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9
Test Procedures
Raychem-IM-H57548-HWATsystem-EN 16/08
9.2
Fault Location Tests
There are three methods used for finding a fault
within a section of heating cable:
1. Ratio method
2. Conductance method
3. Capacitan
ce method
1. Ratio method
The ratio method uses resistance measurements
taken at each end of the heating cable to approxi-
mate the location of a
bus wire short.
A shorted
heating cable could result in a tripped circuit break-
er. If the resistance can be read on a standard ohm
meter this method can also be used to find a fault
from a bus wire to the ground braid. This type of
short would trip a GFPD and show a failed reading.
Measure the bus-to-bus heating cable resistance at
each end (measurement A and measurement B) of
the suspected section.
A
B
A
B
A
B
Braid
Figure 21: Cable resistance measurement 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.
To locate a low resistance ground fault, measure
between bus and braid.
