CU Change Complexities

[Is it live?]

Hi, I am a newboy to this sparky stuff and I am doing a CU change as part of a qualifying job at a customers house. The existing CU needs changing as the customer wants RCD protection, so a simple CU change job. However the customer has had a house extension a few months ago and the electrician installed a second CU to feed this (1 x 32A Ring for power, and 1 x 16A Radial for lights). The surprise is that they appear to have fed this second CU from an old breaker in the original CU (not sure at capacity) using 6mm T&E. This feels wholly wrong to me, and I propose installing Henley Blocks between the service isolator and then running new tails to both of the CU's along with upgrading the main earth to 16mm and the bonding earths to 10mm using a Main Earth Bar. In an ideal world I would get rid of the second CU, extend the 2.5 power & 1.5 lighting circuits to the extension using crimps and heat-shrink (but this may not be practical). So the questions is will the assessor review the install of the existing second CU because I will be fitting proper sized tails to the Henley Block (I will test it anyway)?

 

[shanky887614]

just use one bigger board if doing a board change anyway

 

[markc123]

Obviouslly the capacaity of the breaker is a concern - but nothing wrong with feeding a smaller CU off a breaker in the main CU/DB....Without seeing the install, i'd probably hazard a guess that 6mm is perfectly fine for the second smaller (garage type) CU.

The assessor won't have a problem with a second CU providing the adiabtic equation is applied to the feed. I'd be suprised if the assessor didn't look at the secondary CU, infact he'll probably target it lol.

Another thing, don't get too cocky - theres literally no such thing as an easy cu change

 

[Johnuk]

when u do a cu change you got to have a spare or two for future add ons

 

[Octopus]

Could you not fit one new board replacing the 2 units?

 

[Is it live?]

Have thought about this see question and there may be an issue extending the 2.5 ring and 1.5 radial to the new CU location. Would need to crimp join and heatshrink the run and this is in a garage and I don't like to leave visible (so I could put joints into some sort of joint box (any suggestions for best type welcome)).

 

[Is it live?]

Just looked at Wagobox https://www.************/shop/junction for creating joint for extending the cables. Does anyone have any experience of them for a permanent extension method in a garage environment. Main question is 'are the lids hard to get off to stop prying fingers'?

 

[jeremy]

Are you sure the 1.5mm lighting is on a 16A? other than that, I see nothing (ordinarily) wrong with having a 2nd CU. If there's nothing wrong with it apart from maybe incorrect MCB choice, why go to the trouble, and expense to your customer, of changing it.

 

[Is it live?]

Whoops typo on my part, the lighting cct is 1.5mm fed from a 6A MCB not 16A - Sorry

 

[Lucien Nunes]

You can get all kinds of joint boxes and enclosures in which to put your Wagos safely and securely. The Wagobox is just one option, as it happens not my favourite. I would use an adaptable box and gland the cables in. Takes 10 mins and is 100% permanent. Not wanting to make joints is a very poor reason to leave a less-than-perfect CU arrangement. The time saved not having to test the two CU's will more than make up for the time spent extending the circuits to all reach one new unit.