Unwanted Electrical Surprise in Airing Cupboard - Old Cable

[Simon Pawson]

Hi,

Over the weekend I replaced the broken central heating timer at my girlfriends. The next stage is to fix the zone valve in the airing cupboard and, whilst I'm there replace the wiring to the immersion heater as it isn't in the best of conditions and looked a bit old and the cable is tight across from the FCU to the cylinder. The FCU looks a bit old, with curved corners and the switch looks an old design.

I tested for live then isolated the socket circuit (single MCB for all sockets) and retested to make sure they were safe then removed the FCU cover. I was slightly surprised to find that the FCU wasn't off a spur from the power point in the bedroom behind the airing cupboard but was wired into a ring. What was more of a shock was that the earth wasn't the modern single copper but looked like multiple steel wires. The cable insulation hasn't broken down and wasn't brittle (in fact it looked like PVC). After an hour or so of moving furniture and making myself unpopular as whoever had fitted the power points had fillered them in so you had to break a seal round the edges to get into them I have found a power point that has that wiring and have now tested and sadly the suspect wiring is in a ring so I can't just isolate it and provide power from elsewhere. In fact the live/neutral were all

The house was built in 1968 and was supposed to have been rewired. The meter has company seals and documentation from 1990. The company fuse (which was in backwards) doesn't have any seals so presumably the rewire happened after then. The rest of the rewire looks reasonable - expensive MK Sentry non-split box - the only dubious bit being no separate earths to the metal boxes and some of the bend radii in the sockets.

Can anyone identify the cable? Could they have tested it for soundness and not replaced it as it will require a lot of redecoration if they couldn't have pulled it through.

Any ideas? Should I be worried?

Thanks,

Simon

[Christian McArdle]

When was that copper shortage again? IIRC, they used steel or aluminium for a bit back then, but is was never particularly satisfactory, along with the extra-thin-walled copper pipe from the same period.

Christian.

[Dave Plowman (News)]

I'd guess at 7/0.029 cable - the imperial predecessor to 2.5mm. The earth has three twisted conductors usually bright plated, but still copper. The line and neutral 7 of the same.

[Mike Harrison]

Are you sure it's not just tinned copper..? I've seen this in old wiring.

[Andrew Gabriel]

1968 will predate metric cable, and before then, the cable used for ring circuits and imersion heaters was standed, including the earth. So I suspect this is a bit of the original T&E which was not replaced in the rewire. Unless it's in bad condition, it won't need replacing now either; cable from the first PVC installations is still perfectly servicable providing nothing has damaged it. The thing to watch is that none of the strands break in the screw terminal -- this was all too easy to do. ISTR (vaguely) there were 3 strands forming the earth conductor.

The aluminium T&E I have seen is all single stranded. Multi-stranded sounds like it would make a nice firework, regardless if it was used in wiring or a real firework;-)

[Mike Clarke]

Sounds like the old 7/029 pre metric stuff. Providing that it's got PVC insulation and not rubber then it should be OK. I'd be very surprised if they used rubber insulation when the house was built in 1968. Was the cable black or grey. Grey is almost certainly PVC, black might be rubber but black PVC does exist.

[Mike Clarke]

Early '70s I think. I remember using some aluminium cable at the time. In fact I just threw out a short offcut from the junk box yesterday, it was a bit fatter than the copper equivalent and a bit more flexible. The conductors were copper clad so looked similar to the copper stuff until you looked at the cut end.

The

[Mike Clarke]

And when fitting several wires into one terminal there was also a tendency for the cowboys to snip off a few strands to make it a bit easier :-(

[Ric]

Indeed - you can get it from all good fetish shops!

[gribblechips]

Got some in my hand as I speak from a kitchen radial I re routed at the weekend. Grey PVC outer. Looks about 4mm2 Tinned copper conductors seven strand each including earth. Says it`s "to BS 2004" . So how old would that be? Any particular reason why they stopped using stranded earths even on quite heavy stuff like the 6mm2 I replaced it with? Just interested.

[Andrew Gabriel]

I thought it was because the strands tended to break. Basically, they made the strands thicker, which more often means you only need one of them;-) IIRC, 16mm² has a stranded earth, and can't remember if 10mm² does or not.

[Malc]

My immersion is exactly the same and is wired into the 13 amp socket ring main. Given the difficulty of rewiring it I have left it alone for now but I do think about what I turn on when I've got the immersion on.

-- Malc

[Andy Wade]

It certainly does (4 mm^2).