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56
7
Test Procedures
Raychem-IM-H58067-IceStopRoofGutterDeIcingCOM-EN 18/01
7.4
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. Capacitance method
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 insulation
resistance 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 27: 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%
To locate a low resistance ground fault, measure
between bus and braid.