On 25/08/2012 13:17, Dave Plowman (News) wrote:
In article ,
Paul G wrote:
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 ?

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.

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.

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.


--
Regards,
Martin Brown