On Jun 26, 10:25 pm, webpa wrote:
On Jun 25, 8:03 am, Seán O'Leathlóbhair wrote:





I am not sure if this is an appropriate group for this question. If
not, please suggest a better one.

I have a light in the house which I have wanted to switch to a low
energy bulb for a long time. The hold up was that I needed a very
small bulb. At last, I have found a small enough bulb but something
odd occurred as soon as I put it in.

When it is switched on, it works as expected.

When it is switched off, it blinks every few seconds. So, I guess
that there must be a problem with the switch If it is passing nothing
then it would seem impossible for the bulb to do anything. I did not
notice any problem with the previous incandescent bulb but I guess
that if the switch is leaking a tiny amount, the filament would glow
too little to be seen.

I have a few questions:

What is going on? Is a tiny current leaking, building up a charge in
a capacitor somewhere until a sufficient voltage builds up to spark in
the bulb and discharge the capacitor, and then the cycle repeats.

Is it safe?

Will it wear out the bulb very fast?

Is it likely to be enough to replace the switch? (Actually three
switches can turn this bulb on and off).

Might I have to replace the wiring? (Much harder than just replacing
the switches)

--
Seán Ó Leathlóbhair

You have a more complicated circuit than you think. If you have 3
switches, each capable of turning the lamp on and off irrespective of
the positions of the other two switches, then the switches are not
directly connected to the lamp. The switches are connected to a (-n
electromechanical) relay or a solid-state relay. The relay provides
power to the lamp...the switches control the relay. I suspect leakage
somewhere in wiring between the switch(s) and the relay...which, if
solid-state, may require only a few milliamps to trip the relay.
Could also be that the control relay is defective somehow.

More complicated than the common two switch set-up but not necessarily
that complicated. I have not traced the wiring to be sure how this
particular installation works but I am reasonably sure that it does
not involve a relay. I have researched how it may work and I have
described that elsewhere in the thread. The switches need to be more
complicated than typical. They need two inputs and two outputs. Each
input is always connected to one of the outputs but the connections
are reversed when the switch is changed. The live goes to one input
of the first switch. The two outputs of the first switch are
connected to the two inputs of the second. This continues through as
many switches as you wish. Finally one output of the last switch is
connected to the bulb. The neutral is connected normally. So, if any
switch is changed, the live will go down the other wire through the
rest of the system. Since only one output of the last switch is
connected to the bulb, if it was on, it goes off but of it was off it
goes on. This set-up is rare in the UK but the necessary switches are
available, I have seen them in my local hardware shop. They can be
used for the more typical two switch set-up by simply ignoring one of
the terminals. I have read that this set-up is more commonly used in
some other countries such as Spain.

--
Seán Ó Leathlóbhair