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Questions and answers

For detailed instructions – see our User and installation handbook as well as the Quick installation guide.

More about frequency inverters

Frequency converters, EMC interference, earth currents and storage damage?

Frequently asked questions with answers
Below are some of the questions we usually get. If you have any questions, please feel free to contact us.

  • Which version of the handbook should I use for the NFO inverter?
    It depends on which version of the inverter you have.
    If the inverter has a two-row terminal block for signal cabling use handbook version 2.xIf the inverter has a three-row terminal block for signal cabling use handbook version 3.x Publishing dates for handbook: Ver 3.1 – 2006-06-01 / ver 3.2 – 2007-05-02 / ver 3.4 – 2009-03-19 / ver 3.5 – 2012-01-04​


  • The inverter starts but does not drive the motor/pump etc 
    Check that the run signal is connected to plinth 5. See figure 1 in the handbook.Is positive or negative logic used?  Check jumper S1 – see figure 3 in the handbook.Check that the run signal is correctly connected depending on the logic. Check that Autotuning is done with the correct motor data, chapter 5.5 in the handbook.

  • The display shows “Stop”. How can I change to run mode?
    Hold down SHIFT and press STOP to enter External mode.

  • The display shows “Stop”. How can I change to run mode?
    Hold down SHIFT and press STOP to enter External mode.
  • The “AC Fail” alarm is triggered
    The AC Fail alarm is due to input voltages into the inverter and not the inverter itself. Check the mains voltage.
  • A “PTC Temp” alarm triggers.
    Is the motor protection thermistor (correctly) connected? There should only be a PTC resistor connected IF the motor safety thermistor is used.​
  • The “ImagnLow” alarm is triggered during installation
    Check that the motor is connected to the inverter and that all the switches between the inverter and the motor are switched on.

  • Can I install NFO Sinus without a filter and without shielded cables?
    Yes, the inverters meet the norms for EMC directive 2004/108/EG for emissions from equipment in houses, offices, shops and similar environments (EN 61000-6-3) and immunity for equipment in industrial environments (EN 61000-6-2) without extra accessories or shielded cables. The directive came into force on 20 July 2007.

  • How can I reset all parameters (factory reset)?
    Follow the instructions in chapter 5.13 in the User and installation handbook (chap 5.12 in 2.x handbook)

  • What does Intrinsic EMC mean?
    It means that the equipment is interference free in itself and can be installed without EMC filters, shielded cables or other EMC classed installation accessories.

  • Can you run several motors in parallel from one frequency inverter?
    Yes, you can, if the motors are the same size and have identical loads. Enter the total current and the power of all motors when autotuning the parameters I-Nom and P-Nom. For the other parameters enter the value for one motor.  (Correct dimensions>>)

  • Can you use a RCD together with NFO Sinus?
    Yes, it works brilliantly – even residual current devices for personal protection. An NFO Sinus draws at maximum 2 mA in the earth cable and residual current devices for personal protection trip at 30 mA. Circuit breakers for fire prevention trip at higher currents depending on where they are installed.

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