Electric Power Generation, Transmission, and Distribution eTool
Grounds protect workers if lines and equipment that were correctly deenergized in accordance with 1910.269(m) become energized, which can occur from a variety of sources. Ground connections may be used to create equipotential conditions (see Equipotential Zone) and provide protection by eliminating potentially hazardous voltage differences in several ways. If the normal feed is inadvertently closed, grounds cause a short circuit and an overcurrent device (for example, breaker) to trip, deenergizing the system. Grounds can also discharge induced voltage from any nearby energized lines, including those energized by a lightning strike. In addition, grounds can discharge the voltage from any unexpected backfeed from a generator, and they may cause the generator's overcurrent device to trip.
Grounding Impedance Protective grounding systems must use proper equipment and be designed, installed, and arranged to reduce any stray voltage to a safelevel. If reenergizing occurs, the grounding impedance (resistance) must be low enough to ensure the prompt operation of protective devices (for example, fuses and breakers). To ensure protective grounds will protect workers, grounding methods must employ good engineering controls such as those contained in IEEE 1048: Guide for Protective Grounding of Power Lines.
Installing grounds must be done in the proper sequence using a live-line tool. To install a ground, the point to be grounded on the equipment must first be tested to be sure it is not energized. The ground end (away from the equipment to be grounded) must be connected first; the line end (at the line or equipment to be grounded) must then be connected using a live-line tool (for example, hotsticks, switchsticks, shotgun sticks) (see 1910.269(m)(3) and (n)(5) and (6)). The ground end goes on first.
To remove a ground, the line end must first be removed with a live-line tool. The ground end may then be removed. (See 1910.269(n)(7).) The ground end is removed last.
The installation and removal procedure should be reviewed in the job briefing before work is started.
Testing Grounded Equipment
If the grounded equipment needs to be tested and the test requires the temporary removal of the grounds, then workers must use live-work techniques (insulating tools, rubber gloves, etc.) or remain out of the area from before the grounds are removed until the grounds are reinstalled (see 1910.269(n)(9)).
Situations When Grounding on T&D Lines is Not Required
For work on T&D lines and equipment to proceed as deenergized, all switching and tagging requirements in 1910.269(m) must be met, and grounds must be installed as needed. However, in very limited situations, grounds are not required. (See 1910.269(n)(2).)