MR16 to GU10 to earth or not to earth?

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dmb68
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MR16 to GU10 to earth or not to earth?

Post by dmb68 » Thu Mar 28, 2019 12:31 am

Hi, I've just joined this forum so hoping to get some good advice!
I'm looking to convert some MR16 elv downlights to GU10 LEDs. It looks a straightforward job but I'm a bit confused about the earthing requirements. I have bought some double insulated GU10 lampholders which have a connector inside another insulated box attached to a metal support bracket. There is an earth wire attached to one of the connector poles which is apparently compulsory for cpc.
My existing light circuit has twin and earth running to junction boxes at each light and then twin only to each transformer i.e there is no earth wire, which is normal for 12v lights. The metal light housings have also nowhere to connect an earth wire. .As there is already an earth running between the junction boxes providing cpc and the GU10 lampholder is double insulated am I correct in thinking that I do not need to connect the earth wire to the metal part of the downlight. The led lamp simply sits in the housing and the lampholder fits to the lamp so there is no possibility of any current passing through the metal part.
If I'm correct why is there an earth wire attached to the lampholder and what should I do with It?
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Re: MR16 to GU10 to earth or not to earth?

Post by arco_iris » Thu Mar 28, 2019 9:30 am

:welcomeuhm:

As you will be disconnecting and getting rid of the transformer, and the GU10 fittings must thence be connected into the junction boxes, why not simply connect the earth there...... and to the fitting, to be on the safe side.

(Although the MR16 holders are metal, and "metal fittings must be earthed", from the transformer to the fitting is only 12v so it doesn't apply. The transformer was probably plastic cased anyway.)
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Re: MR16 to GU10 to earth or not to earth?

Post by dmb68 » Thu Mar 28, 2019 10:03 am

Thanks for your reply arco_iris. The lead that goes from the junction box to the transformer is of course just live and neutral, as you say the transformer is plastic anyway. I presume I should change this for twin and earth going to the new lampholder and then attach the supplied earth wire to the metal support bracket as in the picture. As the support bracket will be fastened to the the metal light housing this should sufficiently earth the whole set up - do you agree? I still can't quite understand why a double insulated lampholder should require an earth though - in fact if you buy a modern class 2 downlight the instructions usually say 'must not be earthed' !


https://www.screwfix.com/p/luceco-gu10- ... lsrc=aw.ds
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Re: MR16 to GU10 to earth or not to earth?

Post by arco_iris » Thu Mar 28, 2019 10:32 am

ae235.jpeg
ae235.jpeg (7.88 KiB) Viewed 486 times
^^ this is OP's intended part.

I am not sure that Class 2 fittings say "must not be earthed", I thought they said "need not be earthed". Resident expert OnlyMe might pop in when he's finished work.

Anyway, you're not fitting a double insulated Class 2 downlight, are you. You are using what is basically an adaptor to convert your existing fitting in the ceiling from 12V MR16 to 240V GU10.

Yes, the slotted bracket fitted behind the spring clip will continue the earth, if the fitting is painted, take a patch back to bare metal to make the connection where it clips on.

You just need a length of 0.75mm2 three core flexible cable to go from the JB to the block on the adaptor, the earth fly lead is already supplied.
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Re: MR16 to GU10 to earth or not to earth?

Post by dmb68 » Thu Mar 28, 2019 11:45 pm

Thanks for the info arco_iris - job done and all working, nothing went bang! :wink:
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Re: MR16 to GU10 to earth or not to earth?

Post by arco_iris » Fri Mar 29, 2019 9:33 pm

Thanks for letting us know, not many people we help bother to do that!

Feel free to come back with any other queries, we're generally a friendly bunch......
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Re: MR16 to GU10 to earth or not to earth?

Post by OnlyMe » Sun Mar 31, 2019 10:04 am

arco_iris wrote:I am not sure that Class 2 fittings say "must not be earthed", I thought they said "need not be earthed". Resident expert OnlyMe might pop in when he's finished work.
I would say "cannot be earthed". There might be a parking space in the form of a piece of strip connector but that is not connectected to the appliance.
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