Wiring an earth in LV lighting

[Charlie]

(Apologies if this has been covered before)

Is there reason to wire the earth core in a single room LV Lighting loop where there is one transformer per lamp?

There is nothing to earth so the only reason I can think of is that in the future some might want to replace the low voltage lights with something else (which needs earthing) in the future. In which case they probably want to rewire the whole room anyway.

The diagram below should hopefully clarify things.

240V -------------------------JB | | | | | | | | Tr Tr Tr Tr

[Owain]

"Charlie" wrote | Is there reason to wire the earth core in a single room LV | Lighting loop where there is one transformer per lamp? | There is nothing to earth so the only reason I can think of | is that in the future some might want to replace the low voltage | lights with something else (which needs earthing) in the future. | In which case they probably want to rewire the whole room anyway.

You *must* continue the earth core to the transformers on the mains side as

*all* circuit wiring must have a circuit protective conductor (earth wire). You do not need to connect the earth in the low-voltage side; the low-voltage cable may not be suitable for mains use anyway.

Owain

[Stefek Zaba]

Yeah - the Regs say it's no-fair to assume no-one will want to replace existing fittings with ones that need an earth. (And many LV fittings

*do* need earthing, anyway).

And since you'll be wiring the lighting points with 1mmsq or 1.5mmsq T&E anyway (you will, won't you - you weren't going to use that bit of

2-core flex you had lying around for permanent wiring, were you!?), the 'extra' work in running the E core of the T&E, sleeving it, and either attaching it to the fitting's earth point or coiling it up neatly in its sleeving to earn good karma from whoever makes the next change - which may be yourself in 5 years' time - is scarcely going to blow your time and effort budget...

Stefek

[Charlie]

Stefek,

I've run 1.5mm cable so I have the earth there - I was just very lazy/naughty when I first did it. It's been bothering me since - didn't know if the 240V passing between the junction boxes should be earthed properly.

I think I shall go back and strip the wire back an inch or so to give me the earth and connect it up.

Charlie

[The Natural Philosopher]

Sadly, most transformers have nothing to screw it to.

I usually leave it ina junction box in the ceiling at the end of the mains T & E, and just connect the transformers two wires up...

[Lobster]

Why is that lighting kit which doesn't have any need for an earth (which is a large proportion of it these days) never has a place to park the redundant earth lead? I'll bet there are plenty of instances where not-so-competent amateur electricians have just left the earth wire flapping around uninsulated in the breeze, where it could easily come into contact with somewhere it shouldn't.

Is there some reason? Maybe if there was a non-functional earth wire 'parking' terminal it could be construed as being legally functional or something daft like that??

[Malcolm Race]

AFAIUI the purpose of the earth core in the mains side of he wiring (assuming a double insulated transformer) is to protect the _wiring_ if, for instance,a nail is driven through it. There is a path to earth so the mcb (or whatever) will trip.

Malcolm

[Stefek Zaba]

Not to mention not-so-competent 'pro' electricians, and even more so general builders just doin' a spot o' wirin'...

Shouldn't have thought it's anything like as sophisticated as that - just puts a couple of pennies on the manufacturing cost, which is quite enough to make the beancounters put you on a pyre of lever arch files!

[Lurch]

On Thu, 20 Jan 2005 17:37:27 GMT, Malcolm Race strung together this:

Amongst other things yes, it's not the only reason for it being there.

[ARWadsworth]

So it is the same reason you never get light fittings with 4 decently sized terminals to accommodate 1.5mm^2 cable for loop-in wiring. Damn those pennies.

Adam

[Mike]

Possibly because the kit is 'homogenised' to work Europe wide and over half of them don't have an earth in the lighting wiring. Though I notice more and more transformers are moving to using an external choccy block anyway so you can always use a three pin one.