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


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.

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.

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.

Updated in September 2017

  Mode A Mode B
ER52000 V  
ER58000 V  
ER59000 V  
EX74000   V
EX75000   V
EX76000   V
EX78000 V V
EX78602 V Port 5, 6 V Port 1~6
EX78162   V
EX78900 V V
EX34000   V
EX45900 V  
EX42300 V  
EX38000   V
EX45000   V
EX46900A V  
EX46100   V
EX48000   V
EX48000A   V
EX49000   V
EX49000A   V
EX17008 V  
EX17016 V  
EX17082 V  
X17908 V (Port 2,4,6,8) V (Port 1,3,5,7)
EX17044A V  
EX17008A V  
EX17016A V  
EX17082A V  
EX17162A V  
EX17908A V (Port 2,4,6,8) V (Port 1,3,5,7)
EX24402   V
EX26182 V  
EX26262 V