Switch with neon indicator

In the past I've had touch dimmers that had a neon which worked without a neutral, back in the days of incandescent lamps they probably were able to pull enough current from neutral through the lamp, probably not these days with CFLs. Or just maybe they treated the earth as a "neutral" a bit naughty as it would tip an RCD a few mA more towards tripping.

Drill a small hole in the loft door?

The switch has live & switched live, so the neon would be on when lights off, wrong way round.

OP needs a neutral, assuming not going to connect neon to earth. Earth return isn't allowed, though with a [suitable] stack of resistors the risk would be pretty much zero.

Or maybe mount a neon into the ceiling, its wiring then being in the loft.

NT

Not really or reliably, Is there an earth present? Sounds like a bit of dodgy wiring to me.

Brian

If you are goint to do the latter, you could probably use an led and some little circuit to bleed of just enough th run the little led, but its a bodge.

Brian

As an aside this reminds me of the hotel owners that went into their attic to thaw frozen pipes with an electric heater only to find one already there and switched on...

From when the pipes froze 8 years before!

Mike

If you don't mind the lit neon indicating the loft lights are *NOT* on then you can wire the neon indicator in parallel with the switch.

Otherwise you need a local neutral from somewhere. Deliberately adding earth leakage current isn't a good idea.

Feed the live through a current transformer primary with a pair of inverse parallel LEDs on the secondary. Winding details are left to the student.

Cheers

Like this, perhaps...

He's used just one LED, which isn't great, LEDs shouldn't have reverse current through them, but the clip-on core idea is good.

Cheers

If the switch cable goes straight up from the switch to the loft it might not be that difficult to replace it with a 3 core and earth cable. You could see if the cable can move a little

and he can detect an electric fire, but not necessarily a lightbulb.

Fora fixed installation I see no reason why a very small mains transformer used backwards - i.e. with the low voltage winding in series with the switched load - would not work as well.

That's a great idea. It could be done without a transformer. Assuming one

I like that. Maybe use 4 diodes, one in inverse parallel with a string of three in series to further reduce dissipation. Or a single 1.8V Zener, if you can find one.

Cheers

Yes, it's been a while since those dimmers were removed, the neon was of course on when the lamp was off and vice-versa, so an aid to finding the switch, rather than an indicator that it hand been left on by accident

I did say "naughty"

Buy yourself a light switch illuminator. Requires no neutral. But may need an incandescent lamp.

They are on when the light is off however.

Lateral thinking! I like it!

Providing that "somewhere" is on the same circuit. Borrowed neutrals can cause problems.

Yes you are right. You might get away with only two diodes in the forward direction and one in reverse, and a lower value of resistor.

I've now had an even better idea. Put a 12V 5W festoon car bulb in series with the live circuit. Such a bulb normally takes about half an amp in the car, so 250mA would generate only 6V across it, leaving the rest of the mains voltage for the 60W bulb, and might glow nicely especially if behind a red filter.