Installing an outside light - cable route?

[bernardgreen]

and pulled the cable down through the cavity.

Are you saying the cable comes in from outside into the cavity of an outside wall and then connects to a switch on the inside of the wall ?

If yes then keep an eye out for a damp patch around the switch as it is possible that rain water will use the cable hole to enter the cavity, run down the cable and meet the inside wall at the switch.

 

[Taylortwocities]

So, being in the cavity, the cable will be more than 50mm from the surface of both walls. That will be fine.