Discuss Induced voltage keeping my extractor fan stuck ON in the Electrical Forum area at ElectriciansForums.net

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Nathan Tolhurst

Morning All!

Firstly sorry if this is in the wrong section, it wouldn't let me post in the DIY bit where i thought this should have gone.

I've got a problem with my extractor fan staying on (new installation)

It's a 'manrose' inline extractor fan with a timer.

i've searched countless amounts of times around several forums but cant find a solution so i'm resorting to asking for help


I'm powering the fan from the lighting loom, live to live, neutral to neutral, switched live to switched live.
BUT when i test the circuit when the lights are OFF there is still a phantom/ghost/induced voltage of about 50v still showing and i'm assuming that, is what's keeping the fan in the ON position.

I'm using a digital voltmeter so i'm aware this can be too sensitive etc etc but something is still keeping the fan on.....


Any ideas?

I'm so lost and frustrated at this not working!!
 
Morning All!

Firstly sorry if this is in the wrong section, it wouldn't let me post in the DIY bit where i thought this should have gone.

I've got a problem with my extractor fan staying on (new installation)

It's a 'manrose' inline extractor fan with a timer.

i've searched countless amounts of times around several forums but cant find a solution so i'm resorting to asking for help


I'm powering the fan from the lighting loom, live to live, neutral to neutral, switched live to switched live.
BUT when i test the circuit when the lights are OFF there is still a phantom/ghost/induced voltage of about 50v still showing and i'm assuming that, is what's keeping the fan in the ON position.

I'm using a digital voltmeter so i'm aware this can be too sensitive etc etc but something is still keeping the fan on.....


Any ideas?

I'm so lost and frustrated at this not working!!

What colour did you use for the switched live? If you used black try using grey as switched live and black as neutral. I know this goes a little against convention but then the permanent live and switched live are not running dead against each other. Ideally you would measure the phantom voltage with an analogue voltage meter.
 
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What type of lights are on this circuit? If LED or CF, try changing one lamp to a filament type and see if the problem goes away. If so then, yes, it's probably phantom voltage on the switched line.

Also, try turning the timer to minimum as, occasionally, some types will not switch off if set to maximum time.
 
Morning All!

Firstly sorry if this is in the wrong section, it wouldn't let me post in the DIY bit where i thought this should have gone.

I've got a problem with my extractor fan staying on (new installation)

It's a 'manrose' inline extractor fan with a timer.

i've searched countless amounts of times around several forums but cant find a solution so i'm resorting to asking for help


I'm powering the fan from the lighting loom, live to live, neutral to neutral, switched live to switched live.
BUT when i test the circuit when the lights are OFF there is still a phantom/ghost/induced voltage of about 50v still showing and i'm assuming that, is what's keeping the fan in the ON position.

I'm using a digital voltmeter so i'm aware this can be too sensitive etc etc but something is still keeping the fan on.....


Any ideas?

I'm so lost and frustrated at this not working!!

Nathan, 'ghost' or 'phantom' voltage would not keep the fan running as it is not real voltage. The only reason you are measuring the 50V is because the permanent live is right next to the switched live in the 3 core cable and a 'digital' multimeter or indeed most digital testers will pick up on some of this voltage (others will explain it far better if you want more detail). So your ghost voltage will not be keeping the fan running.

The fan is running on because of one of the following reasons (probably):

1. It has been incorrectly connected up
2. The timer in the fan has become faulty.

Also, you say you have powered it straight from the light, usually there would be a triple pole isolation switch. You also state that this is a new build. Did you fit the fan or did the electrician, if an electrician then it would be sensible to get them back? Lastly, you mention that 'when i test the circuit when the lights are OFF there is still a phantom/ghost/induced voltage of about 50v'. If you are just switching the light off then this will not switch off the permanent supply to the fan so you should still be getting 240V at the permanent live in the fan.

ps.. of course the last point could be, 'are you waiting longer than 20mins for the fan to go off?'
:wink:
 
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make sure that the L and S/L are not reversed somewhere. if they are, that would keep the fan running permanently.
 
Nathan, 'ghost' or 'phantom' voltage would not keep the fan running as it is not real voltage. The only reason you are measuring the 50V is because the permanent live is right next to the switched live in the 3 core cable and a 'digital' multimeter or indeed most digital testers will pick up on some of this voltage (others will explain it far better if you want more detail). So your ghost voltage will not be keeping the fan running.

If the fan SL input is of sufficiently high impedance and has a sufficiently low trigger voltage then the 'phantom' voltage on the switched line may be enough to keep the fan running.

The 'phantom' voltage is real and measurable. It only has to trigger the fan timer, not actually power the fan motor (which is powered by the permanent line).
 
If there is an isolator, what happens if you turn off the fan isolator and turn off the lights, and then turn the fan isolator back on again with the lights staying switched off. Does the fan come on or does it need to be triggered by then switchin the lights on? I'm liking Lee's advice about swapping N and SL around. And some other good points also.
 
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Thanks for all the replies!

