Lighting earth problem

[JonC2010]

Hmm, OK I think I understand everything so far...

In order for me to completely understand what's going on, could it be relevant that the new fittings have two earth wires? One is clearly attached to the metal part of the fitting that attachs to the ceiling fitting. The other comes from deep inside the fitting and is presumably attached to the metal parts of the fitting lower down. This makes sense as the two metal parts of the fitting are separated. What's odd though is that connecting either of these two earth wires to the earth in the ceiling causes the trip.

Another thing I didn't mention earlier that may or may not be relevant is that on on occasion during testing the wall light switch was in the on position when I went back to the consumer unit and tried to reset the trip. The resulting trip actually fused closed the wall switch contact - implying a large short, no?

 

[JonC2010]

P.S. There's an ego-massaging thanks button for that!

There is? I am new to this posting lark!

 

[LiamPope]

Hmmm, normally I'd have expected an experienced pro to have come along by now with a blindingly obvious and simple explanation that I've missed. No luck so far though, so I'll keep trying.

You're sure these earth wires are earth wires? Rather sounds like it but worth being sure.

Have you tried it with no bulbs in the fittings?

It isn't a 12V light fitting or something ridiculous like that, is it?

Replace the welded switch if you haven't already, but that sounds like a symptom rather than the cause.

 

[JonC2010]

Thanks LiamPope, all help gratefully received!

Yes, they are clearly earth wires as both are standard yellow/green banded.

Umm, from memory, with no bulbs nothing happened at all, it only blew fuses when bulbs were fitted.

Definitely not a 12v fitting, and it works fine when no earth connected, lights up a charm.

I actually took the switch apart and prised open the fused contact... it works fine, but I will replace when I have finished with this particular saga!

I am worried now that I have mis-remembered something and that I have typed something incorrectly on here... will have to run through it all again in the flat and make sure. Maybe this evening, but I am on my own and my body might not be discovered for a few days so perhaps I'll delay it!

 

[electronicsuk]

Umm, from memory, with no bulbs nothing happened at all, it only blew fuses when bulbs were fitted.

If that's true then it could be pretty relevant. It doesn't mean for sure that there isn't a fault with the fitting, but it could suggest some fault with one or more of the lampholders. I'd imagine this would be apparent pretty quickly with a visible inspection.

Out of interest, do these fittings take ES (screw in) lamps?

 

[JonC2010]

The light fitting looks a bit like this:

http://www.wilkinsonplus.com/Ceilin...cDPfxIrYzUvEu76RzzM6wutKTeo9AOCB tDs76aYYKg==

It does indeed take ES screw-in bulbs.

 

[maltaron]

I would be very wary about those lights, you have not mentioned where the 5 lives and neutrals from the 5 lamps are joined. It is not unknown for some imported fittings using spare green/yellow for neutral. I have also seen the live choc block (terminal block) fixed to a metal tab on the fitting!!, and a whisker of wire bridged to earth.

 

[JonC2010]

OK, some more information...

I tested one of the light fittings yesterday evening.

The two earth wires are defintiely earth wires, they connect to the two separate metal parts of the fitting.

The live and neutral wires do not connect to the earths, according to my multimeter. This is with bulbs in and without. There seems to be no damage to any lampholder, crimped wires, nothing.

In other words it looks like the fitting isn't at fault. I still have no idea why connecting the earth wires to the earths in the ceiling wiring causes the trip.

It seems it has to be earth/neutral crossover in the ceiling wiring, but why does connecting an earth cause it to trip when there is no fault in the light fitting?

Stumped.

 

[electronicsuk]

It seems it has to be earth/neutral crossover in the ceiling wiring, but why does connecting an earth cause it to trip when there is no fault in the light fitting?

I think you must be referring back to some misinformation earlier in this thread. There is no way a N/E swap or short could cause the problems you describe - the fault would occur regardless of the type of fitting, plastic or metal, earthed or otherwise.

 

[JonC2010]

Any idea what it could be then? If it is a fault in the light fittings then it's a peculiar one. Both fittings cause the problem, and neither show a short between the earths and live or neutral wires. Is it perhaps a problem with the method I am using to detect a short? I am just using the earth test switch on the multimeter and putting the leads on the two wires.

 

[electronicsuk]

Any idea what it could be then? If it is a fault in the light fittings then it's a peculiar one. Both fittings cause the problem, and neither show a short between the earths and live or neutral wires. Is it perhaps a problem with the method I am using to detect a short? I am just using the earth test switch on the multimeter and putting the leads on the two wires.

Earth test switch on the multimeter? You've lost me there. Do you mean continuity check? If so, this is useful up to a point, but as the meter only outputs a very low DC voltage, it isn't guaranteed to show up insulation faults that may become apparent when 230v AC is applied. The way to test these fittings properly is with an insulation resistance tester (often referred to as a Megger), but this is not a DIY piece of kit and would cost an order of magnitude more to buy than what the light fittings cost.

If you're 100% convinced that you're correctly transferring the wiring between the rose and the light fitting, the only thing that can really be at fault here is the fittings. I can't think of any other logical explanation, as unlikely as it would be to receive two failed units.

 

[ban-all-sheds]

Get a basic pendant lampholder and a short length of flex.

Connect the flex to the lampholder and the rose.

Let us know what happens with and without a lamp in the holder.

 

[LiamPope]

Get a basic pendant lampholder and a short length of flex.

Connect the flex to the lampholder and the rose.

Let us know what happens with and without a lamp in the holder.

Not sure what that would tell us we don't know already. Essentially the same as him reconnecting his existing fittings which we know work fine?

 

[ban-all-sheds]

Sorry.

Get a basic Class I pendant lampholder and a short length of 3-core flex.

Connect all 3 cores of the flex to the lampholder and the rose.

Let us know what happens with and without a lamp in the holder.