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It is the contacts that fail, as the contacts approach each other; & the voltage is high; it then jumps across the gap; before the contacts actually mate.

The elements will be designed for a 220V or 240V ac voltage.

The supply voltage is an AC sinusoidal waveform.  240Vac, is the average of the sinusoidal waveform; not the maximum.

The peak voltage is  1.414 times 240Vac., or 339Vac peak.   Now you see the problem, which is timing. If the contacts coming together, coincides with the peak of the hi voltage waveform; "Bang".

If you think back to pre-LED lights in our houses, when we had filament bulbs; you will remember, that bulbs "popped"; often in Winter; just as you were turning them on.

Ever remember being in a dark room in Winter, & turning a light switch on; only to see a flash behind the light switch plate ?

Filament was cold, with low resistance, & therefore drew more current.  Actual point in time, at which the contacts closed, was completely arbitary.

The secret; is to switch the light on, at the zero crossing point, of the 240Vac sinusoidal waveform, where the waveform changes from being negative, to positive (effectively zero volts).


I have made it a habit of using high voltage SSRs (Solid State Relays) with zero crossing switching built in, to switch large loads that cause issues, for conventional mechanical switches.

image.png.17a93771f052ae6ab412b6ec38d1de3e.pngTypical Solid State Replay, with LED to indicate is has been "turned on", by 4-32Vdc input voltage.

So irrespective of what time you "flick the switch", to power the solid state switch (SSR); the SSR, waits until the next zero crossing of the high voltage waveform, before it switches on.   As a full 50Hz mains cycle is 20milliseconds, then the longest you would ever have to wait for the light to come on, would be 10 milliseconds.  You would not be able to detect this delay.

I have a whole house, built 20 years ago, where the light switches only switch 12V dc, & that 12V dc, turns on a solid state switch, which turns on the bulb.

Worked really well for 20 years, & never had to replace a bulb ever. Then along came "hi efficiency" LED light bulbs, & another problem appeared. The highly efficent LED lights, sometimes glow in the dark, as they are so efficient, that the minute leakage current, through the solid state switch "snubber", is enough to cause some LED lights to "glow".  Oh  technology ! ! !


P.S.  I was in NSW recently, in a Bunnings store, & You could not find a filament bulb on the shelf.  Starting to go that way in Qld. also.  Soon, filament bulbs will be a thing of the past, & you'll only see them in museums.

Cheers  Banjo




Edited by Banjo
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