National Electrical Installation Standards

Standards as High as Your Own

Tuesday, March 7, 2023


Hi Code Friends. Section 430.84 indicates that an AC motor controller must open one leg of a single-phase supply or two legs of a three-phase power supply to a motor to stop the motor, if there is a separate disconnect for the power supply to the motor. This method can leave one energized leg of a 230-volt single phase, or one energized leg of a three-phase supply running to the motor. Is this acceptable? Best, Dave Hinkle


Hello Dave and thank you for the great question. Yes, the installation you described in your question is permitted, as long as the motor controller is only serving as the motor controller. This type of installation must have a separate disconnecting means that opens ALL ungrounded conductors to the motor. The reason this is permitted is the controller is only being used to control the motor and the separate disconnecting means is there for purposes of removing the power to the ungrounded coductors serving that motor, for servicing and/or maintenance.

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