Voltage on light circuit when off

[Ed Evans]

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

be aware that some multi meters show 50V when ther is no voltage but the setting you are on is wrong

 

[gazdkw82]

be aware that some multi meters show 50V when ther is no voltage but the setting you are on is wrong

I used 2 different instruments.

Metrel mi300 multi function tester and a fluke t5-600 meter

 

[Lucien Nunes]

be aware that some multi meters show 50V when ther is no voltage but the setting you are on is wrong

I'm not familiar with this behaviour and wonder why they should do so. Can you give me some examples of meters?

 

[pc1966]

Most multimeters have 10M input impedance so will see the results of fairly small capacitive coupling as a sizeable voltage.

 

[Ed Evans]

I used 2 different instruments.

Metrel mi300 multi function tester and a fluke t5-600 meter

it is an error message and you should refer to the manufacturers instructions.

 

[Lucien Nunes]

I meant, to display 50V when on the wrong setting. But thinking about it again, I recall some MFTs giving a warning that the circuit is live with something like '>50V' when resistance is selected. Perhaps some multimeters do that too (none of mine do, not that I am in the habit of trying to test the resistance of a voltage source) but presumably only when a voltage is actually present?

 

[Ed Evans]

I meant, to display 50V when on the wrong setting. But thinking about it again, I recall some MFTs giving a warning that the circuit is live with something like '>50V' when resistance is selected. Perhaps some multimeters do that too (none of mine do) but presumably only when a voltage is present?

When I assess the AM2 candidates doing their I&T part it is very common that they get a 50V reading due to wrong setting.

 

[DPG]

When I assess the AM2 candidates doing their I&T part it is very common that they get a 50V reading due to wrong setting.

MFTs, not multimeters though surely.

 

[Lucien Nunes]

And presumably most MFTs display a similar '>50V' message for excess touch voltage on a loop impedance test.

 

[static zap]

I used 2 different instruments.

Metrel mi300 multi function tester and a fluke t5-600 meter

.... multi-meters have 10M input impedance...

Sounds like a project for me with my hall strappers !
My MFT , ( has 430k Ohm input on VAC-rms ..from memory)
( Will observe With DMM and MFT in parallel )