Why am i getting a potential difference

[RobFurn]

ok so testing a simple bathroom setup , light , switch, fan and isolator.

Was testing at the fan end and for whatever reason I had my test leads acros across Live ( Line) and Switch Live to the Fan (light switch was off but fan isolator closed). Measured 240v ...odd

ok I thought maybe its being pulled to earth from the light, possible if it were a filament lamp but in any case its not.

So I disconnect everything to the light including the switch light junction ( so effectively the switch live is floating and not connected to anything. Measured 150V

Q: How can it still be measuring a PD if its just effectively a trailing wire, There are no shorts BTW, IR was fine >500M

 

[AndyPRK]

Capacitive pick up

 

[RobFurn]

Capacitive pick up, thanks. Quite commen then? and obviously nothing to worry about? how does it occur?

 

[AndyPRK]

Two conductors travelling in parallel.
No connection on one will make it worse.
It picks up voltage.

As you say the lamp was probably the cause for the 240v reading. Completing the circuit back to neutral

 

[RobFurn]

Great thanks again, I wont let the meter stray on things I don't need to test in future, save me from completely undoing everything lol