HP ProCurve 640 Redundant/external Power Supply Shelf J9805A 24-Ports Switch
Three modular power supply slots: Supports redundant power for up to eight HP 2920 Switches: protects against internal switch power supply failures. Supports external power allowing up to three HP 2920 48 Port PoE+ Switches to support 1440W of PoE+ power : allows all 48 ports of a PoE+ switch to offer 30W of PoE+ power at the same time.
External redundant power supply: provides high reliability
Easy configuration: provides full management features, available through connected HP 2920 Switches
Three power supply module slots: allows failure of a power supply in one bay to not affect the other two power supplies