That doesn't work when replying to posts numbered N when N mod 15 = 0.
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No earth cable on light fitting
- Thread starter stephen12345
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I'm not sure why you think that. What's the difference between the two scenarios in terms of the metal casing and how it's connected to some earth point which could, under certain circumstances, bring a potential back to that casing?
You could design some metal-cased appliance to be class I and provide an earth via the connection cord to the case. You could also add the necessary amounts of double-insulation in order to leave the casing unearthed and make it class II. But if you then come along and connect an earth to that casing anyway, how is the end result - from the point of view of what might happen voltage-wise on the casing - any different than if you'd made it a class I design from the beginning?
All you have done is effectively turned it into a class I appliance which happens to have some extra layers of insulation internally between the live parts and the casing.
OK
and Class II metal parts must not be earthed because it is deemed they cannot become live due to a fault - Live to themselves - therefore shall not be made so that they become live because of faults elsewhere.
You'd better fit copper pipe to your bath, then, so that you have a reason for bonding it - or
more precisely, NOT fit plastic pipes in order that you may remove the bonding.
Because, for safety, Class I exp-c-ps must be earthed because they may become live due to a fault - Live to themselves - causing all other earthed parts to become live -
and Class II metal parts must not be earthed because it is deemed they cannot become live due to a fault - Live to themselves - therefore shall not be made so that they become live because of faults elsewhere.
The same reason you do not want to earth (not bond) an isolated metal bath.
...but being double insulated/Class II is deemed to be the better (safer) option.
You'd better fit copper pipe to your bath, then, so that you have a reason for bonding it - or
more precisely, NOT fit plastic pipes in order that you may remove the bonding.
But couldn't that be used as an argument against allowing the use of class I appliances at all? The fact remains that if you earth the casing of a class II device anyway, the result is no worse/riskier than if you'd installed a class I device.
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Reduction of the amount of touchable earthed metal around obviously offers some safety benefits (in general, not in relation to the item of equipment in question).
Although almost always unattainable in practice, the safest option of all would be to have NO touchable earthed metal anywhere in the building.
Kind Regards, John
It could but that hasn't been done?
...but it is worse/riskier than leaving it as Class II.
A car with air-bags removed is no riskier than a car without air-bags - so what?
Your arguments are self-defeating.
It may well be, but as you say, it's not a realistic goal when it comes to the practicalities. If the (minimal) risk of having earthed metalwork on a class I appliance is considered acceptable, then I don't see how taking a class II appliance and, in effect, turning it into a class I appliance by earthing its casing anyway is any less acceptable.
Sorry, not sure what you mean specifically - That it's been used as an argument?
From the possibility of some external fault making the case live, perhaps, however unlikely. But don't forget that a metal-cased class II device introduces its own potential risks which would not be present with class I device.
Actually a good analogy, since introducing air-bags might mitigate against certain risks but introduces new risks which were not present without them.
Agreed - but it's not an all-or-none situation. The less touchable earthed metal there is, the less the theoretical risks - so that it probably makes sense not to earth touchable metal 'unnecessarily' (as per one side of the 'metal bath' arguments).
I understand what you are saying. Indeed, there's nothing to say that a Class I appliance cannot have 'double insulation' (or equivalent) within it, such that the earthing of its exposed outer metal casing is not really necessary.
However, as regards your statement "... If the (minimal) risk of having earthed metalwork on a class I appliance is considered acceptable... " , I could suggest that it may only be considered 'acceptable' if/when it is necessary/unavoidable - i.e. if there is no 'double insulation' (or
equivalent), such that earthing of the exposed metal is necessary for safety.
Kind Regards, John
I too understand what he is saying. I am having trouble understanding why he is saying it.
I suppose one of the things he is saying/implying is that it one should not be allowed to classify something as Class I (and hence earth the outer metal casing) if (as is probably at least sometimes the case) what is inside that metal casing would actually qualify as Class II.
Since there is no 'marking' for Class I (it being the default), I suppose that would require that it 'were not allowed' to NOT put a double-insulated marking on an item if it did, in fact, qualify as such!
Kind Regards, John
I don't think that is what he is saying.
He is saying that he may as well earth Class II appliances because they would then be no worse/riskier than Class I; while discounting the fact that they would then be worse/more risky than unearthed Class II.
It is a fatuous statement.
He is saying that he may as well earth Class II appliances because they would then be no worse/riskier than Class I; while discounting the fact that they would then be worse/more risky than unearthed Class II.
It is a fatuous statement.
Yes, he is.
One thing that gets me a bit confused by all this is the fact that there seems to be a large 'hole' in the classification system. There are surely very many items which have no external metal, so can't be Class I, but don't necessarily satisfy the requirements for being Class II - so what are they?
Kind Regards, John
What items did you have in mind?
Plastic ceiling roses, switches? I suppose if there is nothing to earth then it doesn't matter but they are not Class II, are they?.
Plastic ceiling roses, switches? I suppose if there is nothing to earth then it doesn't matter but they are not Class II, are they?.
That's my point - it seems that anything which is not (and marked) as Class II is, by default, regarded as "Class I" - but that is meaningless if there is no exposed metal to earth!
I wasn't really thinking of electrical accessories - although the examples you give (not to mention plastic CUs) may be valid; mind you, they are made out of pretty tough material, which could well count as 'reinforced insulation', even though they are not marked as Class II. Rather, I was thinking of the countless items and domestic appliances which are plastic encased but which do not claim to be (and may not satisfy the requirements for being) Class II.
Kind Regards, John
But if they have no exposed-conductive-parts....
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