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

JohnW2 said:

Yes, it would provided that the 'over-current tolerance' of the switch were the same as is deemed to be the case for a cable (e.g. able to happily carry 1.45 times its Iz for an hour). However, as you go on to say, we're actually talking about "a switch which has a current rating < the cable" . As you say ..

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Agreed, but as the cable in a ring only has to have a CCC of 20A (albeit with the minimum csa of 2.5mm² still for BS3036 30A fuses - 2 x Iz for an hour) does it not work out the same?
However, you mentioned short-circuit currents so are switches made with that in mind or are they expendable?

Are you talking about a 'spur cable' with downstream OPD protection (as in plug fuses etc.)?

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I was - with regard to PFC.

Not if they were treated like cables - i.e. were required to have over-current protection which would prevent a high current flowing for long enough to cause damage to them.

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Are they? It would seem not - with dimmers anyway

In many ways, it is (common sense). As you know (from some of my talk about 1A BS1362 fuses ) what I have thought deviates a bit from common sense is the concept/belief that over-current protection "is only there to protect cables" -

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Yet, it is.

why not everything else in the circuit (which I suppose is probably what this reg, previously unfamiliar to both of us, is trying to say)?

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Because they are not part of the fixed wiring to which one may connect various appliances which are not mentioned.

EFLImpudence said:

Agreed, but as the cable in a ring only has to have a CCC of 20A (albeit with the minimum csa of 2.5mm² still for BS3036 30A fuses - 2 x Iz for an hour) does it not work out the same?

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I think that bringing ring finals into the discussion is a considerable extra confusion! It would be simpler if we just talked about 32A radials!

EFLImpudence said:

However, you mentioned short-circuit currents so are switches made with that in mind or are they expendable?

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Not necessarily just short-circuit currents - 'overload currents' would probably be more pertinent to the point I was making.

EFLImpudence said:

Are they? It would seem not - with dimmers anyway

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I suppose I should have include a "where practicable/possible" in what I wrote - even an OPD which could clear a very high current fault in microseconds would/could not prevent vulnerable electronic components from being killed.

EFLImpudence said:

Yet, it is.

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I'm not sure what you mean - we have both been introduced to a regulation which appears to require over-current protection for an RCD or switch, not just for cables.

EFLImpudence said:

Because they are not part of the fixed wiring to which one may connect various appliances which are not mentioned.

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Are you talking about my 1A plug fuses. If so, I was not suggesting that they were part of this discussion, other than top remind you of my view that fuses etc. have a potentially useful role in protecting things other than cables. In the context of this discussion, we are talking about switches which are "part of the fixed wiring".

Kind Regards, John

FrodoOne said:

I am sorry to be pedantic and not to mitigate the seriousness of the event BUT, if a "plasterer got electrocuted meanwhile plastering the ceiling" he would be dead, since "electrocution" means "Death caused by electricity"

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It covers death or serious injury.

Not really; it is short for electrical execution.

EFLImpudence said:

Not really; it is short for electrical execution.

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Traditionally, yes - but, as secure implies, it seems that most dictionaries now say 'death or severe injury'. However, what they all appear to still be agreed upon is that is does not cover electric shocks which do not result in 'serious injury or death' (which is the incorrect sense in which many people seem to use the word).

Kind Regards, John

That might be the case - but it won't be long before it means every tingle.


I know you disagree, but language decided by the ignorant is no way for the dictionaries to behave.

EFLImpudence said:

That might be the case - but it won't be long before it means every tingle.

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Who knows?!

EFLImpudence said:

I know you disagree, but language decided by the ignorant is no way for the dictionaries to behave.

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It's not really to do with what I agree or disagree with. The point I always make is that, more-or-less by definition, virtually any evolution of language (if one wants language to evolve) has to start by people using the language in a way that is 'incorrect' at the time (whether one calls that 'ignorant', or whatever).

Of course, some people, maybe even you, would prefer it if such evolution (initiated by 'incorrect use') never happened - but then we would all be speaking the language of Chaucer, Beowolf or even 'cave men' (if they had a language!) - which I don't think is really what most people would want.

Kind Regards, John

JohnW2 said:

The point I always make is that, more-or-less by definition, virtually any evolution of language (if one wants language to evolve)

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Why would any one want it? They don't do it on purpose. Everyone else has to put up with it.

has to start by people using the language in a way that is 'incorrect' at the time (whether one calls that 'ignorant', or whatever).

