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This presentation will cover the foundations of key electrical safety practices for transmission line maintenance for de-energized lines. Different standards and codes will be discussed at length in conjunction with a variety of topics including engineering justifications (modeling, analysis and results) of the standards and the safety codes.
Electric utilities place high priorities on providing their workers with a safe worksite environment for power line construction and maintenance. In addition, regulatory agencies such as Occupational Safety and Health Administrations and the Institute of Electrical and Electronics Engineers, National Electrical Safety Code provide fundamental rules and guidelines to create a safe working environment for workers regarding electrical safety practices.
The personal protective grounding (PPG) practices is used to prevent injury from electric shock and arc hazards and to meet the standards set by the Occupational Safety and Health Administration (OSHA) for workmen maintaining these lines under de-energized condition.
OSHA has three requirements when a transmission line is taken out of service for maintenance and personal protective grounds are applied (Section 1910.269 of CFR):
- “Temporary protective grounds shall be placed at such locations and arranged in such a manner as to prevent each employee from being exposed to hazardous differences in electrical potential.”
- “Protective grounding equipment shall be capable of conducting the maximum fault current that could flow at the point of grounding for the time necessary to clear the fault. This equipment shall have an ampacity greater than or equal to that of No. 2 AWG copper.”
- “Protective grounds shall have an impedance low enough to cause immediate operation of protective devices in case of accidental energizing of the lines or equipment.”
The first step in placing a line for a safe maintenance procedure consists of connecting the de-energized line to the earth (ground), either through the rebar of the concrete foundation of a steel pole, or by connecting the line directly to a ground rod bed near the tower. The purpose of this earth connection is often misunderstood. Even for very low resistance values to ground the connection to earth does not insure the safety of a lineman in contact with the line if it is accidentally energized.
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