Class I or Class II ?

[JohnW2]

Indeed, but it is the opposite which interests me more. What about the equipment which has 'single insulation' in the form of a casing which is totally non-conductive, but such that no-one could seriously describe it as 're-inforced'. I suspect that most of us would think of it as Class II, but it would actually seem that, safety-wise, it would not qualify as either Class I or Class II. Are such items 'banned'??

If they fail to meet the requirements of the Low Voltage Directive then they are illegal. How they meet those requirements is up to the manufacturer.

I guess that you need to tell us about the Low Voltage Directive, then?

It would seem that, since it can't be Class I, an item with a totally non-conductive casing has to be either 'double insulated' or 're-inforced' to qualify as Class II - which brings us back to what Standards have to say about 'reinforced'. I can but presume that if it doesn't satisfy the requirements of Class I, II or III then it would be illegal (just as Class 0 is).

Kind Regards, John.

 

[JohnW2]

A plastic item which had additional safety precautions (double insulation) may be called class II but I don't think it really is.

Indeed. I think that a lot of the confusion comes from the fact that there appears to be just one 'official symbol' (I'm not sure by whose definition) for 'Class II' and 'Double Insulated'. There are certainly plenty of items just around my house which are entirely plastic cased, at least some of which probably aren't even 'double insulated' (therefore relying on 'reinforced'?), which bear that familiar symbol - and therefore are presumably claiming to be Class II.

Kind Regards, John.

 

[stillp]

I guess that you need to tell us about the Low Voltage Directive, then?
quote]
Better guidance than I could write is given here:
http://ec.europa.eu/enterprise/poli...harmonised-standards/low-voltage/index_en.htm

 

[stillp]

A plastic item which had additional safety precautions (double insulation) may be called class II but I don't think it really is.

Indeed. I think that a lot of the confusion comes from the fact that there appears to be just one 'official symbol' (I'm not sure by whose definition) for 'Class II' and 'Double Insulated'. There are certainly plenty of items just around my house which are entirely plastic cased, at least some of which probably aren't even 'double insulated' (therefore relying on 'reinforced'?), which bear that familiar symbol - and therefore are presumably claiming to be Class II.

Kind Regards, John.

The symbol (IEC 60417-5172) shows the equipment is Class II, not how Class II is achieved, which may be:
– basic insulation as provision for basic protection, and
– supplementary insulation as provision for fault protection,
or in which
– basic and fault protection are provided by reinforced insulation.

 

[JohnW2]

The symbol (IEC 60417-5172) shows the equipment is Class II, not how Class II is achieved, which may be:
– basic insulation as provision for basic protection, and
– supplementary insulation as provision for fault protection,
or in which
– basic and fault protection are provided by reinforced insulation.

OK. In that case, all the things around my house which bear that symbol must be claiming to be Class II - and since many of them (e.g. 'wall-warts', laptop PSUs, ELV lighting 'transformers' etc.) clearly are not 'double-insulated' in the obvious sense (I've dissected enough of them to know that!), they presumably must be relying on 'reinforced' for their Class II categorisation...

... which brings us back, again, to the question of the requirements for 'reinforced' insulation.

Kind Regards, John.

 

[stillp]

5.3.1 Reinforced insulation
Reinforced insulation shall be so designed as to be able to withstand electric, thermal,
mechanical and environmental stresses with the same reliability of protection as provided by
double insulation (basic insulation and supplementary insulation, see 3.10.1 and 3.10.2,
respectively).
NOTE 1 This requires design and test parameters more severe than those specified for basic insulation.
NOTE 2 As an example for low-voltage applications, dimensioning of reinforced insulation with regard to impulse
voltage is, where the concept of overvoltage categories (see IEC 60364-4-443 2) applies, specified to comply with
the requirements of the overvoltage category which is one category higher than that specified for basic insulation.
NOTE 3 Reinforced insulation is mainly used in low-voltage installations and equipment but the application is not
excluded in high-voltage installations and equipment.

