PoE max power loss

This is how you would calculate the max power loss on a 100m Cat6 Cable:

Typical DC power resistance loss in CAT6

Typical Cat6 UTP has a 7ohm/100m conductor resistance, resulting in a 7ohm/100m loop resistance. This is 1/3 the (worst case) loop resistance the 802.3af standard will accept.

Voltage Drop in typical data cable

 2* (0.175)*7 =2.5V

@Power dissipated (Pd) in typical data cable

Pd per wire is (0.175A)2 * 7 ohms = 0.214 W per wire

Power dissipated on 2 wires on 2 pairs is:

4 * 0.214 = 0.858 W maximum typical power dissipated per data cable

Note that the 802.3af standard tolerates a 2.45W cable loss, but typical Cat6 UTP cable will result

in only 0.858 W DC power loss over 100m.