AC Mains

Circuit Protection of AC Mains

Design Notes:

Protection Application:
Products that are directly connected to the AC mains (120 to 250VACrms) will be exposed to much more severe surge transients (lightning, load switching, etc.) and short circuit/overload conditions than on DC inputs. Because of this, the protection devices need to be more robust.
Solution Description:
As shown at the left (top), a cartridge or leaded fuse (Pico, 5x20mm, 2AG, 3AG, TE5/TR5) can be used for short circuit and overload current conditions. For surge protection, an MOV should be used. The MOV should be selected based on the expected severity (energy, voltage and peak pulse current) of the transient surge. The specific family (C-III, UltraMOV or LA) can be determined after the surge severity is understood.
Companion Solutions:
Does not apply.
Regulatory Issues:
Standards will vary depending on the product to be protected. Examples include: IEC 61000-4-5 UL1414 UL1449
Unique Features:
Does not apply.
Application Warnings:
When selecting the fuse, be sure to consider the expected temperature in the area around the fuse, as well as the in-rush currents. Failure to take these factors into account may result in premature or nuisance tripping of the fuse.



  • Leaded

  • LA

    Line Voltage Operation Radial Leaded Varistor