Triple-Play Service Deployment

Chapter 4: Troubleshooting the Copper Plant for IP Services
Resistive fault location
Highly resistive faults can be very difficult to detect and correct
during initial testing and almost always worsen over time due to
corrosion and other causes. Resistive fault location (RFL) provides
a reliable and very accurate means for locating resistive faults
before a cable repair is attempted. RFL is a technique that uses a
series of resistance measurements to accurately calculate the
distance to a fault. The test set uses built-in circuits to measure
resistance on a faulted lead and a known good lead in order to
calculate the distance from the tester to the fault. It also displays
the total end-to-end loop length and distance from the far-end
strap or short back to the fault. RFL is known as “strap-to-fault” for
this reason. As stated above, RFL requires a known good wire or
wires to use as reference. This can be the other wire in the pair or
both wires of a separate pair. For a single pair measurement, the far
end tip and ring must be shorted together, and for a separate pair
measurement, the tip and ring of the good pair must be shorted to
the faulted wire of the bad pair.The accuracy of an RFL depends on
correctly setting the cable gauge and temperature, as this affects
resistance.
Figure 4.10 Single pair RFL analysis showing fault at 1087 feet
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