An electrical coupler includes: a sending transformer having a winding for receiving data signals and two windings connected in series with a common point and two terminals to be connected to a first wires pair of a bus to deliver the data signals at the first winding terminals to said wire pair; a receiving transformer having two windings connected in series with a common point and two terminals to be connected to a second pair of wires of said bus to receive data signals on the pair of wires and a winding for delivering said data signals; and a galvanic isolation transformer with a first winding, the terminals of which are connected to the coupler's power supply pins, and second and third windings connected in series with a common point connected to a mechanical ground and the respective free terminals connected to the common terminals of sending and receiving transformers.