Is "the era of dual-RCD CUs long gone" ?

[JohnW2]

In another thread ...

RCBOs, one for each circuit. ... The era of a single RCD is long gone. So is where 2x RCDs were installed.

I would agree that the era of 'a single RCD CU' is 'long gone', and I also accept there's a lot to be said for RCBOs, and that all-RCBO CUs are increasingly being installed.

However, is it really true that 'the era of dual-RCD CUs is also long gone'? An awful lot of them still seem to be advertised, and hence are presumably being bought by someone, but does 'the era is long gone' imply that electricians not only don't install them any more, but haven't for quite a while? - which I personally find rather hard to believe.

I have deliberately offered only a very short list of responses to the poll question, since it's really just a Yes/No question. I would suggest that anyone who would not answer 'Yes' but would like to qualify a "No" answer in some way should probably vote "No", since if they were to give as 'qualified No' response, it would presumably mean that they did not believe that 'the era was over' - at least, not 'totally over'.

Kind Regards, John

 

[SUNRAY]

A one bed flat with 4 circuits does not yet require the additional expense. Personally I'm not convinced it requires 2 RCD's... Sunray Ducks.

 

[mattylad]

What is to replace dual RCD's ?

What do the regs tell us we need now?

Dammit! I got a dual RCD board with plastic enclosure I have not fitted yet, only been hanging onto it for 13 years

 

[bernardgreen]

In 1980 the use of a dual RCD was considered by the electricity supply company to be un-acceptable. The person sent to connect the supply to our building site declined to make the connection,

A phone call to his boss was made to explain that one RCD was for the caravan we were living in and the other RCD was for the supply to the building site. Pointing out that an accident involving electrical tools on the building site could trip an RCD, With only one RCD this would leave us without power in the caravan when first aid might be needed.

This was accepted as being common sense and the person was sent back the next day to make the connection.

 

[ericmark]

Cost is taken with cheap versions as if considering cost will not go for expensive. So Fusebox prices £17.16 for RCBO short, or £12.12 for type AC, £13.19 for type A long. And £119.40 for AFDD type. MCB is £2 and a RCD £19.76 for 63 amp and £25.22 for 100 amp both type A. So under 4 ways RCBO is cheaper. So only as we look at 5 way and over is there really any saving.

Even with 4 MCB's per RCD I have seen nuisance tripping, no faults found, we should check the back-ground leakage will all running is less than 9 mA, but near impossible to do with a new installation as no idea what will be plugged in.

To comply with regulations every installation shall be divided into circuits, as necessary, to take account of danger that may arise from the failure of a single circuit such as a lighting circuit, and reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation.

Not equipment not simply the fixed wiring, I know there was an argument the RCD did not form a circuit, but that is really clutching at straws, however increasing the number of RCD's is not going to necessary increase safety, the same argument which has been put forward for SPD goes for twin RCD it is up to the client to decide if he was to pay for part insurance against damage from surges, or tripping of the RCD, it is suggested the electrician gets a disclaimer signed when not fitting SPD the same applies for not fitting all RCBO, or fitting type A RCD's.

I the undersigned has requested RCBO's/SPD are not fitted and understand the problems associated with not using them.

If the owner is asked to sign that, then in the main I can't seen RCD's being used. The real question is where the property is not occupied by the owner, if a landlord signs the above, would be then be libel for any claims over loss of food or injuries due to an RCD tripping. Would the landlord insurance cover him?

 

[JohnW2]

A one bed flat with 4 circuits does not yet require the additional expense. Personally I'm not convinced it requires 2 RCD's... Sunray Ducks.

Well, as I've (very often!) said, I'm not sure that I necessarily agree with those who believes that 314.1 precludes the use of a single RCD protecting the whole installation, particularly if 'emergency lighting' is installed. Given the existence of power cuts (quite commonly for me), I personally think that 'emergency lighting' is far more important than splitting circuits across two or more RCDs/RCBOs.

For the first ~15 years I was in my present house, I lived with was effectively and 'up-front' single RCD (actually 3 of them, one for each phase, but since each floor was supplied by only one phase, that was almost the same as one RCD protecting a whole installation) without any problems or appreciable 'inconvenience'.

Kind Regards, John

 

[JohnW2]

Even with 4 MCB's per RCD I have seen nuisance tripping, no faults found ....

As I've often said to you, experiences clearly vary. Despite having very many RCDs (probably ~12 in total) without any attempts to restrict the number of circuits are protected by each (and certainly 4 or more in a good few cases), in more than a couple of decades I have experienced virtually no "nuisance trips" (no faults found).

... we should check the back-ground leakage will all running is less than 9 mA, but near impossible to do with a new installation as no idea what will be plugged in.

If one experiences problems, then that would be a useful exercise but, as I've said, in my case it would be (would have been) essentially 'wasted effort'.

Kind Regards, John

 

[JohnW2]

As you might imagine, I'm somewhat surprised by the evolving pattern of voting.

However, I wonder if those of you who are answering "Yes" are taking my question literally enough. I have acknowledged that there is an ongoing progressive move to all-RCBO CUs (hence an ongoing progressive decrease in the proportion of dual-RCD ones), but that's not what I'm asking about.

The question asks whether "the era of dual-RCD CUs is 'long gone' ". My expectation was that people who believe that some dual-RCD CUs are still being installed would answer "No", and even those who didn't believe they were still being installed would also answer "No" unless they believed that no-one has been installing them for several years (the era "long gone").

I suspect that some of you are (as per flameport's statement which prompted this poll) answering in terms of your personal opinion as to whether dual-RCD CUs should still be installed, rather than answering the intended question about whether they are being installed (and have been installed in recent times) (i.e. "the era is NOT long gone").