What colour did you use for the switched live? If you used black try using grey as switched live and black as neutral. I know this goes a little against convention but then the permanent live and switched live are not running dead against each other. Ideally you would measure the phantom voltage with an analogue voltage meter.

switched live is on its own cable - separate from the live and neutral (but its brown)

Ill try switching the neutral and switched wires next

What type of lights are on this circuit? If LED or CF, try changing one lamp to a filament type and see if the problem goes away. If so then, yes, it's probably phantom voltage on the switched line.

Also, try turning the timer to minimum as, occasionally, some types will not switch off if set to maximum time.

Just normal halogen 12v lights

Nathan, 'ghost' or 'phantom' voltage would not keep the fan running as it is not real voltage. The only reason you are measuring the 50V is because the permanent live is right next to the switched live in the 3 core cable and a 'digital' multimeter or indeed most digital testers will pick up on some of this voltage (others will explain it far better if you want more detail). So your ghost voltage will not be keeping the fan running.

The fan is running on because of one of the following reasons (probably):

1. It has been incorrectly connected up
2. The timer in the fan has become faulty.

Also, you say you have powered it straight from the light, usually there would be a triple pole isolation switch. You also state that this is a new build. Did you fit the fan or did the electrician, if an electrician then it would be sensible to get them back? Lastly, you mention that 'when i test the circuit when the lights are OFF there is still a phantom/ghost/induced voltage of about 50v'. If you are just switching the light off then this will not switch off the permanent supply to the fan so you should still be getting 240V at the permanent live in the fan.

ps.. of course the last point could be, 'are you waiting longer than 20mins for the fan to go off?'
:wink:

it definitely isnt wired incorrectly ive checked it multiple times :(

And the timer works - its set to 30 seconds (tested by connecting it and then taking it off an waiting lol...)

If the fan SL input is of sufficiently high impedance and has a sufficiently low trigger voltage then the 'phantom' voltage on the switched line may be enough to keep the fan running.

The 'phantom' voltage is real and measurable. It only has to trigger the fan timer, not actually power the fan motor (which is powered by the permanent line).

Thats exactly whats happening :( - any idea how to fix this :/

If there is an isolator, what happens if you turn off the fan isolator and turn off the lights, and then turn the fan isolator back on again with the lights staying switched off. Does the fan come on or does it need to be triggered by then switchin the lights on? I'm liking Lee's advice about swapping N and SL around. And some other good points also.

The fan stays off waiting to be triggered again by the lights
 
I had this problem with a monsoon fan. I ended up using the brown as perm live, black as neutral and grey as sw live. Seemed to do the trick!


Sent from my iPhone using Tapatalk
 
I had this problem with a monsoon fan. I ended up using the brown as perm live, black as neutral and grey as sw live. Seemed to do the trick!


Sent from my iPhone using Tapatalk

I had exactly the same problem and did the same to rectify it. Maybe it would be an idea to make the use of the colours in this way common practice since the effects of induced voltage can cause such problems?
 
switched live is on its own cable - separate from the live and neutral (but its brown)

Ill try switching the neutral and switched wires next


Have you used two different cables such as twin and earth, or have you used three core and earth. 3 core is brown, black, bare copper (earth), grey.
 
Just normal halogen 12v lights

The clue here is the 12V. If they have electronic transformers rather than wirewound ones, these cannot be counted upon to consume any current at all below a certain voltage (in your case it seems around 50V). Hence, a tiny amount of capacitive leakage from PL to SL, instead of being invisibly lost to neutral via the transformers, is triggering the fan.

Now, if I were designing a fan, I'd think about things like this and make sure the input wasn't so ridiculously sensitive. All it would take is a tiny load across the SL input to dissipate any minor leakage. Of course, if there is one and it's still triggering, it could indicate a switch full of water or something like that causing an excessive amount of leakage to SL with the switch off. But the fact that the problem keeps cropping up suggests a schoolboy error on the part of the fan manufacturer.

Oh, sorry, a solution? Hmm, change one transformer to wirewound (which will absorb the leakage without causing a standing voltage on the SL.) Or change the core layout to keep the SL and PL cores apart (although if they are in separate cables as mentioned it seems unlikely they will be close enough over a long enough distance to have an effect.) Put a small load across the SL input - a snubber cap or Danlers Capload?

'ghost' or 'phantom' voltage would not keep the fan running as it is not real voltage

Oh yes it is! 'Ghost voltage' is just electrician-speak for 'voltage sourced through such a high impedance that we would rather not be bothered to think about it'. By your definition, most of the voltages that make your phone/computer/TV/stuff work wouldn't be real either.
 
You say you have checked it out yet the problem persists - in which case maybe you need a fresh pair of competent eyes to review it.

I've never seen a correctly wired timer fan run all the time.
 
Agree with what Lucien said in post #12. There is absolutely no need for such a sensitive input on the fan - it's only got to detect mains or no mains - it's not a blooming instrumentation amplifier! Daz
 
Try a d/pole switch and switch L and N assuming the supply comes through the switch. Also you could use a changeover switch, switched live on common, neutral on normally closed and live on normally open (double check the wiring before making it live :)). If the permanent supply isd looped through the fittings and there's no neutral in your switch them none of this will apply.

**edit** I suppose you could install a snubber resistor or capacitor at the fan between switched live and neutral, similar to the one that might be used for LED or CFL lamps that flicker when they're switched off.
 
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