1. Lighting circuit safe area, does it need RCD? 2. RCD maximum current smaller than combined rings

[JohnW2]

.... While it may not be necessary to protect "workers" on "Lighting Only" circuits in this way, unskilled workers have been electrocuted in this country by inadvertently coming into contact with non-RCD protected Lighting circuits. This caused regulations to be changed to require RCD/RCBO Circuit Breakers on all (new/altered) final sub-circuits - including lighting only circuits. .... No doubt it will take a few similar deaths in other countries before the regulations are changed in those countries.

In the UK, we're getting very close to current regs requiring RCD protection of everything, but given that these requirements are not retrospective, it will be a very long time before that is reflected by by what one sees in all UK installations. However, in relation to what you say, to repeat something I've talked about many times before ....

... I am yet to be convinced of the effectiveness, particularly the ('impassionate') 'cost-effectiveness' of RCDs (or RCBOs) in relation to the prevention of deaths (and probably also serious injuries). For many years, I have been asking (here and elsewhere) people for reports of occasions on which someone has suffered (and survived) an electric shock which has tripped an RCD/RCBO - since those are the only case in which they may have died in the absence of an RCD (i.e. the RCD 'saved a life'). However, I have so far heard of almost no such occurrences.

In terms of 'cost effectiveness', I observe that the very widespread purchase and installation of RCDs/RCBOs has cost an awful lot ('billions') and that the same amount of money spent on other things (road safety, reduction in violent crime, illicit drug use etc.) would probably have had the potential to avoid far more deaths than is the case with installation of RCDs/RCBOs. In the UK, the number of deaths due to domestic electrocution in a year is appreciably less than the number of deaths on the roads, or due to drug abuse, in a week, and not much less than the number of murders per week.

That does, of course, not mean that RCDs are incapable of 'saving lives'. However, their greatest value is probably not in operating at the time of a shock but, rather, in resulting in the clearance of an L-E fault (of too high an impedance to cause an OPD to operate) before anyone gets a shock - but it is essentially impossible to get any statistics about that. However, I would imagine that (in TN installations) most L-E faults are of sufficiently low impedance to be cleared by an OPD, so RCDs/RCBOs probably don't make all that much difference.

While the cost of RCBOs on each and every circuit is still somewhat higher than having RCDs protecting several circuits with MCB overload protection, the difference is not very great and there is the convenience of knowing which circuit has activated any RCBO concerned as compared to not knowing which circuit has caused an RCD, which is "protecting" (the user of) a number of MCB protected circuits, to trip.

True, but there is also the inconvenience (with a standard RCBO) of not knowing whether it has operated as a result of over-current or residual current - some sort of 'flag' to indicate that would be helpful. Another issue is that, at least in the UK at present, the great majority of RCBOs are single-pole, which introduces a few issues.

Kind Regards, John

 

[flameport]

For many years, I have been asking (here and elsewhere) people for reports of occasions on which someone has suffered (and survived) an electric shock which has tripped an RCD/RCBO -

Unless people visit hospital or some other authority is involved, such things will almost never be reported, so that information will never be available.

 

[JohnW2]

Unless people visit hospital or some other authority is involved, such things will almost never be reported, so that information will never be available.

That's the problem (and would remain a problem, even if they had sought medical attention), and all one can do is to ask as many people as possible. I've been pursuing this quest for years, and have asked the question whenever I've had a chance - in numerous on-line forums, in meetings with hundreds of attendees etc., and have only ever got one or two 'positive' responses (having weeded out those who experienced 'a tingle' at the same time as tripping an RCD {on an 'isolated' circuit} by creating an N-E fault!) - and there is far from any guarantee that even those who gave ';positive responses' would have died in the absence of the RCD.

However, none of that affects my pondering about 'cost-effectiveness'. With only something like a couple of dozen domestic electrocutions per year in the UK, at least some of which are probably of a nature that an RCD could not have prevented, there is very little scope for any 'measure' to have much impact on the number of deaths. There is always the "one death is one death too many" argument, but one has to be fairly impassionate - I imagine, for example, that 'questions would be asked' about the wisdom of spending 'billions' on measures which reduced the number of road deaths by ~20 per year.

... and, of course, at least some of that couple of dozen domestic electrocutions could, for all we know, be examples of someone having died despite the presence of (satisfactorily functioning) RCD protection.

