A device (D) for detecting a fault in an electrical network , the electrical network comprising at least one electrical equipment (E) electrically connected to a first power conductor (C1) and to a second power conductor (C2), the network also being provided with a common conductor (Cc), the device (D) being intended to be connected to the power conductors (C1, C2) and to the common conductor (Cc) at the level of a measurement area and comprising: - a first member (O1) for measuring a first quantity representative of a common mode voltage (V res ) in the electrical network or in the equipment (E) and comprising a sensor formed by two resistive elements (R1, R2) intended to be arranged in a bridge between the two power conductors (C1, C2) and having identical resistance values to each other, the two resistive elements (R1, R2) being connected at a mid-point (T3), the sensor also comprising a measuring dipole (SH) connected on the one hand to the midpoint (T3) and on the other hand to a connection terminal intended to be connected to the common conductor (Cc), the voltage developing between the midpoint (T3) and the connection terminal being representative of the common mode voltage; - a second measuring member (O2) for producing a second quantity (I net ) representative of a network current flowing in the power conductors (C1, C2); - a calculator, connected to the first and second measuring members, the calculator being configured to determine, over a determined observation period, a quantity representative of a so-called "mixed" energy (E mix ) defined as the integral over the determined observation period of the product of the common mode voltage and the network current and conveyed in the measurement area, the quantity representative of the mixed energy (E mix ) being determined from the first quantity (V res ) and the second quantity (I net ). - a first member (O1) for measuring a first quantity representative of a common mode voltage (V res ) in the electrical network or in the equipment (E) and comprising a sensor formed by two resistive elements (R1, R2) intended to be arranged in a bridge between the two power conductors (C1, C2) and having identical resistance values to each other, the two resistive elements (R1, R2) being connected at a mid-point (T3), the sensor also comprising a measuring dipole (SH) connected on the one hand to the midpoint (T3) and on the other hand to a connection terminal intended to be connected to the common conductor (Cc), the voltage developing between the midpoint (T3) and the connection terminal being representative of the common mode voltage; - a second measuring member (O2) for producing a second quantity (I net ) representative of a network current flowing in the power conductors (C1, C2); - a calculator, connected to the first and second measuring members, the calculator being configured to determine, over a determined observation period, a quantity representative of a so-called "mixed" energy (E mix ) defined as the integral over the determined observation period of the product of the common mode voltage and the network current and conveyed in the measurement area, the quantity representative of the mixed energy (E mix ) being determined from the first quantity (V res ) and the second quantity (I net ). <EOS>