Consumer Unit further than 3 metres from the metering position

[WhitleyElectrical08]

Hi all,

I am currently wiring a new build electrical dwelling consisting of standard domestic circuits ie......up/down ring mains up/down lighting etc.... the issue is the architect is adamant the consumer unit has to be in the store cupboard which is approx 12 metres away from the external metering box outside! Which there fore creates a new sub-main so to be compliant with bs7671 does this need to be rcd protected.....does this need to be time delayed type.

Its just a grey area i have never dealt with before and i am going to speak to napits tech support line tomorrow, but i was just wondering if any of you guys have dealt with this before?

Cheers

James

 

[Andy™]

submain is treated the same as normal circuit for if it needs RCD of not. if its TT, it needs an RCD in all cases, in TN, then it may not (i.e SWA, trunking etc)

 

[NozSpark]

First off, Is it TT, TNS or TNC-S??

So long as it isn't TT then you could run the submain off a switch fuse in SWA to the CU

 

[batty]

Architects they don't make life easy.

:|

 

[sparkytim]

It will need Switch fuse or MCB prtection for overload / fault protection but as has been said IF SWA or in Earthed Metal Trunking then NO RCD required if TN supply.

Last one I did I fitted 100 A Switch fuse back to back with Meter box and wired from their in 3 Core 25mm SWA, which provided more then required CPC to Consumer Unit position.

 

[Lee321]

can someone quote the reg please

 

[JUD]

If it's a new build, why couldn't they have put the meter nearer to the CU??

 

[kme]

can someone quote the reg please

Which reg?? For what bit??

 

[Lee321]

the max 3m bit K

 

[Lee321]

duff post

 

[Lee321]

It will need Switch fuse or MCB prtection for overload / fault protection but as has been said IF SWA or in Earthed Metal Trunking then NO RCD required if TN supply.Last one I did I fitted 100 A Switch fuse back to back with Meter box and wired from their in 3 Core 25mm SWA, which provided more then required CPC to Consumer Unit position.

tim are you saying if its tn and 3m+ pvc/pvc it needs rcd? why.

and why a switch fuse / mcb?

 

[Apache]

Is it not a DNO rule?

 

[Lee321]

Is it not a DNO rule?

ah ha

 

[kme]

Yes. If the CU is >3M from HED; some form of isolation (switchfuse, 2 pole iso., KMF etc) is needed at the supply end.

IF it is TT, it MUST have RCD protection, regardless of method of install.

If its TN, then as long as you cover the <50mm in walls / earthed sheath / mechanical protection rules, you don`t need the RCD (hence the use of SWA. Most customers deem to prefer it to galv trunking along the hallway:C)

KME

 

[Lee321]

dno requirement then not a reg on distance

 

[kme]

You got it

 

[Apache]

dno requirement then not a reg on distance

pah - even I knew that

 

[Lee321]

pah - even I knew that

ouch :x

 

[Apache]

ouch :x

Night all

:good night:

:z :z:z

 

[sparkytim]

tim are you saying if its tn and 3m+ pvc/pvc it needs rcd? why.and why a switch fuse / mcb?

I think KME has already clarified, but NO RCD required for TNS or TNCS.

It may be required for TT to provide Shock protection as earth loop impedence will likely be more then max Zs for the Distribution cct.

Why Switch FUSE?

The DNO will only allow THEIR Service fuse to be used to protect YOUR Meter tails up to 3 Meters in length. More then that then YOU have to provide Fault and overload protection.