The utility model provides an earth fault looks snap judgments module and arc extinction harmonic elimination device, earth fault looks snap judgments module includes: phase place fault judgment unitis connected and detects whether there is phase place earth fault among the power distribution network with power distribution network, the unit is judged to the trouble phase place, is connected theelectrical apparatus parameter judgement trouble phase place place phase line that detects according to phase place fault judgment unit with phase place fault judgment unit, wherein, the electrical apparatus parameter that phase place fault judgment unit detected includes neutral point voltage, each looks voltage variation parameter to and each looks ground point resistance parameter. Have the looks of selection time weak point, make things convenient for troubleshooting's advantage.