Wattstopper B277E-P Power Pack 277V 20 Amps Self-contained transformer relay system Available for 120, 220 to 240, 277 and 347 volt systems Capable of switching up to 20 Amps of electrical load (ballast) 1/2 inch snap-in nipple attaches to standard electrical enclosures via 1/2 inch knockouts 1.6" x 2.75" x 1.6"