ABSTRACT:

Earth is the term for ground in many parts of the world, while terre is earth in French and abbreviated to "T" to indicate an effectively grounded system for IEC system descriptions."T" as the first letter of a system abbreviation indicates a ground at the source, while "T"as the second letter represents a separate ground at the load. "N" for the second letter represents the presence of a neutral conductor and the ability to support line-to-neutral loads. Added clarification of systems with neutrals includes "S" for separate, meaning a separate ground and neutral conductor as typical for installations guided by the NEC. "C" indicates the ground and neutral are combined as is often found in North American utility circuits. Isolated medium-voltage systems, whether ungrounded or high resistance, require cable with a 173% insulation rating.