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Of course it starts like that. That is the problem. Don't succumb to it.

Of course, some people, maybe even you, would prefer it if such evolution (initiated by 'incorrect use') never happened - but then we would all be speaking the language of Chaucer, Beowolf or even 'cave men' (if they had a language!) - which I don't think is really what most people would want.

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Why not? We wouldn't know any different, would we?

EFLImpudence said:

Why not? We wouldn't know any different, would we?

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No, we wouldn't, and if one is a person who didn't like 'change' at all, it would be fair enough (presumably welcome).

... but change happens, and in many cases it's not difficult (for most people!) to argue that the changes are at least partially beneficial - even though, in the absence of any change, people would, as you say, "know no different/better". However, language is but a tiny part of the whole. Are there many people who would be happier if there had been 'no changes in anything' since the Victorian era, let alone the days of Chaucer or 'cave men'?

Kind Regards, John

securespark said:

It covers death or serious injury.

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- as opposed to a "shock"!

(See https://www.electrocuted.com/2018/11/02/electrocution-vs-shock/)

The term "electrocution" was coined in 1889 in the US just before the first use of the electric chair and originally referred only to electrical execution and not to accidental or suicidal electrical deaths. However, since no English word was available for non-judicial deaths due to electric shock, the word "electrocution" eventually took over as a description of all circumstances of electrical death from the new commercial electricity. (https://en.wikipedia.org/wiki/Electrocution)

If electrocution has been "watered down" to include (very) serious injury it is in the company of words such as "decimate", the meaning of which seems to have been inflated almost ten times to approach "annihilate" in the minds of many people.

The thing that gets my goat more than anything else is people starting sentences with "So............."

RCD's and death are related to the energy from a shock. So the 30ma is reckoned to not cause death providing the duration is short enough. The numbers used related to defibrillation. The numbers do consider this area, are based on this and are seen as safe. A delayed 30ma type is also available - they can't be used for what might be called final protection - a socket etc. In the early days when they started cropping up in factories attempts were made to use lower trip currents but they proved impractical. They are mostly there to protect against faults in items that are connected to the mains by say a plug. These often do leak low currents to earth so plug enough items in and even a 30ma rcd may trip. Figures used for PAT testing can give an idea of max leakage currents. A side effect is less worry about people drilling holes through live cables, electrocution while playing with it etc. The drilling holes aspect makes installation cheaper and safer. Previously a flimsy earthed bent piece of metal was fitted over cables. General idea shock goes to metal and blows a fuse. That involves a lot more energy than an RCD. The flimsy metal might still be a good idea as it may make cable replacement easier. An RCD can also spot partial cable shorts that might result in a fire before that happens. It also spots N to E shorts.

MCD's aim in life is to limit load and cope with shorts. They are thermal devices to some extent so trip speed depends on the current. At rated load they will take some time to trip. From memory the rapid trip is guaranteed at 5x that. Cable length and size has to be selected so that L to N shorts achieve this. Live to earth achieving it can sometimes be impossible so an RCD has to be added. The supply earth can have too high a resistance for shorts to reach the required current level. Cable is also sized on the basis of it's resistance. That generates heat and the cable can only cope with so much of it. These days on new builds it might even run through insulation and that can mean larger than usual cables being used.

Switches in consumer units etc are intended for isolation, not frequent use. Much the same with all of the items in there. This can also relate to certain boxes that are sometimes fitted along with electric showers. The switch in them isn't intended for frequent use where as say a pull cord shower switch is.

I'm not an electrician but was heavily involved in this area when some of the changes around now were being talked about. I have a renewed interest, we should have our CU upgraded and when hiring some one to do a job I like to know the ins to outs. I can't do the work myself now. Only the correct person that can also provide the correct paperwork once the job is done,

ajohn said:

RCD's and death are related to the energy from a shock. So the 30ma is reckoned to not cause death providing the duration is short enough. The numbers used related to defibrillation. The numbers do consider this area, are based on this and are seen as safe. A delayed 30ma type is also available - they can't be used for what might be called final protection - a socket etc. In the early days when they started cropping up in factories attempts were made to use lower trip currents but they proved impractical.

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RCDs do not limit fault current to 30mA.

