CU installation queries

[a]

Hopefully will get around to fitting the new CU this weekend, it is an MK 16 module unit (split load so only 12 usable ways) but will have a few spare ways for now (4 or 5 spare at installation time). It looks like I am supposed to cut the bus bars to the size of the number of MCBs installed, ie no spare copper prongs sticking up where there is no MCB. But when I come to add a new circuit in obviously the bus bars wont be big enough so I will have to buy a new one (I know they arent expensive but thats not the point :o). I have a few spare MCBs so I guess one option is to put the spare ones in but not wired to anything for now. What is usual practice here?

The current fusebox has all the circuit cables coming up from the floor, clipped to the wall along the side of the fusebox and entering on top. I guess this might be a bit neater inside, but is there any reason the cables cannot enter the new CU at the bottom (they will have to run up behind the MCB DIN rail)? There are cutouts marked along the bottom of the unit, but maybe these are just intended for the meter tails? Because the new CU is much wider than the existing wylex one, for the cables to enter the top I would really have to stand it off the wall rather than mounted flat on the wall.

Finally, the existing meter tails look like 16mm (look a fair bit smaller than the new 25mm tails I have bought) - there shouldnt be any problem connecting the 16 to the 25 with a henley block, and the electricity company can transfer the 25mm to the meter if they ever get around to it?

cheers

Dave.

[Alan]

Usual practice is to not cut the bus bar and use blanking plates in the empty MCB holes. This means that when you do add extra MCB's in the future it's a quick 'n' easy procedure.

Cables entering underneath the CU is fine.

Dunno, but I assume OK. Someone else will confirm soon no doubt.

Alan.

[usenet]

That's the normal thing to do I believe, just leave some unused MCBs in place.

Route it any way you like as long as no wires are pinched and you can do it reasonably neatly.

[Lurch]

On Fri, 27 Aug 2004 14:56:22 +0100, "a" strung together this:

Usual practice is leave the busbar long so the are spare ways to screw MCB's to as and when they're required.

Doesn't sound like it. If there are holes\knockouts on the bottom you can put whatever you want through them, (not water or gas though)!

That sounds just fine.

[Martin Angove]

The problem with this is that most blanking plugs are relatively easy to remove if you have strong nails or if there's a small lever lying around. If there are children around and the box is within easy reach you might like to think about the exposed, unprotected copper which is just a finger-length inside the CU when the blanking plugs are removed.

Personally I'd fit the MCBs now as they can't be removed without at least taking the lid off the CU. Even if they aren't the ones you will end up using (wrong rating for the future circuit perhaps) it's better (IMO) than a blank, and much less hassle than replacing the busbar.

Hwyl!

M.

[Dave Plowman (News)]

And if you leave a screwdriver lying around, that same child might remove a socket and poke their fingers onto the live wires behind?

Most CUs I've seen are well above the height a child can reach - otherwise you'd be asking for trouble anyway. Great laugh switching everything off...

I've just fitted a Crabtree one. If safety with the cover off is important, they're ideal. The line busbar isn't touchable with a finger - it's plastic covered and the MCBs mate via a spade connector. So as safe as is practical.

[Martin Angove]

Well, no. I mean, it takes a lot of fine motor skill and concentration to turn two socket screws maybe 20 or 30 times each before the faceplate comes off, and then the faceplate may well be stuck down with layers of paint or paper anyway. It takes about 2 seconds to stick a screwdriver (or a fingernail as I said) under the edge of a plastic blank plate and twist. Not only that but it is likely in a modern installation that the sockets circuit is RCD protected, whereas the live busbar in a CU may only have the 80 or 100A service fuse as protection.

To me this implies that the fusebox is likely to be within the reach of most toddlers, though I could well be wrong. At our last house (with a suspended ground floor so GF cables could run underneath) the CU was mounted next to the meter about 3ft from the floor in the understairs cupboard. My parents' house where all the wiring runs under the 1st floor due to concrete ground floor has the CU about 2ft off ground level under the stairs.

At the budget end of the market, Volex ones have a similar arrangement (i.e. a covered busbar) and the MCBs screw down to the busbar tongues. Very little live metalwork is exposed. The last Wylex unit I fitted had an uncovered busbar that clamped under the MCB screw and so was much closer to the cover of the CU than usual.

Hwyl!

M.

[a]

it is indeed about 2 feet off the ground next to the meter, although it is inside a small pantry which has a door on whose handle is quite high.

This MK unit does have a busbar cover which I think covers the main chunk of copper but obviously not the prongs - it would be easier if the busbars were plastic coated and you could just remove the plastic on the prongs you needed (but then that would cost extra and they wouldnt be able sell spare ones :o)

[Bob Eager]

We have MK Sentry units (fairly common) and the blanking plates can't be removed without uncrewing the CU cover and removing it.

[ARWadsworth]

I would say most CUs are only at knee height up here in Yorkshire. They are still out of a childs reach as you have to remove the vacuum cleaner, fake Xmas trees and suitcases from the cupboard where they are located to access them. The rest of the CUs are usually in a cellar, where you have to make your way (using a torch as the bulb in the cellar blew in 1999) through the old bumpers and front wings of MK2 Cavaliers/Escorts, broken TVs and redundant microwaves

So do you give Crabtree a thumbs up?

My favourite. All the nasty busbar prongs are gone. No need to kill the main switch to change or add an MCB.

Adam

[Dave Plowman (News)]

I bought it off Ebay rather cheaper than the normal trade price - it was an impulse buy, although I've been meaning to change the old CU for ages. But I've had to order the couple of extra MCBs I need - couldn't find an actual stockist handy.

Yes - I happily worked on it live, and I'm a scaredy puss normally. Not so happy with the old Wylex which had a very exposed busbar when you removed the individual covers.

I always used Crabtree once, but they don't seem to be in favour in this part of the world - no one stocks them anymore. Their 'Classic' range were the best looking accessories ever, IMHO.