This can't be done unless you have a neutral at the switch position. When the switch is on there is no potential difference between the terminals therefore no power source.
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Or, if the box is grounded, there will be line voltage between the load side and the box in a correctly wired normal (not 3-way) circuit.
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There's almost always a neutral in the switch box, occasionally I see an arrangement with power coming into the light box and a separate switch drop but it's fairly rare. Also it'd be possible to power the reminder with a battery in that case, it wouldn't have to draw much power. If the lamp is incandescent you could even use a rechargeable battery or memory backup capacitor to power it and "steal" power to charge the battery when the switch is off.
UK electrical boxes are incredibly tiny compared to those in the US/Canada. Our standard boxes are 2.5" deep but you can get them up to
4" deep in the standard 3.5"x2" size used for single switches and receptacles.
Connecting between line and ground would not be legal by code, but if the circuit is designed carefully it would not be a danger either. I'd lean towards powering it with a battery personally, much safer for the novice.
Right. In the UK the latter is the norm. Lighting circuits are radials and the feed goes from one ceiling lamp to another, with the switch drop from that lamp. Of course if you have floor outlets for table lamps etc you're more likely to find a neutral at the switch.
Yup - although it might be tight to fit all that within the switch back box. In the UK, some are so shallow there's just enough room for the cable.
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I did not address the regulatory issues. But, I assumed he was talking about a few mA of current just to operate a flashing high brightness LED, the the line balance wouldn't be a practical issue unless it tripped the RCD/GFCI/whatever.
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In the UK, neutral is connected to earth at some point - the last possible one being at the incoming main. After that, they are separate. Use the earth cable in the house as a return and you are now not drawing equal current on line and neutral. And RCDs work by looking for a difference in the current flow between line and neutral, so you don't want to impose a load which does just that. Of course, if it's only a couple of milliamps it's unlikely to matter, but in principle it's a bad idea.
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We currently do not have RCDs installed at the fuse box - they are plain wire fuses.
James Sweet mentioned in an earlier post, using a rechargeable battery or memory backup capacitor to power it and "steal" power to charge the battery
when the switch is off.
How would this work with no neutral? I am assuming a large wattage resistor would be required to drop the voltage to a suitable level and using the earth as a neutral? However, I don't think there will be enough space behind the switch plate for the resistor?
If you just need some kind of indicator to show whether a remote light is on or off, you can wire a neon lamp (with resistor) across the switch. In the UK you can buy this ready made as a backplate for a standard single light switch plate. It`s so you can find the switch in the dark. When the neon is on, the light is off and vice versa. It`s not going to beep of course.
In the UK lighting switches are usually single pole, so if that's also the case in the US change to a double pole one and use one pole for the sounder.
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Dave Plowman dave@davenoise.co.uk London SW
On Tue, 3 Jan 2006 12:27:55 +0000, M.Joshi put finger to keyboard and composed:
The neon is probably wired across the switch contacts. When the switch is off the neon sees the full mains potential. When the switch is closed the potential is zero.
Here's my suggestion:
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