Thoughts on fitting RCBOs

[Bill]

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?

[Stephen]

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.

[John Rumm]

Your experience adequately illustrates why the "whole house" RCD arrangement is deprecated - it was never a great idea, and the march of time (and things with leaky input filters) has only made the limitations more apparent.

Practical - yes certainly. Its the "Rolls Royce" solution that gives the best possible discrimination in the even of an earth fault. Obviously its more expensive than other options.

Split load does not have to mean a 50/50 split. Some 17th edition CUs may have say 4 RCDs and some unprotected (aka "high integrity") ways as well (for feeding circuits that meet the requirements for not being RCD protected). You can also arrange the split in various combinations of ways as suits your application.

Without checking I don't know if you can get single module wide RCBOs for this enclosure (and if so if there is really enough space to wire them). You may find you need to replace the enclosure as well.

No, although you probably ought to look at some pragmatic options. You may find a combination of several RCDs covering a two or three circuits each, plus a smaller number of RCBOs would make for a system that is equally effective, but also leave more money to spend on improving other aspects of the system.

[Tim Watts]

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

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.

[charles]

[Snip]

The trouble with replacing the enclosure is that you have the incoming live & neutral to deal with. You can only isolate them by removing the "compnay" fuse. Years ago, before 'privatisation', I needed to repace my CU and arranged for someone to come and remove the company fuse. I said to him that I estimated it was a two hours job, if he came back and and reconnected me then, I could put the kettle on. He came back as suggested. Would that work these days?

[Bill]

In message , Tim Watts writes

Thanks for the comments Tim and others, much appreciated..

Something that I hadn't considered, thank you for that.

MMMMMmmmmm I think that I shall have to start looking at spec's to see how the 2 sizes relate.

Relatively so, the spaghetti over to the right isn't as bad as it looks! Don't panic too much about the "telephone" cable, bottom right, it is the feed to the door bell.

I am fortunate that the CU is mounted on a panel that in turn is mounted on 2" X 2" battens so there is a reasonable amount of space behind it, unfortunately many of the cables were bundled together when it was installed and trying to get a bit of slack to move them around may be difficult, but not impossible. My only restriction in size is that I cannot fit a longer unit, I would need to go for a second one above the existing one.

[Andy Burns]

Bill would appear to have a mains/generator changeover switch before the CU, so maybe that's less of an issue?

[Bill]

In message , charles writes

Ah ha! There was some forward planning here, an unusual event in this house, as the CU is about 4m away from the meter and boards fuse, there is a 100A fused switch near to the meter so that I can isolate the CU. Plus the later addition of the generator transfer switch also gives the same option a bit closer to the CU.

About 10 years ago my parents had a serious failure in their CU that meant it had to be replaced. I pulled the boards fuse and then phoned them afterwards to let them know why and to ask for it to be re-sealed. Despite many meter readers visits, so it must have been seen, it is still not sealed again.

>

[Dave Liquorice]

Hum, so if a leakage fault develops in the immersion (fairly common) it trips off the heating... Remember N-E faults can trip and RCD, though I guess the immersion switch will be DP. Still makes it harder to work on one or the other independantly though.

[Bill]

In message , John Rumm writes

Hi John and others for your comments, all appreciated.

Indeed, filtering is all well and good, but causes lots of other issues.

Although cost is, obviously, a factor I feel it would be worth it to only lose one circuit in the event of a fault. I can only see things getting worse with more electronics making their way into homes and so more filtering, unless of course they are manufactured in a well known far East country where the various components are very obviously missing from the PSUs by the empty holes in the PCBs, Maybe that is an advantage of some of these dodgy imports??? There is no leakage from the filtering because they omitted it to save 5p per unit. But that is another discussion for another day...

Yes, sorry, badly phrased on my part there. I should have just said split.

If no one puts me off the ideas I'm having then checking physical sizes is next on the agenda. Hopefully in the same enclosure, I'm not too worried about doing that. But if it came to a new enclosure then the panic will set in! Although there is plenty of space behind the CU, I would not look forward too much to replacing it.

