On Wednesday 23 October 2013 22:50 Bill wrote in uk.d-i-y:

Hi all, especially the knowledgeable electricians on here.

What are your thoughts on me replacing all of the MCBs in my CU with
RCBOs? At present I have 14 MCBs all protected by one 30mA RCD main
switch. Over the last few years I've had tripping problems from a
trapped L to E fault in a metal clad light unit, it too 10 years before
this became a problem! Water blowing into an extractor fan, water in an
outside light and the big issue of too many switch mode PSUs in the
house. While some of the genuine faults were a pain and time
consuming to locate the SMPSUs are something I have to live with and
they are taking my overall leakage too near the 30mA limit on the CU.

This has been brought to a head by a few trips this evening, no one
circuit being the culprit, leave any 2 or 3 MCBs off and it is happy,
just not happy with all on, I'm assuming something is leaking a bit more
than normal and has taken the main RCD to it's limit. I've left one
circuit off that has a number of SMPSUs on it and so far all is stable
again.

Yes I will turn everything off and check the trip current of the1 RCD in
case it has become overly sensitive, but NOT tonight!

So my thought was to replace the main switch/RCD with a simple switch
and then all of the MCBs with RCBOs, everything will be protected and in
the event of a real problem I don't lose the whole darn house, just the
one errant circuit.

So is it a practical idea? I think so, but would welcome any thoughts,
good or bad about doing it. I know the 17th edition suggests a split
load CU, but that would still leave me with a 50/50% split and a gamble
as to what worked and what didn't.

I have 100% RCBOs (glad I did with the nusiance trips I had the other day!)

I have Hager. Crabtree are (or were) a good brand.

I would advise not putting all the larger RCBOs (32A rings, heaters) next to
each other - apparantly localised heat build up is a problem. I left a 1
module gap every 2-3 on mine and the middle RCBO is a low current one
(lights).

You'll probably need 1 module RCBOs - they are a lot taller than an MCB.

Is your CU tidy inside?

In the worst case, you could replace your CU with a bigger one to give you
more space.

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