Kind Regards, John

 

[AndyPRK]

and no the RCD won't trip over 60A

As has been said, a 60A RCD is designed to allow 60A to flow through it. It you were to put 70A though it, it may get hot and/or its life reduced.

 

[JohnW2]

As has been said, a 60A RCD is designed to allow 60A to flow through it. It you were to put 70A though it, it may get hot and/or its life reduced.

It's not so much that it is "designed to allow 60A to flow through it" (which I'm sure would be no problem, even if appreciably exceeded) but, rather that it is "designed to be able to break a current of 60A", which is a much more demanding requirement.

However, in terms of the OP's concerns, it's no different from Main Switches. They are usually rated at 100A, sometimes only 80A, but if one adds up the ratings of all the MCBs in the CU, it would not be unusual to get a figure approaching 200A.

Kind Regards, John

 

[DetlefSchmitz]

However, I have so far heard of almost no such occurrences.

My report to you, at the time you asked the question, of my son receiving such a bad shock when changing a badly designed GX53 LED lamp (with touchable live parts) and tripping the RCD in the process was one such occurrence. However you decided that it didn't match your assumptions and dismissed it.
Since you are proposing that RCDs don't save lives, I propose that they do.

 

[JohnW2]

My report to you, at the time you asked the question, of my son receiving such a bad shock when changing a badly designed GX53 LED lamp (with touchable live parts) and tripping the RCD in the process was one such occurrence. However you decided that it didn't match your assumptions and dismissed it.

Yep, that's one of the "almost no such occurrences" I've heard of. I can't remember the details, but I very much doubt that I would have 'dismissed' it.

Since you are proposing that RCDs don't save lives, I propose that they do.

Not really. You are 'proposing' that they save lives. I am saying that we just don't know, but that we have very little evidence that they do save a significant number of lives.

I am also pointing out that we can say with certainty that they cannot be saving 'many lives' (since there aren't very many 'lives to save').

Kind Regards, John

 

[AndyPRK]

To be impartial.

Ok, so the RCD tripped. That does not mean your son would have died without an RCD.

 

[DetlefSchmitz]

To be impartial.

Ok, so the RCD tripped. That does not mean your son would have died without an RCD.

Absolutely. But the fact is that unless John sets up an experiment where 1000 people have their RCDs replaced with non-functional plastic boxes and we compared the results over 10 years with another thousand who do... or unless we simply experiment on people by making them touch a live connection without knowing whether they are being protected by an RCD, then we can never know, so in the end we have to rely on John's judgement. I don't see why his judgement should be consider more valid, just because he posts more

 

[JohnW2]

To be impartial. Ok, so the RCD tripped. That does not mean your son would have died without an RCD.

Indeed - but the point is that those who survive a shock which does result in an RCD tripping are those very few who may have died in the absence of an RCD.

If they survive a shock when there is no RCD protection, or when an RCD hasn't tripped, then they obviously can't be a person whose 'life has been saved' by an RCD!

Kind Regards, John

 

[JohnW2]

Absolutely. But the fact is that unless John sets up an experiment where 1000 people have their RCDs replaced with non-functional plastic boxes and we compared the results over 10 years with another thousand who do... or unless we simply experiment on people by making them touch a live connection without knowing whether they are being protected by an RCD, then we can never know, so in the end we have to rely on John's judgement. I don't see why his judgement should be consider more valid, just because he posts more

I think that's all rather unfair

For a start, controlled experiments are not the only way of gaining information - observational studies are also very valid, and are often (as in this case) all one can really do. Do you think that we discovered about the dangers of smoking, thalidomide, asbestos, mercury, lead, X-rays etc. etc.etc. by conducting controlled experiments/trials??

It's absolutely nothing to do with my 'judgement' - I am merely commenting on the paucity of evidence that RCDs save (or have saved) a significant number of lives - coupled with my more general (and I would have thought 'indisputable'!) observation that the scope has never existed for them to save many lives.

As a concept, one cannot (should not) accept that something (in this case, your view) is true, simply because there is not enough evidence to prove that it is not true.

Kind Regards, John

 

[DetlefSchmitz]

I think that's all rather unfair

I think my problem may be that you asked for anecdotal evidence to demonstrate the converse of your opinion, and then dismissed it because it did not prove anything. It may have been better not to ask.

In the real world we cannot run the same situation twice and observe the outcomes.


