Which sequence correctly describes the grounding procedure for a unit substation?

• A. Remove load, open ACBs, open LBF, ground line side of fuse, ground load side of fuse, ground secondary bus.
• B. Ground line side of fuse, remove load, open LBF, open ACBs, ground secondary bus, ground load side of fuse.
• C. Open ACBs, remove load, ground line side of fuse, open LBF, ground secondary bus, ground load side of fuse.
• D. Remove load, open LBF, open ACBs, ground line side of fuse, ground secondary bus, ground load side of fuse.

Answer: (A)

Working safely on a unit substation requires isolating the equipment from all energized sources before applying any grounding. First remove the load to stop energy from flowing to downstream circuits. Then fully isolate the unit from the source by opening the protective devices in the sequence that guarantees complete de-energization of the feeder—first the circuit breakers, then the load-break switch or fuse arrangement. Once the circuit is confirmed de-energized, apply grounding on the line side of the fuse to bleed any voltage present on that side, then on the load side of the fuse to equalize the downstream side, and finally ground the secondary bus to ensure the entire internal bus is at earth potential. This order minimizes the chance of backfeed or hazardous voltage during work and provides a known zero-energy condition. Other sequences that ground before complete isolation or place grounds on the wrong side can leave energized parts or create unsafe voltage differences.