Accidental Earthing of Class II Equipment

[JohnW2]

I do see the problem with a metal class I drill being left on a metal work bench where some one has done some welding and the earth wire has burnt out as a result, and could also cause the live wires to connect to earth as a result.

I'm not sure that I fully understand that but ....

However if the drill has the ability to be clamped in a stand, then the manufacturer must allow for the drill to be earthed as a result.

Quite apart from the discussion about whether it is (or should be) allowed/forbidden to deliberately earth exposed metal parts of Class II items, it is surely the case that, essentially by definition, a Class II item can come into 'accidental' contact with earth without creating a hazard?

Even if I could think of a reason why it would be necessary, it would surely be ridiculous if every Class II item had to come with a warning that it must not be allowed to come into contact with anything earthed?

Kind Regards, John

 

[EFLImpudence]

It is also unwise to use such equipment in an erupting volcano if there is a bus coming.


For goodeness' sake why is this so difficult?

In Class II products it is supposed to be impossible, with a single fault, for the supply conductors to contact, and make live, any exposed-c-p.
Therefore, it is better NOT to earth this e-c-p as if it were it may become live in the event of an earth fault elsewhere.

If you want to clamp a Class II metal drill in a metal pillar, it makes no difference -
EITHER the metal pillar will not become live because of a single fault in the drill
OR if the pillar is already earthed then a fault elsewhere will enliven the pillar and the clamped drill will not make a lot of difference.

 

[JohnW2]

It is also unwise to use such equipment in an erupting volcano if there is a bus coming.

Exactly.

In Class II products it is supposed to be impossible, with a single fault, for the supply conductors to contact, and make live, any exposed-c-p.

Exactly.

If you want to clamp a Class II metal drill in a metal pillar, it makes no difference - EITHER the metal pillar will not become live because of a single fault in the drill OR if the pillar is already earthed then a fault elsewhere will enliven the pillar and the clamped drill will not make a lot of difference.

Exactly.

.... Therefore, it is better NOT to earth this e-c-p as if it were it may become live in the event of an earth fault elsewhere.

That's a separate issue, which we have already discussed at length. As you know, I totally agree with you that it is, in general, desirable to minimise the amount of touchable earthed metal around - whether that be the exposed-c-p of something electrical, a pipe, radiator, sink or bath, structural metal or whatever.

Kind Regards, John

 

[bernardgreen]

it would surely be ridiculous if every Class II item had to come with a warning that it must not be allowed to come into contact with anything earthed?

such as a person who is not wearing clothing that ensures no connection to Earth. Obvious soultion is a pair of rubber gloves when using the appliance. ( people are "earthy" otherwise a neon screwdriver would never light up )

 

[crystal ball]

such as a person who is not wearing clothing that ensures no connection to Earth. Obvious soultion is a pair of rubber gloves when using the appliance. ( people are "earthy" otherwise a neon screwdriver would never light up )

Naked people wearing rubber gloves using "appliances", I don't like where this is going Matron

 

[ban-all-sheds]

I think you'll find that being naked apart from rubber gloves when operating a drill press is a H&S violation.


No matter where you wear the gloves.

 

[EFLImpudence]

...and, strictly speaking - not possible.

 

[ban-all-sheds]

Can't help thinking that somewhere there's a photo which proves you wrong.

Q is, do I want to see it?

In the meantime: http://darwinawards.com/stupid/stupid1998-10.html

 

[SUNRAY]

I regularly link items of sound/video/lighting kit together, much of it is classII and much of it is earthed, creating multiple earth paths to the classII items.
In public entertainment we tend to get quite fussy about safety.

 

[JohnW2]

I regularly link items of sound/video/lighting kit together, much of it is classII and much of it is earthed, creating multiple earth paths to the classII items. In public entertainment we tend to get quite fussy about safety.

As with all such things, it's really down to risk assessments on a case-by-case basis - which usually essentially comes down to judgements as to which of various possible eventualities are more 'likely' than others.

Kind Regards, John

 

[JohnW2]

Despite all that has been said in the other thread, I'm still confused/uncertain ....

... in terms of things within an electrical installation (as I've said, I don't know enough about rules/regulations applying to appliances or 'equipment'), it would seem that a live conductor/part within a single-skin plastic enclosure without a metallic covering is not allowed (by BS7671) if the plastic does not qualify as 'reinforced insulation'.

Given that the absence of a metallic covering means that protection against electric shock cannot be provided by 'Class I' methods, it therefore seems that the situation would only be allowed (by BS7671) if the single layer of plastic did, indeed, qualify as 'reinforced insulation'. Since, for some reason (maybe, as has been suggested, because some other requirement for Class II {not stated in BS7671} is not satisfied), many such items don't come with a Class II marking - so how is one meant to ascertain whether a single-skin plastic enclosure containing live parts is compliant (with BS7671) or not?

Comments already made have implied that I am just being 'awkward', but I genuinely do not know the answer to the above question, and I would be far happier if I could know whether a particular enclosure was, or was not, compliant with BS7671.

Kind Regards, John

 

[SUNRAY]

Despite all that has been said in the other thread, I'm still confused/uncertain ....

... in terms of things within an electrical installation (as I've said, I don't know enough about rules/regulations applying to appliances or 'equipment'), it would seem that a live conductor/part within a single-skin plastic enclosure without a metallic covering is not allowed (by BS7671) if the plastic does not qualify as 'reinforced insulation'.

