Something which takes power from the mains and carries it across an isolation barrier. .... Current that can flow between input and output when someone or something grounded touches said output. .... I don't know what the numbers are for regular commercial devices offhand. I remember for medical devices, limits of 100uA of touch current under normal condition and 500uA of touch current under single fault condition.
Thanks for your detailed reply.
OK - so you're talking about leakage 'through' a PSU. I am actually fairly surprised that there is
any acceptable level of such 'leakage' in a normal Class II item 'under normal conditions' (beyond a tiny amount attributable to inevitable 'stray capacitance') - and, as for 'single fault' conditions, unless that situation is 'qualified' that 'single fault' could result in direct connection between input and output of the PSU, couldn't it.
I'm familiar with requirements in relation to medical devices, but that is a very specialised/different situation which probably has little relevance to consumer Class II items.
However, I continue to be confused about what actually does (and does not) qualify as 'Class II' (see below).
I'm speculating a bit here, but AIUI patio heaters are halogen heaters which run at much much higher temperatures than the other appliances you mention.
Maybe true in relation to most of the appliances I mentioned, but I know from bitter experience that parts of hot air guns get extremely hot
Can you name some of these items?
Anything totally encased in insulating material. Things like wallwarts (e.g. 'USB chargers' etc.) are generally marked as Class II, but my question relates to the situation if they were not so (designed and) marked - would they then be 'not allowed'? .....
At least according to Wikipedia there are actually five classes.
Class 0 - protection by basic insulation only.
Class 01 - protection by basic insulation, plus earthing but with the earth connected via a seperate earth terminal rather than a wire in the mains cable
Class 1 - protection by basic insulation plus earthing through the mains cable.
Class 2 - protection by "double or reinforced" insulation.0
Class 3 - protection by an external SELV power supply.
Wikipedia claims class 0 appliances were banned in the UK in 1989 but I can't seem to find a precise reference in the linked law.
Indeed. BS7671 also recognises Classes I, II and III - and there certainly seems to be a general belief that Class 0 is 'not allowed'. Class '0I' seems a little odd, in as much as it is essentially Class I. However, if that is also 'not allowed' then that would presumably be a problem in a situation in which someone had run a separate CPC in order to install a Class I item on a circuit which had no CPC?
However, this brings me back to my point/question. We're not interested in Class 0 or Class III, and I will ignore Class 01, so we only have Class I and Class II to talk about. If an item is totally plastic encased, then it cannot be Class I per BS7671 definition, since it has no exposed-c-ps to earth. If id doesn't have double or re-inforced insulation, then nor can it be Class II - so, as I asked "What is it?", and is it 'allowed'? Is the answer perhaps ...
... Not every piece of electrical equipment is an appliance designed to an IEC appliance class though.
It would seem that the items I'm postulating would not qualify as any of the 'Classes' - so, I wonder, would they be 'allowed'?
In passing, I see that some of my oldest (plastic encased) wallwarts, although marked as Class II, have a metal earth pin - which begs the question as to what (if anything) that is connected to.
Going back to the earlier comments about leakage through PSUs, BS7671 seems to regard the purpose of 'double or reinforced insulation' as being to provide a barrier between 'accessible' and 'live' parts, and I've always thought (perhaps wrongly) that it was talking about parts which are 'live' under 'normal (i.e. no fault) conditions'. If that were the case, then it presumably would not apply to leakages through PSUs under (even 'single') fault conditions?
Kind Regards, John