Recently　published　papers　have　proved　the　effectiveness　of　electromagnetic　time　reversal　(EMTR)　in　locating　the　position　of　faults　such　as　phase-to-ground　shunt　connections　in　power　grids.　EMTR　directly　transposes　the　idea　of　focusing　energy　back　to　its　source　introduced　in　original　time-reversal　(TR)　methods.　The　current　interpretation　of　EMTR,　based　on　metrics　measuring　energy　or　peak-amplitude　of　focusing,　is　shown　to　suffer　from　ambiguities　that　increase　the　risk　of　inaccurate　fault　location.　After　pointing　out　under　what　conditions　TR　focusing　occurs,　an　original　frequency-domain　reformulation　of　EMTR　is　introduced,　showing　that　EMTR　should　more　accurately　be　interpreted　as　a　correlation　estimator.　New　metrics　based　on　this　observation　are　introduced,　taking　into　account　the　inhomogeneous　transmission　of　electrical　energy　throughout　complex　networks,　enabling　a　direct　quantitative　evaluation　of　the　likelihood　of　locating　a　fault.　Extensive　numerical　simulations　confirm　that　the　proposed　formulation　systematically　improves　the　reliability　of　EMTR　location　estimates　when　faults　occur　in　power　grids　of　realistic　complexity,　highlighting　the　accrued　risk　that　comes　with　the　use　of　metrics　that　measure　the　scale　of　TR　focusing　rather　than　its　quality.