Some opto-splitters just provide electrical isolation between the input and the outputs, but the best types have a separate transformer-isolated
power supply or DC-to-DC converter for the input and each of the outputs. This provides isolation between each and every data link entering the
unit. A quick way to tell if a
unit has this type of isolation: With the
unit unplugged from
power and data links, run a dc
continuity check with a
VOM between pin 1 on each of the data links. If it's an open
circuit to all other pin 1's, the link has full isolation.