EEI SOPD Practice Test 3

Taking Equipment Out of Service for Maintenance

¹Transmission lines, transformers and breakers need regular inspection and repair, and much of this work cannot be done safely while the equipment is energized. Before a crew can begin, the equipment is switched out of service. Breakers are opened to stop the flow of current, and disconnect switches are then opened to create a visible gap between the equipment and the rest of the system.

²Opening the switches is not enough by itself. Someone could close a switch by mistake, not knowing that a crew is working beyond it. To prevent this, each opened device is tagged. A hold tag is a card attached to the switch handle or control that names the crew and states that the device must not be operated. The tag stays in place until the crew that requested it reports that its work is complete and its people are clear.

³Before touching the equipment, the crew tests it to confirm that no voltage is present and then installs grounds. Grounds give any unexpected current, such as current induced by a nearby energized line, a safe path to earth instead of a path through a worker.

⁴Maintenance outages are planned weeks ahead whenever possible. Planners choose times when demand is low, often in spring and fall, so that the rest of the system can carry the load while the equipment is out. Removing a line on a hot afternoon could overload the lines that remain in service.