Power Over Ethernet Interoperability Guide

Earth Ground Loop Issue and Isolating the Oscilloscope

We remember from Chap. 1 that one of the advantages of using data transformers was to physically break up ground loops. In other words, the signal would choose only the paired wires of the cable, because that was the only route available to it, and would then travel down the pair in a strictly differential-mode fashion. On the other hand, there would be no differential-mode noise pickup along the cable since (a) the cable was “twisted” and therefore both wires of each pair would pick up noise equally, and (b) there could be no significant common-mode noise currents either, because though there are natural leakages to Earth ground all along the length of the cable, we have limited that almost ...