Single-gang indicator that lights are on inside a room?

I have one of those, enables me to find the light switch in the dark.

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Reply to
djc
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With just one such neon indicator lamp, I doubt the 1 or 2 mA 'earth leakage' would be a problem (OTOH, 20 or so, _might_ start to cause trouble).

Reply to
Johny B Good

Yes, MK made them (1960s?) in two designs: one was like Dave mentions, a neon over the top of the switch, the other IIRC some sort of blue light surrounding the switch.

Reply to
Tony Bryer

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Appears to be available at £4.98 at B&Q - EAN: 5017490327406

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Crabtree also do one

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Owain

Reply to
spuorgelgoog

From here

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a CMA401 with a MD280/1/2 depending on what colour you would like the light.

Reply to
ARW

AIR the typical mains neon is rated at about 1/10 of a watt, so it would be more like 0.4 mA.

Reply to
Windmill

Thanks. I see that's the same brand you recommended in general recently.

Reply to
Adam Funk

ISTR 1-2Mohm series on those, so 100uA??

Reply to
The Natural Philosopher

AFAIR, the neon screwdrivers use a 220K safety / current limiting resistor in the handle[1]. I'm not entirely sure but I suspect the same 220k value is used by neon indicator lamps as well which, with a

60v running voltage on the neon lamp itself, suggests a current draw approximating 0.8mA rms. I can imagine the use of a 100K resistor to achieve a higher brightness in such mains indicator lamps, suggesting a current draw around the 1.8mA mark.

If the neon lamp rating of 100mW is for the whole luminary (neon plus ballast resistor) then even a 220K resistor is going to exceed this (177mW) so I expect that this is for the bare neon itself (60v by

1.67mA). I think my 'guestimate' of 1 or 2 mA earth leakage is close enough to determine the level of risk of unwanted RCD trips. [1] Neon lamps typically strike at about 90v and 'burn' at 60v. The finger contact on the end of a mains testing neon screwdriver provides ample leakage/capacitive coupling to earth to achieve both requirements with ease.

The neon lamp in the screwdriver handle is small enough to remain struck over a long enough portion of each half cycle of mains to still give sufficient indication with currents as low as a few tens of micro-amps. The 220K ballast resistor is large enough in value to let it do double duty as a safety resistor as well.

Reply to
Johny B Good

I meant a maximum rating of 1/10 watt, but doubtless you're correct about the customary current-limiting resistor.

Reply to
Windmill

Almost nil, I would think, in the UK environment. Overhead powerlines in N. America are said to show occasional 10 KV spikes during severe thunderstorms, and experience long ago showed fairly common failure of electronic equipment in such circumstances, so that might cause RCD aka GFI trips.

Someone said that RCDs incorporated some electronics, presumably to amplify any current differences between L and N sufficiently to trip a latching relay, so I suppose that might cause sensitivity to spikes if response was too fast.

Which has always surprised me, not that I've ever tried to measure my capacitance to earth.

Reply to
Windmill

Our old thermostat (the one that came with the house, & the one I replaced it with when that one stopped working) had 3-core & earth cable (neutral, live, switched live) connecting it to the heating controls. (The new one is wireless, but the plumber installed it in the same place downstairs to cover the cable hole.)

Reply to
Adam Funk

I'm just coming back to this issue.

Why is it that a neon grid indicator costs more than twice as much as a single-gang plate with a neon *and* a 20 A switch in it?

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£5.45 + VAT

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£2.60 + VAT

Reply to
Adam Funk

I figured on that, but more than twice as much?!

No, because I don't want to use something dodgy.

Reply to
Adam Funk

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