Three phase cable size

paulcopeman · May 31, 2014

Can anyone tl ell me how to work out the size of an existing supply cable.
It is a three phase supply into 200A fuses. The cable is buried in concrete ground and so I cannot see any markings on it.
I've had a look at the cables upstream of the fuses and they look to be at least twice as larg as 25 mm tails would be. But on second thoughts 25 mm tails would have double insulation and these cables only have single so could be larger.
Tha cable also looks triangular in shape.
The REC has split the supply from the 200A fuses into two different three phase 100A supply service heads.
I guess SWA cable often surprises me as the cores often look smaller then I would expect.
For example the cores on a16 mm SWA I was working with recently looked more like 6mm to me.
Any explanation would be very much appreciTed.

paulcopeman · Jun 1, 2014

Ur funny mate. Grow up

davesparks · Jun 1, 2014

As far as the SWA vs T&E question goes:

If you look closely at the individual strands in the T&E you will find they are normally circular so you have gaps between each of the 7 strands. But when you look at the strands in the SWA cores you will see they are a different shape which fits much more closely together therefore reducing the physical size of each core.
Also most SWA cores have a thinner insulation layer than T&E.

And as for the size of your 200A cable, the DNO work to their own rules.

D Skelton · Jun 1, 2014

Am I missing a trick here?

OP, get your calipers out. πr[SUP]2[/SUP] x the number of strands

Engineer54 · Jun 1, 2014

davesparks said:
As far as the SWA vs T&E question goes:

If you look closely at the individual strands in the T&E you will find they are normally circular so you have gaps between each of the 7 strands. But when you look at the strands in the SWA cores you will see they are a different shape which fits much more closely together therefore reducing the physical size of each core.
Also most SWA cores have a thinner insulation layer than T&E.

And as for the size of your 200A cable, the DNO work to their own rules.

This will only be the case where the insulation is XLPE, PVC insulated SWA cable conductors will have exactly the same insulation thickness as any other building wire PVC insulated conductor.
The now standard XLPE insulation used in SWA cables, is the major factor for the overall reduction in cable diameter over the older PVC insulated SWA cables and why the CSA of the wire armouring often used for the cables CPC, is smaller than for PVC/SWA/PVC cable.

To be honest with you, i've never really noticed any difference in SWA cables conductor strand shape over other similar circular constructed cables. If i remember, i'll be comparing them tomorrow at work...lol!!

Knobhead · Jun 1, 2014

Forget it............

GMES · Jun 1, 2014

I don't know what I can add to the thread other than!!

[ElectriciansForums.net] Three phase cable size

D Skelton · Jun 1, 2014

Tony said:
Forget it............

You realised where u went wrong didn't ya!

Knobhead · Jun 1, 2014

No I didn’t Damian. The bit I wasn’t sure about is if the conductors are shaped or not.

I defy you to measure a core out of a shaped conductor cable with any degree of certainty.

GMES · Jun 1, 2014

Sounds like aluminium to me!!

D Skelton · Jun 1, 2014

Tony said:
No I didn’t Damian. The bit I wasn’t sure about is if the conductors are shaped or not.

I defy you to measure a core out of a shaped conductor cable with any degree of certainty.

Easy as pie mate

it won't be 100% accurate, but you'll sure be able to know whether or not it's a 70mm cable or a 95mm cable.

If you want certainty, then you would have to take a number of strand diameter measurements at different angles and take the mean of those values. Half that to get your radius.

Brightspark2 · Jun 1, 2014

With SWA you can sometimes get an idea by looking at the gland size and then the gland tables...

Chr!s · Jun 1, 2014

Go armed with some good calipers

Cmil A=D2

To convert to square mm x 0.7854

So 7/0.53 strand

0.53 x 0.53 = 0.281 convert x 0.7854 = 0.22

0.22 x 7 = 1.54 SQUARE.

You just need to remember 0.7854

Cheers
Chris