Recently I have had numerous enquiries for replacing isolator switches for electric showers (typically the pull cord type). On a couple of occasions I have had to replace the wiring entering and leaving the switch terminals due to damage caused by heat. This hasn’t been caused by inadequate cable rating but, rather by inadequate tightening of the terminals themselves. If you find yourself in need of replacing the switch due to malfunction, please make sure that you tighten the terminals fully. A loose terminal causes a poor electrical connection, resulting in arching and heating of the wiring. This damages not only the wiring but also the switch itself – these switches rarely fail for other reasons.
As always, if in doubt, contact a trusted local electrician.