Live Neutral in Lighting Circuit

[nimp]

Hi all, just a quick background first...When we moved into our house 8 years ago, the extractor fan above our hob worked fine, and then just stopped working one day. We have spotlights in our kitchen ceiling, each running off its own 12v transformer and we began to have problems with one light in particular, the bulbs didn't seem to last very long - I pulled the bulb and wires down from the ceiling and noticed that the plastic chockblock had completely melted and fallen apart, and the surrounding insulating tape was all scorched. I checked the wiring with a live indicator "pen" and all seemed to be ok. Recently we had a problem with some of the other bulbs, so I switched out all the transformers for new ones, and thats when I noticed that one of the neutral wires going back into the light that originally had problems was live.

While testing it i knocked the wire with the pen and the lights in the utility room next to the kitchen flickered and there was a spark between the neutral cables and the now live neutral in the same block. I turned off the lights in the utility and the neutral was no longer live. However if the lights in the kitchen are off, and the utility ones are on, the neutral becomes live again.

This must've been what melted the chockblock previously but the other lights were turned off at the time, so the neutral wire wasn't live. I plan to get a qualified electrician in to take a look, but I have a few questions I just wanted to run past people:

1) I assume that the lighting circuit should not be wired this way has anyone seen this before? Is this type of problem straightforward for a professional to rectify (hopefully without pulling my ceiling down to get to the wires!).

2) I suspect my extractor fan may be connected to the lighting circuit - is this the done thing? from what I've read I believe it only pulls around 3 amps.
I'm wondering if a break in the cable for the extractor may be responsible for both the fan not working and the live neutral as the cable to the fan is not showing as live. I know the extractor fan works as I cut the cable and put a plug on the end and it worked fine.

Any advice/guidance would be warmly received
Many thanks
Nimp

 

[paulc2]

Where was the other end of the "live indicator pen" connected?

Its not a switched live that you tested is it? When you wire a switch it, one does it typically using the same colour wire T&E as eg the radial circuit; eg red/black. The red would carry a permanent live to the switch and the black would be the switched live (ie not neutral at all - there is no need to have the neutral at the switch). One ought to put a red mark, or red tape, on the black wire to indicate its a switched live and could be live, but pragmatically there's a lot of wiring out there without it.

Or brown/blue these days, instead of red/black.

 

[swampy2]

The neutral from utility was flickering because of currents return path was broken, you separated the neutrals whilst they were live/power on.

 

[nimp]

Where was the other end of the "live indicator pen" connected?

Its not a switched live that you tested is it? When you wire a switch it, one does it typically using the same colour wire T&E as eg the radial circuit; eg red/black. The red would carry a permanent live to the switch and the black would be the switched live (ie not neutral at all - there is no need to have the neutral at the switch). One ought to put a red mark, or red tape, on the black wire to indicate its a switched live and could be live, but pragmatically there's a lot of wiring out there without it.

Or brown/blue these days, instead of red/black.

Hi Paulc2, thanks for the quick reply - sorry my wording may have been misleading, what I mean is that I have one of those little plastic pens/screwdriver tools that lights up when it detects a current running through a wire - it wasn't connected to anything, I was holding it.

I admit a switched live was my first thought (as it was only live when the lights in the other room were on) but I couldn't understand why it would've been wired into a block with neutral cables, there wasn't a red sleeve around the wire - should it connect to those? without being connected the lights in the utility don't turn on - i'm assuming as the circuit isn't complete

 

[nimp]

The neutral from utility was flickering because of currents return path was broken, you separated the neutrals whilst they were live/power on.

Thanks Swampy2, So it sounds like the wiring is correct and working as expected? do you know what might've caused the chockblock to melt?

 

[swampy2]

The neutral from utility was flickering because of currents return path was broken, you separated the neutrals whilst they were live/power on.

Thanks Swampy2, So it sounds like the wiring is correct and working as expected? do you know what might've caused the chockblock to melt?

Heat from lamps, is there an air gap around fittings?.

 

[paulc2]

A poor connection within the chocblock will cause high resistance, resulting in its heating up/overheating. Or, too small a chocblock for the current (but unlikely in this case, lighting).

 

[nimp]

The neutral from utility was flickering because of currents return path was broken, you separated the neutrals whilst they were live/power on.

Thanks Swampy2, So it sounds like the wiring is correct and working as expected? do you know what might've caused the chockblock to melt?

