32
9
Test Procedures
Raychem-IM-H57548-HWATsystem-EN 16/08
A
B
A
B
A
B
Braid
Figure 22: Low resistance ground-fault test
The approximate location of the fault, expressed as a
percentage of the heating cable length from the front
end is:
Fault location: D = A
x 100
(A + B)
Example:
A = 1.2 ohms
B = 1.8 ohms
Fault location: D = 1.2 / (1.2 + 1.8) x 100
= 40%
The fault is located 40% into the circuit as mea-
sured from the front end
2. Conductance method
The conductance method uses the core resistance
of the heating cable to approximate the location of a
fault when the heating cable has been severed and
the bus wires have not been shorted together. A sev-
ered cable may result in a cold section of pipe and
may not trip the circuit breaker.
Measure the bus-to-bus heating cable resistance at
each end (measurement A and measurement B) of
the suspect section. Since self-regulating cables are
a parallel resistance, the ratio calculations must be
made using the conductance of the cable.
A
B
A
B
A
B
Braid
Figure 23: Cable resistance measurement
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