All-RCBO CUs - because we can?

[seasickstevie]

... 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.

The alarm panel?

When the neighbourhood's had a disturbed night's sleep because the family down the road have been on holiday all week, the stand-bye (hold-off) battery has finally given up, and the self-actuating bell has kicked off at 2am, and no-one in the street has got a clue what to do about it. All because the pond pump has tripped the RCD last Tuesday.

 

[JohnW2]

Some people would rather sit in the dark for five hours waiting for someone to arrive, than operate a few MCBs.

I know. I've known a good few in my family (interestingly, all female). Until her dying day (which was less than 30 years ago), my grandmother would not even touch a light switch (or anything else electrical) - so would literally sit in the dark for hours, or days, if no-one was available to switch on the light!

Kind Regards, John

 

[JohnW2]

The alarm panel? ... All because the pond pump has tripped the RCD last Tuesday.

Yes, I'd expected that one, too - but I reckon you'd be hard-pressed to think of a third (in your average house) .

There are, of course, some 'cons', as well as 'pros' of having any sort of alarm on a dedicated circuit of its own (regardless of how it is protected).

Kind Regards, John

 

[SimonH2]

What do you mean by that? As I said, I have suffered no particular 'inconvenience' in the past 30 years that I would not have suffered with RCBOs.

Obviously everyones' experience is different. I've had quite a few (don't have a number) over a shorter timeframe. One data point I can quote is that we've been in this house for 15 months and had 2 non-intentional RCD trips - both taking out the lights in half of the house as well as the socket circuit that was the source of the trip.

 

[seasickstevie]

... how many of that 'huge number of call-outs' would you say that the temporary loss of several circuits had result in a significant 'safety issue'/danger?

Went out to a 'pensioner's bungalow' a while ago, late at night ... a very cold night, where a couple - both disabled - had spent the whole evening in the freezing cold. The gentleman needed the power on asap for medical reasons. If they'd had a split board at least (yes JW, I know you're referring to RCBOs in this instance, but similar comparison maybe), they could've at least had some lighting and power.

At it was a Sunday night, they'd struggled to find anyone to come out.

Okay I've only mentioned one occasion, it's obviously a very small percentage, there are others, but none-the-less, can have dramatic consequences.

(Sorry to be replying to multi posts simultaneously)

 

[JohnW2]

Obviously everyones' experience is different. I've had quite a few (don't have a number) over a shorter timeframe. One data point I can quote is that we've been in this house for 15 months and had 2 non-intentional RCD trips - both taking out the lights in half of the house as well as the socket circuit that was the source of the trip.

Yes, I did admit that I might have been unusually lucky, and quite probably very atypical. In that same 15-month period, I don't recall any RCD trips (either 'real' or 'nuisance'), but there certainly have been several brief power cuts, all long enough to have been associated with risk had they occurred during the hours of darkness whilst someone was holding a pan of hot oil, up a ladder or on the stairs!

... and, having just done some quick mental totting up, for about 20 years I have been living with about 10 RCDs and 2 RCBOs, which presumably ought to put me at above-average risk of 'nuisance trips'.

Kind Regards, John

 

[JohnW2]

Okay I've only mentioned one occasion, it's obviously a very small percentage, there are others, but none-the-less, can have dramatic consequences.

Fair enough - but do you think that is the only one out of your 'huge number' where you can recall anything approaching a significant 'safety' issue? I've obviously never doubted that it can happen very occasionally - the question being whether it is common enough to justify 'changes' (and see below regarding what changes). And, in any event ....

... we need to remember what I've been talking/asking about - which is whether there really is a good reason (other than "just because we can") why we should move from 'the present situation' to all RCBO CUs - and that 'present situation' (at least, the one I was referring to) was for us to have dual-RCD CUs (maybe also with one or two RCBO circuits). Every suggestion regarding 'safety-based' reasons for such a change have revolved about 'being plunged into darkness' (and/or 'into coldness') - and, as you have agreed in what you have just written, that risk could be alleviated by having a dual-RCD board with a sensible distribution of circuits between the two RCDs.

As far as I can see, there really are no 'safety' advantages of all-RCBO over (sensibly arranged) dual-RCD ones, the only 'advantages' being matters of convenience of one sort or aniother.

Kind Regards, John

 

[seasickstevie]

I suppose the use of 'huge number' is relative , but iro 100 in the last couple of years have been due to RCD tripping. Even say 2% can be of concern.
Like I say, that example was due to single RCD rather than split '17th edition'. But even then, separate RCBOs would've been yet more beneficial, leaving 100% of the lighting on, and maybe the 2nd ring final. Whereas a split (only) board may have taken out 50% of the lighting. These were 'vulnerable' people.

I guess the comment one could make is 'some' instances like this, is ... at what point should people be moving to supported living?

 

[JohnW2]

I suppose the use of 'huge number' is relative , but iro 100 in the last couple of years have been due to RCD tripping. Even say 2% can be of concern. Like I say, that example was due to single RCD rather than split '17th edition'. But even then, separate RCBOs would've been yet more beneficial, leaving 100% of the lighting on, and maybe the 2nd ring final. Whereas a split (only) board may have taken out 50% of the lighting. These were 'vulnerable' people.