To get a quick, ball park, idea of cost I checked on TLC's web site earlier and although scary I managed to not quite fall off my chair. So if it does come to it I'm hopeful to find a slightly cheaper route.

I'm quite happy with the rest of the electrics in the house, all bar one slight anomaly which I can easily sort out, just waiting on a round tuit appearing.

>

[Mike Tomlinson]

In article , Bill writes

Aren't you allowed to replace the RCD with a 100mA one in these circumstances? That would be cheaper than replacing the existing RCD and all the breakers.

[Dave Liquorice]

The RCD is for shock protection. Pretty sure that has to be 30 mA.

100mA ones are for circuit protection and normally time delayed to provide discrimination against downstream 30 mA shock protection RCDs.

[bblaukopf]

I replaced my CU in 2005. EDF said I booking slots were 'morning' and 'even ing'. I booked a disconnect and reconnect* for the morning, and connected a n isolation switch with dangling tails. When the guy came round, slightly c onfused by the work request, I explained I wanted him to disconnect the old CU and reconnect to the isolation switch.

He did it, but he was deeply unhappy about it, and came back in the evening so he could test it, which meant plugging in a socket tester. *ALL* he car ed about was that I had phase and neutral the right way round (possibly wha t he was actually testing was that he'd connected them the right way round! ).

As far as I can see, if I'd had the isolation switch connected to a CU moun ted somewhere random (but legal), connected to a single socket, he'd have b een perfectly happy with my proposed arrangement - so that's what I'll do n ext time, particularly because then I'd have power while working on the old setup.

• The hardest bit was actually booking it. After calling Powergen, then EDF , then Powergen, then EDF, I discovered the magic words 'disconnect' and 'r econnect', which enabled the person answering the phone to connect their br ain to their fingers. They don't apparently have any idea what the words me an, so explaining what you want doesn't get you anywhere.

[Tim Watts]

On Thursday 24 October 2013 08:05 charles wrote in uk.d-i-y:

The might come back 6 hours later and charge you £35 - happened to me, with EDF.

I installed an isolator in the meter box at the same time.

[Tim Watts]

On Thursday 24 October 2013 09:05 Mike Tomlinson wrote in uk.d-i-y:

No.

[Tim Watts]

On Thursday 24 October 2013 09:50 Dave Liquorice wrote in uk.d-i-y:

Yes and I'm absolutely sure - not only 30mA trip, but provide discrimination against downstream 30 mA shock protection

[John Rumm]

Something to keep in mind is that its more difficult to wire a box full of RCBOs unless the wiring is very tidy. So you may well be faced with needing to pretty much "start again" anyway to have a hope of getting it all neatly dressed in the box. Hence the effort difference between keeping the box and installing a new one may be less than you expect.

You could probably find a solution that just uses three or four RCBOs, and then two or three normal RCDs that in practice will work just as well. Just identify which circuits are likely to be high leakage (lots of IT kit, mineral insulated heating elements, water in proximity etc), stuff that is liable to genuine earth fault (circuits outside, socket circuits), and then "other" which is low leakage and risk - lighting, smoke alarms etc.

TLC might have em ;-)

[John Rumm]

There's not much spare height there for single module RCBOs...

You may have to crimp extensions onto some of the circuit ends... especially if the neutrals have been cut shorter than the lives (they both need to reach the RCBO)

[John Rumm]

No now. There may have been times in the past where that was appropriate

- but only where the RCD was there to protect the circuit and reduce fire risk, not if its purpose was shock protection.

It would only be fixing a symptom rather than the actual problem. It would also mean you no longer have adequate shock protection on the circuits that really need it.

[RobertL]

They don't seem bothered any more. I had a CU replaced a few years ago and they cut the seal and pulled the EB fuse but nobody has commented on it being missing.

Do they have some fancy way of detecting meter bypasses these days?

Robert