All Isolated Power Systems employ a special device known as a Line Isolation Monitor, or LIM. This device constantly measures the line-to-ground impedance of both isolated line conductors. Since hazard current is inversely proportional to ground impedance, the LIM calculates and displays the Total Hazard Current (THC) of the system. If the THC exceeds 5mA, an audible and visual alarm is initiated to warn that a first fault has occurred on the system. This signifies that an un-safe fault current could begin to flow through the system if a secondary fault occurred, providing a path for this current. Activation of the LIM alarm does NOT indicate that dangerous fault currents have occurred, only that one layer of protection has been compromised and the potential for this now exists.