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Message started by Flashbang on Nov 10th, 2018, 1:18pm

Title: 3way lighting with a problem
Post by Flashbang on Nov 10th, 2018, 1:18pm


I have a downstairs hall light that is controlled via 3 way switching, comprising of...1 triple gang near front door, 1 double gang upstairs and 1 intermediate switch by kitchen door operating the circuit with the multi gang switches other gangs operating other lights. Never noticed a problem all the while the fitting used 5 x G9 30watt Halogen lamps, but we decided to 'save the planet' and obtain LED replacements rated at 4 watts each. These offer great illumination, but....
When the fitting was turned off the LEDs could be seen to be glowing very slightly!   Took fitting down and checked everything visually and no signs of any issues, then I took a multimeter and checked Sw L to N with switches all Off. 61votls AC recorded hence the glowing LEDs.  Move each switch to its opposite position and the voltage is lost.  
So is it a defective switch or a cable defect?  I guess the easiest way to prove its a switch defect of not opening its contacts correctly, is to replace them all and see what happens? Unless there is a simpler way to test each switch?
Can you guys think of a faster and easier way of checking the circuit?

So LEDs now acting as fault finders too!  :D

Title: Re: 3way lighting with
Post by Lectrician on Nov 10th, 2018, 4:41pm

There is nothing wrong with the circuit as such.  This is a known issue with LEDs and CFLs on long switch drops and two way switching etc.  Where switch cables are quite long, the live down and return run in parallel for a substantial length.  The induced EMF from the live to the switched live causes a voltage to be induced into the switch live.  With normal lamps the induced voltage and current is not enough to do anything, but with LEDs you may notice a glow, and CFLs can flicker.

Leaving one lamp in place is enough to stop this annoying phenomena.

You can fit a resistor to bleed this voltage and current away - Google LED snubber.

Title: Re: 3way lighting with a problem
Post by Flashbang on Nov 10th, 2018, 5:35pm

Of course... Never thought about induced current/voltage in domestic wiring causing a problem!  
Will try a snubber ASAP. Just a pain in the whatsit to undo the light fitting to access SwL and N.  ;D
Thanks for the heads up re snubbers.

Title: Re: 3way lighting with a problem
Post by Natedog on Nov 17th, 2018, 12:40am

You could also try a different brand of bulb.  Some are more prone to this than others, think it depends how good the driver circuit inside them is

Title: Re: 3way lighting with a problem
Post by CWatters on Nov 20th, 2018, 2:39pm

I recently fixed same problem by fitting a ..

0.47uF Class X2 275VAC capacitor

across one of a set of downlights that was giving me this problem.

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