Power Supply 2 Alarm

[Anonymous user]

We have a APC MasterSwith AP7900 that shows a status of "Power Supply 2 Alarm" within the web interface.  Do these units actually have 2 power supplies?  Does anyone know the severity of this error and what needs to be done to resolve it?  It just seems like an odd error since there is only 1 power cable from the unit and it does not seem to have multiple power supplies.

[BillP · Accepted solution]

Hello,

This refers to one of the two internal DC power supplies. Switched Rack PDUs contain a primary and a secondary power supply. (Metered Rack PDUs only contain one since as long as they have input power, the outlets will come on.) These power supplies power the switched relays (and also the Network Management Card). If one fails or faults, then you're OK and should work on getting a replacement. If both fail, then the outlet relays will no longer be predictable and controlled. They will likely stay up and in their current state until the PDU loses input power completely and then subsequently, the PDU won't be able to re-energize them on the next boot and then any attached equipment won't turn on.

Long story short, the Rack PDU should be replaced when you have a power supply fault on either #1 or #2.