Cable size for main entry to house.

[Harry M]

Hi,
Main supply cable entering my house is swa and measures 13.75mm outside diameter, don't know how many cores. I have electric wet central heating with a 9kw boiler plus immersion heaters, dishwasher, washing maching etc. all the normal stuff. House is all electric, no gas supply available here. Worry is the main cable looks small. Looking for some opinions from those more knowledgable than myself.

 

[telectrix]

most likely be 16mm concentric cable. if DNO think that's good enough to fedd a 100A supply, then it;s good enough for me.

 

[Bobster]

DNO will have supplied an appropriate service fuse to protect their cable.

You could always ring and enquire, although be prepared for a lot of faffing around.

 

[Harry M]

Yes, cable is protected by standard 100 amp fuse. Became curious when main entry cable appeared to be smaller than 6mm2 swa I'm planning to use to supply a new garage. Concentric cable not something I've come across and may explain it. Thanks.

 

[Guitarist]

Are you an electrician mate, or an enthusiastic DIY'er?

 

[Guest55]

slowy put the tools on the floor and step away from the work area.
lol.
;-)

 

[Knobhead]

BS7870-311 25mm Al Cu concentric is 12.5mm OD. How do I know? I've just measured the piece I'd got stashed away.

 

[Heisenberg]

BS7870-311 25mm Al Cu concentric is 12.5mm OD. How do I know? I've just measured the piece I'd got stashed away.

This brand is slightly bigger...

http://www.batt.co.uk/upload/files/splitconcentriccablebs7870_1355413546.pdf

:vanish:

 

[Engineer54]

This brand is slightly bigger...

http://www.batt.co.uk/upload/files/splitconcentriccablebs7870_1355413546.pdf

:vanish:

That's for a ''Split'' concentric cable Heisenberg. Not sure if the others are talking about a split concentric or a straight concentric cable above!! lol!!

 

[Heisenberg]

That's for a ''Split'' concentric cable Heisenberg. Not sure if the others are talking about a split concentric or a straight concentric cable above!! lol!!

Straight Con = Combined N/E and only usable by DNO. Is that correct?

 

[snowhead]

BS7870-311 25mm Al Cu concentric is 12.5mm OD. How do I know? I've just measured the piece I'd got stashed away.

Cable shrinks in the cold as well then?

 

[snowhead]

Straight Con = Combined N/E and only usable by DNO. Is that correct?

How many rolls do you want, I'm sure there's some on my Transit pickup.

 

[Engineer54]

Straight Con = Combined N/E and only usable by DNO. Is that correct?

Not really, but 99% of the time, it would only be the DNO's using a concentric cable as a combined N-E cable!! They use split concentric as well, when replacing a damaged TN-S PILC cable, where the system hasn't been PME'd...

 

[Heisenberg]

Not really, but 99% of the time, it would only be the DNO's using a concentric cable as a combined N-E cable!! They use split concentric as well, when replacing a damaged TN-S PILC cable, where the system hasn't been PME'd...

I see what you mean, when used by the DNO they use the outer conductors as a combined N/E cable but only they are allowed to do this.
We could of course use it in the same way as a 2 core cable, as long as the CPC function that it is lacking is provided for by other means.
Which is why I was wrong to say only the DNO can use it.

Cheers

 

[Engineer54]

I see what you mean, when used by the DNO they use the outer conductors as a combined N/E cable but only they are allowed to do this.
We could of course use it in the same way as a 2 core cable, as long as the CPC function that it is lacking is provided for by other means.
Which is why I was wrong to say only the DNO can use it.

Cheers

An example would be as a sub-main cable to an outbuilding on a TT system, where the earthing is being provided by roded systems. Only thing is, the cable, if taken underground would need to be ducted as they do not conform with BS7671 as a direct buried cable having no additional mechanical protection. The DNO's don't have to comply with BS7671, but even they only use it in the short lengths from the street distribution cable joint, to the their service heads!!

In reality, a straight concentric cable is rarely used outside of the DNO arena....

 

[Knobhead]

Have you tried cutting the outer sheath? It's as tough as old boots.

 

[Engineer54]

Not tough enough to stop a sharp stone or other debris getting through it, in a direct burial installation, nor a shovel or garden fork come to that!! lol!!

 

[Knobhead]

So you've not had a play with the new stuff the DNO's are installing. For BS7671 it isn't compliant but believe me it’s as tough as old boots.

 

[Engineer54]

So you've not had a play with the new stuff the DNO's are installing. For BS7671 it isn't compliant but believe me it’s as tough as old boots.

No, haven't touched the stuff for quite a while now Tony!! lol!! Not a real lover of the cable myself, it can be a real pain getting respectful end terminations, that don't look as if it's been installed by a 1st year apprentice!! The DNO don't have that problem, they just split it in the service head willy nilly, no-one ever see's the state of it!! lol!!

 

[telectrix]

no-one ever see's the state of it!! lol!!


only when you pull the fuse, which, of course, you never do. LOL.

​

 

[Engineer54]

no-one ever see's the state of it!! lol!!


only when you pull the fuse, which, of course, you never do. LOL.

​

Not even then, in most of the service cut-outs i've seen!! Generally terminated (if you can call it that) in the square case below the fuse carrier!! lol!!