Abstract: A method of monitoring main contact conditions of main contacts in an automatic transfer switch is provided. The automatic transfer switch is coupled to a plurality of electrical power sources and an electrical load. The method includes: measuring, by sensors, temperatures of a plurality of main contacts coupled to the plurality of power sources; determining if the measured temperatures indicate a temperature rise at one or more main contacts of the plurality of main contacts; in response to determining that the measured temperatures indicate a temperature rise at the one or more main contacts, comparing a current value of the temperature rise with stored temperature rise values that represent main contact damages; and determining an amount of main contact damage at the one or more main contacts based on the comparison.