Ceiling rose still live after switching off circuit

[JakeR]

Hi all,

I have been changing a few light fittings recently, switching off the lighting circuit and checking each fitting is not live with a non-contact voltage tester and electrician's screw driver.

Two fittings down, and all going well.

Then on the third fitting after switching off the lighting circuit (and checking the light no longer switches on), my non-contact voltage tester still detects a voltage if I poke it in the right place...

Is this normal?! Are there any explanations that don't involve there being a problem somewhere?

A quick google might suggest a borrowed neutral? But then why would not all fittings show this?

Any insight would be great!

Safe to say I am not proceeding until I get things figured out

 

[cross thread]

Test with a volt meter ,that type of stick is a guide

 

[JohnD]

I see the original wiring is from the 1970s, hence the green slime (q.v.) and needs replacing at some convenient time. If you are lucky it might just be the cable used for lighting, as other sizes will be from different batches.

Do you have separate upstairs and downstairs lighting circuits, and is that a landing light?

 

[JakeR]

I see the original wiring is from the 1970s, hence the green slime (q.v.) and needs replacing at some convenient time

Do you have separate upstairs and downstairs lighting circuits, and is that a landing light?

This light is in the dining room. There is one main lighting circuit for upstairs and downstairs, and a separate circuit for the under-stairs light (which is next to the dining room, and contains the consumer unit, or whatever it's called these days).

 

[JohnD]

Turn off both lighting circuits and see if that makes a difference. Test with a multimeter.

Add G&Y sleeving to the earth wires at each point you open, and clean off the green slime, especially in switches which need replacing if contaminated.

 

[JakeR]

Showing 5 or 6 volts with either just the main lighting circuit off, or the main and under-stairs lighting circuit off.

I added earth sleeve and cleaned up the green goop when replacing the other fittings

 

[sparkwright]

I see the original wiring is from the 1970s, hence the green slime (q.v.) and needs replacing at some convenient time.

I don't think that is green slime.

It looks more like that gritty bonding agent folk use nowadays before re-plastering ceilings.

 

[JakeR]

I don't think that is green slime.

It looks more like that gritty bonding agent folk use nowadays before re-plastering ceilings.

I think it's both. Definitely green slime from the insulation of the wires, but the gritty bonding agent might also make sense, as the artex was evidently skimmed at some point.

 

[sparkwright]

If it IS a borrowed or shared neutral, I suppose if you had wired up a light fitting in another room incorrectly, this problem could be created somehow.

Green slime will be very sticky.

 

[JakeR]

If it IS a borrowed or shared neutral, I suppose if you had wired up a light fitting in another room incorrectly, this problem could be created somehow.

Green slime will be very sticky.

Would a borrowed neutral give me just a few volts, though?

When I replaced two other fittings, I just carefully replicated the original wiring, which looked reasonable to me.

I also don't understand why there are three live and only two neutral wires at this suspect fitting.

 

[JohnD]

.

 

[sparkwright]

Would a borrowed neutral give me just a few volts, though?

When I replaced two other fittings, I just carefully replicated the original wiring, which looked reasonable to me.

I also don't understand why there are three live and only two neutral wires at this suspect fitting.

Could be many reasons why it is wired like that. They used to use sheathed cable with just one wire in it, particularly up north, for lighting.
Possibly this room has two way switching? Who knows. But I see no cause for concern in the way that particular fitting has been wired.

Voltsticks do give false and misleading readings.

You can sometimes get some very low voltage reading when a circuit is isolated by just turning off a fuse or mcb. However, if there is any doubt all is not well, you should completely isolate the whole house to be sure all is ok. Always work safely and if in doubt always send for an electrician.

As to whether you have a borrowed or shared neutral, further investigation is needed.

As for the 'slime', if it is dry and crumbly, it's likely to be bonding agent. If it's a sticky mess, it's slime.

 

[yorkspark]

The pictures show the pendants connected reverse polarity, the brown should go to the single red not the 2x black conductors

 

[JakeR]

The pictures show the pendants connected reverse polarity, the brown should go to the single red not the 2x black conductors

Thanks. I noticed that, too, and switched it round. Obviously wouldn't account for strange behavior, though.