Twin+Earth Cable Size

imroberts · 1 Sep 2019

Having spent a while at my mums at the weekend tracing an electrical fault in the loft space I'm a little confused by the cable size in use.

The external size of the T+E looks to me like 4mm - it's certainly bigger than 2.5mm and certainly smaller than 6mm. However the live and neutral are both stranded which I believe is never the case with 4mm? The cable is printed on the outside with BS6004 and a brand name however the cable size doesn't seem to be indicated.

Is there any stranded 4mm out there or is this likely to be an old imperial size?

Risteard · 1 Sep 2019

imroberts said:
Having spent a while at my mums at the weekend tracing an electrical fault in the loft space I'm a little confused by the cable size in use.

The external size of the T+E looks to me like 4mm - it's certainly bigger than 2.5mm and certainly smaller than 6mm. However the live and neutral are both stranded which I believe is never the case with 4mm? The cable is printed on the outside with BS6004 and a brand name however the cable size doesn't seem to be indicated.

Is there any stranded 4mm out there or is this likely to be an old imperial size?

All 4mm^2 is stranded.

The 1.5mm^2 cpc will, however, be solid.

winston1 · 1 Sep 2019

The only way to be sure is to measure the diameter of one of the strands with a micrometer or calliper and calculate the CSA (pi x d squared upon 4) and multiply by the number of strands.

EFLImpudence · 1 Sep 2019

winston1 said:
calculate the CSA (pi x d upon 4)

I think you mean pi x d² upon 4, i.e pi x d² / 4

Out of interest, I have never heard it expressed like that apart from you saying it once before.

Is not pi x r² the normal way of saying it?

What do others think? Is it regional?

JohnD · 1 Sep 2019

πr²

winston1 · 1 Sep 2019

EFLImpudence said:
I think you mean pi x d² upon 4, i.e pi x d² / 4

Out of interest, I have never heard it expressed like that apart from you saying it once before.

Is not pi x r² the normal way of saying it?

What do others think? Is it regional?

Yes you are right, thanks, I have now edited my post.

I was taught this method by my physics master at school as an alternative when you measure the diameter. But like you I have never heard of anyone else using it so it is probably unusual rather than regional.

JohnW2 · 2 Sep 2019

EFLImpudence said:
Out of interest, I have never heard it expressed like that apart from you saying it once before. ... Is not pi x r² the normal way of saying it? ... What do others think? Is it regional?

I think it may well be primarily the difference between mathematicians/ theoreticians and engineers.

My father was an engineer, and always talked of πd²/4 (I hate this forums's "pi" character/symbol - that is meant to mean "pi x d² / 4" !), and I've heard many other mechanical etc. engineers use the same. I suppose it makes sense, since (as, indeed, with measuring cable core strands) an engineer will almost always measure the diameter, not the radius, of something. Like you and many of us, I learned it in a theoretical/abstract context (as 'mathematics') where there is no such practical constraint - so radius is probably at least as reasonable.

Kind Regards, John

Risteard · 2 Sep 2019

EFLImpudence said:
I think you mean pi x d² upon 4, i.e pi x d² / 4

Out of interest, I have never heard it expressed like that apart from you saying it once before.

Is not pi x r² the normal way of saying it?

What do others think? Is it regional?

Pi (or 3.141592654... if you prefer) r^2 would be the norm.

SUNRAY · 2 Sep 2019

This was one of the slide rule suggestions to reduce errors

rsgaz · 2 Sep 2019

JohnW2 said:
I hate this forums's "pi" character/symbol

Totally agree, it looks like an 'n' at a quick glance. Change the font to Georgia for a nice pi (it's a bit small in Times New Roman or Book Antiqua)...
π

Harry Bloomfield · 2 Sep 2019

imroberts said:
Is there any stranded 4mm out there or is this likely to be an old imperial size?

All 4mm is stranded. You can confirm the actual size, be measuring the width accurately, then checking tables online. The largest single strand T&E is 2.5mm all sizes larger are stranded.

sparkwright · 2 Sep 2019

I have to ask.

What does this cable in question actually serve??

Astra99 · 5 Sep 2019

It wouldn't be the old imperial 7/029 would it? Red/Black seven strands, bare earth three strands, and all tinned copper if I remember correctly.

RF Lighting · 6 Sep 2019

I think there was a time where none tinned 7/.029 was available and I’ve definitely seen stranded 2.5mm2 from I guess around the time of metrication.

Harry Bloomfield · 6 Sep 2019

RF Lighting said:
and I’ve definitely seen stranded 2.5mm2 from I guess around the time of metrication.

Yes, and you can still buy it.

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Twin+Earth Cable Size

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