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8.4 High and Low Impedance Faults.
Before beginning a fault search it is a good idea to know the severity of the fault. This is
measured in terms of it is resistance or impedance to ground. Faults where the ground is
wet and/or a very large piece of the insulation is missing are found at the low end of the
range (<500 ohms). Conditions where the ground is very dry and/or the actual fault is a
small pinhole where the conductor has a very small ground contact area are found at the
high end of the fault range (>1-3 megohms).
A low impedance fault is the easiest to find since there is more signal to detect.
Generally, the more bars and a higher number displayed at synchronization, the larger the
fault.
A high impedance fault is more difficult to locate. Characteristically, the Receiver may
not detect the signal after moving a short distance away from the ground point. The
higher the impedance of the fault, the closer you must be to detect it.
For Example.
If the A-Frame only reliably points away from the ground connection within 10 feet, then
the A-frame will only detect the fault within about 10 feet. Outside this distance the
signal is too weak to reliably detect.
For this reason we highly recommend tracing and marking the line before searching out
high impedance faults.
8.5 Multiple Faults
Locating multiple faults is the most difficult and confusing fault situation. It is especially
important in this case to accurately trace the faulty conductor before beginning the fault
search. Stay exactly above the line if possible and verify each suspected fault by
monitoring the active number to see which fault has the higher number. Remember that a
very strong or low impedance fault will mask the detection of a weak or high impedance
fault. The safest and best way to find multiple faults is to repair, each fault as it is
positively identified and then continue the search. See
Figure 5-3
.
