1 Reply Latest reply: May 1, 2012 8:32 AM by CCNP:Security RSS

    PoE Switch Bootup Wattage Use


      From what I understand, when you plug in a PoE device, the possible wattage that port could output has to be available and then the proper amound of power can be negotiated.


      For example, if a phone that needs 6 watts is plugged into 802.1af port, the port will initially need 15 available watts.  If there aren't 15 watts available, the device won't get powered on.


      I have a couple questions on that.


      1. 802.1at allows up to 30 watts per port.  Does 802.1at also require 30 watts to be available to power on any device?
      2. What happens when a switch gets reloaded?  Does it power on one port at a time?  Seems like if it didn't the switch might not power up any devices if the startup wattage for all of them at the same time was more than the switch had available?