I believe this requires a thread on its own.

When is a double pole isolator required?

Lets use a common application ... the extractor fan connected to the light in the bathroom ... do you need a double pole isolator for this application if the light circuit is on earth leakage?

A ceiling fan in a bedroom with a light ... do you need a double pole isolator if the light circuit is connected to the earth leakage ?

If the extractor fan is in a bathroom but not connected via the light fitting?

can you fit the double pole isolator in the roof next to the fan ?

Can you use a 5 amp socket outlet instead of a double pole isolator ...between the light and the extractor fan?

Can you use a standard socket outlet for the extractor fan located out of reach in the ceiling.

can you use a combo breaker/isolator in the DB to feed the light circuit made up of lights and extractor fans.

I am sure the reare other questions related to this topic.