Understanding How Poe Works - Cisco WS-C2948G-GE-TX Configuration Manual

Chapter 28 Power Management

Understanding How PoE Works

The Catalyst 4006 switch and the Catalyst 4500 series switches can sense if a powered device is
connected to an PoE module. The Catalyst 4006 switch and the Catalyst 4500 series switches can supply
PoE to the powered device if there is no power on the circuit. The powered device can also be connected
to an AC power source and supply its own power to the voice circuit. If there is power on the circuit, the
switch does not supply it.
Note A powered device is any device that is connected to the switch that requires external power or can utilize
PoE. An access point or IP phone is an example of this device type.
Table 28-3
Table 28-3 Switch Components Supporting PoE
Switch Chassis
Catalyst 4006
Catalyst 4503
Catalyst 4506
You can configure the switch to stop supplying power to the powered device and to disable the detection
mechanism. If your switch has a module that can provide PoE to end stations, you can set each port on
the module to detect and apply PoE automatically if the end station requires power.
Note For information on powering powered devices that are connected to other Catalyst switching modules,
refer to the Catalyst Family Inline-Power Patch Panel Installation Note.
You can power only one device for each port; you must connect the phone directly to the switch port. If
you daisy chain a second phone off the phone that is connected to the switch port, the switch cannot
power the second phone.
The WS-X4148-RJ45V switching modules can supply a maximum of 6.3 W per port and is 100 percent
efficient. To determine the power requirements for your configuration, you need to estimate the
following:
•
•
•
•
Catalyst 4500 Series, Catalyst 2948G, Catalyst 2948G-GE-TX, and Catalyst 2980G Switches Software Configuration Guide
78-15908-01
If the bridge priority of the Catalyst 4006 switch has been lowered administratively and you use the
same configuration in the new Catalyst 4500 series switch, then the switch remains the root switch
and the spanning tree topology does not change.
lists the switch components that support PoE.
Modules
WS-X4148-RJ45V
WS-X4148-RJ45V
Power requirements for all powered devices for the entire switch and for each module.
Maximum power that is available per port for each module.
Total available PoE that is available for the switch (see
documentation).
When using variable power supplies, consider the required system power (see
page 28-9).
Understanding How PoE Works
Power Supplies
Catalyst 4000 Series Power Entry Module
(PEM)
1300 W AC
2800 W AC
1400 W DC
Table 28-1 on page 28-4 and the PEM
Table 28-2 on
—
Release 8.2GLX
28-11