Stray voltage

Stray voltage is the occurrence of electrical potential between two objects that ideally should not have any voltage difference between them. Small voltages often exist between two grounded objects in separate locations, due to normal current flow in the power system. Large voltages can appear on the enclosures of electrical equipment due to a fault in the electrical power system, such as a failure of insulation.

Stray voltage is any case of undesirable elevated electrical potential, but more precise terminology gives an indication of the source of the voltage. Neutral to earth voltage (NEV) specifically refers to a difference in potential between a locally grounded object and the grounded return conductor, or neutral, of an electrical system. The neutral is theoretically at 0 V potential, as any grounded object, but current flows on the neutral back to the source, somewhat elevating the neutral voltage. NEV is the product of current flowing on the neutral and the finite, non-zero impedance of the neutral conductor between a given point and its source, often a distant substation. NEV differs from accidentally energized objects because it is an unavoidable result of normal system operation, not an accident or a fault in materials or design.

In 2005, the Institute of Electrical and Electronics Engineers (IEEE) convened Working Group 1695 in an attempt to lay down definitions and guidelines for mitigating the various phenomena referred to as stray voltage. The working group attempted to distinguish between the terms stray voltage and contact voltage as follows:

In spite of the above definitions, the term stray voltage continues to be used by both utility workers and the general public for all occurrences of unwanted excess electricity. For example, at the annual "Jodie S. Lane Stray Voltage Detection, Mitigation & Prevention Conference", held at the Con Edison headquarters in New York City in April 2009, which attracted the presidents of most major utilities from throughout the United States and Canada, the utility leaders continued to use stray voltage for all occurrences of unwanted excess electricity. The term contact voltage was used only once, possibly because "contact voltage" is generally the fault of the supply, network or installation company. Few companies are willing to openly discuss faults of theirs, let alone ones as life-threatening. It would seem that stray voltage is now the common term for all unwanted voltage leakage as it categorises the fault as part of normal operation, therein limiting liability.

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