3Com Switch 7750 Configuration Guide Guide

660 CHAPTER 60: POE CONFIGURATION
■ The Switch 7750 supplies power through the Ethernet electrical ports on the
service boards. Each service board can supply power to up to 48 remote
devices at the maximum distance of 100 m (328 feet).
■ Each Ethernet port can supply at most a power of 15.4 W to remote PDs.
■ When the Switch 7750 Family supplies power to remote devices, the maximum
total power that it can provide is 2,400 W. The switch determines whether or
not to supply power to the next remote PD it discovers depending on the total
power it currently supplies.
■ When the PoE-enabled Switch 7750 supplies power to remote PDs, the PDs
need not have any external power supply.
■ If a remote PD has an external power supply, the PoE-enabled Switch 7750 and
the external power supply will be redundant with each other for the PD.
External PSE2500-A1
Power System
If PSE2500-A1 power system is taken as the external power supply, the power is
distributed as follows:
1 Input voltage: 100 VAC to 140 VAC
■ One power supply unit (PSU) of the PSE2500-A1 power system can supply
1,250 W of power, and two PSUs can supply up to 2,400 W of power.
■ If the PSUs of PSE2500-A1 power system need to work in redundancy mode,
three PSUs are required and they work together to supply 2,400 W of power.
2 Input voltage: 200 VAC to 240 VAC
■ One PSU of the PSE2500-A1 power system can supply 2,500 W of power.
■ If the PSUs of PSE2500-A1 power system need to work in redundancy mode,
two PSUs are required.
PoE-enabled Boards The following boards of Switch 7750 Family supports PoE:
■ 3C16860
Setting PoE
Management Mode
Switch 7750 Family manages PoE in either auto mode or manual mode. Through
the setting of the management and PoE priority, the switch determines whether to
supply power to newly added PDs when the power supply is almost fully-loaded.
■ auto mode: When the switch is reaching its full load in supplying power, it will
first supply power to the PDs that are connected to the ports with critical
priority, and then supply power to the PDs that are connected to the ports with
high priority. For example: port A is of critical priority. When the switch is
reaching its full load and a new PD is now added to port A, the switch will
power down the PD connected to a port with lower priority and turn to supply
power to this new PD.
■ manual mode: When the switch is reaching its full load in supplying power, it
will neither take the priority into account nor make change to its original
power supply state. For example: Port A has the priority critical. When the
switch is reaching its full load and a new PD is now added to port A, the switch
will not supply power to this new PD.
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In auto mode, when the switch is reaching its full load in supplying power, the
switch decides whether to supply power to remote PDs on a port based on the