Heat from lamps, is there an air gap around fittings?.

There between the upstairs floorboards, and the ceiling in the kitchen - so theres a bit of room, but not a lot, when replacing the transformers I did change the bulbs to ones that send the heat downwards - the opposite of Dichroic(sp?).

 

[Taylortwocities]

what I mean is that I have one of those little plastic pens/screwdriver tools that lights up when it detects a current running through a wire

No it doesnt. It is meant to indicate if there is VOLTAGE present. Nothing to do with current.

But you'll not be able to find anything with those devices, except a headache.
They lie, or dont say anything. I have one and it bleeps if its near a mobile phone.

Use a proper two probe voltage indicator, or a multimeter. Then you'll stand a chance.

 

[nimp]

what I mean is that I have one of those little plastic pens/screwdriver tools that lights up when it detects a current running through a wire

No it doesnt. It is meant to indicate if there is VOLTAGE present. Nothing to do with current.

But you'll not be able to find anything with those devices, except a headache.
They lie, or dont say anything. I have one and it bleeps if its near a mobile phone.

Use a proper two probe voltage indicator, or a multimeter. Then you'll stand a chance.

Thanks - As a diy'er it does what I need just fine, I've never had a problem with it at all - If I'm getting to the level where I need to spend any long amounts of time troubleshooting then I'll call a qualified person in

**edited - I've just re-read this and realised it may come across differently to how I intended, I apologies if this has offended you Taylortwocities - that wasn't my intention.

 

[nimp]

A poor connection within the chocblock will cause high resistance, resulting in its heating up/overheating. Or, too small a chocblock for the current (but unlikely in this case, lighting).

So do you think it would be safe (especially since I've now changed the bulbs to those that put the heat outwards) to reconnect the wire and take a look at the block in a couple of days and see if the problem remains? I would monitor it closely.

 

[securespark]

Make sure to strip back the copper wire to clean bright wire before reterminating in a new terminal.

 

[Taylortwocities]

Thanks - As a diy'er it does what I need just fine, I've never had a problem with it at all -

The big issue is that it does not tell you anything about the condition of the Neutral conductor.
A large number of the faults in an electrical circuit are due to problems with the neutral.
So while it can be a quick check - that there's voltage present/the switch works/the fuse hasn't blown - you need a multimeter or other 2-probe tester to find a fault in the neutral (return) leg.

 

[ban-all-sheds]

As a diy'er it does what I need just fine

But you'll not be able to find anything with those devices, except a headache.
They lie, or dont say anything. I have one and it bleeps if its near a mobile phone.

Use a proper two probe voltage indicator, or a multimeter. Then you'll stand a chance.

A multimeter, at least, is an essential tool to have if you want to work on your electrics. It is just as important to have that correct tool as it is to have screwdrivers to use on screws instead of the point of a vegetable knife, wirecutters to use instead of nail scissors, wirestrippers to use instead of teeth, and so on.

Neon screwdrivers are questionable from a safety POV as they use your body as a current path, and they and voltsticks are unreliable - to safely check for voltage you must use a 2-pole tester, such as a proper voltage indicator or a multimeter.


This looks ideal for a household starter set - multimeter, voltage indicator and dedicated continuity tester, all in a handy case: http://www.amprobe.eu/de_DE/showproduct/115/Junior-Set/

PDF brochure: http://www.amprobe.eu/de_DE/downloadfile/115/beschreibung_1/

All in German, unfortunately, as is the blurb on each product:

Multimeter: http://www.amprobe.eu/de_DE/showproductdata/487/Hexagon_55/

Voltage indicator: http://www.amprobe.eu/de_DE/showproduct/1672/2100-Alpha/

Continuity tester: http://www.amprobe.eu/de_DE/showproduct/481/TESTFIX/

but it should be available in the UK - the company is now owned by Fluke, contact them (http://www.fluke.co.uk) for info on where to buy.

If not, there are sellers in other parts of Europe: https://www.google.co.uk/search?q=amprobe+("junior-set"+OR+1333)

Right now the English specs are still lurking on the Internet Time Machine from when Beha was an independent company:

http://web.archive.org/web/20060920022629/http://www.beha.com/files_uk/multimeter/93549.pdf


Also see another discussion here: //www.diynot.com/forums/viewtopic.php?t=26282 It's a few years old, so specific model number advice may be obsolete (and prices will be higher), but the generic advice is still sound.