They are mostly there to protect against faults in items that are connected to the mains by say a plug. These often do leak low currents to earth so plug enough items in and even a 30ma rcd may trip. Figures used for PAT testing can give an idea of max leakage currents.

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I do not see what difference the plug makes to what you are saying.
The reference to plugs was more to do with the hazard of hand tools usage; not their earth-leakage.
The RCD's primary purpose is to protect people when they, the people, unwittingly become the earth path.

A side effect is less worry about people drilling holes through live cables, electrocution while playing with it etc. The drilling holes aspect makes installation cheaper and safer. Previously a flimsy earthed bent piece of metal was fitted over cables. General idea shock goes to metal and blows a fuse. That involves a lot more energy than an RCD.

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If you are referring to capping, then that is not its purpose.

The flimsy metal might still be a good idea as it may make cable replacement easier.

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Maybe.

An RCD can also spot partial cable shorts that might result in a fire before that happens. It also spots N to E shorts.MCD's aim in life is to limit load and cope with shorts. They are thermal devices to some extent so trip speed depends on the current. At rated load they will take some time to trip. From memory the rapid trip is guaranteed at 5x that. Cable length and size has to be selected so that L to N shorts achieve this. Live to earth achieving it can sometimes be impossible so an RCD has to be added. The supply earth can have too high a resistance for shorts to reach the required current level. Cable is also sized on the basis of it's resistance. That generates heat and the cable can only cope with so much of it. These days on new builds it might even run through insulation and that can mean larger than usual cables being used.

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indeed, but not the primary purpose of their introduction which is the protection of the person.

Switches in consumer units etc are intended for isolation, not frequent use. Much the same with all of the items in there. This can also relate to certain boxes that are sometimes fitted along with electric showers. The switch in them isn't intended for frequent use where as say a pull cord shower switch is.

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Not so.

I'm not an electrician but was heavily involved in this area when some of the changes around now were being talked about.

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Interesting.

I have a renewed interest, we should have our CU upgraded and when hiring some one to do a job I like to know the ins to outs. I can't do the work myself now. Only the correct person that can also provide the correct paperwork once the job is done,

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Sort of.

securespark said:

The thing that gets my goat more than anything else is people starting sentences with "So............."

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Same here. That's one of the (many) things which irritate me (not to mention BAS!). I think the French, who are very protective about their language, are doing much the same with "Alors....". Another of my pet hates is "Can I get ...", which is totally 'standard' language for my daughters.

However, as I've said, change happens (in everything). What seems to get overlooked is that some of the 'correct' language which people like EFLI would like us to be using today (because it was regarded as 'correct' during our upbringings in, say, the 60s) was, back then, regarded as 'incorrect' (and perhaps irritating) by our grandparents ... not to mention my grandfather's views about men with long hair, or my grandmother's views about women who wore clothing which left their ankles or shoulders (let alone more!) exposed!

Kind Regards, John

RCD's protect fault paths to earth. Those can be faults as is an appliance that decides to do that. Yes maybe a person providing the path isn't a fault. Depends on how it happens - result of a fault in an item plugged in or drilling a hole in the wrong place. There is a catch all in the regs concerning sockets and rcd protection. It's intended to prevent faulty appliances giving shocks. The sockets are seen as safe - the modern ones used with the correct plugs are. May not be if they overheat.

Switches do have cycle / use lives. Personally I wouldn't rely on frequent use of the items of the type I am referring too.

Interesting - yes it is. RCD's for instance would be coming. I've rewired 2 house. First one no problem. 2nd one needed to be authorised to connect up the mains and was. That one was wired ahead of the standards as they were due to be changed. Factories often had there own electricians and the boards at the time discussed changes with them long before they happened. They would also have some one who could authorise some one to connect up the mains. Main reason here is cabling, testing etc. In my case both properties were tested as they should have been at the time. They still would be now. Regs - well they are intended to be met. That isn't a problem really. Neither is design if some one can do it.

The paperwork aspect is another matter - these days an electrician should leave something or the other what ever they do. Some don't due to the amount that is needed or they may not even be registered. Lack of the correct paperwork can cause people problems.

LOL My first rewire was my fathers house. He flatly refused to have a plastic consumer unit fitted. He worked at a different place to me but was one of the people the boards talked to about gas and electricity in general. Not an electrician but well aware of what problems crop up for other reasons.