Light fitting earth wire?


Postby ant1 » Thu Jul 19, 2012 8:57 pm

Hello all,

A friend is installing a new light fitting over his grand-daughter's bed; it's fed by a twin and earth flexible cable from a 13A socket which is easier for her to reach. The fitting is all plastic but for the mounting base which is metal. The connection block is in a small plastic sealed box in the base. The makers assure him that an earth wire isn't required as it's double insulated but I'd thought that it should still be available, if unconnected - and that in any case the metal base should be earthed although it's isolated from the fitting as it's available for a user to touch. It does actually have an unthreaded screw hole but no screw.

He's fitting a three-core flex anyway but I'd be interested to know the current legalities if someone has a moment to reply.

Regards Ant, and thankyou!
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Postby ericmark » Fri Jul 27, 2012 5:59 pm

It is common to have Class II (Double Insulated) with metal. The touch control lamps would never work if earthed.

I will admit years ago I also struggled with the whole idea of earthing. What I could not understand was if nothing was earthed then touching a live cable would not be a problem so why earth? There are many reasons to earth and in the main it is to protect from more than one fault. There are other reasons.

But one has to still consider that in an earth free environment one would not get a shock. This has been now recognised and where RCD's are used then bathrooms do not need earthing as a risk assessment will show to earth everything when the supply is RCD protected can be more of a problem than having no earth.

This of course means we now rely on the RCD to make things safe and as a result old houses without RCD protection have problems.

However there is still no 100% safe method it's all down to a risk assessment. As a consumer one has to accept that the manufacturers risk assessment is correct and when they say it does not need an earth that is the safest way to go.

To try to earth could in fact be dangerous. I will give an example. The electric drill. If one earths the drill and it is placed on a metal surface and some one welds then the earth cable of the drill can end up taking 120A and a 1.5 mm sq cable can't take that current it melts. So the manufacturer has used extra plastic between the electric bit and the metal gear box so there is no need to earth.

Clearly as well as the risk of a welder melting the cable there is also a risk the user of the drill will drill through a live wire. Could also do this with a battery drill. So there is however two or more risks and the manufacturer has decided which is the greater.

OK there may be a case where they have got it wrong. But that is rare so one follows the manufacturers recommendations in fact that is a requirement of the regulations.

So I would always recommend do as the manufacturer says.
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