DIY Doctor UK DIY Forums

Hi all, my first post so here goes...

I have recently changed my dis board as weve had a kitchen extension done. ive put in a new kitchen ring, new lights and cooker supply. I have fitted all the circuits with C type RCBO's at there correct rating.
When the work was inspected, i was told that i they should be type B RCBO's.
I have scanned the regs and the OSG (17th etd) but can find no regulations stating that i MUST fit B type.
Two reasons that type B RCBO's werent fitted are that they are impossible to get for a merlin gerin board and due to the oven having a fan (motor), the fridges having Motors and the lights being florescent then type C's are more appropiate any how.

Any advice would be appreciated...

Many thanks (in advance)
Mark

So long as the neutral loop and earth loop impedances are within required limits and you have not used Ali-tube cable I can see no reason why type C should not be used.
The prospective short circuit current is the limiting factor and this should have been all noted on the installation certificate.
Very simple a type B will allow 5 times the rated current before the magnetic part of the RCBO works and a type C will need 10 times rated current before it works.
So for a 32 amp RCBO you need 320 amp for it to trip so the line / neutral impedance needs to be less than 0.7 ohms so assuming Ze of 0.35 then R1 + Rn needs to be 0.35 ohm so what are the reading taken?
All best Eric