Flashing lights?

[andrewpreece]

How do you know the switches are in good repair?

Andy.

[andrewpreece]

Don't think it can be this; the original post gives me the impression that the same effect occurs with filament bulbs. These would not respond at all to the kind of energy that stray capacitance can account for. I would change switches, and if that fails, insulation test the cables ( with bulb disconnected of course ).

Andy.

Andy.

[outofthewoods]

In my home we have a light bulb on the landing that can be activated by a switch at the bottom of the stairs or at the top. For the last year we have had to make sure that the light is switched off by using the same switch that switched it on . If you switch it on down stairs and then off upstairs after nine seconds it gives a flash of light and continues to do so until someone (usually me) has to switch it back on and then go down stairs and switch it off . Its almost as if there is a capacitor in the circuit, or some kind of leakage, I tried changing bulbs, and have now got an energy saving bulb in it but it is just the same result. Can anyone think of a reason for this The switches seem to be in good repair. There has to be an answer to this, I just cant think of it yet. Thanks chris

[Ian Stirling]

It's the capacitance of the wire causing a minute amount of current to be fed to the bulb through the switched wire being next to a live (millionths of an amp, utterly harmless, you wouldn't feel it if you licked the wire). (Don't lick wires) This is then rectified, and charges the capacitor in the ballast. Once it gets to somewhere over a hundred volts, the lamp tries to start, and uses up all the energy in the capacitor, and the process starts again.

I think it may slightly degrade the lamp life, due to the repeated starting attempts.

If you have a clue electronically, I'd go with taking two 1W 270K resistors, putting them in series, and wiring across live and neutral before the bulb.

[Frank Erskine]

Almost certainly one of the switches is at fault (or a loose screw connection).

Check that all the screws are tight, then consider replacing one or both of the switches - they're dirt cheap, really! The downstairs one sounds suspect, but either could be at fault.

[Bob Eager]

Does this happen regardless of the starting switch position? In other words, is the bahaviour tied to the use of a particular one of the link wires that run between the upstairs and downstairs switches? Insulation failure, partial short, faulty switch...

[Set Square]

Did *you* change anything a year ago when this started happening? For example, was either switch removed while decorating - and could possibly have been re-wired incorrectly?

I can't quite work out how incorrect wiring would account for your problem, but it's worth checking, anyway. The live feed should go to CON on Switch 1. NC on switch 1 must be connected to NC or NO on switch 2 (it doesn't matter) and NO must be connected to the other one. Finally, COM on switch 2 must be connected to the lamp. [I think that there are other ways of doing 2-way lighting, but this is the easiest to understand!]