We have designed a large room with 40 light fixtures, each with a step dimming ballast. Two 277V circuits feed this area from a 480/277V, 3 phase, 4 wire panel. Say the circuits are LP-1 and LP-2 (both on phase A). For our purposes, each ballast has 3 wires: a neutral, and 2 hots. (Feeding either hot lights the fixture's lamps at 50% brightness; feeding both hots lights the lamps at 100% brightness.) Each circuit (LP-1 & LP-2) has 2 wires, of course, a hot & a neutral. However, note that while the ballast has 2 hot leads, it only has 1 neutral lead. Neutrals for the 2 circuits were originally sized based on load, and are #10 from the panel to a local J-box. From the J-box to each fixture, #12's were run. The neutral lead in the ballast itself is #16. The neutral home runs were originally sized correctly for the load of the fixtures on that circuit. The electrician has asked: what neutrals does he connect? Currently he's connecting 1 neutral per fixture: the neutral for circuit LP-1. The neutral for LP-2 (again, same phase, same panel) isn't connected or run. Will this suffice? Or must he run the neutral for LP-2 also, in essence creating a parallel neutral feed from the panel, and connect both neutrals to the ballast's neutral lead? Please educate me. What's the right way to wire the neutrals here? Thanks for your time helping on this - you guys make the world safer and smarter.