Abstract: A data communication system for an industrial plant includes a plurality of communication stations which are interconnected by a coaxial cable that is required to pass through one or more hazardous areas. The communication stations are energized from a source of alternating voltage of commercial frequency and are arranged to transmit over and to receive from said cable communicating signals that have frequencies which are substantially higher and that have an energy level which is substantially lower than that of the frequency and energy level, respectively, of the power source. Each of said stations is coupled to the cable by an individually associated intrinsic safety barrier each of which includes an iron core transformer. Each transformer includes a primary winding connected in circuit with the associated station and an inductively coupled secondary winding that is connected between the sheath and the internal conductor of the cable.