Wiring - no earth for lighting

[Perry Gunn]

as part of our lounge renovations SWMBO has decided that she wants brushed chrome fittings for the mains sockets/telephone point & light switch.

The only issue is that, being a fairly old house, although it's been rewired and the ceiling light points are earthed, the switch is twin core with no earth wire - and I need to earth the metal light switch plate.

Given the tortuous route of the lighting cables I can't see anyway of adding an earth without ripping out masses of floor upstairs.

There is a mains socket nearby, so would it be safe to channel in some conduit vertically down from the light switch to below floor level and run an earth wire from the ring main to the switch?

Thanks

Perry

[Chip]

On Mon, 04 Jul 2005 08:19:54 GMT,it is alleged that Perry Gunn spake thusly in uk.d-i-y:

I would say (gut reaction) no to using the ring main earth because it combines 2 circuits and makes the lighting safety dependent on the ring. If you're going under the floor though, any possibility of running say a 2.5mm single green/yellow to the CU (and label it there)?

Pedantically the answer is 'rewire' but that's unhelpful, a separate earthing wire would be certainly better than the unearthed situation you have now, and better than relying on another circuit for the earth.

[Andy Wade]

When was it re-wired? It seems very odd to have earths at the ceiling points but no earth wires in the switch drops.

Then stick to all-insulated switches.

That wouldn't comply with the wiring regs[*]. It would be better than having no earth at all though.

[*] Specifically Reg. 544-01-01 which requires the earthing to be run in the same wiring system as the live & neutral, or in the immediate vicinity thereof.

[Christian McArdle]

Pretty common as a cost cutting exercise if the existing switch drops are good condition T&E, as it saves a whole load of redecorating. However, it should have been pointed out as such a penny pinching exercise by the electrician at the time.

I believe I've seen some double insulated chrome fittings somewhere (which don't require earthing), but I may have dreamt it.

Christian.

[Perry Gunn]

On Mon, 04 Jul 2005 13:30:03 +0100, Andy Wade waxed lyrical about:

About 15-20 years ago (we've only owned it for the last 2) - the documentation is somewhere in the huge mass of paperwork the previous owner gave us (they owned the house for 32 years and I think that they kept *every* receipt!).

It looks like the lighting circuits were replaced and then a separate earth wire was added later (it's easy to see this in the loft), and all the cables appear to be in good condition.

The drop to this switch is very difficult to get at as it comes down in metal conduit which is buried inside a pier that was constructed to support an RSJ when an interior wall was removed. I don't know exactly where the conduit runs to as it appears to have been routed to avoid the RSJ.

Unless I can persuade SWMBO that metal faceplates are a no-no, it looks like it may have to be the separate earth wire run back to the CU (as suggested by Chip) - thank god I've still got most of the floor up!

[Perry Gunn]

On Mon, 04 Jul 2005 12:20:31 GMT, Chip waxed lyrical about:

Thanks, I guess I'll have to try the separate earth wire back to the CU - unless I can persuade Cindy to give up the chrome look, but I won't hold my breath :-)

As I write this, I've just had a thought - if I'm able to run the separate earth wire vertically up into the floor void of the room above, would it be acceptable to connect it to the earth at the ceiling rose?

Perry

[Christian McArdle]

If you are able to do this, run 1mm T&E instead and abandon the original wiring.

Christian.

[John]

So it will have done under the 15th edition.

Is the steel conduit earthed at the other end ?.

If it is, then the earth is provided via the steel conduit, this method of earthing is very common in industry, and all you need to do is connect the face plate to the back box.

A little advice is to double check the nuts on either end of the conduit are tight, and check the earth connection at the top.

J

[Andy Wade]

Did you mean "if the existing switch drops are good condition PVC twin" rather then T&E?

[Christian McArdle]

Yes, that's exactly what I said. ;-)

Christian.

[Andy Wade]

Then it wasn't re-wired properly. Lighting circuits have required earths since about 1966.

It sounds as if running a separate earth wire from the switch back to join the earth at the ceiling rose (following the route of the switch drop as closely as you can) would be the simplest option.

[Chip]

On Mon, 4 Jul 2005 14:52:46 +0100,it is alleged that "Christian McArdle" spake thusly in uk.d-i-y:

Ditto, agreed. :-)

One point though, make sure that the ceiling rose IS earthed, and doesn't just have the earth wires connected but not actually doing anything.

[usenet]

Isn't it legitimate to use the metal conduit as the earth still? I'm sure others will confirm/deny.

[Perry Gunn]

On 4 Jul 2005 14:52:02 GMT, [e-mail] waxed lyrical about:

Perhaps that's what's been done - as I can't find the other end of the conduit without taking up lots of flooring, is there an easy way to check if the metal conduit is earthed?

Perry

[BigWallop]

You have checked to see that the earth conductor hasn't been chopped off short at the switch points?

[BigWallop]

The dangerous way to check for earth continuity is to touch a metal object over the live and (should be) earthed parts, but that's not a recommendation. :-)

The safe way is to use a multi-meter on the ohms setting, and, with the power off at the Consumer Unit, test across the live / neutral, the live / earth then the neutral / earth paths. If the readings across the live / neutral path and live / earth path is very close to the same readings, then it should show that the point is earthed properly.

[Perry Gunn]

On Mon, 04 Jul 2005 15:22:10 GMT, "BigWallop" waxed lyrical about:

yes, it's only twin-core cable not T&E.

It's actually 3 runs of cable within the conduit - it's a triple switch - I didn't mention this before as I thought it would only complicate matters and, from the point of view of providing an earth for the switchplate, doesn't change the central lack-of-earth issue.

This is what makes the idea of having to replace the runs a bit of a nightmare they switch two separate ceiling lights and a pair of wall lights and if I have to run new cable there will be a lot of upstairs floor that has to be taken up.

Perry

[BigWallop]

And the conduit isn't visible at the ceiling rose at all? Bugger!!! If the rose has an earth point, then it should be possible to pull a new green/yellow through the conduit to the switch point from there. That's if you can find the other end of the conduit away from the switch of course.

[John]

It is still fine to use conduit. He needs to get a circuit tester and test to see if the conduit is earthed, just test between live and the back box.

They can be bought cheap enough form any DIY store.

J

[Adrian C]

OK, an out-of-the-sky idea...

How about running a low voltage transformer isolated supply (so earthing unnessary) to the switches and contactors (relays) near to the ceiling rose? You could probably extend this to provide whole house "nobody's at home" security lighting.

Dimming would be a bit difficult though...

-- Adrian