Neon indicator for bathroom fan switch


Postby Tortoise » Mon Jan 19, 2009 1:57 pm

I have installed an in-line extractor fan in the loft above my bathroom operated by a ceiling mounted pull switch. The switch has a neon indicator light which is wired to show when the switch is ON.

All works fine and when the switch is ON, the neon glows as expected and the fan operates. But I'm puzzled as to why the neon still glows very dimly when the switch is OFF.

Any ideas?
Tortoise
Posts: 5
Joined: Mon Jan 19, 2009 1:49 pm

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Postby ericmark » Tue Jan 20, 2009 1:04 pm

If one takes a neon and you connect just one end to a live cable and connect other end to large body which will act as an aerial and partly ground it the neon with light. These are sold and called neon screw drivers.
If the item the switch supplies, does not effectively short the outputs together then a neon can pick up allsorts of stray voltages.
I would be rare to connect a extractor fan to a neon isolator as in most cases either three wires need isolating and a special three pole isolator would be used or a double pole light switch would be used again with no neon.
Air thermosiphoning through the fan may be rotating it enough to generate the power required to light the neon?
This is why neon screwdrivers cause so much hassle when they also light when not expected. Like holding florescent tubes under power lines they will also light.
ericmark


Postby Tortoise » Tue Jan 20, 2009 1:52 pm

Thanks very much for the reply.

Not sure if you've not fully understood me or I'm just not fully understanding your reply though!

You refer to a neon isolator which I don't think is what I've got. All I've got is power to a fan, with the live feed connected to it via a ceiling pull switch. The neon indicator is connected between the switched live and a neutral return.

However, after reading your reply and seeing something else somewhere about false indications on neons (something to do with the capacitance affect of adjacent cables?), I get the impression that it's not that unusual for this sort of thing to happen.

I guess the main question therefore is whether I should be worried. From my understanding so far, I can't see any reason why I should be.

I'd be interested to know if you agree though!

Thanks again.
Tortoise
Posts: 5
Joined: Mon Jan 19, 2009 1:49 pm


Postby ericmark » Tue Jan 20, 2009 4:14 pm

I would agree nothing to worry about
ericmark


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