It varies, on logic plus the screwhead is pretty much flush with the faceplate, so certainly touchable. On the other and accessories designed for screwcaps (whether or not the screw-caps are actually fitted) tend to ave deeply recessed screws,
When are fly leads necessary?
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True, but I still think it extremely improbable that anyone would get a significant shock by that process.
Of course, if we are 'scraping barrels', it's not unknown with a plastic accessory and plastic backbox/pattress that tightening the screw to result in damage to insulation of a 'trapped conductor, potentially to the extent that the screw could become 'live'. In that case, one is totally sunk if the screw is metal, since there is nothing one can earth to deal with the situation - only bernard's nylon screws could prevent that 'risk' - and, as I've said, I've never known anyone to use them routinely (if at all)!
Kind Regards, John
Which could mean the 'fault' could go unnoticed for a long time, until someone finds it.
Indeed. In fact, I would think that in a high proportion of cases (of something which itself is very rare), it may well go unnoticed 'for ever'. However, that's really just another way of saying that it is extremely unlikley to result in anyone coming to harm.
As I've said, it's for individuals to decide how ultra-cautious they want to be. However, as I've implied, those who are concerned about the (extremely rare) possibility of faceplate screws becoming 'live' should perhaps turn their attention to the (I presume) countless millions of examples of plastic accessories mounted on plastic boxes (mainly 'plasterboard' ones) - perhaps by campaigning for the use of metal screws wo be 'banned' in such a situation?
Kind Regards, John
Why don't plastic switches have a metal bar riveted to the screw holes and an earth terminal so that the screws will be earthed?
Cost - or deemed unnecessary?
Cost - or deemed unnecessary?
Depends.
I would probably combine your two options and say "deemed inadequately 'necessary' to justify the cost"
It's always impossible find any facts in these situation, but I have to wonder whether (despite all the discussions and expressions of concern, here and elsewhere) anyone has ever suffered significant harm as a result of a live faceplate screw? If we knew the answer to that, it might help to answer your question
Kind Regards, John
Yes, I always think that when people mention touching the screws in face-plates.
It would be rather difficult to 'touch' one in a way that an electric shock caused muscle contractions such that one could not let go (of the screw).
It would be rather difficult to 'touch' one in a way that an electric shock caused muscle contractions such that one could not let go (of the screw).
Quite so - and it's similar to quite a few of the 'concerns' that are frequently discussed here. I am undoubtedly regarded by some as being unwise, perhaps even 'reckless' because of some of the things I often say about 'incredibly small risks' but when we get to the stage (as I just have) of questioning whether an extremely small theoretical risk has ever been realised (in all the decades of electrical installations), I do think that some 'realism' or common sense is probably required - not the least to put some of these 'incredibly small risks' into perspective in relation to all the risks which inevitably exist in life!
Yes, I almost wrote that myself. I would think that, even if someone somehow managed to get a shock in such a fashion, it would be of extremely short duration, since virtually any muscle response (voluntary or involuntary) would result in 'disconnection' from the screw head.
Kind Regards, John
The flylead is a requirement in the regs, when the only cpc is connected direct to the metal back box, essentially when the only cpc is via metal conduit, 2 core swa armour, micc pyro or similar
I'm not quite sure what you are saying,unless it's just 'a statement of the obvious'.
Unless I have missed it, I am not aware of any regulation which explicitly requires 'flyleads'. However, if there is no 'CPC wire' entering the backbox (i.e,. if it is earthed by conduit or 2-core SWA armour etc.), then there obviously is a need/'requirement' to make an 'earth connection' to a switch/FCU etc., and probably also to the metal faceplate of a switch, and the only way that can be achieved in that situation is by having a 'flylead' from the (earthed) box to the accessory.
In the case of a metal faceplate of, say, a lightswitch, I doubt that many people would be comfortable with it only being earthed via faceplate screws.
Kind Regards, John
Something else i've noticed is that plastic boxes tend to have large "bosses" around the screws, this dramatically reduces the chance of a wire getting trapped compared to metal boxes which just have the lugs floating in mid air.
True - particularly when there is a metal insert into which the screw goes, since there then has to be plastic around it to keep it in place. Having said that, I've certainly seen conductors 'trapped' in plastic boxes, although I don't recall any having come to any significant harm as a result.
Kind Regards, John
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An argument otherwise known as Survivorship Fallacy. Not worthy of you.
Anecdotes are essentially meaningless, so you're probably right in terms of my personal (very limited) personal experience.
However, I would say that (particularly in the absence of alternatives) it is perfectly valid to use 'collective experiences' as a means of trying to get a handle on the probability of a perceived risk. Indeed, a fair bit of my professional life necessarily has to use such an approach.
For example, as I wrote in this very thread, although we quite often see, and discuss, concerns about faceplate screws 'becoming live', I do have to wonder whether anyone has ever (say in the last 50 years) come across, or heard of, a case in which anyone has come to significant harm (let alone died) as a result of a 'live' faceplate screw. If the answer is 'no', then that goes a fair way to giving us an idea of the probability of such an event, and therefore helps us to view such a perceived risk in perspective in relation to risks in general.
I would similarly ask if anyone has ever (say in the last 50 years) come across, or heard of, a case in which anyone has come to significant harm due to something electrical, in a situation in which an SPD or AFDD, if present, might have prevented that harm.
Kind Regards, John
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