Is 120 volts too much to be inductive/capacitive?

[hellopaul2]

Hello.

I have been trawling through the surprisingly common "my CF light flashes every few seconds because there's 50 or so volts going through my wires when they're switched off" posts in this forum.

Predictably, I have a very similar situation - but I have the gift of 120 volts when measured with a digital multimeter on the terminals or bayonet lightbulb holder contacts of one of my lights (when switched "off"). Before I investigate further, I thought I'd just ask whether 120 volts is too much to be merely induced/capacitive current, considering the house is a medium/small 3-bedroom, 2-storey house, with no excessively long wiring runs. The light fitting in question is wired up to two 2-way switches, but they're only about 6 metres apart.

I suspect that the 120 volts is too much, and I should do further investigation, but just wondered if anyone had experienced such a high induced/capacitive voltage (outside of a transformer!). I haven't had the flashing light thing, but I haven't sat and stared at the (off) light yet.

- Paul

 

[ricicle]

Trying measuring that voltage with a filament lamp in circuit or with a moving coil voltmeter !

 

[hellopaul2]

Is the reasoning behind measuring it with a moving coil meter or a filament bulb that if the current is tiny (caused by an induced voltage) then neither will register anything, but if it's a large current (caused by dodgy wiring) then the meter/bulb will register it?

I should add that one of the first things I "corrected" after moving into this house was the "earth" wire connected to a brass light switch...which was actually a live cable. And yes, my wife and I did get a couple of shocks from the switch. So I don't have much faith in the wiring.

 

[securespark]

If it's induced and you put a filament lamp in circuit, the current will indeed vamoose.

 

[bernardgreen]

I suspect that the 120 volts is too much, and I should do further investigation,

120 volts is quite normal. It is sometimes higher.

The switched live runs along side a live wire and an earth wire and this forms two stray capacitors with the switched live being the mid point. As the capacitors are approximately the same size the midpoint voltage will be half way between the live voltage of 230 volts and the voltage on the earth wire which is ( hopefully ) 0 volt. In older systems with no earth wire the stray capacity will pull the switched live to 230 volt.