Method for detecting an absence of connection of a polyphase electric meter to a neutral of an electrical power supply network, the polyphase electric meter being connected to a plurality of phases of the electrical power supply network, the polyphase electric meter injecting signals into the electrical power supply network by means of powerline communication via one injection phase from among said plurality, an impedance of predefined capacitance (C 1, C 2, C 3) existing between each phase and the neutral, characterized in that the polyphase electric meter carries out the following steps: - obtaining (301; 402) measurements of RMS voltage between each phase and a connection point intended to connect the polyphase electric meter to the neutral; - calculating (302; 403) an index R representative of a ratio between the RMS voltage measured for the injection phase and a sum of RMS voltages measured for the other phases of said plurality; - comparing (303; 404) the index R with first and second thresholds, the first threshold being defined on the basis of the theoretical minimum value of the index R and the second threshold being defined on the basis of the theoretical maximum value of the index R, taking into consideration precision tolerances of said impedance capacitances and precision tolerances of RMS voltages delivered by the electrical power supply network via said phases, when the polyphase electric meter is not connected to the neutral; - comparing (303; 404) the RMS voltage value measured on each phase other than the injection phase with third and fourth thresholds, the third threshold being defined on the basis of the theoretical minimum RMS voltage value and the fourth threshold being defined on the basis of the theoretical maximum RMS voltage value, taking into consideration said precision tolerances, when the polyphase electric meter is not connected to the neutral; and - detecting (304; 405) that the electric meter is not connected to the neutral when the following conditions are met: - the index R is higher than or equal to the first threshold and is lower than or equal to the second threshold; and - the RMS voltage value measured on each phase other than the injection phase is higher than or equal to the third threshold and is smaller than or equal to the fourth threshold. - obtaining (301; 402) measurements of RMS voltage between each phase and a connection point intended to connect the polyphase electric meter to the neutral; - calculating (302; 403) an index R representative of a ratio between the RMS voltage measured for the injection phase and a sum of RMS voltages measured for the other phases of said plurality; - comparing (303; 404) the index R with first and second thresholds, the first threshold being defined on the basis of the theoretical minimum value of the index R and the second threshold being defined on the basis of the theoretical maximum value of the index R, taking into consideration precision tolerances of said impedance capacitances and precision tolerances of RMS voltages delivered by the electrical power supply network via said phases, when the polyphase electric meter is not connected to the neutral; - comparing (303; 404) the RMS voltage value measured on each phase other than the injection phase with third and fourth thresholds, the third threshold being defined on the basis of the theoretical minimum RMS voltage value and the fourth threshold being defined on the basis of the theoretical maximum RMS voltage value, taking into consideration said precision tolerances, when the polyphase electric meter is not connected to the neutral; and - detecting (304; 405) that the electric meter is not connected to the neutral when the following conditions are met: - the index R is higher than or equal to the first threshold and is lower than or equal to the second threshold; and - the RMS voltage value measured on each phase other than the injection phase is higher than or equal to the third threshold and is smaller than or equal to the fourth threshold. - the index R is higher than or equal to the first threshold and is lower than or equal to the second threshold; and - the RMS voltage value measured on each phase other than the injection phase is higher than or equal to the third threshold and is smaller than or equal to the fourth threshold.