Stray voltage

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".

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, the presidents of most major utilities from throughout the United States and Canada continued to use stray voltage for all occurrences of unwanted excess electricity.

In New York City, a woman, Jodie S. Lane, was electrocuted in January 2004 by a five-foot by eight-foot metal road utility vault plate that was energized by an "improperly insulated wire.

Ungrounded metal objects close to electric field sources such as neon signs or conductors carrying alternating currents may have measurable voltage levels caused by capacitive coupling.

[7] However, in overhead transmission work on or near high-voltage lines, safety rules require connecting a conductor to earth ground during maintenance.

Classical electromagnetic induction can occur when long conductors form an open grounded loop under and parallel to transmission or distribution lines.

Failing insulation is essentially a high impedance fault which will allow current to flow through any available path to ground, a condition which can cause shocks or fires if left unmitigated.

This leakage can occur when there is damage caused by physical, thermal, or chemical stresses to insulation on power lines, especially but not limited to underground or underwater cables.

Electrical leakage can occur also from moisture, salt, dust, and dirt buildup on open air insulators in overhead power distribution.

Today, stray voltage on farms is regulated by state governments and controlled by the design of equipotential planes in areas where livestock eat, drink or give milk.

The stray currents from railways create or accelerate the electrolytic corrosion of metallic structures located in the proximity of the transit system.

Metal pipes, cables and earthing grids laid in the ground near tracks may have a much shorter usable and safety functional life.

Where this bonding is not provided or has failed, a severe hazard of electric shock or electrocution is presented when circuit conductors contact the case.

Potential differences between pool water and railings, or shower facilities and grounded drain pipes are common as a result of neutral to earth voltages (NEV).

A contact voltage condition can arise spontaneously from mechanical, thermal, or chemical stress on insulation materials, or from unintentional damage from digging activity, freeze-frost seizing, corrosion and collapse of conduit, or even workmanship issues.

WEPCO had measured on the farm currents because of stray voltage <1 mA, the "level of concern" set by the Public Service Commission of Wisconsin, but the court ruled on procedural grounds that the utility could be found negligent under common law even though they met the state standard.

The jury found that Xcel subsidiary – Northern States Power Company – was "negligent with respect to the delivery of electrical service."

Consolidated Edison in New York City has had frequent incidents of stray voltage,[21][22] including the electrocution death of Jodie S. Lane in 2004, while walking her dog in Manhattan.

[24] As a result, the City of Boston government started a program to detect, report on, and repair stray voltage hazards.

[25] Toronto Hydro pulled all employees off regular duty on the weekend of January 30, 2009 to deal with ongoing stray voltage problems in the city.

[28] In March 2013, Californian Simona Wilson won a $4 million lawsuit against her power company after stray voltage from an electrical substation near her house repeatedly shocked her and members of her family whenever they were in the shower.

[citation needed] Stray voltage is generally discovered during routine electrical work, or as a result of a customer complaint or shock incident.

Some incipient electrical faults may also be discovered during routine work or inspection programs which are not specifically focused on stray voltage.

High-impedance digital or analog voltmeters may measure elevated voltages from non-energized objects from the coupling and in effect provide a misleading reading.

By contrast, if an object being tested is in contact with a current source, or coupled by a very large capacitance (possible but unlikely in this context), the voltage will drop only slightly as dictated by Ohm's law.