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Chapter 8: Power Over Ethernet Overview
GE-DS-82 and 82-PoE Ethernet Managed Switch User Manual 213
The data pairs are used. Since Ethernet pairs are transformer coupled at each end, it
is possible to apply DC power to the center tap of the isolation 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.
Figure 100: Power Supplied over the Data Pins
When to install PoE?
Consider the following scenarios:
• • You're planning to install the latest VoIP Phone system to minimize cabling
building costs when your company moves into new offices next month.
• • 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.
• • Management asks for IP Surveillance Cameras and business access systems
throughout the facility, but they would rather avoid another electrician's payment.
References:
IEEE Std 802.3af-2003 (Amendment to IEEE Std 802.3-2002, including IEEE Std
802.3ae-2002), 2003 Page(s):0_1-121
White Paper on Power over Ethernet (IEEE802.3af)