On 23/10/2013 22:50, Bill wrote:
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.

Yes I am competent to do it, just nervous that I may have missed a
fundamental flaw in the idea.

If it matters the CU is a Crabtree Starbreaker with a single 80A
switch/30mA RCD and 14 MCBs and a DIN mount bell transformer.



Apart from the cost, am I crazy?


I have done exactly what you propose.

I previously had a MK metal clad CU with split rails.

there were 2 off 6A MCBs feeding two lighting circuits (up and down) and
4 MCBS fed from a 30mA RCD. the 4 MCBs were for cooker, immersion, left
hand side ring main, right hand side ring main.

I basically ended up replacing the entire CU with a Curve Unit. You can
get them from Denmans. I have a double pole on-off switch and can have
up to 19 RCBO's I took the opportunity to split some circuits and add
new ones.

I now have:

outside & garage lighting
ground floor lighting
first floor lighting
loft lighting
smoke, heat, CO detectors and intruder alarm
boiler & immersion
garage & outside sockets
front left sockets
front right sockets
Rear left sockets
Rear right sockets
loft sockets
Kitchen sockets
cooker

and I have 5 spare ways for the future.

since doing it, I have not had a single trip. Prior to all this, I had
all the problems you describe.