Electrical Safety and Facility Integrity: Evaluation of AC Power & Grounding Issues

Abstract AC Power Grid electrical grounding is purposely joined to/gets electrically coupled with below-grade metal assets, and sometimes with cathodic protection (CP) systems. The typical North American power grid is supplied by 60-cycle-per-second (or Hertz, Hz) alternating current (AC) electricity. Larger facilities are usually receiving three-phase AC power, with three separate power-delivering legs and one common neutral wire forming the circuits. At a large oilfield water management facility in West Texas, two studies were needed. For one, AC power grounding conductors on site were showing large AC current flows, in the range of 3.5 to 18 amperes (A) AC with significant fluctuations. At the same time, various copper grounding and bonding wire damage patterns were observed, mainly in relation to a salty produced-water spill inside one secondary containment structure which housed at least 12 API-12F (1) above-ground storage tanks (ASTs). The operator wanted assurance that on-site electrical grounding was working effectively, and to be advised whether grounding and bonding repairs were needed. A later site shut-down and facility maintenance/repair event finally isolated a starter motor, operating at 60-Hz power, with a partial electrical fault. The motor was replaced. That fault condition flowed only about 1.5 A AC, a possibly lethal current level.