On 06/12/2019 16:19, Lawrie Davidson wrote:
One thing I've always been slightly puzzled about. My back room has
two sets of lights. There is a double switch by the door, one of the
switches only works the set of lights near that switch. The other
switch works the other lights which have their own switch on the
other side of the room, obviously a two-way switch. If both switches
on the double switch are switched off there's no problem. But if one
of the the two-way switches on the double switch is switched on and
it's switched off the other side of the room on the two-way switch,
there is a very faint glow from the lights on the other side of the
room. I know that sounds absolutely confusing, but if anyone can
understand it, I wonder whether it's dangerous if I forget and leave
the two way switch the wrong way round which leaves the lights
faintly on.

I am guessing that the lamps in question have LED or CFL lamps rather
than filament?

If so, this is a relatively common problem. It results from a
combination of low energy lighting which needs only a tiny current to
start to glow faintly (or sometimes to flash intermittently), coupled
with all the extra wire in a two way switching arrangement.

If you look at a typical wiring diagram for two way switching:

http://wiki.diyfaq.org.uk/index.php/...tching_circuit

You can see that you may end up with a long length of cable connected to
the live input of the lamp, but with the other end disconnected at one
of the switches. This wire is said to be electrically "floating". Since
it is running very close beside other live wires, it can pick up a
voltage induced by its closeness to the other wires. That voltage is
enough to cause the symptom you see.

Its not dangerous, since there is very little current involved - if you
put any significant load on the wire its voltage will fall away quickly.






--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/