http://hyperphysics.phy-astr.gsu.edu/hbase/electric/gfi.html http://hyperphysics.phy-astr.gsu.edu/hbase/electric/gfi.html http://hyperphysics.phy-astr.gsu.edu/hbase/electric/gfi.html GFI http://hyperphysics.phy-astr.gsu.edu/hbase/electric/gfi.html Ground Fault Interrupter http://hyperphysics.phy-astr.gsu.edu/hbase/electric/gfi.html GFI