When reading the output of a VFD with a multi-meter you may see high readings. For example, a 460VAC output may read well over 500VAC (sometimes up to 1000VAC). This is normal, due to the VFDs output being a PWM waveform. Most multi-meters are "RMS" meters. This means that the meter is averaging out the signal it is reading.

As seen below, the output signal from the VFD is a DC square wave that is rapidly switching on an off. This is called pulse-width modulation; PWM for short. This signal will also have transients or spikes. These spikes add to the average reading causing the higher voltage to appear on the multi-meter.To find out what the proper voltage reading really is it is recommended to use a multi-meter with a low pass filter option or use the VFDs output voltage monitor.