Watthour-meter measuring circuit including a detection of an incorrect line connection

Analog signals from a mains-voltage sensor (1), a phase-conductor current sensor (2), and a neutral-conductor current sensor (3) are conducted each to a separate input of a basic multiplexer (4), an output signal of which is conducted to an input of an analog-to-digital converter (5). A demultiplexed digital signal from the output of the analog-to-digital converter (5) is conducted to an input of a digital signal processing circuit (6) provided for the calculation of the power delivereed to a load. Both current sensors (2, 3) are advantageously made as Rogowski coils. The use of Rogowski coils or of one inductive current sensor together with a shunt in connection with a digital signal processing instead of expensive measuring current transformers is advantageous. The disclosed multiplexing brings the costs of the measuring system embodiment with two simultaneous current measurements closer to the costs for a usual measuring system with a single current measurement.