Is metal stud-work required to be earthed?

[JohnW2]

Indeed. Although John w question was whether it had ever tripped and the person hasn't died, so I would assume someone had an only 30ma shock at some point due to not directly touching earthed metal, even if most mains shocks would be more than that or less

That was, indeed, my question, but I don't fully understand the rest of what you're saying. Could you perhaps clarify?

As Simon has said, an RCD in no way limits the shock current, only it's duration. However, bear in mind that whether or not a shock of a particular current proves fatal depends upon the duration, as well as magnitude and path, of the shock current - so that there is a theoretical possibility of an RCD preventing death even if the shock current is considerably more than 30mA.

Kind Regards, John

 

[JohnW2]

Well as per your first post, I certainly might have died, I'm certainly glad there was an RCD. Given my lake of experience of electric shocks there's a good possibility my other hand was touching earthed metal on the back of the cooker switch rather than the other one....

Fair enough, but I was just going by what I was told - both dave1x and yourself said that the shock was only "across one hand", and what I wrote in response was qualified by "unless there were some other path from yourselves to earth"

I'm not sure what would have had to have happened to fulfill your criteria, lying in a metal earthed bath with live wires connected into my heart?

That might do it It's obviously never going to be possible, in retrospect, to be sure of anything (when the person survives). However, the sort of case in which I would say that it was likely that an RCD might have prevented death would be one in which there was only one 'obvious' point of contact (usually a hand). In that situation, it's probable (although not certain) that the other point of contact was 'remote' (e.g. the other hand/arm or a leg/foot), so that it's likely (although not certain) that the path through the body was a 'potentially dangerous' one.

I'm happy there's a significant window of opportunity for an RCD to save a life by tripping due to an electric shock.

Don't get me wrong - just as I fitted seatbelts to my car long before they became compulsory, so I installed RCDs before any regulations required them. Given that the downsides seemed minimal, it seemed worth having them if there was any conceivable chance that they might one day save my life, or someone else's life. I'm just far from sure how many lives they actually have saved, and hence whether the hundreds of millions, if not billions, spent on buying and installing them have been spent in the best way to 'save lives' of our population.

But I have no direct evidence for obvious reasons.

There never really can be much 'direct evidence' ... if, in the absence of an RCD, a person suffers an electric shock and dies, one can never know what would have happened in the presence of an RCD. If, in the presence of an RCD, a person suffers a shock which trips the RCD and survives, one can never know what would have happened in the absence of the RCD. The only things of which one can be certain is that if a person dies despite operation of an RCD, then nothing other than a faster-acting RCD (if such exist) could have saved them, AND if they don't die (or suffer serious injury) when there is an RCD, than an RCD would have made no difference.

Kind Regards, John

 

[John D v2.0]

Yep agreed John. Simon's point was the RCD wouldn't limit the magnitude only the duration, but I was saying that other external circumstances may limit the magnitude, such that the shock is only 30ma for 30ms.
Since you point out that death risk is a function of both magnitude and duration as well as the nature of the shock I think we are basically in agreement, just you want harder evidence then me to be sure.

 

[John D v2.0]

I'm just far from sure how many lives they actually have saved, and hence whether the hundreds of millions, if not billions, spent on buying and installing them have been spent in the best way to 'save lives' of our population.

me neither, but the cost to find that out may also be higher!
How should the balance between doing something based on limited information or increasing that information. The reality is a blend of both, look at the part p rules.

 

[JohnW2]

Since you point out that death risk is a function of both magnitude and duration as well as the nature of the shock I think we are basically in agreement, just you want harder evidence then me to be sure.

Indeed - although, as I have just written, I find it hard to see how 'hard' (or harder) evidence will ever be available.

Even with seatbelts, it's much the same at the level of individual cases. If a person survives an accident with a seatbelt, one cannot know for sure whether what would have happened in the absence of a seatbelt, and if they die whilst not wearing a seatbelt, one cannot know for sure whether they would have died with a seatbelt. However, in this case, there are enough incidents for one to be able to see that the introduction of seatbelts led to a reduction in the number of deaths (although maybe the same, or even higher, number of 'serious injuries' {cases which would have been deaths in the absence seatbelts}). There are so few electrocutions, that the impact of RCDs on the number is difficult/impossible to determine - although it is clear that there has not been much of a reduction (given that there were so few in the first place 'to reduce').

Kind Regards, John

 

[JohnW2]

me neither, but the cost to find that out may also be higher! How should the balance between doing something based on limited information or increasing that information. The reality is a blend of both, look at the part p rules.

One also has to factor in the practicality of limited resources.

As I often say, given that, at the time (of the start of introduction of RCDs), there were probably about 100 times deaths on the roads than domestic electrocutions (ones that could conceivably have been prevented by RCDs), one cannot help but wonder whether spending the "hundreds of millions" on some aspects of road safety may have saved more lives. The ideal would, of course, be to 'do both', but 'we' doo/did not necessarily have the resources to do that.

Kind Regards, John

 

[John D v2.0]

The road safety budget is gigantic though! Due to the high cost of a fatality it has to be.

 

[JohnW2]

The road safety budget is gigantic though! Due to the high cost of a fatality it has to be.

Maybe, but road safety was just an example. Given that domestic electrocution represents a tiny proportion of accidental/traumatic deaths in the UK, there are undoubtedly other areas where "a few hundred million" could make a significant difference (and potentially a greater difference than do RCDs). Such an investment in 'efforts' might even have an appreciable impact on such issues as smoking, drinking, obesity, diet etc. etc.

One has to remember that even if RCDs could abolish all domestic electrocutions (which is clearly an unrealistic expectation), the effect on the total of accidental/traumatic deaths would be almost unnoticeable.

Kind Regards, John

 

[ban-all-sheds]

If, in the presence of an RCD, a person suffers a shock which trips the RCD and survives, one can never know what would have happened in the absence of the RCD.

I guess that saying "let's try it again, only this time without the RCD" would not be a viable option....

 

[SimonH2]

I believe that sort of experiment is hard to get past the ethics committee

 

[JohnW2]

I guess that saying "let's try it again, only this time without the RCD" would not be a viable option....

Neither of us usually like 'guessing', but on this occasion I think I can say fairly confidently that your guess is correct.

Kind Regards, John

 

[ban-all-sheds]

I believe that sort of experiment is hard to get past the ethics committee

elf'n'safety gone mad.

 

[JohnW2]

elf'n'safety gone mad.

I'm not sure that it's mad in this particular case!

I'm old enough to remember the days before formal Ethics Committees, at least as we now know them, existed, and there was certainly some 'interesting' medical research undertaken in that era - scientifically probably 'superior' to what we can do these day, but .....!!

Kind Regards, John

 

[ban-all-sheds]

It was meant to be a joke.

 

[EFLImpudence]