Magnetic fields only pose a concern when nearby. In many cases a combination of these two means exist. For example, dimmer lighting circuits run in a building containing chopped sine waves may radiate energy which is picked up through the air by a guitar pick-up or cable. EMI can travel as electric or magnetic fields or a combination of both. Electric fields create voltages in the circuits they strike.
Magnetic fields create current in the circuits they strike.
In order for the current to flow there must be a loop for this circulating current. The magnetic field may strike the loop in only one place, such as a ground conductor or one conductor of a balanced line. 60 Hz, will be a greater EMI threat. What Its Effects Are While it is possible for EMI to enter a piece of equipment through the air and be picked up by the circuits within the equipment, this is rare. It more commonly enters the equipment via the AC power cord or the interconnecting signal or control wire connected to it.