 

[ban-all-sheds]

Of course, but I thought the idea (at least, of 'double insulation') was that of 'belt and braces' - i.e. if the outer insulating casing broke (one 'fault'), one would then be confronted by a second insulating barrier which would also have to be broken before live parts were exposed.

Is that like wearing 2 pairs of pants?

 

[stillp]

You're forgetting the trousers BAS. Two pairs of pants would be triple insulation.

 

[JohnW2]

You're forgetting the trousers BAS. Two pairs of pants would be triple insulation.

If he's talking American, and doesn't wear underpants, it may only be double! I'm mildly surprised that BAS did not cite 'double condoms'

Kind Regards, John.

 

[JohnW2]

5.3.1 Reinforced insulation
Reinforced insulation shall be so designed as to be able to withstand electric, thermal,
mechanical and environmental stresses with the same reliability of protection as provided by
double insulation (basic insulation and supplementary insulation, see 3.10.1 and 3.10.2,
respectively).

I suppose I should have guessed that it would say something like that - which is not really all that helpful to us.

I have to say that, in recent times, I have only rarely seen what I would call proper 'double insulation', so maybe most manufacturers are relying on single, but tougher ('reinforced') insulation?

Kind Regards, John.

 

[Grizzly]

How can an all plastic item be Class I if there is nothing to which a cpc can be connected?

An earth connection may be used for purely functional, rather than protective purposes, so wouldn't be a cpc.
For instance, a switched-mode power supply (say for a laptop etc.) will need an earth connection for the leakage, but could be fully plastic encased, and not even bring the earth connection out to the output connector/terminals (I have experienced many PSUs like this).

Is it Class II? No, because it has an earth connection, and so will not bear the Class II construction mark. It's definitely Class I.

 

[stillp]

7.3.2.2 Class II equipment may be provided with means for connection to earth for functional
(as distinct from protective) purposes only where such a need is recognized in the relevant
IEC standard. Such means shall be insulated from live parts by double or reinforced insulation.

 

[stillp]

5.3.1 Reinforced insulation
Reinforced insulation shall be so designed as to be able to withstand electric, thermal,
mechanical and environmental stresses with the same reliability of protection as provided by
double insulation (basic insulation and supplementary insulation, see 3.10.1 and 3.10.2,
respectively).

I suppose I should have guessed that it would say something like that - which is not really all that helpful to us.

The problem is John that you're assuming the constructional requirements are given in 61140, when they're not. 61140 sets objectives, which the product committees have to decide on the means to fulfil. The standard for a specific product should be more informative.

 

[JohnW2]

An earth connection may be used for purely functional, rather than protective purposes, so wouldn't be a cpc.

Indeed, but I don't see that this does (or necessarily can) make it Class I ...

Is it Class II? No, because it has an earth connection, and so will not bear the Class II construction mark. It's definitely Class I.

I'm far from convinced, and certainly would not say 'definitely'. All definitions of Class I which I have seen require that exposed-conductive-parts be 'earthed' (connected to a CPC of the fixed wiring). In the absence of exposed-c-ps, that definition obviously cannot be fulfilled. I seriously doubt that a high proportion of electricians would call such a thing Class I.

There clearly is no prohibition of a CPC entering an item of Class II equipment. Given the general requirement that fixed wiring cables have CPCs, it is common for a terminal (connected to nothing) to be provided for terminating a CPC within a Class II device.

Kind Regards, John.

 

[JohnW2]

The problem is John that you're assuming the constructional requirements are given in 61140, when they're not. 61140 sets objectives, which the product committees have to decide on the means to fulfil. The standard for a specific product should be more informative.

Yes, I realise that - which is why it was not very helpful.

If the objective (for 'reinforced' insulation) is to achieve the same 'reliability of protection' as that afforded by double insulation, then I suppose the next thing I have to ask about is the nature of the requirements for the degree of 'reliability of protection' afforded by double insulation - since we are otherwise at risk of getting into some circular arguments!

Kind Regards, John.