Industrial contactor frequency influence
The contactor coil has a 50/60 HZ limit at its rated AC voltage, but the contacts do not care about sine-wave frequencies. They will work just fine from DC to 10's of KHZ. If arcing is an issue you can install 40 mm MOV's rated for 50% above the contactor voltage across the contacts.

They will cut way down on arcing when the contacts open under load.

Leakage current will be in the uA range.