether the garage is attached or how distant.
Seeing as it's boxed it is actually better than the distribution company isolator, as theirs is a similar switch surface mounted on the meter board. It certainly does the job, and an isolator in the meter tails will make life oh-so-simple. But that still leaves you with the problem of how to connect it - break the seal and pull the suppliers main fuse is the consensus. Reason: you can't break the meter seal to get at that end of the tails, and when live they aren't much fun to wire up. No matter how steady your hand, I'm sure beads of perspiration will form on your brow.
Certain distros will fit an isolator for you, NEDL will for me.
I've talked with the distro and they are fine with me breaking the seal on the main fuse, they will even replace it for free as long as I obtain a certificate of conformity for the installation when i've finished.
The distribution board currently looks like this,
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I want rid of the two sets of tails leaving the meter, this will obviously mean breaking the lower meter seal. Will the distro company get upset about this?
I used Unibond bathroom and shower sealant from the local shed. Expensive at 8 quid a go but it's so bloody waterproof it's v.difficult to smooth it after application 'cos it sticks to
*everything*. Flexible too, the only thing that broke it in our case was for some reason the shower tray managed to drop a few mm (don't ask why, I dunno yet!) and the stuff stretched and broke the grout on the surrounding tiles resulting in much leakage.....
The moral to this tale is if yer tray doesn't drop this stuff is good! IMO obviously.
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