What is the PoE power pins assignment mode A & B?

PoE Solutions

There are two modes of PoE, A and B. Mode A delivers power on the data pairs of 100BASE-TX or 10BASE-T. Mode B delivers power on the spare pairs. PoE can also be used on 1000BASE-T Ethernet, in which case there are no spare pairs and all power is delivered using the phantom technique.

What is PoE Mode A?

In mode A, pins 1 and 2 form one side of the 48 VDC, and pins 3 and 6 form the other side. These are the same two pairs used for data transmission in 10BASE-T and 100BASE-TX, allowing the provision of both power and data over only two pairs in such networks. The free polarity allows PoE to accommodate for crossover cables, patch cables and auto-MDIX.

What is PoE Mode B?

In mode B, pins 4–5 form one side of the DC supply and pins 7–8 provide the return; these are the "spare" pairs in 10BASE-T and 100BASE-TX. Mode B, therefore, requires a 4-pair cable.

The PSE (power sourcing equipment), not the PD (powered device), decides whether power mode A or B shall be used. PDs that implement only Mode A or Mode B are disallowed by the standard.

Can you mix PoE and non-PoE?

Yes. Power over Ethernet does not disturb normal switch transmission of data. Both PoE and non-PoE devices can connect to the same PoE switch.
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Updated in Jan. 2023

	Mode A	Mode B
EX78000	V	V
EX78602	V Port 5, 6	V Port 1~6
EX78900	V	V
EX45900	V
EX42300	V
EX46900A	V