In　the　field　of　arc　fault　detection,　it　is　universally　acknowledged　that　it　is　very　hard　to　judge　whether　there　is　an　arc　fault　through　signals　of　the　main　line　when　a　masking　load　(such　as　air　compressors,　lamps　with　dimmers,　and　so　on)　is　in　parallel　with　a　resistive　load,　which　always　tends　to　be　a　fire　hazard.　Meanwhile,　it　is　annoying　that　the　normal　currents　of　some　appliances　are　very　similar　to　the　arcing　ones.　In　this　paper,　we　have　found　the　principles　of　a　novel　detection　method　called　high-frequency　coupling,　putting　the　neutral　line　(N)　and　the　live　line　(L)　through　the　current　transformer　(CT),　which　results　in　asymmetrical　distribution　of　magnetic　flux　in　the　core　and　the　only　high-frequency　components　left　in　the　secondary　output　of　the　CT.　So　it　is　possible　for　series　arc　fault　detectors　to　be　free　from　the　masking　loads　and　distinguish　between　the　arcing　and　the　nonarcing　clearly.　Thanks　to　this　convenient　method,　an　arc　fault　detector　based　on　the　microcontroller　unit　(MCU)　has　been　proposed　to　detect　arc　faults　effectively　by　means　of　simple　multi-indicators.　The　experimental　results　show　the　accuracy　of　arc　fault　recognition,　in　all　the　masking　tests,　can　reach　a　high　level　and　the　detector　can　detect　an　arc　fault　within　a　short　time.