Voltage on light circuit when off

[gazdkw82]

0.1μF is common, I can't see that a larger value would be needed for any reasonable amount of leakage, and the larger case would be harder to fit in a back box or wherever it's going.

BTW did you ever do any insulation tests on the switching as I recommended? It would be good to confirm that you are not simply concealing an actual fault.

Thanks. I will grab a bunch of 0.1μF RC snubbers.

I'm hopefully going back round this weekend. I will IR test then.

 

[pc1966]

You should find them in various places, example here from RS:

PMR209MC6100M100R30 | KEMET RC Capacitor 100nF 100Ω Tolerance ±20% 250 V ac, 630V dc 1-way , Through Hole, PMR209 | RS

uk.rs-online.com

The type like that would need legs sleeved of course, some come with insulated wires already:

https://uk.farnell.com/roxburgh/xeb1201/cap-0-1-f-250vac-20/dp/1187659

 

[gazdkw82]

I think I'll order the ones from cpc

https://cpc.farnell.com/ampohm-wound-products/fe-sp-hdr23-100-100/contact-suppressor-0-1uf-100r/dp/FT00715

 

[pc1966]

Yes, though I had posted another one earlier!

 

[gazdkw82]

Update on this......

I confirmed the insulation was in good order. Customer ordered and fitted the snubbers.

Problem solved.

Thankyou for the help and advice.

I wont be so confused if I come across this again.

 

[redrain357]

i have installed some down lights and have the problem of a light glow all the time when switched off. i understand induced voltage but dont have the problem on my other downlights so can only assume its a cheaper fitting.i have read about snubber and looks like a discharge device for the circuit. is this correct and what one is best to use?

 

[pc1966]

Snubbers were originally intended for switching circuits to dampen the electrical noise generated by the arcing of contacts. They consist of a capacitor and resistor in series, the capacitor (typically around 0.1uF) passes a small current at 50Hz supply frequency but is quite low impedance to fast pulses, and the resistor (typically around 100R) serves to dampen any high frequency oscillations resulting from having inductance (motor, relay coil, etc) and capacitance together.

But now they are often put in parallel with one or more LED lights to provide an alternative path for the very small current that you can get passing via the capacitance of cables (in particular long runs for two-way switches, etc).

The part listed above from CPC is probably the best one to get, cheap enough and has insulated flexible wires that allow it to be fitted more easily in parallel with the LED light(s) (i.e. from L to N of one of the lights).

 

[redrain357]

o

Snubbers were originally intended for switching circuits to dampen the electrical noise generated by the arcing of contacts. They consist of a capacitor and resistor in series, the capacitor (typically around 0.1uF) passes a small current at 50Hz supply frequency but is quite low impedance to fast pulses, and the resistor (typically around 100R) serves to dampen any high frequency oscillations resulting from having inductance (motor, relay coil, etc) and capacitance together.

But now they are often put in parallel with one or more LED lights to provide an alternative path for the very small current that you can get passing via the capacitance of cables (in particular long runs for two-way switches, etc).

The part listed above from CPC is probably the best one to get, cheap enough and has insulated flexible wires that allow it to be fitted more easily in parallel with the LED light(s) (i.e. from L to N of one of the lights).

oh just one thing supply frequency is 50hz but voltage is around 240v will that be the same specs or diff for .1uf and 100r

 

[telectrix]

regarding neons. yesterday i fitted a LED bulkhead light for a client, fed from a IP 55 switch with neon "switch finder". the neon is connected across L and S/L so it lights up when switch is off. unfortunately, with the switch off, the lamp flickers, due to getting a reduced voltage via the neon. a quick vasectomy on the neon wires sorted that problem.

 

[pc1966]

o

oh just one thing supply frequency is 50hz but voltage is around 240v will that be the same specs or diff for .1uf and 100r

The values are not critical.

Typically T&E is around 200pF/m or so capacitance, so 100m of cable is about 20nF

With 0.1uF = 100nF = 100,000pF shunting a high impedance load you would see around 1/6 of the supply voltage so around 40V which is (hopefully) below a value that will cause the LED driver to charge to the point it can light the LEDs themselves.

I doubt most installs have anything near 100m of cable for an individual light feed or strapper!