22 | Installation, Operating, and Maintenance Manual
Rev. 05JUL2016
Appendix D: Important Power Considerations
Grundfos recommends that the Magna GEO pump be wired directly to the mains power supply.
NOTE: Connecting the pump high voltage to the “T” side of the heat pump compressor contactor could cause
premature contactor failure due to contact pitting.
The Magna GEO motor is controlled by a small frequency converter, which converts the power supply to DC
voltage. Therefore, the 230 VAC mains voltage must be converted to DC voltage before the frequency converter
can control the motor. The conversion is accomplished with a rectifier and a capacitor. The load of an ECM
pump behaves as a capacitive load and not as a motor load like a standard pump. When turning the power
supply on, the capacitor will act as a short circuit (as it is “empty” – it has not been charged) and therefore the
current is only limited by the sum of resistance in the NTC resistor and the resistance in the coil in the mains
filter. If the power is turned on when the supply voltage is at its highest point, the in-rush current will become
much higher than the rated current, but only for a very short period of time (less than 0.0015 seconds, 1.5
msec). After this period of time, the current will drop to the rated current.
If the pump is powered on and off by an external relay, the contact material of the relay must be capable of
higher in-rush currents. Grundfos recommends using a minimum 16 Amp relay for 230 VAC switched voltage,
and a minimum of 250,000 electrical operation cycles at 4.0 Amps. A typical example is the Omron G7L general
purpose relay. There is no advantage in switching the pump power on and off with a relay, since the UPC Geo
controller turns the pump on and off with the low voltage connection. However, if required, special attention
should be given to selecting a relay that meets the Grundfos recommendations.
IMPORTANT: Controller must be grounded to avoid any stray voltages that may be present.