Abstract: A filter system for removing selected frequencies from AC power provided on at least two phase lines and a neutral line includes a phase-to-phase filter for removing a first selected AC component at a first frequency from the AC power wherein the frequency component has a line-to-phase displacement within first or second ranges. A phase-to-neutral filter is also provided for removing a second selected AC component at a second frequency different from the first frequency from the AC power wherein the second frequency component has a line-to-line phase displacement outside of the first and second ranges.

Abstract: An electrical supply has a transient suppressor in which a transistor switch connects a resistor across the supply to dissipate an overvoltage condition. The control for the transistor switch turns the switch on at a first overvoltage condition and turns the switch off when the voltage drops to a level less than that of the first overvoltage level.