⚡ Check Your Knowledge: Answer Reveal! ⚡ Answer: C. 30 inches. Why: NEC 110.26(A)(2) says the working space in front of electrical equipment must be the width of the equipment or 30 inches, whichever is greater. The panel here is only 20 inches wide, so the 30-inch minimum wins. The space doesn't have to be centered on the panel, but the equipment doors must be able to open at least 90°. Why not the others: A (20 in.): That's the panel width. It only controls when the equipment is wider than 30 inches. B (24 in.): That's the entrance/egress width for large equipment (1200 A or more, over 6 ft wide). It isn't the working space width. D (36 in.): That's the working space depth for a 120/240V panel, not the width. Bonus answers: Depth: 3 feet (Table 110.26(A)(1), 0-150V to ground). Height: 6.5 feet or the height of the equipment, whichever is greater (110.26(A)(3)). Takeaway: Working space is a box: 30" wide, 3' deep, 6.5' tall at minimum for a typical residential panel. Don't store anything in it, because it needs to stay clear. Great job to everyone who played along!