install part tnc-s advice from sparks

[spanky]

Hi - looked at job today - kitchen which is in extension.

There is a sub main feeding a separate consumer unit - this is a concentric cable which the installer has split the outer un insulated copper into 2 with 1/2 for neutral and 1/2 for earth.
The incoming supply is TNS
Is this acceptable? I realise the problem with broken neutral elsewhere in install at meter
Would running a separate 16mm earth and using outer concentric as neutral only be a solution?
The intention is to fit new RCD consumer unit on end of sub main for kitchen install. Will have hard time trying to sell new sub main cable

what would you do? any advice or suggestions welcome - thanks

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• spanky
• 14 Apr 2011
• 1

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• spanky
• 14 Apr 2011
• 1

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• spanky
• 14 Apr 2011
• 1

Untitled

• spanky
• 14 Apr 2011
• 1

Untitled

• spanky
• 14 Apr 2011
• 1

 

[Lectrician]

You cannot use that cable as a submain - it is (as you correctly state) straight concentric as opposed to split concentric.

Even if you ran a new earth and used the concentrics as a neutral, you would have a single insulated neutral which is not permissible.

Your only option is to run a new submain really.....

 

[spanky]

You cannot use that cable as a submain - it is (as you correctly state) straight concentric as opposed to split concentric.

Even if you ran a new earth and used the concentrics as a neutral, you would have a single insulated neutral which is not permissible.

Your only option is to run a new submain really.....

Thanks very much for your prompt reply - my heart sank when i saw this as i knew it was dodgy and i was only there to price the kitchen for kitchen contractor.

Did'nt think of the single insulated neutral issue only the TNC-S bit

You know what its like - you go to look at a small job and end up telling someone their house needs rewired - they think you're at the lash.

Back on phone tomorrow - wont do job unless rectified

 

[aaronjb]

You know what its like - you go to look at a small job and end up telling someone their house needs rewired - they think you're at the lash.

Depends on the customer I suppose, but have you thought about pointing them toward this thread?

I know if I was the customer in question I'd come here, read the thread, maybe flick through your past posts (if there are any) and come to my own conclusions (in this case just reading this thread would be enough to satisfy me that you weren't just saying it to pull a fast one)..

As I say, depends on the customer I suppose (if they're relatively young it'd work, if they're .. more mature, it might not)

Then again, if I'd looked at that wiring (as a lay person) I'd have been a tad concerned with the previous sparks work - I can't believe they aren't already anyway!

 

[OwainDIYer]

Then again, if I'd looked at that wiring (as a lay person) I'd have been a tad concerned with the previous sparks work - I can't believe they aren't already anyway!

That wiring looks messy enough to be on an American electricians' forum.

 

[Spark123]

Do you have a 20ft barge pole?
What you have is actually probibited by the ESQCR in section 8.4 here (hence is illegal):
http://www.legislation.gov.uk/uksi/2002/2665/made

 

[ericmark]

I have a 20 foot barge pole. We use it as one would expect to push the bow of the narrow boat around when the wind has pushed us into something. No bow thrusters. It is wet and covered with mud from bottom of the cut. There is no way I would use it to move any electrical wires. Although it may look like the poles used with the trams to move the pick-up across I would not consider the insulating qualities match in any way. I would not even trust my 20 foot barge pole on split phase 110 volt never mind 230 volt to earth.

 

[Spark123]

Nah, I wouldn't touch it with one!

 

[Buzx1313]

You cannot use that cable as a submain - it is (as you correctly state) straight concentric as opposed to split concentric.

Even if you ran a new earth and used the concentrics as a neutral, you would have a single insulated neutral which is not permissible.

Your only option is to run a new submain really.....

better tell that to the electricty suppliers

 

[RF Lighting]

They don't work to BS7671

 

[Lectrician]

You cannot use that cable as a submain - it is (as you correctly state) straight concentric as opposed to split concentric.

Even if you ran a new earth and used the concentrics as a neutral, you would have a single insulated neutral which is not permissible.

Your only option is to run a new submain really.....

better tell that to the electricty suppliers

As RF says, they do not have to comply to our BS7671.

Straight Concentric IS NOT compliant under BS7671 - yes, DNO's use it everyday, I think we are all aware of that.

 

[ban-all-sheds]

And they combine earth and neutral too - something else the consumer's not allowed to do, and something else this bozo has done.

 

[spanky]

Hi

Thanks for the replies and the link to the statute.

Passed on bad news to Kitchen contractor - let him deal with customer!

Had a look at some cable prices on TLC

16mm 3c swa 5.92 +vat/m

10mm t&e 4.25 +vat/m

not sugesting using 10mm t&e by the way - just highlighting that the swa is only slightly more for all that extra copper and steel - whats that all about!

 

[Lectrician]

Use some SPLIT CONCENTRIC

http://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1096466372#7

 

[JohnW2]

Had a look at some cable prices on TLC
16mm 3c swa 5.92 +vat/m
10mm t&e 4.25 +vat/m
not sugesting using 10mm t&e by the way - just highlighting that the swa is only slightly more for all that extra copper and steel - whats that all about!

Yes, I've often wondered about that. If one compares like with like (16mm² T&E is 4.81 + vat/m), the price differential betweem 3-core SWA and T&E is remarkably small - particularly at the low end (1.5mm² 3-core SWA = 1.04 +vat/m, 1.5mm² T&E = 0.95 + vat/m).

It seems to make little sense. Quite apart from the steel, I would have thought that the manufacturing process would be appreciably more complex/expensive for SWA. Indeed, even if the materials and manufacturing costs were identical for both, I would have expected T&E to be very much cheaper because of the (I presume) vastly larger market (and, I suspect, greater degree of competition). So, indeed, "what's it all about?"!

Kind Regards, John.