Count on the high interupting rating of our most widely-used Class L fuse. When it comes to protecting service entrance equipment, feeder circuits, and circuit breakers, A4BY fuses have been the industrys favorite. The A4BY is a 100 percent rated device and may be applied at continuous currents up to its ampere rating. A 4-second minimum time delay at 500 percent rating allows the A4BY to pass normal current surges and to coordinate with ground fault relays. Use for mains, feeders, circuit breakers, loadcenters, panelboards, switchboards and metering centers.