Does only wiring 2 poles of a 3 pole overload relay have any effect?
Thermal overload relays are sensitive to the heating due to current flowing in the heater elements. The thermal sensing element in a three-phase overload is calibrated to trip based on the current flowing in all three heaters. If only two heaters are used, the overload will have a lower temperature for a given current, so the trip level will be higher than it should be. If the relay is used for a single phase motor the current must flow through all three heaters for the sensing element to trip at the proper current.