Weird Voltage reading

[Eric1066]

Hi,
I'm having an issue with a light. Its a fitting that also has another 3 fittings on the dimmer switch.

Basically, one of them isn't working. I changed the bulb and nothing. I tested the bulb, it is fine.

So, I decide to take the fitting off and see if power is actually getting to it, and there is.

So I decide the problem must be where the bulb screws in. No problem, I'll check that and fix it, no problem.

However, when I tested to see if power was getting to the fitting as I said earlier, I noticed something... it didn't read a steady voltage. It was all over the place to be honest. Up and down... sometimes even showing 0v for a mere moment. I also noticed when it sort of does stabilise on a voltage, even if its only for a second or two, it was 215v rather than the average or appx 230v.

Is that because its on a dimmer switch? Or is something else going on?

All help is always greatly appreciated.

 

[roys]

Swop the dimmer switch for a normal switch then do your testing, or even disconnect the dimmer and connect the live and switched live together into a Wago or terminal block, this will allow you to check for voltage at the fitting. It would be remiss of me not to say isolate before changing your switch and be very careful if you are going to be doing live testing.

 

[binky]

Sounds like a loose connection to me

 

[Eric1066]

Swop the dimmer switch for a normal switch then do your testing, or even disconnect the dimmer and connect the live and switched live together into a Wago or terminal block, this will allow you to check for voltage at the fitting. It would be remiss of me not to say isolate before changing your switch and be very careful if you are going to be doing live testing.

Yeah, I'm gonna take the dimmer off and wago the wires together, and see what difference it makes.

Thanks!

 

[Murdoch]

Please let us know what happens

 

[Geoff1946]

If three lamps are working and one not surely the fault has to be on the feed to the duff one? Probably a broken connection where-ever that one connects to the rest. It can't really be the dimmer.

 

[Murdoch]

Which type of light bulb is it? GU10, SES, ES, ?

 

[Eric1066]

Sounds like a loose connection

If three lamps are working and one not surely the fault has to be on the feed to the duff one? Probably a broken connection where-ever that one connects to the rest. It can't really be the dimmer.

It's the second light of four...

They are connected in a standard fashion, from 1 to 2 to 3 to 4. If there was a loose connection at 2, then 3 and 4 wouldn't work. But also, wouldn't the weird V reading affect the other 2 working lights in some way? It doesn't, they seem to be working fine.

#2 isn't working because the fitting itself isn't working. I've taken it apart and found the problem, fixing that. But once that's done, I'm guessing it will also work fine.

I'm just freaked by the strange V readings.

If it's working should I just forget about it? Or is there something more sinister?

I'm going to swap out the dimmer just to eliminate it as an issue. If the reading is still going up and down but everything works, could be my meter???

The bulbs are standard screw bulbs. E27. They are 'dimmable' LED bulbs.

 

[Eric1066]

Which type of light bulb is it? GU10, SES, ES, ?

E27 'dimmable' LED

 

[ProDave]

E27 fittings can sometimes be very poor, and some E27 lamps are odd sizes. The result can be the contact that makes contact to the screw thread, does not and needs a bit of bending to adjust it.

 

[binky]

E27 fittings can sometimes be very poor, and some E27 lamps are odd sizes. The result can be the contact that makes contact to the screw thread, does not and needs a bit of bending to adjust it.

Second that, it's usually the centre prong gets flattened.

 

[Murdoch]

Third that. Specially common on older fittings

 

[Eric1066]

Third that. Specially common on older fittings

Thanks for the responses.

It's none of those though. Where the neutral screws in to the fitting, that has broken off. So there was no circuit. I've soldered it in place. I knew whatever the reason the fitting wasn't working I'd fix that... still don't know why the voltage goes up and down. That's the question.

 

[Marvo]

Glad you found your fault. Usually soldering isn't used in an electrical installations, it doesn't age well and solder joints often fail over time. Mechanical connections and terminations are the preferred method for connecting wires to accessories..

Did you try removing the dimmer and connecting power direct to the lights? Were you also getting weird voltage readings with the dimmer out of the circuit? Also what tester are you using?

Testers, especially cheap ones, have a very high internal input impedance which means they're prone to displaying a wandering inaccurate reading when there's a missing neutral. More expensive testers have a lower impedance (Lo-Z range) on their input that stops them displaying what's known as 'ghost voltages'

Cheap testers are also only designed to measure voltage accurately only when the supply is a nice smooth sine wave shape with a frequency of around 50 cycles per second. The output of a dimmer is a distorted and complex waveform the can be very high frequency and have very sharp corners that doesn't resemble a nice smooth sine wave. The theory behind this gets complicated fast but in laymans terms testers that are cheap can't interpret the high frequencies and choppy waveform shape a dimmer makes and can sometimes display either complete jibberish or a reading that wanders seemingly random all over the place or even a steady reading that's simply incorrect.

Understanding how your tester works and its limitations is critically important. If you don't it you'll end up running yourself ragged chasing problems that don't exist and there's a likelihood you can also get a shock when it gives you a false zero reading on a circuit with a dimmer or speed controller and you assume it's dead and touch something.