A method of determining impedance comprising: supplying power to a powered device from a power sourcing equipment at a first current limited level, I.sub.lim1; measuring, at a plurality of times a voltage associated with the output of the power sourcing equipment; determining a minimum voltage, V.sub.min1, of the measured plurality of voltages; determining an associated time of the determined V.sub.min1; removing the supplied power from the powered device; subsequent to the removing, supplying power to the powered device from the power sourcing equipment at a second current limited level, I.sub.lim2, the I.sub.lim2 being different than the I.sub.lim1; measuring, at the determined associated time in relation to the beginning of the supplying power at the I.sub.lim2, a voltage associated with the output of the power sourcing equipment, V.sub.min2; and determining an impedance responsive to the V.sub.min1, V.sub.min2, I.sub.lim1 and I.sub.lim2.