Ceiling downligts replacement.

[JohnW2]

Yes. .... Presumably not in the Class 2 parts.

Could you perhaps help me understand (or, at least, comment upon) these couple of snippets from the MIs for a luminaire (which nowhere say that it "must not" be earthed, or must not have an earthed conductor entering it) ...

Thanks.

Kind Regards, John

 

[ban-all-sheds]

One can only assume that they have done the decent thing and provided for ongoing continuity of cpc even though their light doesn't actually connect to it.

 

[Taylortwocities]

One can only assume that they have done the decent thing and provided for ongoing continuity of cpc even though their light doesn't actually connect to it.

Obviously

 

[EFLImpudence]

Could you perhaps help me understand

Why do you keep asking about this?
I have answered before - I think correctly.

You have found one instruction which does not state "Must not be earthed" so find another which does.
I did write "They do generally (always?) state "This {appliance} must not be earthed".

Look at it logically.
Why bother to make Class 2 products?

Have you earthed the chuck (or the body if metal) on your Class 2 drill? If not, why not?

 

[JohnW2]

Obviously

Indeed so. It seems eminently sensible to me, particularly given the regs' requirement that a CPC be run 'to every point'. However, I posted that as part of the a discussion about MIs saying that a Class II item "must not" be earthed and/or that an earthed conductor must not enter such an item.

Kind Regards, John

 

[EFLImpudence]

and/or that an earthed conductor must not enter such an item.

I'm not sure anyone has said that but I don't see why it should matter if the conductor has the same protection as the live conductors.

 

[JohnW2]

Why do you keep asking about this? .... You have found one instruction which does not state "Must not be earthed" so find another which does.

I'm not being awkward, but I am struggling to find one which does contain such a statement.

For fairly obvious reasons, items which come with fitted 2-core cables and plugs do not usually seem to come with such a statement. Class II items intended for hard-wiring by the end-user are relatively uncommon, and light fittings are one of the few which are - which is why I've been looking at them, but have not yet found such a statement.

What sort of products are you thinking about which "generally (always?)" come with such a statement?

Look at it logically. Why bother to make Class 2 products?

We've discussed this before, and there are some aspects which still confuse me a bit.

The most obvious answer is that, as far as I can see, an item of electrical equipment (other than ELV) has to provide protection against electric shock EITHER by being enclosed in an earthed metal casing/enclosure (Class I) OR by having double/reinforced insulation (Class II), and (unless I'm missing something) I'm not aware of any third option. If that is correct, then if (as is commonly the case) the item does not have a metal casing/enclosure (which could be earthed), then there would appear to be no alternative to making it as Class II.

Where I'm less sure is in the situation where there is a metal casing/enclosure (which could be earthed) but the manufacturer nevertheless chooses to make the product (and describe it as) Class II ('beneath the metal'), and I'm not sure why they 'bother' to do that. You and I agree that creating unnecessarily earthed exposed metal is generally undesirable, but I very much doubt that manufacturers are sufficiently 'public spirited' to make Class II metal-encased products simply for that reason.

Kind Regards, John

 

[EFLImpudence]

Page 16

http://www.free-instruction-manuals.com/pdf/pa_387427.pdf

 

[JohnW2]

Page 16 ... http://www.free-instruction-manuals.com/pdf/pa_387427.pdf

Fair enough - that's one, at least. Cooker hoods, like light fittings, are amongst the few things intended for end-user hard-wiring.

Do you have any thoughts about the reason they make such "must not" statements (and as prominently/'dramatically' as that one), when they do? I'm certainly not aware of any regulatory reason why one cannot earth any exposed metal parts of a Class II item. There obviously is no need to earth such an item, but nor do I see any reason why it should not be done (other than the general undesirability of creating 'unnecessarily earthed metal' - which, as I said, I find hard to believe would be their reason).

I suspect we are probably talking about ignorance, in that they probably believe that 'it is not allowed' to earth metal parts of a Class II item.

Kind Regards, John

 

[EFLImpudence]

The most obvious answer is that, as far as I can see, an item of electrical equipment (other than ELV) has to provide protection against electric shock EITHER by being enclosed in an earthed metal casing/enclosure (Class I) OR by having double/reinforced insulation (Class II), and (unless I'm missing something) I'm not aware of any third option. If that is correct, then if (as is commonly the case) the item does not have a metal casing/enclosure (which could be earthed), then there would appear to be no alternative to making it as Class II.

I don't know - switches and ceiling roses are not officially Class 2 but if there IS nothing to earth then presumably actually making it Class 2 would be futile.
How can we bond plastic pipes?

Where I'm less sure is in the situation where there is a metal casing/enclosure (which could be earthed) but the manufacturer nevertheless chooses to make the product (and describe it as) Class II ('beneath the metal'), and I'm not sure why they 'bother' to do that.

It is considered safer than earthing products.

You and I agree that creating unnecessarily earthed exposed metal is generally undesirable, but I very much doubt that manufacturers are sufficiently 'public spirited' to make Class II metal-encased products simply for that reason.

You will have to ask them why they are so philanthropic.

 

[JohnW2]

I don't know - switches and ceiling roses are not officially Class 2 but if there IS nothing to earth then presumably actually making it Class 2 would be futile.