Fair enough, but you probably know what question is coming next (since although almost, you haven't quite completely answered it) ... what proportion (if any) of these cases do you think would have represented an appreciable risk to anyone if they had had (sensibly wired) dual-RCD boards?

As I said early on, a wild estimate of the marginal additional cost (at today's prices) of all UK households having all-RCBO (as compared with dual-RCD) CUs is probably in excess of £2billion, and the question to be asked is whether the 'advantages' offered by the RCBOs justify that much money being spent on them, rather than on something else.

I guess the comment one could make is 'some' instances like this, is ... at what point should people be moving to supported living?

Indeed - particularly if they were such as to not be 'safe' for a few hours, even if they had a dual-RCD CU (hence at least 'some light and some heat').

Kind Regards, John

 

[Notch7]

Do some electricians when quoting for a board change offer the customer the choice?

IE: you can have a shiny new metal split board, or a shiny new metal rcbo board for xyz extra.

How much more are we talking? £150 or so?


I dont know what percentage of board upgrades identify an old existing problem, so maybe an rcbo could make the install a bit easier (I dont know, just pondering). I imagine there must be times when an old pre rcd board is upgraded and the new one suffers from trips.

I do know when our electrician wires orangeries, sometimes it is easier to go back to the board even if its not strictly necessary, since the extra cost is offset by not having to carry out testing of existing circuits -some of our jobs are one very old houses.

 

[seasickstevie]

I always give people the choice, partly because, as you say it can reduce the overall inconvenience if just one circuit suffers nuisance tripping as opposed to something like 50% of the installation.

But often RCBOs is the natural choice because the width of the CU is greatly reduced, and sometimes it's the best way of getting a board into a restricted space.

 

[SimonH2]

... but there certainly have been several brief power cuts ...

Well yes, a power cut is more of a problem since it will take out everything (not just 50% as with a split board) and may well also take out streetlighting which in our house is sufficient illumination to get to the bathroom and back at night without turning any lights on. I've recently mentioned this in relation to the church and hall which currently have no emergency lighting. Plus there's no street lighting near church anyway so that wouldn't help if it were an internal problem.
However, power cuts are something we can generally not do anything about other than installing (eg) battery backed systems (UPS for boiler and emergency lights). Deciding whether to go split board or RCBO is something we can make an individual choice over.

But often RCBOs is the natural choice because the width of the CU is greatly reduced, and sometimes it's the best way of getting a board into a restricted space.

That is indeed a good argument for RCBOs. In our house, the original house has been rewired and the size of board fitted would not allow the space for separate RCDs - there's an RCD used as the main switch so the whole of the original house is on one RCD. The extension is the same, so in effect we have a split board arrangement as far as circuits go - original house (lights, sockets, smoke alarms, boiler) on one RCD, extension (kitchen sockets, lounge sockets, cooker, lights, shed & greenhouse) on another. My intention is to combine everything into one board using RCBOs (it would be a struggle to get the width for two RCDs anyway) - eventually !

 

[JohnW2]

But often RCBOs is the natural choice because the width of the CU is greatly reduced, and sometimes it's the best way of getting a board into a restricted space.

That's an interesting point, which I confess has not occurred to me before - and I agree that it would be a distinct advantage in a few (albeit, I would think, not all that many) cases.

Kind Regards, John

 

[JohnW2]

Well yes, a power cut is more of a problem since it will take out everything (not just 50% as with a split board) and may well also take out streetlighting ... However, power cuts are something we can generally not do anything about other than installing (eg) battery backed systems (UPS for boiler and emergency lights). Deciding whether to go split board or RCBO is something we can make an individual choice over.

I don't really see those as truly different issues - the causes may be different, but the effects (inconvenience and potential dangers) are the same.

The question to be asked of (or considered in relation to) a customer is "Could a sudden loss of all lighting create a degree of inconvenience and/or potential danger that you would like to be protected against it?". If the answer is "yes", then the only way to address it (for all possible causes) would be to install some sort of emergency lighting (which could be very simple and cheap) - particularly if, as in my case, the situation is more likely to arise as a result of power cuts than RCD trips. If you just install RCBOs, not only will that probably be much more expensive, but it won't provide protection against some causes of situation the customer wants to be protected against.

Kind Regards, John

 

[SimonH2]

Yes, they may be different causes with the same effect - that doesn't mean we have to treat them identically.
If the risk is a true danger, then yes - treat them the same. I've been (albeit fairly briefly) in an environment where the aim was "no matter where you are, and if the place is full of smoke, you can still see to navigate to an exit without having to know your route. In many cases that's dealt with by lots of lights, or these days lots of strips of LEDs. In that particular case, all the corridors and stairwells were permanently lit and they'd gone for luminous markers along all the walls at skirting level. In the event of fire, got on your hands and knees below the smoke, and follow the green arrows - when the arrows turn to round dots, you've reached an exit door/stairwell. Only works with permanently lit areas - hence the qualification about them being so.

If it's inconvenience then part of the question is "how much is that inconvenience worth ?". With a split board, however you split it, you will have a selection of circuits that if tripped will (eg) stop your heating - and if the householder is the type that can't/won't reset something themselves then minimising that is "a good thing".

But now we're talking about it, I'm thinking that an emergency light where each of our smoke detectors is (and maybe powered from the alarm circuit) wouldn't go amiss. Then it's whether to make them standalone or use maintained fittings and replace the ceiling rose with them.