System and method for fault contactor detection

A motor starter system comprising:

• solid state switches for connection to an AC line for controlling application of AC power to the motor;
• a fault contactor having contacts;
• a motor wiring circuit for operatively connecting the solid state switches and fault contactor contacts with motor winding terminals;
• a voltage sensor for sensing AC line voltage and motor terminal voltage;
• and
• a control circuit for controlling operation of the solid state switches and the fault contactor, including de-energizing the fault contactor in an off mode where AC line power is not supplied to the motor winding terminals, the control circuit detecting AC line voltage and motor terminal voltage in the off mode and detecting an error condition responsive to sensed AC line voltage being substantially different from motor terminal voltage in the off mode.

A method of fault contactor detection prior to motor starting comprising:

• providing solid state switches for connection to an AC line for controlling application of AC power to the motor;
• providing a fault contactor having contacts;
• electrically connecting the solid state switches and fault contactor contacts with motor winding terminals;
• sensing motor AC line to neutral voltage and motor terminal to neutral voltage;
• controlling operation of the solid state switches and the fault contactor prior to motor starting, including de-energizing the fault contactor in an off mode where AC line power is not supplied to the motor winding terminals, detecting AC line voltage and motor terminal voltage in the off mode and detecting an error condition responsive to sensed AC line voltage being substantially different from motor terminal voltage in the off mode.