Question:
Why is my PF soft starter tripping on F40 No-load fault?

Answer:
The F40 fault is typically NOT a failure with the PF soft starter but improper parameter programming of the soft starter or an issue with other devices connected to it.

The F40 fault is actually a pre-start fault usually caused by a momentary loss of control power to the PF control module or loss of the start input signal to the PF control module. When the control power or start input signal returns, then the PF soft starter is in a pre-start condition mode again and it will go through all of its prestart checks that it normally does. The PF soft starter checks the voltage drop across the SCR's during prestart.

If the motor is connected to the soft starter, the voltage drop across the SCRs would normally be between 0 to 25V. If the drop is greater, then a No Load fault would occur. What might be happening is that the motor might be starting to coast to a stop and having some residual voltage or magnetism, then trying to restart because the start signal or control voltage has returned and the sensed voltage is above 25V, thus causing the F40 fault.

Solutions

1. Verify the correct motor type (line or delta). Is the motor connected to T1-3 (lower 3 terminals) for a Line motor and a T1-6 for a 6 lead Delta motor.

PICTURE 1. LINE CONNECTION

PICTURE 2. DELTA CONNECTION

2. Verify parameter number 15 Motor Connection is correctly to Line (for three lead motors) or Delta (for 6 lead wye delta or star delta motors).

3. Verify if there is an isolation contactor installed on the line or load side of the PF controller that it may be trying to open (chattering contacts) while the PF is in prestart mode.

4. Verify the start control circuit is not chattering. for example, PLC output, relays, float switch. This cannot be seen with a digital or analog meter, a scope would need to be used to see the chattering. Another way to check this is to jumper out the device that may be causing the issue for one start. If the motor starts fine without getting the fault, the issue is with the start signal device. If they still get the fault, the issue is elsewhere.

5. If a PLC program is being used verify that it may be initiating incorrect start and stop commands.

6. If you are attempting a flying start with the controller, verify that there is a significant time delay for at least one second before a restart signal is issued to the PF controller.

7. Verify the start signal and control voltages are not dropping too low especially if multiple devices on control line.

8. Verify the setting for any of the PF Auxiliary contacts are set to External Bypass when using an up-to-speed external bypass starter connected to an PF auxiliary contact. If the Auxiliary Contact configuration is set to Normal this will cause a F40 fault.

If using an At Motor Disconnect Switch on the load side of the soft starter, verify that it is closed.

Note: Parameters 117 [V Shutoff] and 113 [I Shutoff] have no effect on the F40 fault. The F40 fault is a pre-start fault and parameters 117 and 113 are used for detecting SCR shut-off.

For additional information please contact your nearest authorized distributor, sales representative, or call our customer service or technical support lines.