Common Alarms-What To Look For - nvent 910 Series Installation, Operating And Maintenance Instructions

8.3 COMMON ALARMS—WHAT TO LOOK FOR
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Follow the proper Electrical Code requirements for your particular installation.
• Terminal connections that are not tight can add resistance to an RTD circuit. Check the
tightness of all screw terminal connections at time of installation and during subsequent
maintenance checks.
• 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 controller reads and what the RTD actually measures. This again is
normally not a problem since the controller compensates for all but the worst cases of this.
• 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 as a failure mechanism.
8.2.2 GROUND FAULT
Ground fault alarms can be due to incorrect installation as well as leakage resulting from wet
system components or faulted cables.
The 910 Series Controller detects ground faults by summing the outgoing and return trace
currents through an internal 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 neutrals return to the controller and are not connected directly to
the distribution panel. This can be a common problem if the installation is a retrofit situation.
• On paralleled circuits, be certain that ALL neutrals return. The late addition of a circuit may
not be obvious.
Use the monitoring feature available at the 910 Operator Console or the Model 780/GCC-9000
Group Communications Controller to view the measured ground fault current at the heat
trace controller. If this value is at the maximum that the controller can measure, it is usually
an indication that the wiring is incorrect. If the value is less than 250 mAmps then an actual
ground fault condition may exist in the cable.
IMPORTANT: The controller monitors the integrity of the ground fault (GF) detection transformer
and associated wiring. If a fault is detected, the controller will report a GF value of 300 mAmps.
The 910 has a wide range of alarming features that may be selectively enabled or disabled to
allow the monitoring and indication of trouble conditions. Described below are the different
alarm conditions available on the 910, their meanings, and possible causes.
8.3.1 High TS 1/ TS 2 Temperature
This alarm appears when the temperature exceeds the HIGH TS ALARM temperature setting.
Cause of Alarm:
• Alarm temperature setting too close to maintain temperature
• Flow of hot product
• Steaming out lines
• Incorrect tracer wiring
8.3.2 LOW TS 1/TS 2 TEMPERATURE
This alarm appears when the temperature decreases below the LOW TS ALARM
temperature setting.
Cause of Alarm:
• Alarm temperature setting too close to maintain temperature
• Flow of cold product
• Empty pipe
• Damaged, wet, or missing insulation