All-RCBO CUs - because we can?

[JohnW2]

Recent discussions have stimulated me to think about all-RCBO CUs - since we are probably heading for the day (albeit fairly distant) when they will become the norm.

Considering the pros and cons, the 'pros' are fairly clear. The main (fairly massive) 'con' at present is cost, but that may change. The only other one I can think of is the small adverse effect on fault-finding, so long as they don't give an indication of whether they have tripped because of overload or residual current (but even that is at least partially cancelled by making fault-finding easier in some respects).

There will be a few situations (e.g. if there are two or more final circuits with unavoidable appreciable earth leakage) in which all-RCBO is the obvious (maybe the only sensible) way to go. However, more generally ...

.... particularly while cost remains a major issue, I wonder if we are moving in this direction simply "because we can" - i.e. I wonder if (other in the specif situations mentioned above) there really are enough problems (presumably mainly those of 'convenience') associated with not having all-RCBO CUs to justify a widespread change to using them.

Speaking personally about my own electrical installations, I can't really think of any occasion in the last few decades (since I started having RCDs) when not having all-RCBO CUs presented any appreciable problem, or even significant inconvenience.

Kind Regards, John

 

[AndyPRK]

well when retrofitting, you need to ensure there is enough room in the top, and cables aren't in the way.

I guess for a small flat, in makes sense to have RCBO's.
But on large house, still sensible to have RCD or mix

 

[JohnW2]

well when retrofitting, you need to ensure there is enough room in the top, and cables aren't in the way.

Indeed - but I was really talking about CU changes or new builds. Furthermore, they're getting smaller, so easier even for retrofitting - those Wylex 'Minature DP RCBOs' we've recently been discussing don't look a lot taller than MCBs.

I guess for a small flat, in makes sense to have RCBO's. But on large house, still sensible to have RCD or mix

Sensible, perhaps - but, as I said, I think we're gradually moving in the direction of advocating all-RCBO for everything.

Kind Regards, John

 

[fluorescence]

How many posts do we see on DIY forums, both here and elsewhere, asking why their RCD is tripping and they don't know which circuit is causing it?

IMHO If you're replacing a consumer unit in 2019, RCBOs really should be the only option to consider & RCBO's should have been made mandatory in the 18th edition IEE regulations. RCBOs are already quite cheap (can be bought for as little as about £12 each) and would only get cheaper with higher demand.

You might only replace your consumer unit once every 30 years or so, so why would you scrimp?

I guess for a small flat, in makes sense to have RCBO's.
But on large house, still sensible to have RCD or mix

Why would you want a large house with more circuits all on just two RCDs? If one of the RCDs trip, you may have a nightmare trying to figure out which circuit is causing it.

edit: formatting

 

[ban-all-sheds]

I think we're gradually moving in the direction of advocating all-RCBO for everything.

All RCBO & AFDD is coming...

 

[JohnW2]

IMHO If you're replacing a consumer unit in 2019, RCBOs really should be the only option to consider & RCBO's should have been made mandatory in the 18th edition IEE regulations. ...

As I said, that appears to be where we are heading - and I was asking whether people thought there was a reasonable justification. You clearly think that there is.

RCBOs are already quite cheap (can be bought for as little as about £12 each) and would only get cheaper with higher demand.

Yes, as I said, they will get cheaper. Currently, you would probably only get questionable ones for £12 (most are double that, or more) and, in any event, even £12 is about five times more than a (decent) MCB.

How many posts do we see on DIY forums, both here and elsewhere, asking why their RCD is tripping and they don't know which circuit is causing it?

Quite a few - but that's essentially just a 'convenience' issue. Anyway, in reality, in most cases (probably nearly all cases other than those due to N-E faults), it's easy enough to identify what circuit is resulting in the trip, the difficulty (when there is one) being in ascertaining what it is within that circuit that is causing the trip - and that would be exactly the same with RCBOs.

A very rough calculation would suggest that, at today's prices (for reputable products) the marginal difference between all UK households having all-RCBO CUs and their having MCB+2RCD ones would probably be in excess of £2billion.

Kind Regards, John

 

[JohnW2]

All RCBO & AFDD is coming...

If anyone buys them!

 

[fluorescence]

I wandered away from your question somewhat and went on a bit of a ramble. It happens.

As I said, that appears to be where we are heading - and I was asking whether people thought there was a reasonable justification. You clearly think that there is.
Yes, as I said, they will get cheaper. Currently, you would probably only get questionable ones for £12 (most are double that, or more) and, in any event, even £12 is about five times more than a (decent) MCB.
Quite a few - but that's essentially just a 'convenience' issue. Anyway, in reality, in most cases (probably nearly all cases other than those due to N-E faults), it's easy enough to identify what circuit is resulting in the trip, the difficulty (when there is one) being in ascertaining what it is within that circuit that is causing the trip - and that would be exactly the same with RCBOs.

A very rough calculation would suggest that, at today's prices (for reputable products) the marginal difference between all UK households having all-RCBO CUs and their having MCB+2RCD ones would probably be in excess of £2billion.

Kind Regards, John

 

[JohnW2]

I wandered away from your question somewhat and went on a bit of a ramble. It happens.

I think you actually responded to my question usefully, since you made it clear (with some reasons) that you do feel that a move to all-RCBO CUs is justified. That's what I was wanting people to tell me - so far it seems to be essentially 1-1 !

Kind Regards, John

 

[Notch7]

Rcbo populated CUs are becoming available

This one MK Sentry £160

https://www.screwfix.com/p/mk-sentry-12-module-6-way-populated-main-switch-consumer-unit/8318p

It seems to get rid of the compromise that exists when choosing circuits to go on a split board.

