A fault protection circuit for use on a spur of an IEC 61158 Fieldbus network comprising a fast acting current limiter adapted to limit the spur current to the level of a reference current when the spur current reaches said reference current, control means adapted to monitor the spur AC and/or DC current and/or voltage, and isolation means adapted to apply a shunt short circuit isolation to said spur upon receipt of an activation signal from the control means, in which the control means is adapted to control the level of the reference current, and in which when said control means detects one or more pre-determined fault conditions on said spur it activates the isolation means and lowers the level of reference current.