Cable connecting consumer units

[Desie]

Guys can you please advise.
I have a main consumer unit feedinga secondary one in my extension. The secondary unit is fed via a 32a MCB in the main unit. The secondary unit runs a couple of sockets and lights and no more.

Is this the normal way to do it?
and
What size should the cable be connecting the two? At the moment it looks like it could be 2.5mm or 4mm at best.

 

[ban-all-sheds]

It's very common.
and
If it's clipped to the surface, 4mm² is OK. How long is the cable between the two CUs?

 

[Desie]

Thanks Ban
The cable is no more than 15m

 

[ban-all-sheds]

That'll be OK for a few sockets & lights.

You do need to confirm that it's 4mm² and not 2.5mm² though. They are very close in external dimensions - the easiest way to check would be to look and see if the main conductors are stranded or not. 4mm² is multi-stranded, 2.5mm² is solid.