I guess it cuts the risk of a trip knocking out a freezer. The option to have a no rcd protection isnt possible in many circumstances for a freezer, so limiting the risk to one circuit must be better.

I think somebody on here said if an rcbo trips it isnt known whether that us overload or earth fault, but I guess if its only 1 circuit, those 2 fault conditions are prob easy to identify....

 

[plugwash]

Some trips can certainly be found quickly either by turning off circuits or by IR testing (though that for most people means calling in an Electrician which immediately adds a bunch of cost and time). Others are intermittent faults where the RCD trips often enough to be really annoying but infrequently enough to make diagnosis by elimination methods very difficult (say once a week or so). This is compounded by the fact that MCBs are only single pole so to fully isolate a circuit requires opening the CU and disconnecting the wiring.

RCBOs can help to narrow down the problem and reduce the inconviniance when a problem happens but as John hints at the benefit is reduce by the UK tradition of using a small number of high-power socket circuits. So even with RCBOs there can be a substantial amount of equipment on one breaker.

The problem is that there are no good stats on this sort of stuff. There is no central database that tracks all RCD trips. No database that tracks the amount of time and money householders spend dealing with RCD trips. No database that tracks how much more quickly the cause of those trips could be found with RCBOs and how much agro would be saved in the meantime. So we are stuck with making descisions based on anecdotes.

 

[EFLImpudence]

I'll put a spanner in the works by saying that the people who write the regulations just appear to have an attitude that that they can write whatever they want with no regard to the expense being justified or not. Two billion pounds could save a lot more lives if spent in other areas; e.g. the roads.
If they are that important, why not make them statutory?
Then there might be AFDD and/or surge protectors and whatever they decide to include.

Also, is the creeping coverage of a bit more regulation with every edition.
Firstly, RCDs were a requirement for sockets likely to be used for outside tools - fair enough, I suppose - but then it is for concealed cables - which, in effect covers just about everything unless installed intentionally to negate this, then all sockets - even upstairs in wooden-floored buildings, then lighting circuits are included.

As far as electrical safety is concerned,one RCD covering the whole installation was adequate, then two were required in the pretense of other safety considerations, namely not all the lights would go out and some sockets would still work - could they not have thought of that at the time?
A demand for an RCBO on every circuit would do nothing more for electrical safety - merely cause less inconvenience (if you want that, then you can have them fitted) so, in my view, would be a step too far and over-stepping the remit of the regulation writers.

There are a few other regulations which have nothing to do with electrical safety - merely a good idea anyone could do if they wanted -therefore they should not appear in the electrical regualations.

 

[EFLImpudence]

I forgot - the farce of non-combustible consumer units is a good example of what I mean.

 

[JohnW2]

Rcbo populated CUs are becoming available .... This one MK Sentry £160

Given that's the way we seem to be heading, that doesn't surprise me - even though I had personally noticed very few of them on offer.

I guess it cuts the risk of a trip knocking out a freezer. The option to have a no rcd protection isnt possible in many circumstances for a freezer, so limiting the risk to one circuit must be better.

True, but that particular issue can be addressed by having just one RCBO for a dedicated freezer circuit, with all other circuits being protected by two RCDs. In most houses, there is nothing other than a freezer circuit which is critical enough to need that.

I think somebody on here said if an rcbo trips it isnt known whether that us overload or earth fault, but I guess if its only 1 circuit, those 2 fault conditions are prob easy to identify....

That will have been me, and I did admit that it was a minor issue. However, I did fairly recently encounter one example. A friend of mine was suffering intermittent trips of an RCBO on a kitchen circuit, which eventually turned out to be due to an intermittent L-N short in an appliance. Although, as I said, fairly trivial, had it been an MCB that was tripping (or had there been an indication that the RCBO had tripped because of over-current), we would not have wasted time looking for water leaks and doing IR testing!

Kind Regards, John

 

[JohnW2]

Some trips can certainly be found quickly either by turning off circuits or by IR testing (though that for most people means calling in an Electrician which immediately adds a bunch of cost and time). Others are intermittent faults where the RCD trips often enough to be really annoying but infrequently enough to make diagnosis by elimination methods very difficult (say once a week or so). This is compounded by the fact that MCBs are only single pole so to fully isolate a circuit requires opening the CU and disconnecting the wiring.

All true - but I'm not convinced that RCBOs necessarily make that much difference (as per next point).

RCBOs can help to narrow down the problem and reduce the inconviniance when a problem happens but as John hints at the benefit is reduce by the UK tradition of using a small number of high-power socket circuits. So even with RCBOs there can be a substantial amount of equipment on one breaker.

Again, agreed.

The problem is that there are no good stats on this sort of stuff. There is no central database that tracks all RCD trips. No database that tracks the amount of time and money householders spend dealing with RCD trips. No database that tracks how much more quickly the cause of those trips could be found with RCBOs and how much agro would be saved in the meantime. So we are stuck with making descisions based on anecdotes.

Sure, and we're never going to have any reasonable stats about such things - only anecdotes and personal experiences. However, except in cases in which having RCBOs enables a houseowner to identify the cause of trips (and have that cause addressed by repair/replacement, if it is an appliance problem), I'm not sure that RCBOs would have a major impact upon the amount of time and money spent dealing with RCD trips - since, once it has become necessary to call out an electrician, the resultant costs are probably not usually going to be all that much greater in an 'MCB installation' as compared with an 'RCBO one'.

Kind Regards, John