Non-copper wire in ring main?

Ewan MacIntyre wrote on Saturday (03/01/2004) :

I would suggest it is aluminium, which would be bigger due to greater losses and feel softer to bend. It was used in response to the high price of copper in the 1970's.

It did have problems with poor connections resulting in over heating, so it would be worth while replacing it with copper, along with the sockets. The only uses I have heard of for steel, was for telecoms where the steel was copper plated.

I hadn't considered aluminium - I'll check with a magnet next time I have access to it. A good excuse to go under the floor again...

Thanks

Ewan

During the Rhodesia crissis ( UDI etc 1965 onwards) aluminium was used in house wiring due to copper shortages - dreadful stuff - breaks easily at screw terminals. During the same period stainless steel was being used for plumbing.

OTOH are you sure that you haven't come across a bit of the old 7/029 used around then - seven strands of 29 thou copper that was usually tin plated - this was a pre-metrication standard.

Andrew Mawson

I have seen tin-plated copper wire in some older installations; that looks silver. Are you sure its steel ? Is it magnetic ? If its silver right through, its probably aluminium, and I personally would remove every last bit I could find.

Steve

Sure it's not the old 7/0.29 copper which was tin plated? Have you cut it to see if it's copper in the middle?

ISTR that was pretty standard in most house in the '15A round pin plug ' era...

It was also used for the best part of 20 years for ring mains, too.

I'd suggest _not_ cutting it.

Neither should really be left in situ long-term (if you're already at the floorboard lifting stage). Aluminium, in particular, has a habit of working fine for years and then creating problems when you start to touch it - particularly if you cut it and then try to re-join it (screw terminals through a decades-old oxide layer - lovely).

It's a fair bet that it's either 7/0.29 or aluminium, but I think a definitive identification can wait until it's heading for the scrap pile.

-- Smert' spamionam

Hello Ewan

If it bends easier than copper then it's aluminium.

Aluminium was a big test in electrical and telecomms industries a few decades ago. Not sure of the exact reasons why it's now not used, apart from a rapid degradation in salt-air conditions, but it's a common reason why adsl can't be installed and it's not used now.

Thanks for all the comments.

I've now investigated the layout of the ring, and it's likely that one or more of these cables will need replaced anyway, as I'm raising sockets to a proper height and so the cables are too short. I'll repost once I've cut a piece open.

Unfortunately, this same ring has my computer on it, and all our network gear. The longer the power is off, the louder the shouts are from upstairs that the broadband isn't working... ;-)

Ewan

Time for rigging a temporary supply, if you know what's good for your ears (and you will be able to keep us informed as to your progress - or lack off ! :~)

I meant at an end which was being worked on - the OP stated he was adding sockets. Sorry not to state the obvious. ;-)

Yes -- one of the design aims of the 30A ring circuit was easy conversion from a 15A radial system (by making the ring start and end at two existing 15A outlets, converted to 13A of course). Hence the two schemes used the same cable (and you were allowed to keep the two 15A fuses at each end of the ring early on too).

Personally, I've only ever seen solid cored aluminium T&E.

But it was also used on new builds which only ever had ring mains until the arrival of the current 2.5 TW&E - which was part of metrication.

The old common copper house wiring sizes were 1/0.44, 3/0.29 and 7/0.29 Wonder why those sizes?

Aluminium very quickly coats itself with a hard oxide layer which is an excellent insulator*. This can make getting a good contact area very difficult, and special techniques are required such as hard sharp contact serrations to break through the oxide and/or chemicals to remove and keep the oxide away until the contact is assembled. Add to this that if you do get a poor contact and it heats up, it rapidly gets worse, and aluminium burns (important component in fireworks), and it's a disaster waiting to happen.

Aluminium is used in the supply infrastructure, but in that case it is assembled by people who (in theory at least) know its dangers and use components specifically designed for use with it.

In telephony, the problem is mainly that of dissimilar metal corrosion, particularly in the presence of any moisture, and very much speeded up in salt-air, acids, or alkalis. BT stuff their streetside distribution points with desiccant bags in areas where aluminium wiring is used. I have one aluminium phone line, and in my experience, the connections in the streetside cabinet last around 5-6 years before they corrode through. You get about 2 weeks advance warning by seeing modem speed rapidly dropping off, before finally being completely cut off, but phoning BT and saying "my line's going to break in a week's time" just doesn't wash.

• A couple of years ago, I was breadboarding a circuit which used a couple of power MOSFETS directly switching mains. As a temporary measure, I used a bulldog clip to clamp a MOSFET to an aluminium heatsink. When I got to adding the second MOSFET into the circuit, I clamped that to the same heatsink. It was only after all the testing when I was disassembling the breadboard circuit in order to make up the real thing, that I suddenly realised that I'd had full mains voltage between the two mounting surfaces of the MOSFETS. The thin layor of aluminium oxide which inevitably forms on the heatsink was all that stopped it going bang!

I worked for a company that manufactured household wiring out of Aluminium, this could be that product, I think it was last manufactured in early 70's.

Rick

Yup. I done that, tho it was only 120v DC across it...