Project Overview

Background

Complaints related to contact voltage for pedestrians and animals have long been an area of concern and subjective interpretation for utilities, regulators, and the public. Sources range from induction of voltage onto metallic infrastructure--such as conduits, water pipes, and gas pipes--to unanticipated current paths created by grounding configurations and connection impedances. Although steady-state 60-Hz stray voltage and elevated NEV issues have been a long standing concern, the increasing use of nonlinear (or harmonics-generating) electronic equipment--such as variable-speed drives, personal computers, and residential appliances--is continually adding to these elevated voltage potentials. Additionally, momentary or transient neutral-to-earth voltage and its impact have become a more recent topic of study. In light of these developments, there is a need to establish a collaborative effort to standardize proper measurement protocols, to better understand the coupling issues related to stray voltages, and to evaluate cost-effective solutions. In particular, these efforts must encompass all aspects of stray and elevated voltages to include 60-Hz, proliferation of harmonic loads, and issues related to transient voltage loads.

The concerns associated with voltage potentials at publicly and privately accessible locations are numerous and include:

  • Personnel safety related to touch potentials.
  • Animal contact areas related to health and productivity impacts.
  • Shock hazards at residential water and gas pipes.
  • Harmonic frequency currents caused by nonlinear loads.
  • Resonance conditions on power circuits creating magnified neutral-to-earth voltage potentials.
  • Impacts of power-line carrier communication technologies and other transient switching devices on the magnitude of stray voltages.
  • Voltage potentials on rail, gas, and water line installations near power line right of ways.
  • Different opinions on specifications for measurement equipment, measurement protocols, and measurement durations.

Although research has been conducted in nearly all of these areas, there tends to be a lack of consistency in terms of understanding how significant the impacts are and whether or not a specific measured value is at or below a specified "level of concern." EPRI's research provides electric utilities and regulatory organizations with an opportunity to better understand the range of issues surrounding the subject of measurable voltage levels at human and animal contact locations and provides unbiased and credible research geared toward developing acceptable methods to evaluate and address concerns over contact voltages.

Project Summary

Each year since 2004, EPRI research in this area has considered the most important concerns associated with elevated neutral-to-earth and metallic-object-to-earth voltages at human and at animal contact points by promoting consistent and repeatable assessment methodologies, sponsoring workshops, and creating a repository of case studies and general information. These and other project efforts are geared toward expediting problem identification and resolution.

The project results are distilled on this Web site to promote the widespread dissemination of research results where that information benefits affected parties. The areas where this Web site provides that information include:

  • Measurement equipment and protocols
  • Mitigation techniques and devices
  • Modeling and simulation approaches
  • Impacts on humans and animals
  • Approaches for understanding limits and levels of concern
  • Links to relevant industry information
  • Select case studies

Project Return on Investment

Since the mid-1980s, EPRI has been assessing nuisance shocking related to contact voltages, beginning with elevated voltage potentials on gas pipelines, publications on shocking occurring at swimming pools, and comparisons of animal sensitivities to stray voltage. EPRI has sponsored testing on dairy cows, field investigations, laboratory testing, and power-system modeling to better understand the impacts of parametric variations on stray voltage levels. EPRI is extremely appreciative of the electric utilities that sponsor this research and of the organizations that have conducted credible human and animal physiological research in contribution to the industry's understanding of the subject matter.