That is the question I'm always asking (and never really get an answer) - about this apparent 'third option' (neither Class I nor 'formal' Class II) which exists in terms of 'common practice', but which does not seem to have a regulatory basis.

It is considered safer than earthing products. ... You will have to ask them why they are so philanthropic.

You and I (and undoubtedly others) agree that it is safer not to have unnecessarily earthed metal around but, as I've said, I find it hard to believe that philanthropy on the part of manufacturers is their reason for such 'warnings'.

As I've recently written, I suspect that they (incorrectly) believing that earthing a Class II item is 'not allowed'.

Kind Regards, John

 

[EFLImpudence]

Do you have any thoughts about the reason they make such "must not" statements (and as prominently/'dramatically' as that one), when they do?

Because it is considered hazardous to do so and saying "Please do not earth it" is less emphatic - the same as "This product must be earthed" and not "Please earth this product".

I'm certainly not aware of any regulatory reason why one cannot earth any exposed metal parts of a Class II item.

Because it is considered hazardous.

There obviously is no need to earth such an item, but nor do I see any reason why it should not be done

Because it is considered hazardous.

(other than the general undesirability of creating 'unnecessarily earthed metal'

There you go.

- which, as I said, I find hard to believe would be their reason).

Ok. It makes their product safer.

Perhaps there are rules. Are there any hand tools which are still Class 1?

I suspect we are probably talking about ignorance, in that they probably believe that 'it is not allowed' to earth metal parts of a Class II item.

That is your view but you will have to ask them.

 

[JohnW2]

Because it is considered hazardous to do so and saying "Please do not earth it" is less emphatic - the same as "This product must be earthed" and not "Please earth this product".

I would say that a "This product must be earthed" statement (for a Class I item) deserves far more emphasis than a ';warning' against unnecessarily earthing a Class II item.

Because it is considered hazardous. .... Because it is considered hazardous. ... Ok. It makes their product safer.

I think we will have to agree to disagree, since I find it hard to believe in your "philanthropy" explanation. I don't think one ever sees "this metal sink must not be earthed", despite the fact that unnecessarily earthing a sink (e.g. if plumbed in plastic) undoubtedly creates a far greater potential hazard than does unnecessarily earthing a light fitting or cooker hood - and, of course, bernard would presumably disapprove of any such warning!

In passing, those MIs you linked too contain a good few "musts", including the following, and I wonder what you think about them ...

... and must be connected to the electricity supply via a double pole switch having a 3mm minimum contact gap on each connector.
... The fuse must be rated at 3 Amps.
... The connection point must be placed in a position adjacent to the appliance so as to be readily accessible for an engineer in the event of a breakdown.

Kind Regards, John

 

[EFLImpudence]

Ok. fair enough - forget the 'musts'.

However, if you agree that not earthing that which does not need earthing is a good idea (and would be more hazardous - less safe - if it were), why are you so unable to accept as true an instruction which states this?


Also, why are you wondering about products (your third option) which cannot be earthed and thinking some special description should be given to them?
Were wooden cabinets housing early electrical appliances called Class 2 or was it taken as obvious that it was impossible to earth wood and no one would get a shock from the casing.
Perhaps modern stupidity is the reason the OSG finds it necessary to state "Plastic pipes do not require bonding" rather than "Plastic pipes cannot be bonded you idiot".

 

[JohnW2]

However, if you agree that not earthing that which does not need earthing is a good idea (and would be more hazardous - less safe - if it were), why are you so unable to accept as true an instruction which states this?

It's not that I am unable to accept it - as you are aware, we think similarly about such matters, and I would not usually 'unnecessarily earth' anything, even in the absence of such a 'warning'.

However, not everyone necessarily agrees with us. Some (quite probably including bernard in some situations) would undoubtedly see earthing of a Class II item (if there were 'earthable' conductive parts) as 'belts and braces' protection - since, as you know, a judgement as to which approach is the 'safer' (or 'less hazardous') depends upon one's personal opinion/judgement as to which of two 'eventualities' is the more likely. I therefore feel that something which appears to be an authoritative statement implying that earthing 'is not allowed' is probably inappropriate.

Also, why are you wondering about products (your third option) which cannot be earthed and thinking some special description should be given to them? Were wooden cabinets housing early electrical appliances called Class 2 or was it taken as obvious that it was impossible to earth wood and no one would get a shock from the casing.

As I keep saying, maybe I'm missing something - but I read the regulations as saying that the 'third option' does not exist - i.e. protection against electric shock has to be provided by either an earthed metal casing or by double/reinforced insulation. I'm obviously not saying that one should even think of 'earthing' a non-conductive casing (c.f. a plastic water pipe), but my reading (perhaps/probably wrong) suggests that if there is not a metal casing to earth, the only other available 'allowable' option is for it to be Class II.

Do you therefore believe that there is some acceptable option (regs-wise) which is neither Class I nor Class II?

You seem to feel that a 'plastic (or wooden, or whatever) box' affords adequate protection, but does it not have to qualify as "double/reinforced" insulation (i.e. 'Class II') in order for it to be 'allowable'? I imagine you would not accept a box made out of paper or cardboard, and that you would not accept a covering of PVC tape. What about a thin/flimsy plastic box? Where are you drawing your line?

Kind Regards, John