In grid-redundant mode, all four power supplies must be available in the system and power should be supplied from two different power sources. Power supplies must be configured in pairs. Power supplies 1 and 2 form one pair, and power supplies 3 and 4 form the second pair. Ideally, separate physical power cabling from two independent utility grids is recommended to feed each pair of power supplies. In case one source power fails, the remaining power supplies on the other circuit continue to provide power to the system.