Fluctuating voltage on a lighting circuit - advice please!

[The General]

Apologies - gotta go - wife wants to watch 'catch up' telly on the computer, so I won't be able to answer any more questions! Will check again tomorrow - but thanks to all for your advice and guidance so far.
cheers

 

[Lucien Nunes]

Of course none of the above rules out bad connections and possible arcing across faulty accessories causing random effects, but most of the findings can at least be explained in terms of cable layout, induced voltages and the way CFL innards work.

 

[Marvo]

Sounds like two different problems and possibly two different solutions to them. I'm not entirely sold on the fluctuating voltage when the light is on, usually even a small voltage fluctuation (5-10%) will result in the lamp getting noticeably dimmer and brighter although with CFL maybe not so much. I'd be interested to know how large the fluctuations were when the light was on.

 

[Tidy Max]

I have just had to draw out Luciens explanation. Interesting stuff. I didn't know the cap would charge off the meter.

 

[MarkyRR]

Something that may help you.....have a look at the other roses on the circuit. I was called to a similar issue last week. With experiences in the past, I went for a physical look first of all.....unscrewed a couple of ceiling roses to have a quick look for anything obvious. 2nd one I remove, I discovered burned out N terminal, sheathing burn away on one N loop leg. Stripped everything back to good cable, replaced rose with new item & all perfect. No more issues, everything testing as it should.

Even though I had asked customer if shed had any work done recently (answered 'no'), turns out TV aerial guy had wired a socket outlet for his booster box into the pendant!

By the way, isn't "strapper" a term we all learned way back in college??

 

[MarkyRR]

How on earth do you edit posts here?? Really want re-word some of what I've just typed!

 

[The General]

Thanks for suggestions MarkyRR - will take a look at rest of lights!

 

[Octopus]

How on earth do you edit posts here?? Really want re-word some of what I've just typed!

You "look" at your post and in the brown bar below you should see the word "edit" - select this and hey presto you should be able to edit your post!

 

[MarkyRR]

Thanks....I've tried that, but each time I edit, I can't seem to click 'accept' (or similar) to finish the edit. I know, numpty, but hey ho

Ok, now edited this to say I've edited my other post! Seems it works fine on my mobile but not my desktop! Just my luck.

 

[baldsparkies]

Evening all.

I got called out to investigate a problem with a two-way switch on a landing light and I was expecting to find a DIY bodge with incorrectly wired 3-core. However, it was more interesting than that!

Customer reported that when the light was off, after 5-10 minutes it would briefly come on/flicker and then go off again and then repeat - but it also depended upon which of the two 2-way switches was off/on.

Assuming (I know, I know!) that there aren't any junction boxes with wires being swapped over inadvertently then the wiring is correct, so I wanted to check that the switches were operating correctly and tested voltage to earth from the L1 and then the L2 terminals, before flicking switch and checking again. Interestingly, when I checked voltage betweenL1 and L2 the reading kept fluctuating between around 180v and 220v and I don't mean that I checked it several times and got different readings, but as I was watching the figure went up,down,up,down in a regular pattern. This was repeated when I checked the L & N terminals on the ceiling rose with the light on, and it read a fairly constant 40V when the light was off.

I'm guessing that as the lamp in the light was a CFL this voltage is enough to have caused the flicker every 5-10 minutes, but I'm struggling to understand what is causing the fluctations?! With every other circuit switched off and just the lighting circuit on the voltage was still present.

Also on that circuit were smoke alarms, which I took out (no change) and was reliably informed by customer that there were no aerial boosters or similar items in the loft. Solar panels on roof, but I'd also isolated these when testing.

Any suggestions for what else I could be looking for, and (if anything) what to do about it!?

Thanks for your help/advice.

The PL & SL were in parallel at L1 & L2 along with the blue & red cores of 3-core. The yellow core ran to the COM terminals at both switches, with blue & red at L1 & L2.

What's all this about ??
Look don't over complicate all this !! the set up from your description is the norm.
Disconnect the strapper (electricians term for the 3 core used to provide 2 way switching)
Convert to standard 1 way switching PL & SL.
See if the problems cured,pointing to strapper or faulty unused 2 way switch which are now out of circuit as the culprits.
If not check connections, continuity, and run some IR tests.
Its a process of elimination and the above is a quick way to determine where the problem may be.
I reckon IR fault switch fault or bad connection will ultimately be the problem.
Look for the simple stuff 1st

 

[Lucien Nunes]

Those answers by the OP were in response to my specific question about the 2-way wiring arrangement. They helped me understand a possible cause for the lamp flashing periodically when off with both switches one way, but not with both switches the other way. The choice of cores in the cable, and which of the two standard 2-way hookups was used, both have a direct bearing on whether capacitance was a valid explanation, which it was. You're also right that there might be one or more simple problems at work here and IR readings would be very useful.

 

[SirKit Breaker]

I haven't read the full thread on this.

When did the problem start, is it recently or has it always been there?

To be honest i don't like to preach, but i have always found that fault finding is far easier if you start at the beginning and work through it methodically. So i stick to the norm.

Continuity, Ins Res. These will highlight the majority of wiring faults. I always disconnect the faulty circuit completely from the installation so there can be no confusion on the circuit being tested.

I am not implying that any of the advice in other posts is not relevant, but jumping in and trying to second guess will take longer, and usually end up with you going around in circles.

Cheers.............Howard