Both engineers, one at the drive mfg. and one from the meter mfg. recomended that we ground the motor casing to the conduit at one end and the conduit to the vfd casing at the other end using 4 awg welding cable, lugs and grounding clamps. This was to insure that there was a good connectionfrom motor to vfd case and hence to ground for the conduit. The explanation was that this would trap any radiated signal and take it to ground. Why the ground wire which runs the entire length with the motor leads doesn't do this, I don't know. The drive engineer said that if that didn't take care of it, to disconnect the 6 awg at the motor end and leave the vfd case end connected. the explanation was that the broadcasted signal would be picked up on the conduit and drained back to the case of the vfd. For the record the conduit is IMC outside the building and EMT inside the building.
