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User Manual – Gigabit PoE Supply NPS-30W | BDA 579 V2 2020/06
Appendix
7.2.2 PoE Standards
These standards are part of IEEE 802.3 general standards.
802.3 af – defines PoE classes 0-3.
802.3 at – uses the same classes, but introduces class 4 as well.
802.3 bt – uses the same classes as 802.3 af and 802.3 at, but introduces class 5 to 8 as well.
7.2.3 Classes and discovery process
Discovery is a process of PSE, determining the power requirements of the PD. Once PD and PSE are connected, PSE
sends out a short voltage impulse, reads the returned value and provides power accordingly. This is valid for PSE with
class (also called active).
No class (passive) PSE, acts as a classic power supply, hence no discovery is implemented, and PSE supplies deliver cur-
rent at all times.
Class
Standard
Power required by PoE class at the
Powered Device (PD)
1
IEEE 802.3af
0.44 – 3.84 W
2
3.84 – 6.49 W
3
6.49 – 12.95 W
4
IEEE 802.3at
12.95 – 25.5 W
5
IEEE 802.3bt
25.5 – 40 W
6
40 – 51 W
7
51 – 62 W
8
62 – 73 W