Unlabled wiring puzzle

[nh3simman]

I have just installed 3 extract fans on the roof.

The electrician has made wiring changes at the DB in the basement so now I have a problem.

There are 3 unlabled isolators and I don't know which one belongs to which fan.

I bet my assistant that I can identify exactly which isolator belongs to which fan by only making 1 trip to the roof. (no use of measuring instruments necessary).

How is is done?


[this is just a puzzle, so dont tell me that the DB is supposed to be within view of the fan]

[chillin out]

Run one fan and get a cup of tea.

Then switch it off and put on another.

Go to the roof, the one you just turned on will be running.
The one that was running while you were having your tea will be warm, and the other that you didn't touch will be cold.

Chillin:) :)

[nh3simman]

Chillin', you need harder problems...

[Argus]

Better still, get the electrician to sort it out while you have a cup of tea.

[jcmorris2]

I am so dumb, nice puzzle.