Rockwell Automation 1783-BMxxx Stratix 5700 Ethernet Managed Switches User Manual - Manual (Page 89)

Rockwell Automation Publication 1783-UM004E-EN-P - June 2014 89
Switch Software Features Chapter 3
Power Consumption Values
You can configure the initial power allocation and the maximum power
allocation on a port. However, these values are only the configured values that
determine when the switch turns on or turns off power on the PoE port. The
maximum power allocation is not the same as the actual power consumption of
the powered device. When you manually set the maximum power allocation, you
must consider the power loss over the cable from the port to the powered device.
The cutoff power is the sum of the rated power consumption of the powered
device and the worst-case power loss over the cable.
The actual amount of power consumed by a powered device on a PoE port is the
cutoff-power value plus a calibration factor of 500 mW (0.5 W). The actual
cutoff value is approximate and varies from the configured value by a percentage
of the configured value. For example, if the configured cutoff power is 12 W, the
actual cutoff-value is 11.4 W, which is 0.05% less than the configured value.
Because the switch supports external removable power supplies for PoE/PoE+
and can configure the budget per the power supply used, the total amount of
power available for the powered devices varies depending on the power supply
configuration:
• If a power supply is removed and replaced by a new power supply with less
power and the module does not have enough power for the powered
devices, the switch denies power to the PoE ports that are in Auto mode in
descending order of the port numbers. If the switch still does not have
enough power, it denies power to the PoE ports in Static mode in
descending order of the port numbers.
• If the new power supply supports more power than the previous one, and
the switch now has more power available, the switch grants power to the
PoE ports in Static mode in ascending order of the port numbers. If it still
has power available, the switch then grants power to the PoE ports in Auto
mode in ascending order of the port numbers.
IMPORTANT For power to be assigned accurately, the total wattage of the power supply
must be manually configured via the Device Manager Web interface or CIP.