If there is no connection to earth, where exactly are these leakage currents flowing?
No earth cable on light fitting
- Thread starter stephen12345
- Start date
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That's obviously true but, as I have repeatedly said, the discussion appears to have been simply about the general undesirability of having 'unnecessarily earthed metal' around the place, regardless of whether it is the outer casing of a Class II electrical appliance or something totally non-electrical.
What on earth does that mean? You are surely not suggesting that the 'double or reinforced insulation' is not even able to withstand continuously the p.d. between supply voltage and earth, are you?
I don't really understand that, either. Where do I find the corresponding requirements in relation to the ability to "safely carry fault current" for the exposed-conductive parts of a Class I item?
Kind Regards, John
Why should I not suggest that?
In the appropriate product standard or basic standard, where else?
Indeed, when it comes to some of the class II things I've seen, I've had to wonder at just how good the double insulation really is. For example, I remember some years ago having a metal desk lamp, a cheap, modern replica of an older style adjustable lamp. It was supposedly class II, but after looking at the construction and how the wiring was routed I was concerned that the double-insulation might not actually last that long with movement. I rewired it with a 3-conductor cord and bolted an earth securely onto the metal base with a solder tag, and felt far more comfortable handling it afterward.
That's true in some situations, but consider something like a metal bathtub which has metal taps fitted on the wall above it, i.e. not bolted to the tub so as to provide metallic contact.
In the event of some external fault raising the potential on the pipework and the taps significantly, if you were sitting in the water and reaching out for one of those taps, would you rather the bathtub was at the same potential or that it was supposedly isolated from earth, but in reality almost certain to have some sort of earth potential on it, even if through a relatively high resistance of the building structure?
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... because it seems to imply that the Class II item could be diabolically dangerous?
In the absence of a relevant specific product Standard, I presume that the 'basic Standard' would be BS7671, and I haven't seen any such requirements in it. ... and, anyway, what are these exposed-c-ps that could not safely carry fault current until a protective device operated - aluminium foil, perhaps??
Kind Regards, John
Through any other path to earth which is provided by connection or contact with the units concerned.
Take a group of typical class II things like a TV, VCR, DVD player, audio amplifier, satellite receiver etc. all interconnected. Then grab a Belling-Lee coax plug or satellite F-connector which has earth potential on the shell and go to connect it to the appropriate unit. The current which results as one contacts the devices while holding an earthed connector can be quite enough to give a definite "bite" in some cases.
(And once that connector is in place, the whole lot is then earthed through that external connection anyway, so why not put a secure earth on it from the supply at the outset?)
Well it darned well should be! If you are seriously suggesting that some metal-cased class II device might suffer some sort of insulation breakdown if the case ends up earthed, then I would have severe misgivings as to its double-insulation properties and therefore its safety.
No, it implies that the item, like all electrical equipment and appliances, is designed to be used as specified by the manufacturer, not to be connected to some other potential.
No, BS7671 is not a basic standard! It has nothing to do with product requirements, it is a standard for electrical installations. Relevant basic standards might be 61140, 60335 series, etc.
Yes, aluminium foil might be an example. Would you expect the manufacturer of an item of Class II equipment to test the exposed metal parts for fault current withstand?
Indeed - What else is one to make of it?
That the item is to be connected as specified by the manufacturer, not otherwise. Any item connected to the wrong potential can become dangerous.
What if somebody takes that piece of metal-cased class II equipment and stands it on something which is earthed, or pushes it back against something which is earthed?
What if it's a piece of equipment intended to be used handheld? Are the manufacturer's instructions going to include statements that the user must wear insulating rubber boots and not touch anything earthed while using it? (I'm sure that would inspire user confidence in its safety!)
If the nature of the equipment is such that that is foreseeable then the manufacturer must take it into account in his design.
Most equipment intended for hand-held use is Class II, and is only used for short periods.
Won't you have to qualify supposedly?
Either bonded or isolated, it doesn't matter, does it? It depends what you do next.
An extraneous-c-p do you mean?
I really can't buy that argument. If a Class II item could not be relied upon to withstand supply p.d. between its internal parts and the outside of it's casing, then is simply would not be safe.
No, but if the concept of Class II is to believed, there would be no need for them to - since there should be no way that fault current could flow through through those exposed parts.
Kind Regards, John
This seems to be getting plain silly. We're not talking about connecting equipment designed for 12V to 230V, or equipment designed for 230V to 1000V - we're talking about the outer casing of something allegedly safe (and safe to touch) coming into contact with earth potential, a potential which is ubiquitous within almost all premises. If an item becomes "dangerous" under those circumstances, it is simply a dangerous item.
Kind Regards, John
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