If, as a result of the above comments, any of you wish to change your vote, this poll is configured such that you can.

Kind Regards, John

 

[ericmark]

In a home we don't want to lose lights if there is a fault with some thing plugged into sockets, we also don't want even in an emergency extension leads trailing up or down the stairs.

So safe split for sockets is side to side of the home, and the sensible split for lights is floor by floor, so near impossible to do that with two RCD's.

It only requires one RCBO with a high integrity consumer unit to allow sockets split side to side and lights split upper and lower, however a RCBO is a RCD so that means three not two RCD's duel means two, so yes I think the days with only two RCD's have gone.

Maybe not yet into the era of all RCBO's but that was not the question, the big question is if worth having freezers on a RCD shared with many other items, I am not saying a circuit dedicated to freezer, but I am saying keeping the items using the same RCD as freezer to a minimum. A RCBO is less than £20 and a freezer full of food looking at £200 at least, so having the kitchen ring final on it's own RCBO makes sense.

OK having 14 RCBO's like I have in my own house may be going a little OTT, but two RCD's/RCBO's is going the other way, yes I know most caravans use just two RCD's in series, but even the rows of terraced houses had 4 rooms and a stair way, often with the out houses now linked to main house, so far bigger than a caravan, and also a caravan has in the main 12 volt lighting.

 

[JohnW2]

In a home we don't want to lose lights if there is a fault with some thing plugged into sockets ...

... and, as I said, nor do we want to lose lights if there's a power cut, and nothing about the arrangement (or number) of protective devices in the CU can do anything about that.

As I always say (because it's true ), the only thing which avoids loss of lights in a power cut is emergency lighting, and that will also address the (very rare) situation you seem to fear. Why adopt a 'solution' which only addresses 'half' of the potential issue (and a much smaller 'half' in my house!) ? when there is a solution which will address all of the potential issue?

Kind Regards, John

 

[securespark]

I remember in 1986 fitting a 10 Milli shower circuit. Norweb chap came to check it over.

He would not connect it until I swapped the 45A MCB for a cartridge fuse and swapped the MEBs to 6mm².....

 

[JohnW2]

I remember in 1986 fitting a 10 Milli shower circuit. Norweb chap came to check it over. ... He would not connect it until I swapped the 45A MCB for a cartridge fuse and swapped the MEBs to 6mm².....

Did he offer any explanation for that daft 'requirement'?

Kind Regards, John

 

[securespark]

I talked to him about it. I said the adiabatic supported 4mm². I asked him what the PILC size was.

He told me it should be 7/.052 so I said in that case, 4 is fine. But ultimately, I had to cave.

He also said the characteristics of the MCB were not right for the circuit. Can't remember why.

In those days, if you didn't get passed, you didn't get connected.

 

[JohnW2]

I talked to him about it. I said the adiabatic supported 4mm². I asked him what the PILC size was. ... He told me it should be 7/.052 so I said in that case, 4 is fine. But ultimately, I had to cave.

The fact that 4mm² was adequate (if that was true) obviously does not, in itself, necessarily mean that 10mm² would not also be acceptable.

A number of moons ago, I illustrated that there was a theoretical problem with using 'oversized' (T+E) cables - although I doubted (and still do doubt) that it is ever a problem in practice.

A larger size of T+E will mean a larger CPC and therefore a higher PEFC. Particularly if Ze is very low, it is probably not impossible that the CPC of the larger cable would not be (adiabatically) adequate for the increased PEFC - but, as above, I very much doubt that this is ever the case in practice.

Kind Regards, John

 

[sparkwright]

As you might imagine, I'm somewhat surprised by the evolving pattern of voting.

However, I wonder if those of you who are answering "Yes" are taking my question literally enough. I have acknowledged that there is an ongoing progressive move to all-RCBO CUs (hence an ongoing progressive decrease in the proportion of dual-RCD ones), but that's not what I'm asking about.

The question asks whether "the era of dual-RCD CUs is 'long gone' ". My expectation was that people who believe that some dual-RCD CUs are still being installed would answer "No", and even those who didn't believe they were still being installed would also answer "No" unless they believed that no-one has been installing them for several years (the era "long gone").

I suspect that some of you are (as per flameport's statement which prompted this poll) answering in terms of your personal opinion as to whether dual-RCD CUs should still be installed, rather than answering the intended question about whether they are being installed (and have been installed in recent times) (i.e. "the era is NOT long gone").

If, as a result of the above comments, any of you wish to change your vote, this poll is configured such that you can.

Kind Regards, John

I would say SOME dual RCD boards are still being fitted, but not many - which may suggest the era of dual RCD boards has long gone. They are not as widely used as they were 13 or so years ago, which tells me the era is dead - even though people still fit them from time to time.

If people didn't believe dual RCD boards were still being installed, why would they vote no? And if they believed no one had installed them for several years, why is that any different to the previous sentence?

I feel even though dual RCD boards are still made, and fitted from time to time, the era of dual RCD boards may be long gone, or at least becoming long gone, as I haven't noticed many people using them - because of relative cheapness and easieer fault finding.

For what it's worth, the last dual RCD board I fitted was about five years ago. And the last one that someone I know would have installed is around five years ago too.

In short, dual RCD boards appear to be out of favour now and totally undesirable, notable exceptions where cost is important, but the benefits to both the electrician and the customer of all-RCBO boards are so strong, the era of dual RCD boards has passed.

So, what am trying to say is that even though dual RCD boards are still made and sometimes installed, the 'era' of dual RCD boards has gone - because I believe we are now in the 'era' of all-RCBO boards.

Well we are, aren't we?