Cause : DC Bus Overvoltage comes when the DC bus voltage exceeded the trip point. When a Yaskawa E7 drive displays a "DC Bus Overvoltage" alarm, it indicates that the voltage level on the DC bus of the drive has exceeded the acceptable threshold. 

• 208-240Vac: Trip point is ≥ 400Vdc 480Vac: Trip point is ≥ 800Vdc

1. Surge voltage present in the drive input power.
   • Install a DC link choke or an AC reactor.
   • Voltage surge can result from a thyristor convertor and a phase advancing capacitor operating on the same drive input power system.
2. The motor is short-circuited.
3. Check the motor power cable, relay terminals and motor terminal box for short circuits.
4. Correct grounding shorts and turn the power back on.
5. Ground current has overcharged the main circuit capacitors via the drive input power.