Interlogix NS3702-24P-4S User Manual - Manual (Page 381)

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specification allows two options for using these cables for power, shown in Figure 1 and Figure 2:
The spare pairs are used. Figure 1 shows the pair on pins 4 and 5 connected together and forming the positive supply, and the pair
on pins 7 and 8 connected and forming the negative supply. (In fact, a late change to the spec allows either polarity to be used).
Figure 8-1: Power Supplied over the Spare Pins
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 8-2: Power Supplied over the Data Pins