I'm trying to add some sockets to a bedroom upstairs, and I'm in the process of working out how best to break into the ring and extend it by a socket or two. (We have 1 double socket in each of the two larger bedrooms and a single socket in the small bedroom! What a waste of a 32A MCB)
Anyway, something I've been wanting to figure out for a while is what's on each circuit. A picture of my CU can be found at
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left to right I have:
32A - Shower
32A - Downstairs ring. This also runs the extension/conservatory light (plus probably 1 double socket), floodlight and garage (via FCU). I believe there may be a spur also (hence 3rd live wire) which is the wire running diagonally up to the right at the edge of the picture - I think this goes to a single socket into the old larder (currently running freezer + microwave).
32A - Upstairs ring
6A - Downstairs lights + landing light (two way switch)
16A - Upstairs lights
6A - unknown
What I'm after really is an idea of the size of wiring I need to use to extend the ring (I'm planning on just breaking into it at an existing socket, and then taking one wire to a new socket, and then joining the two sockets together to rejoin the ring).
Also - any ideas what size wiring I've got based on that picture? The 2nd
32A MCB seems to have a thicker wire going into it - which would be the spur. Unless of course, the spur is for the conservatory/extension which then has a FCU running to the garage.
Also, any idea of the size of the wiring for the shower circuit? Its an
8.5kW shower and it would be interesting to know if they installed a large enough wire to go to 9.5kW maybe in the future.
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?
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
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.
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.
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.
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.
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:
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The first red holder from the switch looks to be a ring circuit due the two
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.
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All in all, it is a normal installation for this size of dwelling, but as I
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
1mm wiring and the white one has 2.5mm then its probably wired wrong, if they've all got 1mm then I'm stuck. I guess its hard to see the difference in the pictures (hence putting up uncompressed pictures).
And I'll drill through the joists to add my ring extension, using 2.5mm.
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.
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