Case of the unknown circuit

[David Hearn]

A while back I asked people to aid me in working out what my electric circuits were. Well, I've now done some further investigation and things are a little more strange.

I have 6 circuits:

32A - electric shower 32A - downstairs ring including a FCU off to the garage and a single socket radial off the same MCB. 32A - upstairs ring (including a spur somewhere off it to feed a socket which the immersion heater comes off. 6A - downstairs lighting 16A - upstairs lighting and loft lighting 6A - unknown.

People had suggested that someone had wired up the wrong MCB to the upstairs lighting and the unknown 6A MCB thinking the 16A should be for the immersion heater. However, upon further investigation, I've found that the immersion heater socket is a spur from the upstairs ring. We don't actually use it, and the plug/socket is slightly scorched!

I've also found that the unknown 6A circuit goes somewhere upstairs via the cavity (in the same direction as the shower cable - straight up) - where it ends up, I've no idea. Also that 6A MCB is dead. I noticed that it would turn off very easily at almost the slightest touch when the others took a little more force. I checked with a multimeter and the MCB makes contact at about 2/3 on, but when fully on its disconnected. As a result, this circuit has never been on for the 6 months we've lived here and there's nothing electrical that we know of that isn't working - so we've no idea where it goes.

Any ideas what the unknown circuit is going, what it may be connected to? I can only assume that it was for something which isn't used any more - but you'd have expected them to have disconnected it at the CU! It does mean that I have a spare slot in my CU - which may be useful for something in the future.

Incidentally, both the upstairs lighting circuit (I think 2.5mm T&E) and the unknown circuit (possibly 1mm T&E) appears to be in grey T&E where the rest is in 100% white T&E. It may have had white on it at some point as it is clearly grey, but around the curved edges looks almost like white paint was on it as some is still there with an almost flaky appearance (the flat part is grey). For the lighting circuit, this is both at the CU end, and the loft end where the lighting comes off it. It looks the same sort of stuff as the white T&E and is marked with the Henley trade name (250V specced).

Thanks

D

[David W.E. Roberts]

Quick top posted guess :-)

The spare 6A breaker was for the upstairs lighting - looks the correct rating and cable. The 16A breaker was for the immersion - again the correct rating and cable.

The 6a breaker failed. Some North American horse rider with big hat and spurs decided that the easiest way to fix things was to connect (upstairs) the immersion feed to the lighting circuit, and connect the immersion heater to a 13A socket.

If you look hard upstairs you may find where this was done. If so, you might be able to undo it. i.e. replace the breaker with a new one, reconnect the lighting, reconnect the immersion to the 16A direct feed.

As I say, this is only a guess.

Cheers Dave R

[Christian McArdle]

TV booster? Disused lighting circuit?

Possibly maybe it had some lights on it once. When a persistent short meant it could no longer be used and the short could not be located, those lights were transferred to the other lighting circuit.

Christian.

P.S. Your immersion shouldn't be off the ring main, although you'll get away with it if you don't actually use it much. Unfortunately, as a back up it is the worst possible situation, as you'd probably need that ring main for fan heaters if your boiler goes t-u.

P.P.S. 16A is normally considered too much for a lighting circuit. Many fittings are required to be fused at 10A (or even 6A).

[David Hearn]

What I may do (if I can't find an obvious reason for the circuit needing to be there) is to move the lighting across to a new 6A MCB and whilst I'm at it, rejiggle the whole CU such that the 32A feeds are at the switch end (currently they're at the far end!).

We've been in the house for 6 months and we've never yet used the immersion heater (mainly because the socket it was plugged into had been pulled off the wall and there were two screws rattling around inside it!). Personally I can't see there being any need to use it unless there's a major problem (ie. boiler death) - but as you say, may well need to use the ring for heating...

Incidentally, how do people get cables up through a cavity once the house is used? I'm amazed that someone managed to get the shower cable from the CU to the loft via the cavity. Straight up is one thing (which this is) - but I can't imagine how someone would start to try doing it horizontally or diagonally. Annoyingly, the bathroom is directly above the CU. Not exactly easy to lift floorboards when there's a toilet and bath spanning them (plus its fitted on top of lino, so we can't take that up without cutting round everything... ;) I doubt I'll ever get to see what wiring goes under there.

When I added some sockets, I assumed that 2 2.5mm T&E cables coming up from above the boiler was the ring for upstairs. Certainly one went to a socket, and the other disappeared somewhere. I fitted all the sockets I wanted in the room, cut into the ring only to find it was 3 core + earth! Wasn't

2.5mm - but the 3rd core had made the 1mm look like the size of 2.5mm (heating control I guess). The other wire was the ring, and I can only assume, that the in and out of the ring don't actually come via the same point from downstairs. 50-50 chance of me picking the wrong wire. Had I picked the right wire, I'd be none the wiser. Typical though that I didn't have a 4 connector junction box around and it was only an hour or so off starting to go dark! I've now made a map of the wiring in that room and put it under the floorboards. Shame people didn't do that at time of installation!

Thanks

D

[Bob Mannix]

That would be my *very strong* suspicion also.