Metal light fitting with no earth

[happypeter]

Hi,
The missus bought this 2nd hand light fitting off ebay (apparently from john lewis). I'm just wondering why there's no earth connection. The shade, bulb holder and ceiling rose are all metal.

I always thought anything with a metal casing should be earthed? Is it safe?

thanks

 

[winston1]

It is double insulated so it does not need and should not be earthed. The two squares inside each other indicate double insulation.

 

[happypeter]

Ah ok, 2 squares thanks. Looks like I'm going to have to put this one up then

 

[plugwash]

I always thought anything with a metal casing should be earthed? Is it safe?

As Winston says it has the "double insulated" symbol, which means it has been designed so that if installed correctly a fault is very unlikely to result in any exposed metalwork becoming live.

The problem is that caveat "if it's installed correctly". Installing it correctly means that all connections need to be made and all single-insulated conductors contained within the terminal box. That can often present practical problems when trying to fit such a fitting to existing wiring. So such fittings often get installed incorrectly in a way that does not maintain the "double insulation" and therefore does not meet current safety standards.

Having said that such installations are probably not terribly dangerous in practice, simply by virtue of being on the ceiling where they are rarely touched.

 

[happypeter]

Thanks for the explanation. Am I right in thinking its the plastic enclosed connection box that makes it double insulated or is there something special about the wiring too?

 

[sparkwright]

Thanks for the explanation. Am I right in thinking its the plastic enclosed connection box that makes it double insulated or is there something special about the wiring too?

Yes, it's the plastic connector box which makes it double insulated.

It can be a struggle, if not impossible, if you have more than one cable coming out of the ceiling.

Unfortunately people find their own methods which compromise the double insulated-ness of it all.

 

[happypeter]

It can be a struggle, if not impossible, if you have more than one cable coming out of the ceiling.

See what you mean. Luckily I could pull the old ceiling rose into the loft and dangle a new cable down to the fitting. Thanks for the info

 

[JohnW2]

Yes, it's the plastic connector box which makes it double insulated.

I can but presume that they are relying on the fact that the requirement is that there has to be "double or reinforced" insulation, and that they regard that insulation as being 'reinforced', since I can't see anything 'double' about it!

Kind Regards, John

 

[EFLImpudence]

You shouldn't just leave the ceiling rose in the loft but use a proper junction box, then -

is the light flex long enough to connect to that junction box ignoring the light connector?

 

[bernardgreen]

so it does not need and should not be earthed

My opinion is that the exposed metal parts could be Earthed as a extra layer of protection even though the manufacturer's say it is not necessary.

If you do not use the Earth wire in the cable then do not cut it short. If ( when ) you change the lamp then the new fitting may need to be Earthed

That said the lamp does have triple insulation on the cable First layer Blue/Brown, 2nd layer White sheath and 3rd layer of what appears to be fire proof sleeve

 

[JohnW2]

My opinion is that the exposed metal parts could be Earthed as a extra layer of protection even though the manufacturer's say it is not necessary.

We've often discussed this, and one of the problems is that a lot of MIs say that the item 'MUST NOT' be earthed. There certainly is an argument (often presented by EFLI) that 'unnecessarily earthing' anything increases the risk of electric shocks (in general), but that's not really much of an issue when it's on a ceiling.

Kind Regards, John

 

[bernardgreen]

Earthing the item will result in an RCD tripping if the lamp becomes wet, ( ceiling rose under a water leak ).

Without an Earth the damp rose and surrounding plasterboard will have a potential that could be hazardous to someone touching it.

 

[JohnW2]

Earthing the item will result in an RCD tripping if the lamp becomes wet, ( ceiling rose under a water leak ). Without an Earth the damp rose and surrounding plasterboard will have a potential that could be hazardous to someone touching it.

We know that and, in terms of faults in the item, what you say is obviously right (albeit a very small hazard when on a ceiling). However, I was pointing out what MIs often say, and also reminding you of the argument that 'unnecessarily' earthing any metal will theoretically increase the risk of electric shocks due to faults in (or silly dealing with) other items.

Kind Regards, John

 

[plugwash]

Thanks for the explanation. Am I right in thinking its the plastic enclosed connection box that makes it double insulated or is there something special about the wiring too?

What makes an item "double insulated" is going through the design looking for any reasonable fault condition that could cause the case to become live and designing it out. For a light fitting generally this will mean using insulated and sheathed cables rather than single insulated individual wires for internal mains voltage connections and where the cable does have to break out to individual wires doing so within an insulated sub-enclosure. Care must also be taken to ensure wires are not damaged where they pass through metal panels.

So the plastic box is part of the overall design that allows the fitting to be "double insulated", but only part of it. You can't just add a plastic terminal box to any old fitting and call it double insulated.

 

[BS3036]

For a bit of light relief... I just fitted a wall light which had instructions saying double insulated - do not earth. It was a shallow metal box fitted to a metal bracket which was first screwed to the wall. As described by other people above, it only met the requirement if you arranged a provided sleeve so that it penetrated into the wall, as otherwise the user wiring was not double insulated. The bracket interestingly had a tapped hole with an earth symbol, but no matching screw was provided.
Actually I prefer to believe that the safest use of this luminaire is as an earthed class 1 device. I suspect the chinese called it class 2 simply to:

• save a screw and washer
• to be able to sell it to places that often didn't have earths