What causes insulation to deteriorate and what can be done about it?

Cause: Contact material is scattered around because of arching due to excessive load capacity.

Countermeasure: Switch the load using a contactor rather than switching a load directly using a switch. 

Cause: Many water drops may have penetrated the Switch due to severe changes in the ambient temperature at high temperatures. Liquid may have penetrated the Switch and carbonized due to arc heat. 

Countermeasure: Remove the cause, install the Switch in a box, or used a Sealed Switch.