ABSTRACT
The causes of spikes or electromagnetic pulses on a power line or conductor are lightning, large inductive equipment shutting off, and magnetic pulses created by nuclear activity. Lightning and nuclear activity create common-mode pulses between power lines or between conductors and ground, whereas the equipment-type disturbances create a differential-mode type of pulse between the lines. Power supply filter capacitors pumping current to ground should be eliminated. To eliminate the common mode, the electromagnetic interference filter employs common-mode inductors and feed-through capacitors to ground. The common-mode inductor has one value assigned to it. The inductance value is written above the Z for Zorro, say 10 mH, which is a typical value. Some filter manufacturers have designed common-mode inductors that also function partially as differential-mode inductors. In some cases, engineers think that common-mode inductors require a balanced sine wave for the common-mode source to work properly.
