Damage may occur when call logging computers and PABX’s are connected via some distance. Damage may occur due to inductive loops and ground potential differences.

This occurs due to the dataline forming part of the inductive loop, which is formed by the line on the one side and the power cable on the other side.

The greater the change of current, the higher the voltage.

This can be overcome by installing an optical isolation device. As the loop is broken, no equalization currents can flow, so no damage occurs.