Just got a correction notice on a building that we wired. The correction notice says that we need to install "grounding bushings" on a branch circuit. Basically out of a 480v panel, there is a branch circuit that runs to a closet where a disconnect is mounted. Out of the disconnect it feeds a plenum heater. The reason for the correction is cause we used concentric knockouts for the pipe. We also have our egc ran in the pipe. Am I missing a code section which requires me to have bonding bushings, on a 480v branch circuit, using concentric knockouts, while also having an egc installed with the circuit conductors?
I realize that if I didn't have an egc in the pipe while using the concentric, it would justify using bonding bushings. Any clarification would be appreciated.