Wiki first safety page - SECOND DRAFT for comment

[IJWS15]

DIYer so apologies if this is already covered.

Would suggest more emphasis on not touching the supplier's fuse, it seems to be lost in a long paragraph.

In terms of testing for dead should they not be testing all conductors back to the same point they used to test the tester in the first place? What if they are all at 240v ??? - don't assume they are reading this before they start, they will probably be reading it after they have started something, got it wrong, and and looked on the internet for an answer to a problem they have created.

I wouldn't worry too much about stressing repeatedly the need to seek competent help, I feel I know what I am doing (I undersand I may be wrong) and would ignore the advice for the things I do undertake but those a little uncertain may actually take the advice and call an electrician.

 

[stillp]

You're absolutely right to point out the risk of injury from secondary effects, such as falling off the ladder. Is it worth adding that RCDs don't reduce the secondary risk at all?

Thanks. I'd be intertested to hear the views of others, but I'm personally inclined to think that it's probably best to keep that section about 'risks' as brief and simple as possible, and therefore wonder about the worth (on balance) of adding detail.

I'm not even convinced that what you suggest is actually strictly true. I suspect (but don't know for sure) that, particularly if the current through the person is modest (i.e. not much above 30mA) for what (in practice, not spec) is unlikely to be much more than 30msec might well reduce the chances of those secondary injuries, at least to some extent.

Is that your only comment on the draft? If so, I'm flattered

To all: I hope to be posting the third (hopefully 'final-pre-posting-into-wiki') draft later tonight - so, if there are any more comments, I'd be grateful if you could speak out soon. Thanks.

Kind Regards, John

I'll check later, but I believe the reaction threshold for adults is about 10mA for 5 ms. A normal RCD will have no affect on that whatsoever.
That was the only thing that leapt out at me. I'll try to have a better look at your draft this evening, but I'm away on a 'jolly' at the moment with a machine safety committee.
I take your point about the length of the risk section. it might be better to separate the shock risk from the secondary risk to avoid an overlong paragraph.

 

[JohnW2]

Isolation can also be achieved by disconnecting cables inside CU?

Indeed it can, but I personally have definite reservations about the wisdom of mentioning this to DIYers. As I said in relation to proving a voltage detector, the great majority of DIY work is not, in itself, going to require the CU to be opened. I do question the wisdom of advising them to open it and 'do things inside it' solely in order to achieve isolation. I accept that this is the only way to achieve 'double-pole' isolation (which some,including yourself, feel is essential in TT systems) for a single circuit, but I nevertheless seriously doubt that we should be advising DIYers to do it. Quite apart from the potential hazards of 'playing around inside a CU', identifying the correct neutral to disconnect (and then reconnecting it to the right place) could be fairly challenging for some of them. I think we need to keep our advice as simple as possible.

As well as jewellery, tie back long hair??

Yes, that's probably worth adding. Thanks for your comments

Kind Regards, John

 

[JohnW2]

Would suggest more emphasis on not touching the supplier's fuse, it seems to be lost in a long paragraph.

I'll have a look/think, but I thought this was already pretty clear. It's actually quite a short paragraph, and the "Never" regarding touching the supplier's fuse is the only word in that paragraph which is bold (maybe even also red in the final version), so I would have thought that it already 'stands out' pretty well.

In terms of testing for dead should they not be testing all conductors back to the same point they used to test the tester in the first place? What if they are all at 240v ???...

I'm not sure I fully understand. Are you talking about a situation in which L, N & E were all at 230V? If so, I agree that standard 'testing for dead' would not identify that - but it's an 'almost impossible' situation. Ironically, it's one of those situations in which a neon screwdriver or voltstick would (probably) identify the problem. Unless I'm missing your point, I don't think this is something we should be talking to DIYers about.

- don't assume they are reading this before they start, they will probably be reading it after they have started something, got it wrong, and and looked on the internet for an answer to a problem they have created.

I'm sure that's going to be true sometimes, but if they've already started the work (and survived), it's a bit late to be telling them about testing for dead, isn't it?

Thanks for your comments.

Kind Regards, John

 

[JohnW2]

I'll check later, but I believe the reaction threshold for adults is about 10mA for 5 ms. A normal RCD will have no affect on that whatsoever. ... I take your point about the length of the risk section. it might be better to separate the shock risk from the secondary risk to avoid an overlong paragraph

Very brief currents well under 10mA (in fact, well under 5mA) can certainly result in 'startle' responses which can result in unpredictable (reflex or conscious) motor responses which could result in falls from ladders etc. - just as could any sudden and unexpected stimulus (e.g. a clap of thunder, flash of light, unexpected 'prod' or even a bee landing on one), and I obviously agree that an RCD can do absolutely nothing to prevent that. All I said was that I suspeced that reducing the duration of (>30mA) shocks probably 'reduced the secondary injury risk to some extent' - and I suspect taht is probably true ('to some extent').

My main concern is not the physiology, but the desire to keep the risk section very brief and clear. It already warns that RCDs may not prevent "death or serious injury" (without indicating whether 'primary' or 'secondary') and I thought that was probably enough. However, in view of your comments, I'll play with the wording to see if I can take on board your comments without increasing the length or complexity of the paragraph too much. Watch this space.

That was the only thing that leapt out at me. I'll try to have a better look at your draft this evening, but I'm away on a 'jolly' at the moment with a machine safety committee.

Many thanks - I look forward to hearing any further comments you may have. My hoped-for timelines have already slipped a bit, so waiting a bit longer will do no harm!

