In the DC power configuration, the router contains either two or four DC power supplies, located at the lower rear of the chassis in slots PEM0 through PEM3 (left to right). You can upgrade your DC power system from two to four power supplies. The DC power supplies in slots PEM0 and PEM2 provide power to the lower fan tray, DPC slots 6 through 11, and SCB slots 1 and 2. The DC power supplies in slots PEM1 and PEM3 provide power to the upper fan tray, DPC slots 0 through 5, and SCB slot 0. Four power supplies provide full redundancy. If a DC power supply fails, its redundant power supply takes over without interruption. For existing power supplies, each DC power supply has a single DC input (–48 VDC and return). For high-capacity power supplies, each DC power supply has two DC inputs (–48 VDC and return).