31
High Current Readings/Alarms
The following summarizes some of the possible causes and solutions for heat tracing high current readings or alarms.
Possible Cause
Recommended Solutions
Self regulating heater or power limiting
heater current may exceed set value
during normal operation or start-up
operation.
Increase high current alarm set point (if approved by project engineer).
For startup operation current alarm nuisances, it may also be desirable to
increase the delay time (before a current reading is done after turn on) set
in the controller.
Self-regulating or power limiting
heater may be operating at cooler
than design pipe temperatures due to
processing conditions and thus heaters
may be drawing higher current values.
Increase high current alarm set point (if approved by project engineer).
Self-regulating or power limiting
heater may be operating in its cold
start regime.
When reading current on one of these type heaters, it is necessary to read
the current at steady state. One may have to wait as long as 5 minutes
for heater steady state values. After five minutes the current value will
continue to drop as the pipe or equipment begins to warm.
Heater circuit may be longer than
anticipated in the design stage.
Verify installed length (if possible) and if different review design. If length is
different but performance-wise the “as built” design is acceptable, initiate
“as built” drawing change and change controller high current setting.
Wrong heater wattage or heater
resistance may be installed.
Check heater set tags or markings on heater cable against installation
drawings. As an additional check, disconnect heater from power and
measure DC resistance.
Heat tracing may be powered on
wrong voltage.
Recheck heater supply voltage.
Current sensing circuitry may have
encountered a problem.
Use a different current clamp type meter which is known to be accurate
and do a comparative reading. Investigate current measurement circuitry
further. Note that one should only read heater currents when the heater is
100% on.
Field heater wiring is improperly
labeled and/or connected such that
the heater and the circuit number are
not matched.
Trace out the circuit wiring from the field back into the panel and
subsequently to the controller. Wherever possible, turn the circuit “off” and
“on” and watch for an appropriate response. If this is the problem, redo the
wiring.
Short circuit in a series resistance
circuit.
Disconnect heater from power, meg between each of the conductors and
ground for proper dielectric rating. If okay, measure resistance of circuit for
agreement with design values.
