Aluminium Twin and earth?

andy1984 · 20 May 2009

Came across some twin and earth that ive not seen before guys and was after some advice on whether its ok.

Its a TNCS supply with the tails coming from the meter into an old 60A switchfuse. From the sswitchfuse runs a twin and earth cable for about 20 metres to the Cu on the other side of the house. An earth cable (earthing conductor) runs from the service head up to the switchfuse where it is choc-blocked to the cpc of the twin and earth.

Now, the cores of the twin and earth look to be about 16mm but could it be an imperial size?

I would say the cores look like aluminium but they may be tinned copper i suppose, did they ever do aluminium twin and earth?

The cpc in the cable i would say looks a bit smaller than the live conductors, maybe only 10mm.

Im just trying to establish the cable type so i can work out if the 60A fuse is giving the protection it needs.

Sorry no photo's, i know how everyone likes them!

Thanks.

RF Lighting · 20 May 2009

It will be tinned copper, and if it is, it will be an imperial sized cable.

AFAIK, the only aluminium cables in use it his country are SWA (and DNO cables)

It's almost impossible to size a cable without seeing it in the flesh.

You could measure one of the strands with a micrometer, find the CSA with πr², and multiply it by the number of strands.

Then you can apply your derating factors, fusing factors, and VD calcs to see if it complies.

Also you will need to check that the CPC is sufficient. It was undersized in many imperial cables.

Also, is there any signs of any green slime in / on / around any of the cable or switchgear?

JohnD · 20 May 2009

tinned copper stranded cables were in use up to about the late 1960s. I remember aluminium cable used to be popular in the states due to cost but I don't think it is popular any more.

if you count the strands, there are diagrams/tables telling you how many strands of what sizes in what imperial cables. If you can estimate the mm size that will give you a start.

count the earth strands too as it will be different and may be smaller than you would expect.

edited: bah. too slow

djaa · 20 May 2009

the answer to your question is yes and still do aluminium, its a cheaper answer to copper but can become very brittle. the recommended length for tails for the supplier fuse is 3m. & a 60amp fuse in todays modern consumer socitity is too low, the smallest aluminium cable available is 16mm, mainly used by electrical suppliers.
Hope this helps

securespark · 20 May 2009

Yes, there was a period when alu T&E was commonplace. When copper was scarce, they introduced it. But it was not a success. The csa had to be bigger, as alu is not as efficient a conductor, and it was fragile.

It could well be 16mm². Clipped direct, that has a CCC of 66A, 1 cable single phase.

RF Lighting · 20 May 2009

And don't forget, alu cables must not be terminated into brass terminals

andy1984 · 20 May 2009

Thanks RF

i thought it would be more likelly tinned copper- wasnt aware that this would suggest imperial though, although i did fear it.

I will try to measure it tomorrow with a mic or vernier. My main concern would be the adequacy of the cpc but i would also check out the vd and current carrying capacity.

Dont suppose anyone's got any charts showing data for such imperial cables have they or decent links?

Im thinking its probably 14th edition or something, well before my time anyhow!

Or if anyone had any idea what the imperial size was that looked like 16mm?

Thanks again.

RF Lighting · 20 May 2009

Our wiki knows everything

//www.diynot.com/wiki/electrics:other:14edtables

andy1984 · 20 May 2009

Thanks for the added info guys

Unfortunetly, whoever installed the new CU (ive been adding some light fittings and testing ring circuits after the rewire guy left the house 90% finished) has utilized this main old twin and earth rather than run in a new one.

I will try to size it better tomorrow when i get chance for another look.

andy1984 · 20 May 2009

aaahhhhh, the wiki............of course

i better hope its a 19/0.44 then hadnt i!

securespark · 20 May 2009

The weight of it is a giveaway. If you can get hold of a free end and lay it your palm (THE CABLE!!), you can assess the weight.

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Aluminium Twin and earth?

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