57
7
Test Procedures
Raychem-IM-H58067-IceStopRoofGutterDeIcingCOM-EN 18/01
A
B
A
B
A
B
Braid
Figure 28: 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 measured
from the front end.
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 (measure-
ment A and measurement B) of the suspect section.
Since self-regulating cables are a parallel resis-
tance, the ratio calculations must be made using the
conductance of the cable.
A
B
A
B
A
B
Braid
Figure 29: Cable resistance measurement