I was recently on a PQ investigation where another PQ consultant was in the middle of a lengthy investigation into possible circulating ground currents (I was there as a kind of second opinion). In the course of my conversation with the consultant he informed me that when he had brought in a contractor to bond the building steel he specifically instructed them not to bond the motor frames to the building steel because it would violate article 250 of the NEC. I am not an expert in the application of the NEC but I don't think what he said is correct. The motors are provided with a grounding conductor which provides for fault clearing. He went on to say that bonding the motor frames would create ground loops. Could any one clear this up for me? I have always been under the impression that if you had a facility with a well bonded steel structure that it was a good practice to bond the exposed metal parts (such as motor frames)to the steel.