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• Check the specifications for the particular cable being used to ensure that it does not have
excessive capacitance when used in long lengths. This can cause a temperature offset
between what the control module reads and what the RTD actually measures. This again is
normally not a problem since the control module compensates for all but the worst cases
ofthis.
• Lastly, it is possible for the RTD itself to fail on an intermittent basis but this failure mode
should be considered unusual. This kind of failure is probably the most difficult to find but
fortunately it is also the least likely failure mechanism.
6.2.2 GROUND FAULT
Ground fault alarms can be due to incorrect installation as well as current leakage resulting
from wet system components or faulted cables.
WARNING:
Fire Hazard
A ground-fault alarm may mean the heating cable has been damaged or improperly installed
and must not be ignored. Sustained electrical arcing or fire can result. To minimize the risk
of fire if the alarm has tripped, shut off the power to the heating cable and repair the system
immediately.
The control module detects ground faults by summing the outgoing and return trace currents
through a current transformer. Under normal operating conditions (no ground fault condition)
this current will be zero. When there is a flow of current from one of the trace supply wires to
ground, a ground fault condition occurs.
If a ground fault alarm is present on start-up of a new installation it is likely due to a wiring
error or damaged cable. To verify this condition:
• Check that the heating circuit neutral conductor returns to the control module’s current
transformer and is not connected directly to the distribution panel.
• On paralleled heating circuits, be certain that all neutrals return. The late addition of a
heating circuit may not be obvious.
The monitoring feature of an external programming device may be used to view the measured
ground fault current. If this value is at the maximum that the control module can measure, it is
usually an indication that the wiring is incorrect. If the value is less than 100 mA then an actual
ground fault condition may exist in the cable or associated wiring.
IMPORTANT: The control module monitors the integrity of the ground fault (GF) detection
transformer and associated wiring. If a fault is detected, the control module will report a
GF value of 300 mA.
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