Consumer unit wiring

When putting the wires under the floorboards are there any preferences with repect to how I should route it? Currently all the wiring appears to go into channels cut into the joists between the nails! I can now see how some people can put nails through such wiring. Anyway, to avoid me having to take up more floorboards than I may need to, what is the opinion of drilling a hole through a joist and running a wire through that? I realise that this will stop me from being able to move the wires around once all the boards are up (whereas in channels they can just be layed down - possibly done that way for ease of installation) - but realistically, when's that going to happen?

Thanks.

Chopping the top out of joists was a hideous practise that, rightly, is frowned on - drilling a hole is the accepted way to do it. The picture of your CU worries me tho' - the cable to all the fuses, apart from the shower, all look the same size... Are they? or is it just my boggly old eyes? HTH, Richard

This should be 2.5mm T&E.

However, looking at your picture, something appears to be wrong with cable sizings.

The first position does appear to have the thickest cable - which it should, but I can't easliy tell whether it is 4mm^2 or 6mm^2. The second position appears to have 2.5mm T&E.

However, I am concerned about everything to the right of there - it appears to use a small cable, possibly 1.5mm^2. Certainly this is not enough for a 32A ring circuit, or even a 16A circuit.

Generally, the immersion heater, if there is one is run from a 16A (blue) MCB. You wouldn't normally use 16A for a lighting circuit. I would expect the two white carriers to be the lights at 5A each. Could you re-check that.....

Exactly. Apart from being a bad idea for the joists, it is not allowed in the wiring regulations either. You should drill a hole through each joist at least 50mm down from the floor and 50mm up from the ceiling below to avoid the risk of nails reaching the cable.

That is what you should do.

.andy

To email, substitute .nospam with .gl

The 32 amp is running a whole house ring by the look of the picture. The 16 amp is for a water heater or something. (?)

The CU is wired the wrong way around !! all those red ways should be nearest the switch.

The shower feed looks like 4mm but should be 6mm for an 8kw and 10mm for 9kw - that means the shower cables should look like the tails that feed the WHOLE box.

I'd agree with this.

A spur for a double ganged socket outlet should be wired from a ring main in 4 mm (or bigger) cable or, alternatively, continue the ring through the new socket, IMHO.

Professionals? - comment please ?

Nick

The consumer unit should have 16mm double insulated tails from the meter, but yours has only got double insulated on the black phase and the red phase is open to being more easily damaged and exposing the bare conductor. They are all 16mm though, so are normal for this type of installation.

The fuse configuration I'd say is back to front, with the heaviest load appliance (shower) being taken from the furthest point from the supply side of the bus bar. This can cause lights to dim a bit more than they should when the shower is switched on and off, and can also cause heating along the full bus bar because all the heaviest use loads are furthest from the supply.

Working from the switch, the first white cartridge is lighting and looks to have a 1mm cable which is normal. The blue cartridge is for a heater of some sort (water) and looks to have a 2.5mm cable, this to is normal. The second white fuse is also lighting and looks to have 1mm, which again is normal and a good idea to separate lighting over two supplies in case one pops, you have the other as a sort of backup for safety.

The first red holder from the switch looks to be a ring circuit due the two red 2.5mm cables going to it, which is normal. The second red fuse seems to be a ring circuit as well, but also has a spur off to somewhere (?) because it has three red 2.5mm cables connected. The last red connection has a 6mm cable attached, by the look of it. For a load of around 7 or 8 killowatts over a short length of cable, then this guage would probably take it without complaining to much. But I would not chance going any higher in the Watts rating on this, no matter how short a run this cable is. I'd say it is safer to go with 10mm on a load over 8 kW and reduce the effect of any possible heating totally and completely, and also gives a less resistive path back to earth with the thicker conductor that is already supplied in it. But then I always err' on the side of caution with these things.

I'd also say the earthing conductor, which currently looks like a 16mm cable, is also quite normal for this type of installation, but I'd like to be able to see where it is connected at the other end.

All in all, it is a normal installation for this size of dwelling, but as I said in the first paragraph, I think it is back to front. Although others will probably disagree with this idea.

A 2 gang socket can be run as a spur from a ring using 2.5 T&E, but the OP is proposing to extend the ring not add spurs.

Adam

You could use 4mm but 2.5mm will do.

Erm - could you explain that a little simpler (I did do an Elec Eng degree though - honest!). Is it the tails that's a problem, or the design of the CU itself?

The lights do dim/brighten when the shower is turned on/off - so that might explain why its more noticable than I might have expected.

The blue 16A MCB most certainly does the upstairs lighting - someone (when I enquired about this before) wondered if someone had accidentally swapped the lighting and the immersion heater over (which is fed from a single socket in the airing cupboard). This is possible, and I will check this sometime by plugging a light into that socket and turning off the 6A MCB and see if it goes off (which is pretty much how I've worked out which circuit goes where). This socket though used to be attached to the wall at some point in history, now its lying on the bottom of the airing cupboard and rattles - so I've avoided using it because a.) I've no idea what's inside (ie. conductive or not conductive), b.) there's holes in the back of the socket which are accessible and c.) We get plenty of water from our central heating! It's on my job list of things to check out though!

Further (larger, less compressed) pictures of the CU can be found at:

This could either be a single socket, or maybe the feed to the garage (via a FCU at the end of the kitchen).

That's fine - the shower is working fine at the moment and we've got no plans to change it. It was more of a "I wonder..." type thought.

Its an old-ish install in a 1930's semi. We've got no plans to replace the CU (if we did replace it, I'd probably do it myself, but planning on doing nothing other than just a new CU and swap circuits over (no plans on rewiring etc - plenty of other jobs needed) - which probably isn't really worth it - except maybe like to put RCD's onto the rings + shower (I know about freezers being tripped!) ) I take it that it would just be a job of putting a 2nd set of tails from the meter output (there's a few spare holes to add some more tails) and wire it to a new CU. Then move a circuit across at a time. Of course, remove the incoming main fuse first though!

So - can I expect that the immersion circuit and the upstairs lighting circuits are the wrong way around? Should it be 2.5mm cable for the immersion heater, and 1mm (or more) for the lighting? If the blue MCB has

And I'll drill through the joists to add my ring extension, using 2.5mm.

Thanks for your (and everyone else's) help.

The blue 16 amp definitely has 2.5mm connected to it. It is clear that the cable connected to it a heavier guage than in the two white 6amp cartridges.