Disappearing voltage

[iwire4]

Can anyone help?
A customer has a light fitting in a bedroom (5 bulbs) which is switched two ways with a dimmer switch by the door and a switch by the bed.
He states that at some point he switched it on and nothing happened. He assures me they were working at some point before!!!!! He replaced all the bulbs to no avail, hence calling me in. It did seem strange that all the bulbs went in one go.
i opened up the ceiling rose and all wiring seemed sound. I did a voltage test to try and determine when the dimmer switch was closed. I couldn't get any readings at the switching wire at all. There was 240volts at the live loop, which was reassuring.
I disconnected the live to the light and did the test again. This time I got 240volts when the switch was closed and nothing when open ( I assume from that the switching is working properly). It must be the light fitting then. I replaced it with a pendant. Job done I thought. Switched it on and again nothing. On testing again I had the same result as before. The switching wire was dead whether the switch was on or off.
I then removed the bulb. Normal readings resumed - 240volts at switching wire when closed and nothing when open.
i asked the customer if anyone had interfered with the switch wiring or anything else before the light failed. He assures me they were working and then stopped working. It was a while ago though.
Has anyone come across this before or explain what is happening. Is is a neutral issue?
Any help would be very much appreciated.
Ian

 

[Hellmooth]

Dodgy dimmer switch?

 

[iwire4]

Thanks for that. Trial and error. I can try replacing the dimmer switch. Would that give those types of results?

 

[Leesparkykent]

Is the fitting at the end of line or are other lights not working?

 

[Hellmooth]

Could always try a normal switch and see if it works ok, if it does then it would point towards a dodgy dimmer switch, if not then I'd be testing further!

 

[Spoon]

Try replacing the dimmer switch with a normal switch. If the lights work then you know the dimmer is faulty.

 

[iwire4]

It's not the end of the line. Other lights are working.

 

[iwire4]

Ok, looks like the way to go. Cheers..

 

[davesparks]

240V which is there with no load, but disappears when load is connected is better known as a ghost voltage.
Why on earth did you think that replacing the light fitting would fix a problem with the switched live not becoming live?
For a ghost voltage to appear on the switched live then it is most likely that this is no longer connected to where it should be. I'd go with a wire broken off at one of the switches or a faulty dimmer.

 

[Taylortwocities]

What are you testing the voltages with? please say it is a two probe voltage tester or a multimeter.

 

[iwire4]

You live and learn. The 240volts was at the switching wire and done with a proper two prong voltage tester Not an electrical screwdriver which has duped me in the past.
Thanks for the replies. I will go to the switch and go from there. Ghost voltage. One for the memory bank.
Cheers.

 

[Leesparkykent]

Did you test for voltage with line and neutral and line and earth?

 

[iwire4]

I only tested between line and earth

 

[Leesparkykent]

I only tested between line and earth

Well go back and test between line and neutral :6: Lol

 

[iwire4]

Doh!!!!!!!!

 

[davesparks]

You live and learn. The 240volts was at the switching wire and done with a proper two prong voltage tester Not an electrical screwdriver which has duped me in the past.
Thanks for the replies. I will go to the switch and go from there. Ghost voltage. One for the memory bank.
Cheers.

You should be able to discern a ghost voltage from a real voltage with an AVI, assuming you fully understand how it indicates these things.

 

[Guest77]

Can anyone help?
A customer has a light fitting in a bedroom (5 bulbs) which is switched two ways with a dimmer switch by the door and a switch by the bed.
He states that at some point he switched it on and nothing happened. He assures me they were working at some point before!!!!! He replaced all the bulbs to no avail, hence calling me in. It did seem strange that all the bulbs went in one go.
i opened up the ceiling rose and all wiring seemed sound. I did a voltage test to try and determine when the dimmer switch was closed. I couldn't get any readings at the switching wire at all. There was 240volts at the live loop, which was reassuring.
I disconnected the live to the light and did the test again. This time I got 240volts when the switch was closed and nothing when open ( I assume from that the switching is working properly). It must be the light fitting then. I replaced it with a pendant. Job done I thought. Switched it on and again nothing. On testing again I had the same result as before. The switching wire was dead whether the switch was on or off.
I then removed the bulb. Normal readings resumed - 240volts at switching wire when closed and nothing when open.
i asked the customer if anyone had interfered with the switch wiring or anything else before the light failed. He assures me they were working and then stopped working. It was a while ago though.
Has anyone come across this before or explain what is happening. Is is a neutral issue?
Any help would be very much appreciated.
Ian

Gasp .

 

[SJD]

Always suspect a dimmer which in these circumstances - 230V with no load, but no voltage as soon as any appreciable load is connected. It is (usually) a trivial & quick job to remove the dimmer switch & link it out (e.g. stuff the cables into a Wago) and see what happens. Obviously isolating the circuit first. Otherwise it is possible to waste a lot of time imagining perfectly good light fittings are at fault.

 

[Darkwood]

Hi iwire4 ...

Can you please either fill your profile info in or provide us with your experience level and competence.

The reason I ask is your posting in the main forum which with the way your question is asked it is to be assumed you are a qualified practising Electrician.

Can you confirm this as reading through your various replies, you have implied you have not carrying out the correct test procedures, this kind of fault finding should be a simple task if correct procedures are followed.

If you can oblige and express your level and experience we can see if your thread need moving to the appropriate area Thankyou.

 

[telectrix]

Gasp .

THOUGHT YOU'D USED YOUR LAST GASP....... A BIT LIKE THE LABOUR PARTY. :devil2: