Neon indicator for 3-way garage lights

[Paul G]

My garage is attached to the house with a 3-way lighting circuit. Sometimes the family leave these lights on and this is only discovered when someone goes outside and notices the fact. One of the light switches is inside the house (next to an internal door into the garage) while the remainder are at either ends of the garage. I'd like to add an indicator to the indoor switch to show when the lights are on. Because it's a 3-way circuit, I think I need a new cable from the lights to this switch. It's a single gang box but I am struggling to find a switch with neon indicator that is fed separately. I'm sure this is all achievable using a modular faceplate but frankly I'm hoping to avoid the expense (of modular).

I am hoping someone can confirm I need to add a new cable for this, and suggestions for a switch+(separate) neon indicator faceplate ?

Thanks Paul

[The Natural Philosopher]

The neon on just about any switch I have seen is actually completely separate and juts 'happens to be' wired to the swich, but its easy enough to disconnect it.

You are correct that you need to know what the voltage at the light is which is not something you can sense from one side of a two way switch.

And that will require a separate lead from the switch, or some way of sensing current being drawn (complicated)

And for that reason its not that common to find a changeover switch with a neon..In fact I cant recall having seen one.

A different option might be to place a DP isolator with neon in the house that controls the lighting in toto. Then if that is off, the garage will always be off.

I have such in my spare bedroom/workshop to control all the power points on the bench, so that I don't need to remember what I left plugged in and switched on.

Seriously the best option I can think of is to get a separate neon indicator of a nice size and shape and butcher a cheap faceplate to take it

This is actually the only example I can find outsode of RS components of what used to be so common we even had a punch tool made for it..

to say junk yards and indeed old isolation switches are full of equipment with these in them....

[Andrew Gabriel]

You can make one up using MK Gridswitch (or other manufacturers' equivalent products).

Yes, you will need a new cable, at least a neutral, and possibly a live if the circuit arrangement is such that the house switch isn't logically the last one directly feeding the light.

Alternatively, forget the manual switches, and use an occupancy detector to switch the garage light. That's how mine works.

[Dave Plowman (News)]

Slightly against regs, but a neon or LED (with suitable dropper and diode) can be fitted to the switch plate and get its return from earth.

If you don't want to fit a neon to the plate, you'll be into using a grid switch system to get the two way, intermediate, and neon. But at least you won't have to run in new cabling.

[NT]

The description is about as clear as mud, so I can't comment on the wiring.

There are a few options for a separately wired neon:

- mount a neon in a standard switch faceplate

- use a light up spacer behind ditto

- use a screwed together neon FCU, bring the neon connections out separately

NT

[Martin Brown]

Also against regs and dissipating at least a watt when the main lamp is on would be a dropper resistor of about 5.6R in the common line with an LED and a reverse diode each protected by a 1k resistor. 100W bulb will draw a shade 1/2A so 5.6R gives about 2.8 v enough to light a red LED. You may have to adjust values and allow a large power disippation safety margin depending on the actual lighting used.

There may be more elegant code compliant ways to monitor mains current flow with active is on based on a reed relay surrounded by a solenoid and bridge rectifier. Never seen one though.

I have a similar problem with a neon for a manual switch for a CH pump where I have settled for an anti-sense neon circuit. The neon is lit when the switch is open and the load is not being driven.

[Bob Minchin]

Find a miniature mains transformer - secondary voltage irrelevant. Wind a turn or so of insulated wire through the odd gaps in the core and use this as a current transformer with a neon across the 240v winding. You might have to play with the number of turns but the neon will strike when the lighting circuit draws current.

[Andrew Gabriel]

If you're going to play with current transformers, bare in mind that if you leave the windings open-circuit so no current can flow, the voltage output will go very high. You may break down the insulation, and/or give yourself a belt. Not sure how a neon as the burden (current transformer load) would cope with a filament lamp switch-on surge or a short circuit, but I wouldn't be surprised if it blew up.

[Huge]

"bear"

You're welcome.

[NT]

a filament lamp consumes about 8x run current during starting, so you'd need a more complex circuit to avoid frying the led. bridge rectifier, zener, resistor, led.

NT

[The Natural Philosopher]

I'll tip my hat to a solution that I (a) hadn't thought of and (b) seems an entirely simple and elegant way of doing it!

[Andy Wade]

Possible alternative non-electrical solution - if it can be done in a visually acceptable fashion: drill through the dividing wall and insert a perspex rod (light pipe), preferably coloured.

[Dave Liquorice]

True enough but not for very long and LEDs can take a hefty overload for short periods. Might get away with it, or not... B-)

If you are going to stick something in series back to back 5W zeners of suitable voltage (both) would probably be better, no risk of a larger than expected current draw frying the LED. I don't like the power dissipation in either the series R or back to back zeners.

We don't know te topology of the wiring which switch of the three is the intermediate, which is the live end and which is the load end of the two way circuit.

A small mains transformer (recovered from an old wallwart?) wired across the light with a bit of bell wire (as it's LV and isolated) to a convient indicator. I know breaks the don't want to run a wire part of the spec.

[Bob Minchin]

You will find that in practise, the core saturates and the voltage on the secondary limits as a result. In any case as the neon strikes around

100v or so, the voltages are enough for a tickle but the OP is playing with mains anyway.

[Bob Minchin]

Thanks!

It is a useful technique for indicating that high currents are flowing too, whilst only loosing a small amount of power. I use a similar set up to switch on my workshop dust collector when any of my multi-horsepower woodwork machines are switched on.

The transformer can be swapped for the coil of a sensitive ac relay. A few thick turns round the solenoid and the relay closes when current flows.

Bob

[Richard Russell]

Referring to the Wikipedia article, if you wire your 3-way switching using what they call the 'alternative' system it should make it easier to achieve. Indeed it specifically states "an optional additional lamp can be connected at Terminal A as a pilot lamp" and "it has the advantage of allowing loads at both ends of the switched circuit to be controlled from either end":

[Dave Liquorice]

way"... B-)

[Dave Plowman (News)]

extension of a one way.

L1 L1 0===========0 0===========0============= Line | \ / | C 0================================O C \ / \ / 0===========0 0===========0============= Switch return L2 Optional L2 Intermediate

[Richard Russell]

It can easily be extended to 3 (or more) switches:

[NT]

I guess if youre willing to take a gamble. Better to have something that will last though, I'm pretty fed up with maintenance.

Perhaps the path could just be optical. So far I've little idea of the layout, physically or electrically

NT