Two wire combined power and data network system segment with fault protection device

A segment of a two wire combined power and data network system for automation comprising a trunk, a spur mounted thereon and a fault protection device, in which said fault protection device comprises:

• a current measurement component for monitoring the current of said spur, a computer processor which is provided with a computer program comprising a failure status determination algorithm, and an
• isolation mechanism for fully or partially isolating said spur from said trunk upon receipt of an activation signal from said computer processor;
• in which an output of said current measurement component is fed to said computer processor;
• in which when said computer program is run on said computer processor said computer processor subjects said output to an intermittent fault count over time step and a fault duration step of said algorithm;
• in which said computer processor satisfies said intermittent fault count over time step if it detects a pre-determined number of separate faults over a first pre-determined time period occurring on said output
• in which said computer processor satisfies said fault duration step if it detects a fault which persists for longer than a second pre-determined time period occurring on said output;
• in which said computer processor is arranged to issue said activation signal upon determination of a failure status on said spur when said computer processor satisfies the intermittent fault count over time step and/or the fault duration step of said algorithm;
• and
• in which said computer processor is configured such that it counts an intermittent fault in the intermittent fault count over time step whenever it detects that the current of said spur transitions from any of a no-device attached current range, a normal operating current range or an upper current limit to another of said no-device attached current range, normal operating current range or upper current limit.