Designing to Avoid Hazardous Transferred Earth Potentials

``Grounding´´ is not an absolute phenomena, but rather a relative expression of conductivity to a common earth plane. Use of modifying adjectives such as ``effective´´ recognizes the existence of less than complete conductance. It follows that if current is conducted through these ground paths, a difference in potential will exist. When alternate conducting paths bring the potential from one location into proximity with the potential of another location, potential difference may exist across insulating elements which exceed their insulating capabilities and can be dangerous to personnel. this can involve primary, secondary, and control systems. Some case histories are presented, one of which has parameters that cause it to be particularly revealing of the basic problems involved.