The FCC Rules-Part 15, Subpart J, sets regulations in the US to minimize the interference potential of devices using RF energy incidentally as an intermediate step an end function other than communication. Examples of these devices are digital equipment and switching power supplies. Devices or systems covered by this definition into two classes.
Class A (Consumer)-computing devices for use in commercial, industrial or business areas.
Class b (Consumer)-computing devices for use in residential areas.
The FCC conducted emission limits for these two classes starts at 450Hz as shown in Fig.A