Earth connection blows fuse

[russellm72]

Hi

I wonder if anyone can offer me some advice.

I have this evening replaced my ceiling light fitting in my bedroom with a spotlight unit.

I had no problems removing the rose and fixing the unit to the ceiling through the joists of course, but the electrical connections are causing me a bit of concern.

I employed the simple method of removing the old live and neutral and simply fixing them to the new unit. The only problem is the earth connection. The previous plastic light fitting didn't have one but I assumed the new metal one should be earthed. Indeed, there is an earth wire clearly screwed into the hidden part of the fitting. The new fitting has three connections namely live, neutral and earth. Now connecting the live and neutral wires the light works fine on the switch. However if I also connect the earths together the fuse in my CSU blows.

The instructions, which are a bit ropey, suggest the light should be earthed into the exsisting terminal box.

I suspect its a bad idea to leave this earth wire out but does any one know why it blows the fuse when I attempt to connect one.

Many Thanks

Russell.

 

[triumphman]

I would recommend that you don't touch the light fitting with just the live and neutral connected because you will probably find it is LIVE.
Either there is a fault with the fitting or the connections you have made are shorting to the body of the fitting.
One other possibility is that the screws holding the light to the ceiling have pierced the lighting cable, although it is unlikely it is not unknown for the cable to be trapped between the joist and plasterboard

 

[russellm72]

Yeah I have touched the light fitting and it aint live.

I was careful with all my connections and no wires are visible so dont think they can be shorting on the casing.

Also i went up to the attic and checked I hadn't pierced any of the cable and it was fine.

 

[TexMex]

Yeah I have touched the light fitting and it aint live.

I think Triumphmans suggestion not to touch the light fitting was intended as a bit of saftey guidance, not as a diagnostic procedure.

It sounds like the fitting only becomes live once you turn on the light. This is causing the short to the correctly fitted earth, and your fuse is doing its job.

You seem to have eliminated the less likely of Triumphmans, suggestions (the pierced cable), but this leaves the other two. Either: The switched return is somhow shorting to the fitting body itself. Or: The fitting itself is faulty (and dangerous).

If your connections have been made neat and have no whiskers that can short to anything, then this just leaves the last option. If you can't test the fitting with a multimeter then return it, from whence it came, for a replacement.

Do not be tempted to remove the earth wire and continue using it.

 

[securespark]

From what you have said, there MUST be a short to earth, otherwise the fuse would not fail.

 

[phil_ballard]

As my old lecturer would have said, "The fuse didn't fail! The fuse worked...."

 

[chickoo]

I suspect it is most probably faulty fitting, i had a similar situation and i narrowed it down to testing the fitting itself atlast. I got it replaced and it worked fine.

Big lesson learnt and never took things for granted about fittings since then.

 

[russellm72]

Hi,

Thanks for all the help. I took it apart again and noticed a sneeky wee contact between a live wire and the metal back plate. Rectified, the earth wire fitted and it's working like a dream.

At least I know my fuse box is doing what it's intended to do.

Muchios Grazias for all your comments.

Rusty