Pls help identifying T&E cable size.

[AL_n]

I have some old white-covered twin & earth mains cable with its pos & neg insulated in red & black.

The red & black wires are both 7-strand, and each individual strand is about 1mm thick. Where all 7 strands are tightly together, the total thickness of each pos or neg 7-strand cable is approx 3mm (not including the red/black insulation).

The earth wire is single-strand and approx 1.5mm thick.

The overall outside dimensions of the cable (the white outer covering) is:

13.5mm wide and 7.5mm thick.

Please tell me what this is in mm-squared terminilogy.

Many thanks indeeed...

Al

[charles]

It's probably 7/.044 which was rated at 36 A. 4.5mm is the metric equivalent.

[AL_n]

charles wrote in news: [e-mail]:

Many thanks for that. Now for the dumb question! What is the max wattage of electric shower I can use this for? Probably none, right?

Al

[charles]

do the maths - 8kW.

[Dave Plowman (News)]

I'd say probably 7/0.29. That was the old equivalent of 2.5mm ring cable. But 7/0.44" is also possible - you'd need to measure a strand more carefully. The 0.29" etc is the diameter IIRC.

[AL_n]

charles wrote in news: [e-mail]:

Thanks; that's encouraging. I'm not challenging your math, but the TLC cable calculator below says says I'd need 10mm cable for an 8kw shower. (same for a 7kw one). Perhaps they factor in some overkill to cover themselves and/or perhaps make more profit? The length of my cable run is

12metres.

Calculator I used is here:

TIA

Al

[Dave Plowman (News)]

You first need to make *absolutely* sure what the cable you have is. The

13.5mm overall width of the T&E says to me it's more likely 7/0.29. That was a lot wider than 2.5mm TW&E.

Measure a strand with a digital caliper.

[Bob Minchin]

Erm 0.029" I think you mean.

The problem is the OP said about 1mm and 0.029" is under 3/4mm

Accurate measurements and simple calculation is needed.

[Andrew Mawson]

The only 7/ 029 I've worked with was TRS which in that era invariably was black. O/P iirc is saying a white sheath.

Andrew

[Mike Clarke]

I've come across plenty of PVC 7/029 in the past, but only grey.

[charles]

I don't have any 7/029 clips left (I do have 1/029 though), but 2.5mm clips are only 10mm across. That's why I suspected 7/044. The stranmg diameter also seem to agree with .044

[charles]

No, there was PVC in Imperial sizes. I re-wired my house in in 1964 using PVC.

[charles]

12m is quite a long cable run for a shower, so yes, you might need a thicker cable.

[harry]

As the earth wire is single strand, it must be 7/029. Rated at 20 amps, equivalent to 2.5mm these days.

Commonly used for wiring sockets, usually a ring main

[John Rumm]

If you go from the overall size, and compare with the figures in the last column of the table here:

That suggests something around the 6mm^2 mark, or its imperial equal.

[John Rumm]

While 7/.029" could be treated as roughly equal to 2.5mm^2 these days (it actually a bit more), its inappropriate to describe it as "20 amps". The rating will depend on the installation method.

The 14th edition quotes a "clipped direct" rating of 25A, which seems rather conservative given that's less than the 27A quoted for 2.5mm^2 in the same circumstances these days.

[spuorgelgoog]

But the 14th Edition would assume rewireable fuse, but the current edition assumes MCB and has an optional derating for rewireable fuse?

Owain

[John Rumm]

Indeed, there is a de-rating factor 0.725 allocated for re-wireable fuses now. Hence my comment about 25A rating being conservative in a modern setting - the 2.9mm^2 that 7/.029 is approximately in modern money, would probably have a clipped direct rating of around 34A with MCB protection.

[AL_n]

John Rumm wrote in news: [e-mail]:

I measured another piece of this cable. I am relying on a tape-measure, not a micrometer; the OD appears to be to be possibly 7mm x 13.5mm, which is close to the '6.8 x 13.1' stated as the OD of 6mm^ cable. However, would the insulation thicknesses be the same in the 1970s/1980s as it is today?

Somewhere buried in my house, I have an imperial micrometer. If I can somehow manage to find it, I'll be able to measure the exact thicknesses of the copper wires.

6mm^ certainly does ring a mental bell. ISTR seeing a lot of it in the late 1980s. ISTR using it to run power to a Baby Belling (small) cooker back in the early 1990s..

Anyway, assuming it is 6mm^, and I use a circuit breaker at the end of my

12m run, I would like to use it to feed a 7.5kw shower.

I have some vague recollection of hearing someone say it was frowned-upon to connect two or three shorter lengths of this stuff together, when feeding a high-wattage appliance. It that a hard-and-fast rule, or is it okay to have a couple or more joints using those round, hard plastic 30A junction boxes?

Thanks to all for the help. Al

[Dave Plowman (News)]

I did, sorry.

I'd rather an accurate measurement than 'about'

And the overall diameter of the conductor was said to be about 3mm, which says 7/0.029 to me.

But I don't have any handy to check.

The only way is to measure a single stand *accurately*.