Under floor heating system problem
- Thread starter North
- Start date
DI status is irrelevant wrt to the earthed layer.
DI means that it's made in such a way that nothing bad will happen as a result of a single failure within the product. I've got several DI appliances etc. If I were to start banging nails or drilling or screwing into them, the fact that they are DI would do SFA to reduce the risks I would face.
DI means that it's made in such a way that nothing bad will happen as a result of a single failure within the product. I've got several DI appliances etc. If I were to start banging nails or drilling or screwing into them, the fact that they are DI would do SFA to reduce the risks I would face.
What if you go and get them yourself - not delivered?
Of course it does.
Not because it is electrical, that is true, but because you have earthed it.
If you earth a bath it is the bath which has become less safe.
If you earth metal shelves it is the metal shelves which have become less safe.
If you earth a metal tool cabinet it is the metal tool cabinet which has become less safe.
If you earth a Class II item it is the Class II item which has become less safe.
I agree. The equipment itself cannot become any less safe, but the environment it's in may become so. But, the distinction is so fine that in practical terms there is no difference.
Why ?
I have some 12V equipment where the metalwork is part of the circuit - but it's still earthed. If the supply is floating WRT earth then no problem earthing either side of the output. If the output is not floating, then it's hard to see how it's Class II/DI.
I am not 'arguing for it'. As you know, I wouldn't do it. However, I am saying that I'm not sure that there is any real basis for manufdacturer's saying that it "Must not be earthed". We seem agreed that that statement is nothing to do with the electrical functioning (or electrical safety) of the item itself, and that the only apparent justification is that by not earthing it one is making the environment slightly safer. However, the same is true of all thsoe baths, metal shelves, metal cabinets, metal window frames etc. etc., and I cannot recall any manufacturer of such products stating that they "Must not be earthed"!
Only if it were being used in a manner/location in which PELV would not be acceptable (regulatory-wise). Otherwise, the arguments above would still apply.
Kind Regards, John
OK, I'm not going to argue about the semantics - I would say that it is the environment that becomes less safe, rather than the equipment, but there's nothing to be gained by arguing about the words.
Whatever, my point remains. Although all those situations are, IMO, identical in terms of the safety of the environment, only when the item in question is an item of Class II electrical equipment do we see the manufacturers saying that it "Must not be earthed"; at least IME, I have never seen instructions for a bath, metal shelves, metal tool cabinet or whatever saying that the item "Must not be earthed". That seems to imply that the manufacturers of Class II electrical equipment seem to feel (I believe incorrectly) that the effects of earthing exposed metallic parts of Class II electrical equipment is, in some way, more of a potential hazard than would be earthing the bath or whatever.
Maybe I've missed it, but I have not seen anything in BS7671 which prohibits the earthing of any exposed parts of Class II equipment which are made of conductive materials.
Kind Regards, John
... but they did say follow the manufacturer's instructions - probably why the manufacturer states it.
I suppose now, since we only have to take account of the MIs, you will say it no longer applies.
Why doesn't BS7671 forbid earthing spoons?
You say you agree about unnecessary earthing so why do you keep on asking why?
Why does the OSG say that plastic pipes "do not require bonding" instead of pointing out that it is not possible and if you do it you are an idiot.
If that's the case, then the manufacturer must have some reason for stating it. If it really were simply because (as you, BAS, myself and others believe) it is desirable to avoid 'unnecessarily earthing' anything, if the same manufacturer manufactured metal baths, shelves, cabinets or what ever, do you really believe that they would include "Must not be earthed" in their instructions??? I think not - which, as I said, implies to me that they have the (IMO mistaken) belief that there is a reason for saying "Must not be earthed" which is specific to (Class II) electrical equipment.
You would need to ask the authors of the OSG about that!
Kind Regards, John
I presume it is because people are used to earthing metal parts of appliances and instead of a lengthy explanation of the reasons simply state "must not be" earthed.
Had they said something like "should not be earthed" it would probably lead to lengthy discussions about what they really mean.
Then you needed to ask the authors of BS7671 why the don't prohibit and all the manufacturers why they do.
Maybe, but it's the "Must" that I think is a little inappropriate, particularly given that there is seemingly no regulatory basis for it. As we know, there are situations in which some people would advocate earthing things which you and I would feel were better ('safer') not earthed - so it's not 'black and white'.
As for BS7671, it does not really say anything about avoidance of 'unnecessarily earthing' things that don't need to be earthed. You've already commented that manufacturers cannot 'prohibit' but, as for the reason why they (often, not always) say "Must not...", I continue to suspect that they are under the mistaken belief that they are reflecting 'regulations' (BS7671 or otherwise).
Kind Regards, John
What nonsense! There is no such thing (in this context) as "CE approval". Have they declared any particular "British, European and International standards" with which the product is claimed to conform?
Which is probably nothing more than "we've always done it that way". There's probably been some folklore at some point saying that Class II equipment must not be earthed*, and the manufacturer's have just followed that line and seen no reason to change it. Lets face it, there's no real reason that an extractor fan "must" have an isolator (good reasons why it's useful, but no "must") yet I can't recall seeing any instructions without this mandatory.
* And indeed, there are some good reasons, in many situations, for not earthing it.
What situations do you envisage where it would NOT be a good reason NOT to earth it?
Perhaps they know it is safer not to earth it otherwise there is no point going to the trouble of making it Class II.
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