OK. It was probably well over 10 years ago when I last looked,
and my recollection was that 2kW seemed to be the max available
Funny you should say that. One weekend I ended up working in an
unheated office (warehouse sized open plan one). I was given a
fan heater. On the 2kW setting, I felt nothing, but on the 1kW
setting, it sent me a nice breeze of warm air. On further
investigation, I realised that at 2kW, the exhaust air was hotter
and didn't make it more than about 2 feet from the fan heater
before just going vertically up missing me, whereas at 1kW,
the air continued to move perhaps 4 feet horizontally before
changing direction, so it caught me.
I am not sure. The technology was sold to and continues to be used in south
The square pin is allegedly easier to make a decent high current self
wiping contact with than the old round pins, and I suspect what happened
was somethig like this.
(i) let's move to ring mains cos we need a LOT of sockets these days,
and we can't radial wire them all, and ringing them is a bit safer and
relaxes cable constraints.
(ii) let's go to a new and better type of plug.
(iii) now each appliance has its own plug, rather than one socket per
room (or floor?), how much do we realistically need to rate a single
point at...3KW sounds nice. Oh. Thats 13A then? Right. 13A it is...
(iv) Mmm. What will the cable stand. Ok, about 30A seems right for the
sort of cable that isn't TOO heavy. Lets standardise on 30A or 32A fuses
(v) what about lights? Oh sod it. do them on spurs cos they are always a
nightmare with cables flkying everywhere, and you seldomn need a lot of
current for em. say fused at 6A - that is 12 x100w bulbs,. Thats plenty
for a house.
(vi) What about all these other plugs and sockets? Oh sell em to someone
who wants em. Africans will do.
(viii) I need to set up sockets for msall lamps on lighting
circuits...oh well use teh 5A old style plugs if you must. At least
people won't be able to plug cookers into em. and they shold take 6A
before the MCB trips.
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.
On Sun, 04 Jan 2004 00:34:25 +0000 (GMT), Dave Plowman
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
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... ;-)
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.
Simon Avery, Dartmoor, UK
uk.d-i-y FAQ: http://www.diyfaq.org.uk /
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 shall be very surprised indeed if this is anything but tinned
copper PVC covered cable. I have seen a lot of this around, and in
general there's nothing wrong with it, exept that it does not conform
to current standards (being multi-stranded rather than single). If
the insulation is OK (not nibbled by rats etc) it should be perfectly
OK for some considerable time to come.
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