An electric motor controller for controlling an electric motor and methods of determining a loss of phase condition for at least one phase of three-phase input power provided to an electric motor controller are provided. The controller is configured to obtain phase sample data representing an input power electrical characteristic for at least one phase of three-phase power received by the controller and receive direct current (DC) bus data representing a measured DC bus electrical characteristic. The controller is also configured to calculate a ratio between the phase sample data and the DC bus data, and determine that a loss of phase condition exists for a phase of the three-phase power when the ratio exceeds a predetermined threshold.