2 live wire arriving at my lights

Cricri

All,
I've got another thing puzzling me in my electrics: all my lights seem to have 2 neutral wires.
I decided to try to measure voltage between live and each neutral with my Fluke, and albeit one reported 240V as expected, the other reported 170V!
Also, the electrician connected both neutral together, is that the right thing to do?
Thanks!

tower

I guess the neutral is looped to each fitting. normally you have a looped live (in and out to next fitting) same with the neutrals and a switch line (down to the switch and back to operate the light).

The voltage my be a back feed from another fitting.

If you have used an electrician why are you testing it?

Pincher

There is a main trunk cable, carrying LIVE, NEUTRAL and EARTH.

This goes from light to light in your ceiling, hence TWO LIVE wires and two NEUTRAL wires at the light. Obviously the light would be on permanently if wired like this, so the LIVE is not directly connected to the light, but goes through a third cable to the wall switch first.

I suspect you have a dimmer switch, versus a simple contact, hence 170V.

Cricri

Ah, so I should connect them both or I might disconnect the neutral of the next light. I'll make sure to do that.
tower: When I say "the electrician", I meant "whoever did this before I bought the house 3 weeks ago". And I'm fiddling with it because I change lights, and because a professional did it doesn't guarantee it was done well For instance, I just reconnected the hob extractor light: the cowboy who did it just twisted wires together and covered them with electric tape, so I stripped the wires clean, soldered them and insulated them with heat shrink.
Pincher: Ah, good idea, but I don't have a dimmer as far as I know (or it's hanging somewhere ion a cavity!).

tower

One of the common mistakes people make when changing a light fitting is putting all the reds(browns) together and all the blacks(blues) together. forgetting about the live to the switch and the returning switch-line. try and mark the cables with tape so you know what goes where.

Pincher

Heat shrink? You have an electronics background then?

Strictly speaking, you should use heat resistant sleeving, if the area is subject to a lot of heat. Heat shrink becomes brittle and carbonise under long term heat. The carbonised heat shrink can also conduct electricity, so it is a potential circuit breaker tripping mystery.

I had a plastic terminal block above a 100W light bulb, which worked for many years. The lighting circuit breaker started tripping, intermittently, and it took me ages to work out the terminal block had carbonised. Changed to a heat resistant one, and no more tripping.

penrhyn

This is how modern ceiling roses are wired.

Cricri

penrhyn: nice diagram, although I've never seen a light in my house which is connected to 2 "blue" wires (including the live from the switch). But very informative. The only thing I'd add is a potential earth connected to the light chassis.

Pincher: well I do play with electronic sometimes in my spare time, but I'm a mechanical engineer. You've got a point though, I think I should have used a screw terminal instead of heat shrink, but I didn't have any at hand :S

tower: well in my case, the neutrals and lives were already bundled together, so I'm really following your advice and putting the cables back like they were. I didn't originally, but I had to take the lamp down again to polyfilla a bit (I did a terrible job as I'm no plaster expert, but that's another story). I plan to connect the light again tonight, so will do as it was before (I'll probably have to use a different screw terminal though as the one built in the lap is too small for the 2 neutrals).

evans007

The drawing should have either a brown brown twin and earth cable coming from the switch, or in older wiring red red, although many houses have red black from switch to light with bad practice not oversleeving the black with red, i did a job yesterday where the cowboy used brown blue twin and marked the blue with black tape! As for your 170v have you made sure that all connections in light line are tight even in slightest looseness can give off faulse readings if all else fails do a 500v megger test but make sure all lamps are out!! good luck