What should the voltage be across the mains switch when off?

DetlefSchmitz said:
Not really. LEDS light up through stray capacitance when they are supposed to be off, which is quite normal. It is possible to buy what used to be called 'snubbers' to connect across the lamps to reduce the stray voltages. A couple of people on this forum have a part number for this ready to hand and may come along and advise.
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A snubber is the wrong device. Snubbers are used to reduce electrical arcs at switch contacts by maintaining a small current across them. All that is needed is a simple film capacitor.
 
aptsys said:
All that is needed is a simple film capacitor.
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The resistor has two functions when used as a contact ( arc ) suppressor,

(1) it limits the current when the closing closing switch contacts short out the charged capacitor.

(2) it provides a fusible element should the capacitor fail as a short circuit

When the device is being used as a snubber to snub a glowing lamp then function (2) is essential.
 
bernardgreen said:
The resistor has two functions when used as a contact ( arc ) suppressor,

(1) it limits the current when the closing closing switch contacts short out the charged capacitor.

(2) it provides a fusible element should the capacitor fail as a short circuit

When the device is being used as a snubber to snub a glowing lamp then function (2) is essential.
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That's not correct at all. An RC network is used on a snubber so that you can control the frequency response of the device. Nothing to do with the capacitor failing short circuit as this wouldn't matter - if it fails short the load would just power up as if the switch was closed. The resistors used are not fusible resistors either.
 
aptsys said:
if it fails short the load would just power up as if the switch was closed
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or the capacitor would self cremate depending on the current the load was taking. Most manufacturers include a warning about failed capacitors "switching on" the equipment and the risks this un-intentional "switch on" can cause to people or/and equipment
 
aptsys said:
Use a Y2 capacitor
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We are not talking about filtering noise, we are talking about absorbing the energy that is induced onto the Switched Live by the stray capacitance in the cables.

Y1 would be better Y1 class capacitors are rated up to 500 Vac, with a peak test voltage of 8 kV. Y2 capacitors have 150 to 300 Vac ratings and a peak test voltage of 5 kV.

From HERE

When does capacitor reliability become critical to safety?
Line filter capacitors are classified either as X-capacitors or Y-capacitors. X-capacitors are connected between line and neutral, to protect against differential mode interference. Their failure does not create conditions for dangerous electric shock, although it can create a fire risk. However Y-capacitors are designed to filter out common-mode noise, and are connected between line and chassis; if they short-circuit, they create a risk of shock to the user.

How are Y-Capacitors designed and deployed to ensure safety?
Y-capacitors are designed to enhanced electrical and mechanical reliability standards. Capacitance values are also limited to reduce the current passing through the capacitor when AC voltage is applied, and reduce the energy stored to a safe limit when DC voltage is applied. Capacitors must be tested to applicable standards to qualify them for use as Y-capacitors.
 
bernardgreen said:
We are not talking about filtering noise, we are talking about absorbing the energy that is induced onto the Switched Live by the stray capacitance in the cables.

Y1 would be better Y1 class capacitors are rated up to 500 Vac, with a peak test voltage of 8 kV. Y2 capacitors have 150 to 300 Vac ratings and a peak test voltage of 5 kV.

From HERE

When does capacitor reliability become critical to safety?
Line filter capacitors are classified either as X-capacitors or Y-capacitors. X-capacitors are connected between line and neutral, to protect against differential mode interference. Their failure does not create conditions for dangerous electric shock, although it can create a fire risk. However Y-capacitors are designed to filter out common-mode noise, and are connected between line and chassis; if they short-circuit, they create a risk of shock to the user.

How are Y-Capacitors designed and deployed to ensure safety?
Y-capacitors are designed to enhanced electrical and mechanical reliability standards. Capacitance values are also limited to reduce the current passing through the capacitor when AC voltage is applied, and reduce the energy stored to a safe limit when DC voltage is applied. Capacitors must be tested to applicable standards to qualify them for use as Y-capacitors.
Click to expand...

It's not doing any "absorbing" - this isn't a TVS or Surge Arrestor. We're using a capacitor's complex impedance to place a load across a lamp. This is no different to a normal configuration of any safety capacitor. We're also not talking about energy being "induced" into the switched live, it's being coupled in, so as long as the capacitance between neighbouring conductors is a few times less than the capacitor placed across the lamp, the lamp should not illuminate.
 
aptsys said:
so as long as the capacitance between neighbouring conductors is a few times less than the capacitor placed across the lamp, the lamp should not illuminate.
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Precisely. so what is the capacitor's function ? Is it not absorbing ( or other word of your choice ) the energy that has been coupled into the Switched Live
 
bernardgreen said:
Precisely. so what is the capacitor's function ? Is it not absorbing ( or other word of your choice ) the energy that has been coupled into the Switched Live
Click to expand...

No, that's why complex impedance is useful in this case, we're using the imaginary impedance to present a load. The capacitor itself doesn't get hot.
 
Even simpler fix for this shown in David Saver's most recent youtube video, just put a neon indicator connected across the lamp terminals and stray voltage will be absorbed by the neon. If you have a room of spots you would only need one, genius idea!

 
dannyboi2003 said:
Even simpler fix for this shown in David Saver's most recent youtube video, just put a neon indicator connected across the lamp terminals and stray voltage will be absorbed by the neon. If you have a room of spots you would only need one, genius idea!

Click to expand...

This doesn't always work. Many LED lamps will still illuminate or flash as the neon only clamps the voltage to 70V or so.
 
Indeed. I have a string of 2W coloured LED gls lamps outside that I run at 55V - at 240V, and hence the full 2W each, 40 lamps are "a bit bright" :cool:
They run nicely, at reduced output, off 110V or 55V from a transformer.
 
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