Given that the absence of a metallic covering means that protection against electric shock cannot be provided by 'Class I' methods, it therefore seems that the situation would only be allowed (by BS7671) if the single layer of plastic did, indeed, qualify as 'reinforced insulation'. Since, for some reason (maybe, as has been suggested, because some other requirement for Class II {not stated in BS7671} is not satisfied), many such items don't come with a Class II marking - so how is one meant to ascertain whether a single-skin plastic enclosure containing live parts is compliant (with BS7671) or not?

Comments already made have implied that I am just being 'awkward', but I genuinely do not know the answer to the above question, and I would be far happier if I could know whether a particular enclosure was, or was not, compliant with BS7671.

Kind Regards, John

I happen to agree with you John and frequently question whether a classII device is truly so, but I end up just accepting the statement that it is indeed classII.

As I mentioned earlier I regularly mix different classes of entertainment kit and the only consideration I give is to signal path earth loops but most of it is balanced so the issue is not big.

 

[JohnW2]

I happen to agree with you John and frequently question whether a classII device is truly so, but I end up just accepting the statement that it is indeed classII.

Yes, but, as I said, I'm talking about things which make no claim to be Class II - and hence which may, or may not, be acceptable (per BS7671) as a means of enclosing (otherwise 'exposed') live parts in an electrical installation.

Kind Regards, John

 

[EFLImpudence]

... in terms of things within an electrical installation (as I've said, I don't know enough about rules/regulations applying to appliances or 'equipment'),

I don't know about the rules either but I do not really understand your logic.

it would seem that a live conductor/part within a single-skin plastic enclosure without a metallic covering is not allowed (by BS7671) if the plastic does not qualify as 'reinforced insulation'.

I think you are looking at things from the wrong perspective.
Reinforced insulation (or a second layer) is not necessarily very thick so is probably thinner than any plastic casing which is strong enough for its purpose.
Asking about paper thin such parts is pointless unless you can supply an example.

Given that the absence of a metallic covering means that protection against electric shock cannot be provided by 'Class I' methods,

The outer metal covering of a product is not there to prevent contact with an internal live conductor. Its existance, and the fact that it might itself become live, means it must be earthed.

it therefore seems that the situation would only be allowed (by BS7671) if the single layer of plastic did, indeed, qualify as 'reinforced insulation'.

It's not disallowed because the reasons for Class I or Class II being employed do not apply nor occur.

Since, for some reason (maybe, as has been suggested, because some other requirement for Class II {not stated in BS7671} is not satisfied), many such items don't come with a Class II marking - so how is one meant to ascertain whether a single-skin plastic enclosure containing live parts is compliant (with BS7671) or not?

They are not Class II because the hazard does not exist.

Comments already made have implied that I am just being 'awkward', but I genuinely do not know the answer to the above question, and I would be far happier if I could know whether a particular enclosure was, or was not, compliant with BS7671.

The answer (specifically) does not exist because the question is invalid.

These are just my views using logic and common sense. I have no specific knowledge of any thinking by the authors of the regulations, but your questions seem similar to someone asking "As we cannot bond plastic pipes, should we replace them with metal ones? or "Should I install a bonding conductor from the MET anyway and connect a lump of metal to the end of it? "
One cannot get a shock from plastic products, plastic pipes or light switches, therefore they do not come within the scope of the rules applying to products from which one might receive a shock.

I suppose.

 

[JohnW2]

I think you are looking at things from the wrong perspective. Reinforced insulation (or a second layer) is not necessarily very thick so is probably thinner than any plastic casing which is strong enough for its purpose.

I find it hard to believe that it is as simple as that. If they just meant 'an insulating material', they would surely just say so - they have surely added "reinforced" for a reason?

Asking about paper thin such parts is pointless unless you can supply an example.

How about 'chockboxes', particularly the opaque white (rather than transulcent) ones, which appear to be particularly brittle? I've just done this, just with my fingers (no tools) to one of them ...

... do you really regard that as "reinforced insulation"?

The outer metal covering of a product is not there to prevent contact with an internal live conductor. Its existance, and the fact that it might itself become live, means it must be earthed.

Indeed. I said nothing about it preventing contact with live conductors. I was saying that it afforded 'protection against electrical shock' - which is the same language that the regs use.

It's not disallowed because the reasons for Class I or Class II being employed do not apply nor occur.

Do you really mean that? 'Basic protection' (e.g. the insulation of a 'single-insulated' cable) alone is not allowed, otherwise 'single-insulated' singles would be allowed. One has to have additional protection against electric shock, the two most common methods being double (or reinforced) insulation or an earthed metal barrier.

They are not Class II because the hazard does not exist.

The hazard only "does not exist" (is deemed not to exist) if there is something acceptable in addition to 'basic protection' (if, indeed, there is 'basic protection').

.... your questions seem similar to someone asking "As we cannot bond plastic pipes, should we replace them with metal ones? or "Should I install a bonding conductor from the MET anyway and connect a lump of metal to the end of it? "

I really don't understand that. I am merely asking whether, for example, the chockbox that I have just shattered with my fingers is or is not, per BS7671, adequate protection against electric shock if it contains live parts (which may not even have 'basic protection').

Kind Regards, John