Power Solution for Bus Bar Differential Protection Use the SEL-487B Bus Protection and Breaker Failure Relay to protect bus systems with up to 18 terminals (54 CTs) and 6 protection zones. Differential and directional current elements provide increased security and fast fault detection. The SEL-487B provides accurate, timely monitoring and metering of busbar, feeder, and substation signals. Terminal currents, breaker and disconnect positions, station dc voltage levels, and three-phase voltage are continuously monitored and updated. Simplify interconnect wiring using multiple communications protocols and ports. Use different ratio CTs and nondedicated CTs with the SEL-487B. Use CT ratios that differ by up to a factor of 10:1. Use the same CT for differential protection, metering, backup relaying, and other functions.