Voltage on light circuit when off

[gazdkw82]

Friend of mine has phoned. He needs my help because his lights in the hallway keep flashing dimly whilst in the off position.

He has measured nominal voltage when the lights are turned on and 50v when the lights are turned off.

I dont have much information to work with yet but thought I would ask for a heads up on how to approach this. Iv not had a fault like this before.

The offending lights are via a 3 gang 2 way switch. Could this be induced voltage? If so, how would I confirm this and how can I remedy it?

He has said he changed the lamps for LED and they flash even more obvious now.

I will obviously check connections and test Zs, probably I/R switch live to neutral/earth etc...

I thought I'd just ask for a heads up on how to approach it.

My friend is an electronics wiz so he has some knowledge on the basics. I would imagine he bas tried the obvious

 

[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!