weirdest fault i ever did see

[gordy71]

Today went to a fault find where the 2 way lighting is playing up. All the switching is ok but when the upstairs is off but downstairs is on, There is 50v backfeeding up the neutral to the upstairs fitting? The practical effects of this is that the bulb will flicker every so often. The customer said that by replacing the energy efficient bulb with an old style one it stopped it and the voltage disappeared? All the other lights on the circuit are showing this problem, but with voltages from 12-60v I suspect it is a loose or borrowed neutral from somewhere but tested continuity from circuit neutral to neutral bar but nothing buzzed up. The supply polarity is correct and no voltage coming in on the supply neutral. There was a cable with low IR but this has now been disconnected. Any ideas cos im stumped?

 

[matt.leung]

could be a doddgy switch...

 

[Doc Hudson]

Sounds like normal induced voltages between circuits, where it is insufficient to be noticeable on GLS lamps, but the electronics on many energy savers can detect it and cause the flicker. Often more noticeable with the cheaper low energy lamps. We have a few threads on this and similar topics in our archives.

Doc H.

 

[Andy™]

inductance most likely. filament type lamps will allow this small current to flow though un-noticed. CFL builds up enough to 'start', then suddenly runs out of power. which is where the flickering comes from

 

[m4tty]

I know someone who's got this exact same problem mate and I asked on here about it few months ago. 50v showing when fitting is off. Energy saver flickers but incandescent won't light up. I tried an analogue meter in case it was inductance from another cable but there was defo 50v there when off. Bottom of 2 way lighting and it had borrowed neutral between lighting circuits. Can't help but will be watching this thread with interest as I've got to go back and have a go at it soon. Good luck

 

[gordy71]

So what would be the cause of this inductance? And upto 60v? Surely this cannot be left like this? The problem was bought up on a pre board change test, a number of faults have been identified throughout the house so a day of fault finding and rectifying tommorow! If its a borrowed neutral which i dont think it is as i said no continuity between the circuit N and N bar it needs to be found before the c/u is changed.

 

[Andy™]

cables running parallel induces voltage in another

not really applicable to domestic, but in larger installs, you sometimes need to short live conductors to earth after isolation to remove induced voltage

and whilst it may be 60V, its current will be severely limited. if you used a low ohm voltmeter, you would probably not get (much of) a voltage reading anyway

 

[SPECIAL LOCATION]

So what would be the cause of this inductance? And upto 60v? Surely this cannot be left like this? The problem was bought up on a pre board change test, a number of faults have been identified throughout the house so a day of fault finding and rectifying tommorow! If its a borrowed neutral which i dont think it is as i said no continuity between the circuit N and N bar it needs to be found before the c/u is changed.

If you were getting a full 60v all the time on the cables ALL of your GLS lamps would be glowing dim ALL of the time.....

As Andy & Doc say, it is just induced off some other wires that are carrying full voltage!

:|

 

[says-les]

You could try connecting a Drummond test lamp between the neutral and earth. 50V power source will give only a glow of the lamp filament if the 50v is not being induced.

You could contact the energy saver lamp manufacturer for support. They will be sympathetic and may offer to visit the installation (hopefully).

Have you heard of third harmonic current?

Cheers

says-les

 

[SPECIAL LOCATION]

So what would be the cause of this inductance? And upto 60v? Surely this cannot be left like this?

Just to add Gordy71......

When you are on a site and think there is something that you cant suss out....

Keep one part of your head firmly grounded in the basics of electrical theory...

& voltages & currents and resistances....

AND

remember where you meter leads are connected to....

If one probe is floating free or onto a cable that is not connected to anything then the "Apparent voltage"

is NOT the same as a "REAL VOLTAGE" between two conductors that are connected back to a source of energy....

Some meters will show 20+ volts with only one probe connected...

20V with respect to 'air'!!!!

REMEMBER WHAT 50V looks like across a GLS lamp....

Heres a picture to help using a dimmer to provide the 50v...

well 49.something and a 60watt lamp....

Your described symptoms are classic induced voltages....

which, when present highlights one of the problems of energy saving lamps they don't tell you about!!!!!!

flicker... flicker.... flicker....

Like a ghost light...

which becomes REALLY visible when the nights get darker earlier!!!

 

[Sidewinder]

AVO 8!

 

[Evans Electric]

Ah the trusty Drummond , we keep it as the second tester TBH. And as said when this question arose before , this will appear more often as the GLS lamps are replaced by Energy savers.

I remember a couple of jobs with recessed fluorescent fittings in offices , never noticed till someone worked late in the dark, on some of the circuits the tubes were glowing or what we called Barbers poleing . Spirals along the tubes .

 

[Lannielectrical]

Sounds like a loose neutral I had the same problem on a job When I installed some led lights once the switch was turned off the LEDs stayed on tested it and it was reading 50v on neutral had to go around all the circuit and tighten up the connections found a loose neutral retested and it was fine

 

[skydog]

i know this might sound dumb, but theres no singles involved in this installation is there ?

 

[Steve3948]

Above post by Andy is correct, there has been a thread about this before and it's to do with the 2 way and parallel paths.

You will find its with the 2 way with live and switch live across strappers.

It only effects some low energy so trying a different brand will sort it. Lamp manufactures are aware of it.

The transient voltage charges up a capacitor in the lamp until it discharges by illuminating the lamp for a second.