Preventing Electrocutions by Undetected Feedback Electrical Energy Present in Power Lines
The potential for electrocution because of feedback electrical energy should not be underestimated. NIOSH investigations indicate that workers may not be aware of the extreme danger of electrocution and electrical injuries associated with feedback energy. These cases demonstrate that the problem of feedback electrical energy in electrical transmission and distribution systems is always present and that diligent efforts should be applied to safeguard against it. "Fuzzing" a line is a standard practice to test for the presence of high voltage in power lines. "Fuzzing" is accomplished by bringing a metallic object, such as a pair of lineman's pliers, close to a power line while watching for an arc and listening for a buzzing sound. This method does not reliably detect low voltages and should not be used as the only test for electrical energy in power lines. Once fuzzing has determined that high voltage is not present, low voltage testing equipment, such as a glowing neon light or a light-emitting diode, should be used to determine whether low voltage is present.
RECOMMENDATIONS
The following NIOSH recommendations should substantially reduce the number of electrocutions caused by undetected feedback electrical energy in power lines. Particular emphasis should be placed on the first two recommendations.
Universal Precautions
- Extreme caution must be exercised by persons working on or in the vicinity of unverified deenergized power lines. All persons performing this work should treat all power lines as "hot" unless they positively know these lines are properly deenergized and grounded.
- Persons should also be instructed that "fuzzing," although an accepted practice to check for high voltage in power lines, is not a reliable test method. As reported in Case No. 1, lower voltage levels can be deadly, and may not be detected by the practice of "fuzzing." "Fuzzing" must be done only after power lines have been deenergized and properly grounded. Because of the possibility of a feedback circuit, the person performing the work should personally ground all lines on both sides of the work area unless he/she is wearing the proper protective equipment.
Training Programs
- Training programs for linemen should emphasize proper procedures for working with electrical transmission and distribution systems and their associated dangers.
- Training programs for linemen should include basic electrical theory that addresses electrical distribution systems and the identification, evaluation, and control of the dangers associated with these systems. Because the danger of feedback energy is always present, an improved method of deenergizing these systems should be stressed.
Protective Equipment and Work Practices
- Power lines should not be repaired or otherwise accessed without adequate Personal safety equipment unless the worker personally verifies that the line is deenergized and properly grounded.
- Workers must be specifically instructed to wear proper protective equipment, such as gloves and sleeves, required for the task to be performed.
- Linemen must be instructed to treat all power lines as energized unless they personally deenergize them by establishing a visible open point between the load and supply sides of the line to be repaired, by opening a fused disconnect, by opening a fused switch, or by removing a tap jumper if the load permits.
- Workers must verify that the power lines have been deenergized.
- Workers must provide proper grounding for the lines. Unless a power line is effectively grounded on both sides of a work area, it must be considered energized even though the line has been deenergized. Lines must be grounded to the system neutral. Grounds must be attached to the system neutral first and removed from the system neutral last. If work is being performed on a multiphase system, grounds must be placed on all lines. Lines should be grounded in sight of the working area and work should be performed between the grounds whenever possible. If work is to be performed out of sight of the point where the line has been deenergized, an additional ground should be placed on all lines on the source side of the work area.
Detection of Low Voltage
- Persons working on or in the vicinity of power lines should be provided with appropriate safety and protective equipment and trained in procedures that address all magnitudes of voltages to which they may be exposed.
- Procedures should be established to perform a dual voltage check on the grounded load and supply sides of the open circuit. Once the "fuzzing" method has determined that high voltage is not present, low voltage testing equipment, such as a glowing neon light or a light-emitting diode, should be used to determine if lower voltage is present.
Preventing Electrocutions by Undetected Feedback Electrical Energy Present in Power Lines
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