Discrimination on upstairs board

[South Spark]

Saw an installation today where an upstairs consumer unit is run off a 40A MCB in the main board.

Two problems

1) Both boards are protected by 30 ma RCD so no discrimination.

2) There's a 40 A MCB in the second board as a dedicated shower feed - the installers have put a 10.8 kw shower on it and of course it keeps tripping the 40A breaker in the main board.

My question is - assuming the cable feeding the secondary consumer is adequate and I feed the upstairs board from on a separate mini consumer unit with a 60A breaker and 30 Ma RCD does that count as a new consumer unit for testing and certification purposes? i.e will I have to sign off on all the upstairs circuits?

 

[bigbaddave]

What size cable feeds the second board?

 

[Guest55]

if you feed the upstairs with a new mini rcd CU you still wont have discrimination with the rcd upstairs.
its just bad design all round to be honest , you need to get rid of the rcd in the upstairs CU.

the shower needs to be on a 10mm cable direct from the downstairs CU

 

[South Spark]

If the RCD is taken out of the upstairs unit and replaced with a switch and the whole thing's run off an RCD protected garage unit then that should be discrimination sorted.

Or as the the cable feeding the upstairs unit looks like 10mm MICC perhaps that counts as mechanically protected and doesn't need RCD protection at the origin.

 

[Guest55]

or connect the pyro to a 50amp rcbo in the downstairs CU , saves money on a new garage mini CU and gives discrimination to the shower upstairs.
;-)

 

[South Spark]

Got any pictures of how pyro should be terminated ? Cos this one don't look too pretty.

Don't think I'll get an RCBO compatible with this board old Wylex MCBs - NB0 - Split RCD - way ahead of its time RCDs labelled BS 4293.