reduces investment and maintenance costs. PoE can be used with all network components that
require little power (max. 12.95 W).
Which Ethernet connectors of a device are capable of PoE can be found in the operating
instructions of the relevant device.
Cable used for the power supply
● Variant 1 (redundant wires)
In Fast Ethernet, the wire pairs 1, 2 and 3, 6 are used to transfer data. Pairs 4, 5 and 7, 8 are
then used to supply power. If there are only four wires available, the voltage is modulated
onto the wires 1, 2 and 3, 6 (see variant 2). This alternative is suitable for a data transmission
rate of 10/100 Mbps. This type of power supply is not suitable for 1 Gbps since with gigabit
all 8 wires are used for data transfer.
● Variant 2 (phantom power)
With phantom power, the power is supplied over the pairs that are used for data transfer, in
other words, the power is modulated onto the data cable. With Gigabit, all eight wires of the
Ethernet cable are used for data transmission and power supply according to IEEE 802.3at.
With 10/100 Mbps, four wires of the Ethernet cable are used for data transmission and
power supply according to IEEE 802.3af.
With PoE, there are power generators (Power Source Equipment, PSE) and power consumers
(Power Devices, PD).
Whether a device (power consumer) supports variant 1 and variant 2 or only variant 2 can be
found in the operating instructions of the relevant device.
A power generator (PSE) can supply the power consumer (PD) either over:
● Variant 1 or
● Variant 2 or
● Variant 1 and variant 2.
Endspan
With endspan, the power is supplied via a switch that can reach a device over an Ethernet
cable. The switch must be capable of PoE, for example a SCALANCE X108PoE, SCALANCE
X308-2M POE, SCALANCE XR552‑12M.
Midspan
Midspan is used when the switch is not PoE-compliant. The power is supplied by an additional
device between the switch and end device. In this case, only data rates of 10/100 Mbps can be
achieved because the power is supplied on redundant wires.
Description
2.9 Power over Ethernet (PoE)
SCALANCE W1780/W1740 according to IEEE 802.11ac Web Based Management
26 Configuration Manual, 11/2019, C79000-G8976-C485-03
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