Switch with neon indicator

[Kit Jackson]

I've got some lights in the loft with the switch in the passageway below. It's not unknown for the loft lights to be left on all night or even all weekend if I don't notice the switch.

I'd like to replace the switch with one that has a neon indicator. The problem is that the lights have been wired with a loop-in circuit so that the power runs from ceiling rose to ceiling rose and only the switched live is taken down to the light switch. The neon switch I've got seems to require the neutral to be present as the neon is soldered between the live and neutral on the load side of the switch.

Is there any way to wire this so the a neon switch would work without the need to drop another cable from the rose to the switch? Or can you get neon switches that will work without the need for the neutral to be present?

Kit Jackson

[Andy Burns]

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.

[Adrian Caspersz]

Drill a small hole in the loft door?

[tabbypurr]

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

[Brian Gaff]

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

Brian

[Brian Gaff]

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

[Muddymike]

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

[Martin Brown]

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.

[Syd Rumpo]

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

[Syd Rumpo]

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

[Michael Chare]

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

[The Natural Philosopher]

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.

[Dave W]

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

60W incandescent bulb in the loft, it takes 250mA. Six 1 amp diodes wired as three back-to-back pairs all in series with the switched live, would drop about 1.5V and dissipate 0.6W overall per bulb. Wire a LED in series with a 470 ohm resistor across the diode array, to give about 2mA into the LED. If there are other bulbs in the loft, use LED types to keep the overall current down. Of course house all the components in an insulated box.

[Syd Rumpo]

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

[Andy Burns]

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"

[harry]

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

They are on when the light is off however.

[newshound]

Lateral thinking! I like it!

[harry]

[Mike Clarke]

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

[Dave W]

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.