Frequency inverter with brake resistance and method for monitoring the functionality of a brake resistance during the operation of a frequency inverter

The converter (2) has a measuring unit (10) measuring electric voltage that rests against a brake resistor (8). An evaluating device (12) is connected with the measuring unit for comparing measurement values determined by the measuring unit with stored comparison values. A switching device (6) is connected with the evaluating device that triggers shutdown of intermediate circuit voltage of the brake resistor if the measurement values display a duty cycle of the brake resistance that exceeds a threshold value of the duty cycle given in the evaluating device. An independent claim is also included for a method for monitoring operation of a braking resistor in a frequency converter.