Bathroom extractor problem.

[whistler]

Bathroom has a ceiling extractor fan, which is wired correctly with isolation switch outside bathroom, and cord pull on off switch in bathroom. The fan has overrun so has a permanent live connection.

Everything works ok, but very occasionally when a light is switched on in another room, it triggers the fan to start running. This only happens occasionally.

Any ideas why this happens?

 

[AndyPRK]

Voltage spike induced onto the swl wire.

If you had the same pull cord for light and fan it shouldn't happen.