NO EARTH FOR LIGHT FITTING

[bernardgreen]

for all we know it may be using part of the metal body to pass either + or - 12v to the lamps.

Provided the other side of the 12 volt is not already earthed then earthing one side would not cause any more problems than earthing one side of a battery in a torch.

If the instructions are not clear or in another language as they often are then contact the retailer or manufacturer to clarify or use your own good judgement. Just because its metal or has a metal case doesn't mean it "has" to be earthed.

I do use my own judgement based on over 40 years experience of electronics 30 of which have been in designing equipment. And investigating failure modes of equipment.

I will accept that the operation of some very poorly designed and cheaply built electronic "transformers" may be adversely affected if there is a capacitve coupling of their output to an earthed metal case.

If they are that sensitive then the design is poor and as a result I would be very concerned that the design would not fail safe in the event of a component failure. Fail safe being that no matter what failed the output remained free of any mains voltage.

 

[ban-all-sheds]

Would you care to read the last sentence of 412.2.2.4?

If you would care to quote it here I will be happy to read it.

No exposed-conductive-part or intermediate part shall be connected to any protective conductor unless specific provision for this is made in the specification for the equipment concerned.

 

[SUNRAY]

DI fittings are generally all plastic..

Like my electric drills?

 

[ColJack]

since when has a drill been a fitting?
and don't be a smart arse..
in a drill the electric connections are made in the plastic bit..

 

[SUNRAY]

since when has a drill been a fitting?
and don't be a smart a**e..
in a drill the electric connections are made in the plastic bit..

Not being a smart a**e just passing a comment, which was offered with humour. I guess I must remember to add one of these

Incidently the motor shaft has electrical continuity (via the gearbox) with the chuck. So it is relying on the copper and carbon deposit within the motor not creating a track from com to shaft.

 

[ericmark]

Double insulated electronic transformer. Apparently designed to have a separation between input (230 Vac ) and output ( 12Vdc ) able to withstand 2000 volts.

When it failed there was enough carbon and vapourised copper deposited on the remains of the PCB to create a conductive path between mains input and the output terminal.

Cutting open an identical unit one has to say that the "designer" obviously had a different set of standards to UK and a lot, an excessive lot, of faith in the insulation used in the components.

If there is mains and a metal ( or otherwise conductive surface ) then I would always earth it even if the ( over confident ) manufacturers say it is not needed.

Many years ago I felt the same about electric drills. I considered I could drill through a cable and as a result the chuck should be earthed. I continued to use the old class I drill until I left it on a metal covered table and some one welded on the table this caused the earth wire to melt and connect to live. I was lucky it was a 110volt drill. This taught me a lesson and I realised that problems can exist both ways both Class II and Class I have some dangers and one has to follow the manufactures instructions and rely on their risk assessment.

As BAS has rightly pointed out "No exposed-conductive-part or intermediate part shall be connected to any protective conductor unless specific provision for this is made in the specification for the equipment concerned." and there is good reason for this rule.

 

[bernardgreen]

Incidently the motor shaft has electrical continuity (via the gearbox) with the chuck. So it is relying on the copper and carbon deposit within the motor not creating a track from com to shaft.

Not if there is a nylon gear in the gear train between motor and chuck.

But that is not always the case and my double insulated drill does have a significant electrical leakage from supply to chuck. Not enough to trip the RCD if the drill touches something earthed but an indication that is it due for an internal clean and maybe new brushes.

 

[SparkyNinja]

Refering back to OP, it would appear that simply this is a class I fitting using a class II component.

Earthing will still be required for the fitting.


As for your question about Double Insulation, the defintition says:

'Insulation comprising both basic insulation and supplementary insulation'

This can be in the method of an additional barrier of insulation for things like drills, or simply no conductive parts such as fully plastic fittings.

 

[bernardgreen]

The transformer has a Double insulation symbol

So the manufacturer of the transformer believes his manufactured item meets the requirements of double insulation.

but the light has an earth wire.

So the manufacturer of the light fitting is possibly concerned about the reliability of the transformer and recognises the need to earth the light fitting to ensure safety of his manufactured item should the transformer fail and in doing so put possibly lethal voltages onto the metal of the light fitting.