Kind Regards, John

 

[JohnW2]

In the thread about the 'Electrics Safety' Sticky ....

However, if ‘we’ were not happy with SP isolation, maybe that would need to be mentioned?

Have taken a chance here. If someone else has covered this, no worries. DP isolation must be achieved on TT systems.
However, identifying TT systems may be tricky for some DIY'ers.

This is a difficult one, which we have discussed at some length, without really reaching a consensus.

IF we decide that we must advise DP isolation for TT installations, then I suspect that we would have to give blanket advice to always isolate with a 'main switch' (or equivalent). As you imply, I don't think we could rely on DIYers identifying a TT installation, and attempting to explain how to do that would, IMO, bring too much detail and length into what is meant to be a 'brief and pithy' safety page. On the other hand, as I wrote recently, I would seriously question the wisdom of advising DIYers to 'play around in the CU' solely in order to achieve DP isolation of a single circuit. Again, apart from safety issues etc., explaining how to do this would IMO detract from the 'brief and pithy' safety messages.

However, if we did advise always to use the main switch, then I suspect that many DIYers would simply ignore that advice.

We all know that, in theory, DP isolation should be used with TT installations, and we may therefore feel that we must advise DIYers accordingly. However, as I've said before, I personally suspect that the danger of SP isolation (with TT) is probably very much overplayed, and may well represent less of a risk than would be posed by 'playing around within a CU' or working in poor lighting after operating a main switch. Do electricians, in reality, always utilise DP isolation before undertaking minor work in a TT installation? Although not an electrician, I have to confess that I very rarely go to the 'hassle' of DP isolation when working on a single final circuit in my TT installation.

Others may have different ideas, but it seems to me that we really have only two main choices -(a) to change our advice to 'always use main switch' (and accept that the advice will probably often be ignored), or, (b) leave it as it is ('main switch is best and MCB/fuse is next-best'), accepting that this will mean that some will use SP isolation in TT installations.

More thoughts?

Kind Regards, John

 

[JohnW2]

I'll check later, but I believe the reaction threshold for adults is about 10mA for 5 ms. A normal RCD will have no affect on that whatsoever. ... I take your point about the length of the risk section. it might be better to separate the shock risk from the secondary risk to avoid an overlong paragraph

...in view of your comments, I'll play with the wording to see if I can take on board your comments without increasing the length or complexity of the paragraph too much. Watch this space.

How about:

• Electricity can, and does, kill, but much more commonly results in (possibly life-changing) serious burns and other serious injuries, including loss of fingers, limbs, sight etc. Residual current devices (RCDs) reduce, but do not eliminate, the risks of death and serious injury due to electric shock. Serious injury, and possibly even death, can also result from falls from ladders etc. precipitated by electric shocks, and RCDs will do little, if anything, to reduce that risk. Do not be complacent – catastrophes and tragedies really do happen.

Kind Regards, John

 

[bernardgreen]

Yes that seems to cover all risks.

Well done

 

[stillp]

Rather than the rather wooly "RCDs will do little, if anything, to reduce that risk." I would suggest "RCDs will not reduce that risk" as a clearer statement.

 

[JohnW2]

Rather than the rather wooly "RCDs will do little, if anything, to reduce that risk." I would suggest "RCDs will not reduce that risk" as a clearer statement.

If I must - but, as I said, I'm not at all sure that it is then strictly true! However, I don't feel strongly about that. I suppose you wouldn't accept "...will probably not reduce that risk..." or "...will usually not reduce that risk"?

Kind Regards, John

 

[stillp]

I don't like words like "usually", or "probably" in guidance like this. They don't help the reader.

 

[JohnW2]

I don't like words like "usually", or "probably" in guidance like this. They don't help the reader.

I didn't think you would! I can live with the 'simple wording', even though I suspect that it it is probably not strictly not true. I suppose a 'clear message' is sometimes more important than accuracy.

Kind Regards, John

 

[stillp]

I just checked IEC/TS 60479 "EFFECTS OF CURRENT ON HUMAN BEINGS
AND LIVESTOCK", and the threshold of reaction is 0.5 mA regardless of time, so an RCD will have zero effect on the reaction.

 

[JohnW2]

I just checked IEC/TS 60479 "EFFECTS OF CURRENT ON HUMAN BEINGS AND LIVESTOCK", and the threshold of reaction is 0.5 mA regardless of time, so an RCD will have zero effect on the reaction.

Well, yes, 0.5mA is usually taken to be the 'threshold of perception' (i.e. the current below which one does not even 'feel it') - and I suppose that the moment one perceives a shock, there is the possibility that (just like with the 'clap of thunder' etc.) it will 'make one jump' - which could result in an accident if one were up a ladder etc., even though direct physiological reflex responses to an electric shock will usually not occur at currents anything like as low as that.

However, as I'm sure you understand, this is obviously not what I was talking about (since RCDs obviously cannot have any influence on situations in which there are sub-30mA currents). I was talking about currents high enough to trip an RCD, and was suggesting that reducing the duration of such a shock current will probably reduce the risk of secondary injury (which is obviously a probabilistic statement) 'to some extent'. I may be wrong, but I suspect not.

However, as I've already conceded, I'm prepared to 'give in' to your view, on the basis that a simple message is probably more importnat than strict accuracy.

Thanks for your interest and input.

Kind Regards, John

 

[stillp]

Well, yes, 0.5mA is usually taken to be the 'threshold of perception'

No, that's something different. The threshold of reaction is the current that causes a muscular reaction, i.e. a movement that might result in falling off a ladder..