Extension supply

[Macca65629]

Hi just looking for some advice,
Extension has been built onto the side of a
house and they are putting in a separate consumer unit (just for the extension) and it will be fed off the existing consumer unit with a 16mm T&E. Distance between the 2 boards approx 6 metres. It’s a big enough extension so that’s why they would like their own board.
The existing board mains fuse is 63A.
Would you recommend my new tails feeding the new CU be terminated in with the incoming supply (meter supply into the existing CU ) or come of the load side of the fuse in the existing CU?
Or any other options?
Thanks in advance

 

[telectrix]

, split tails with henley blocks and fit a 63A switched fuse to feed DB2.

 

[Macca65629]

, split tails with henley blocks and fit a 63A switched fuse to feed DB2.

Would you recommend splitting the tails with Henley blocks beside the meter box or were?

 

[westward10]

Are you a REC.

 

[Macca65629]

Are you a REC.

I have just registered and this is going to be my first inspection,I’m just asking for abit of advice as most of my experience has been in commercial and industrial

 

[Dave OCD]

I'd suggest taking the 16mm from an additional device in the existing CU would be a very poor design as there's a chance of overloading. You need to split the tails after the meter using 100 amp single pole blocks and connect a 63amp metalclad switch fuse for your new 16mm to the extension CU. But there's another consideration as the sub-main may well need additional 30ma RCD protection depending on how it's been installed and the route.

 

[telectrix]

I'd suggest taking the 16mm from an additional device in the existing CU would be a very poor design as there's a chance of overloading. You need to split the tails after the meter using 100 amp single pole blocks and connect a 63amp metalclad switch fuse for your new 16mm to the extension CU. But there's another consideration as the sub-main may well need additional 30ma RCD protection depending on how it's been installed and the route.

last bit.... he could use SWA, to eliminate RCD.

 

[westward10]

What doe IS:10101 say about rcd protection and splitting the supply as we are working from BS7671.

 

[pc1966]

Feeding the 2nd CU from the first CU would mean it is off a MCB (possibly also RCD protected) and likely to have poor selectivity with the protection in the 2nd CU itself.

Feeding it from a switched-fuse off the (split) incoming tails would give the best selectivity, but the remaining question would be if the T&E needs RCD protection. I have no idea under what conditions the ROI regs demand it, but assuming they are broadly comparable to our 18th then either the T&E needs physical protection and/or careful routing to be > 50mm deep in any walls, etc.

Or go for the the safer and more professional option is to use some SWA with proper glands to terminate the armour at the switch-fuse and at the 2nd CU and not require RCD protection (assuming TN, and not a TT supply, of course, that is a whole other can of worms).

Even if going down the T&E route you should really be using some matching glands for cable entry protection and physical support such as these:

32mm Entry Gland for 10 & 16mm Flat T & E | Wiska (WKP32F1016 / 10106243)