If you are trying to measure the contact resistance you will need a constant current source of 10 to 100mA. The open source voltage of the current source doesn't have to be particularly high, and you could just use a 100 ohm resistor with a 5V supply. You will then need a precision amplifier to sense the voltage drop across the contacts. I suspect the 2500V rating is an isolation rationg, and it is irrelevant to a measurement of contact resistance.