Priniciples of Electromechanical Relay Operation
3.18 Dielectric Considerations
The comments in Paragraph 3.09 are also applicable to ac relay actuator
systems with one additional point worth noting: The periodic polarity
reversal that is characteristic of ac voltages applies greater stress to most
insulating material than does an equivalent dc voltage. The result is that a
given dielectric material will likely breakdown at a lower peak ac voltage
than dc voltage.