Adding a second consumer unit

[tdm]

Hi all,

 

I currently have a safe t cut 8 way unit with rcbo supplying the house electrics. I have built a small utility room which will have 4 double sockets,  one for the washer, one for the drier, one for the house water pump, and one for misc, there will also be a basic light, this utility room is not separate from the house per se in that it will share a wall with the dining room, being on the other side of the wall at the side of the house. My plan is to run one radial for the washer on it's own socket protected by a16amp mcb using 2.5 twin and earth and another separate radial for the drier again on it's own socket protected by another 16 amp mcb using 2.5 twin and earth and this second radial will also feed the misc double socket, finally a third radial for the water pump would also have it's own 16amp mcb and be fed via 2.5 twin and earth. All of the above would be on the second consumer unit.

I plan to do this in the following way-

 

I would feed the second unit from a spare 32 amp mcb on the house consumer unit using 10 mm live, neutral and earth 'tails', this second unit would not need an rcbo as it would be protected by the rcbo on the main unit.

 

My questions are, does this seem like a reasonable way to do this? The main house consumer unit is earthed via a 1.8m earth rod buried just outside the back door. Would there be any advantage in the second consumer unit also having an rcbo or would this confuse things? And is there any reason/advantage/disadvantage for the second unit to be the same brand as the original? Would the 10mm tails be the best size for feeding the second consumer unit?

 

many thanks for any replies,

 

tdm

 

[Crossy]

Looks perfectly reasonable to me.

 

No need for additional earth leakage protection unless you want to feed the sub-main from the main switch rather than via an existing spare way in the CU or even from the existing CU bus-bar.

 

How long is the run to the second CU? If not too long you could use 6mm² VAF-G (good for 41A) on that 32A breaker.

 

 

[tdm]

thanks Crossy,

 

I will put the second unit beside the original near the back door of the house and so will use 6m as you suggest. The longest radial will be around 12 metres.

 

Regarding your other two suggestions, feeding the sub main from the main switch, does this mean feeding the live and neutral directly from the main circuit breaker within the original unit (model CSR8E) and taking the earth from the earth bar? There is no other main switch that I can see, just our CU fed from the meter. Or is that what you mean when you say taking the feed from the existing busbar?

 

tdm.

[Crossy]

With the lid off your unit you should be able to access the outgoing side of the main breaker or the outgoing side of the RCD section so you could feed from either of these.

 

But, you would then need to use 10mm2 (assuming a 50A main breaker), if a total load of 32A will be ok for your utility then I'd stick with your original plan.

 

 

[tdm]

Yes 32 amps will be plenty, thanks again, much appreciated!

[TheMysteriousMrTesla]

All good then