Actually - "on paper " there were no "loops" of iron, but due to mechanical asymmetry, it was enough to cause problems - like centering conductors in the CT for accuracy. This was around 1998 ? -- the control rooms used CRTs and they could tell the current levels by how much everyone's screens were shifted. If you entered the electrical sub it could erase your credit cards in your wallet, and the steel toe shoes would vibrate in some spots. - I could probably write a solid 4 to 5 pages on that job on both the oddities and the technical errors and discoveries.