36
The data pairs are used. Since Ethernet pairs are transformers coupled at each
end, it is possible to apply DC power to the center tap of the isolated transformer
without upsetting the data transfer. In this mode of operation, the pair on pins 3
and 6 and the pair on pins 1 and 2 can be of either polarity.
POWER SOURCING
EQUIPMENT (PSE)
POWERED DEVICE
(PD)
SPARE PAIR
SPARE PAIR
SIGNAL PAIR
SIGNAL PAIR
DC / DC
RX
TX
TX
RX
48V
4
5
1
2
3
6
7
8
4
5
1
2
3
6
7
8
+
/
-
+
/
-
Converter
Figure 2:
Power Supplied over the Data Pins
When to install PoE
Consider the following scenarios:
z
You’re planning to install the latest VoIP phone system to minimize cabling
building costs when your company moves into a new office next month.
z
The company staff has been clamoring for a wireless access point in the picnic
area behind the building so they can work on their laptops through lunch, but
the cost of electrical power to the outside is not affordable.
z
Management asks for IP Surveillance Cameras and business access systems
throughout the facility, but they would rather avoid another electrician’s
payment.