I take your point that deaths have (probably) always been low in number. However I doubt that the cost of an electrical installation is really significantly greater than before. Once things are made in quantity their prices get absorbed into a consumer unit package.
I also recognise that RCDs carry a nuisance factor. I have never had a random trip, but it seems that there are quite a few happening to other people.

I guess the point is that the committees are inevitably manned by members of interested electrical manufacturing companies, so there will always be new requirements imposed. If this didn't happen then the economies of making electrical equipment would cause even more companies to give it up, or prices would rise, or standards would fall even lower.

At least with (say) RCDs, we get something tangible for our money. The target of your campaign would better be such things as mandatory EICRs, where money spent almost certainly does not equal value received.

 

[bernardgreen]

in the hospital environment many power sources are protected by 10 mA RCD when they are supplying equipment that connects to the body.

The mechanism of "death by electricity" is a very complicated mechanism.

To re-start a heart that has started to fibrillate ( rapid random contractions that do not pump blood ) the casualty is given an electric shock to stun the heart's nerves and stop it. After the shock the heart can self re-start into an effective pumping rhythm.

Hence a short duration shock ( such as that from a defibrillator ) is very un-likely to kill. Death happens when the duration of the shock is enough to cause tissue damage to vital organs.

Is the 40 milli-second duration before the RCD trips short enough to prevent tissue damage ?

There are too many variables to answer that question.

 

[Taylortwocities]

And 30mA can be enough to kill you. IIRC a current of only 10mA MAY be enough to start AF. That could be fatal in some people.
It’s not a precise science.

 

[JohnW2]

I think my problem may be that you asked for anecdotal evidence to demonstrate the converse of your opinion, and then dismissed it because it did not prove anything. It may have been better not to ask.

I take your point, but the purpose of my 'exercise' was to try to get some sort of handle on the extent of anecdotal evidence - i.e. if I had come across a good few reports of survivors of shocks that had resulted in RCD trips, then that would obviously have appreciably increased the pool of people whose lives may have been saved by RCDs, in which case I would probably be thinking differently about the possible 'answer' (which we will never know with certainty).

I take your point that deaths have (probably) always been low in number.

Surprising though it may be, data on 'electrical deaths' is not all that good. Accepting all the uncertainties in the data, perhaps the most interesting thing is the apparent lack of any marked apparent difference between such deaths in the pre-RCD era as compared with today.

However I doubt that the cost of an electrical installation is really significantly greater than before. Once things are made in quantity their prices get absorbed into a consumer unit package.

That's obviously true to some extent, and the (financial) cost of having RCDs is clearly a lot less than it would have been a decade or two ago. Nevertheless, there must be at least tens of millions of RCDs out there, and they all cost something

I also recognise that RCDs carry a nuisance factor. I have never had a random trip, but it seems that there are quite a few happening to other people.

Same here. I've personally lived with many RCDs for very many years and have hardly ever suffered any 'nuisance trips' - but, as you say, some people appear to be much less lucky. However, unless they became a major issue (which I doubt they are, for anyone), I would never suggest that, in itself, as a reason for not having RCDs.

I guess the point is that the committees are inevitably manned by members of interested electrical manufacturing companies, so there will always be new requirements imposed. If this didn't happen then the economies of making electrical equipment would cause even more companies to give it up, or prices would rise, or standards would fall even lower.

These are, of course, very different issues, and not ones that I have even gone near in my discussions on the subject. In fact, I'm not at all sure that the sort of commercial considerations are much of a factor (in relation to RCDs), since I strongly suspect that, rightly or wrongly, many of those decision makers sincerely believe (as you seem to) that RCDs save a significant number of lives, and therefore have supported the requirement for them on that basis.

At least with (say) RCDs, we get something tangible for our money. The target of your campaign would better be such things as mandatory EICRs, where money spent almost certainly does not equal value received.

I would say that anything with major cost that was being done/proposed in the name of electrical safety' needs to be carefully scrutinised since, as I have said, I this one has to be fairly dispassionate (or is it impassionate?!) in relation to the cost-effectiveness of any such things.

As I've implied, in the final analysis it is probably pretty difficult to justify any major expense in relation to electrical safety (at least, in terms of the reduction in 'electrical deaths'), given that the number of 'electrical deaths' is seemingly so surprisingly low - which is why I tend to talk about possibly diverting resources to totally different things (roads, drugs, violence etc.) rather than to other 'electrical safety' measures.

Kind Regards, John