NO! We are talking about connecting an item to a potential for which it is not intended. Whether you think that is a safe potentail or not doesn't matter, it is still misuse.
No earth cable on light fitting
- Thread starter stephen12345
- Start date
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Just to throw this out there, I was called to look at a fault at a house where the main switch RCD was tripping. The fault was narrowed down to the downstairs lighting circuit and from there the 4 wall lights in the lounge. Lamps out and there was a fault L - E. Further investigation showed the fixing screw of one of the metal class II wall light was almost touching the line conductor as the cable for some reason looped down beside the archetrave box in the wall, before entering the top of the box.
The fixing screw had been driven in at an angle and was sticking out the side of the red plug. As this was a class II light there was no earth terminal so the installer wrapped the cpc around one of the fixing screws, which allowed the RCD to detect the fault. This happened only after around 4 years after the lights had been installed. I wonder what would have happened if the cpc was fitted into an insulated connector block. It's Emma Shaw all over again. There is no mention of flash testing the fitting after installation in the installation instructions.
It is also important to note that the fittings require careful installation to ensure there is no single insulation on the supply cables outside of the enclosed plastic connectors supplied with the fittings. This is frequently impossible with the manufacturer supplied connectors as they often barely have enough room for a single 1.0mm². How many diyers know to either alter the wiring or find another more suitable fully enclosed connector?
The fixing screw had been driven in at an angle and was sticking out the side of the red plug. As this was a class II light there was no earth terminal so the installer wrapped the cpc around one of the fixing screws, which allowed the RCD to detect the fault. This happened only after around 4 years after the lights had been installed. I wonder what would have happened if the cpc was fitted into an insulated connector block. It's Emma Shaw all over again. There is no mention of flash testing the fitting after installation in the installation instructions.
It is also important to note that the fittings require careful installation to ensure there is no single insulation on the supply cables outside of the enclosed plastic connectors supplied with the fittings. This is frequently impossible with the manufacturer supplied connectors as they often barely have enough room for a single 1.0mm². How many diyers know to either alter the wiring or find another more suitable fully enclosed connector?
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Interesting point Freddo. Perhaps Class II is not a suitable form of protection against electric shock for equipment likely to be installed by non-competent persons?
I say "supposedly" because I'm firmly of the belief that in practice it would be almost impossible to isolate something like a metal bathtub from earth effectively enough in the average house so as not to pose a shock risk anyway. Even the IEE Regs. recognized this well over half a century ago by adding to the part about metalwork being either effectively segregated or bonded a clause indicating the bathtubs must be bonded. I find it perplexing that we're now in the 21st century and this seems to have been forgotten.
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I have to agree with John that this is getting rather silly. We're not talking about hooking up the casing to 1000V and then saying "Look, the insulation has broken down."
We're talking about the casing of a device which is quite liable to come into incidental contact with something which is at earth potential in normal use even if not deliberately earthed for other reasons. If you have a metal-cased class II device of some kind which you are using in a kitchen, for example, should you be careful not to lay it down on a countertop where it might rest against the edge of an earthed stove? Or does the manufacturer intend that it only ever be used within an earth-free environment?
An excellent example of how earthing the metalwork anyway was better
A better example of the dangers of incompetent installers and failure to test.
Well, even with somebody fully competent I think in the case described it could have happened. Some of the light fixtures don't exactly make it easy to dress the wiring in neatly and actually see what's happening with it as the fixture is tightened back to the wall (this is one area in which I definitely prefer the American method of installing light fixtures).
Speaking of testing, does the holy grail of BS7671 actually demand insulation testing from exposed metalwork of class II fittings to true earth?
Speaking of testing, does the holy grail of BS7671 actually demand insulation testing from exposed metalwork of class II fittings to true earth?
Goodness! If the casing of a Class II appliance might not "be able to withstand" a pd of 230V between exposed metalwork and contents, I wonder what might happen if one applied a pd of 500V relative to earth to that metalwork (hence ~500V relative to the neutral conductor within the enclosure)
Kind Regards, John
I guess we shouldn't even think about Meggering from L & N joined together to the casing then?
But there should be no paths to earth - it's a Class II item.
You may not.
Not allowed to be.
There's a difference between a short test and continuous stressing of the insulation.I guess we shouldn't even think about Meggering from L & N joined together to the casing then?
I am finding it increasingly difficult to work out whether you are being serious or not! Are you really seriously suggesting that there is some doubt that the casing of a Class II item could "withstand" a pd of 230V across it continuously (even that assuming that a live conductor is in contact with the inside of the case, which is unlikely)??
Within the lighting circuits of my house, I have any amount of 1mm² cable in which one layer of thin PVC insulation has been the only thing separating a permanent live conductor from the CPC in contact with that insulation - and that ~240V p.d. has been virtually continuously present across that insulation for 30+ years - and I have yet to see any evidence that it has been unable to "withstand" that p.d.
Kind Regards, John
But the cable is designed and tested for exactly that application.
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