Consumer Unit to Consumer Unit

[scottb]

I have just had an extension built and would like to know whether I can run an additional consumer unit onto my exsisting CU. The existing is brand new and has been fitted by a professional electrician.

The reason for the additional CU is to keep the new extension on its own CU if possible ?? Plus I can save on having to run all the ring wires back to the existing...

Any advise and suggestions would be very welcome.

Thanks

 

[dw3101]

you can, its not a simple job though.. and it will be a big cable needed.

Preferably armoured too..

What load would you have in the extension? ovens? showers?

 

[plugwash]

10mm or 16mm T&E off a 50A or 63A breaker should be fine provided you don't put too many big loads on the secondry CU

 

[scottb]

The existing is currently a 63A. Should I also put this into the second CU to match the first ?

Do I run 10 or 16mm off the existing breaker into the new unit ?

All that will be on the new CU is 7 Doubles set in bedrooms, 3 spot lights in each of the 4 bedrooms and 4 doubles in the garage - will not be putting any heavy load on in the garage.

 

[Lectrician]

I would install a 16mm Split Concentric. Put this on a 50amp breaker in the old CU. You have to be carefull with the loop impedance of C type breakers at this type of amperage, so make sure this install is tested by a proffesional. I would also recommend you get a prof to install the split con, and second board.

A C type breaker gives a little more discrimination to a B type when used as a submain, although a B type may be fine for your small domestic use.

 

[andy]

16mm Split Concentric.

whats that?

 

[plugwash]

id personally say never fit any C above a C20 on a domestic without good reason

also remember submains are only 5S disconnect requirement so (if your CU can take it) a 45A hrc fuse may be a better bet

 

[ban-all-sheds]

If you want a separate CU in the extension, make it truly separate - split the tails with Henley block(s), go to a switchfuse, then to the CU (in T/E or SWA/S-C depending on the nature of the run).

 

[kai]

Some CU's have a pair of tap-off terminals on the outgoing side of the 100 amp main switch, if suitable you could tap off the second CU from there, via a switch fuse etc. Check with the professional electrician.

 

[Lectrician]

id personally say never fit any C above a C20 on a domestic without good reason

also remember submains are only 5S disconnect requirement so (if your CU can take it) a 45A hrc fuse may be a better bet

Very true on domestics, but i have regularly seen submains trip due to a fault on a circuit fed via the submain. Not good.

 

[plugwash]

the problem with mcbs is thier trip patterns suck for 5s cuircuits

the only way to trip a mch in 5s is to hit the fast trip at which point they trip extremely fast

iirc if you have two mcbs in a row you should ideally aim to always double the fast trip point from a mcb to the one behind it but this isn't always practical because of earth fault loop currents

with fuses you have a nice smooth curve between current and trip time