nvent 910 Series Installation, Operating And Maintenance Instructions page 40

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5.5.12 LOW RESISTANCE ALARM
Purpose: Alarms heater resistance levels that have decreased from the NOMINAL
RESISTANCE setting by more than the selected amount.
Alarm Mask: ENABLE or DISABLE
Range: 1% to 100% (deviation from NOMINAL RESISTANCE)
Procedure: Adjust the LOW RESISTANCE ALARM deviation to the desired value. Note that the
LOW RESISTANCE ALARM must be enabled in order to adjust the LOW RESISTANCE deviation.
IMPORTANT:
• This feature would not normally be enabled. It can be used effectively to guard against
accidental paralleling of heating circuits. Care must be taken when using this alarm feature
with heating cables that exhibit a variable resistance with temperature. Low resistance
alarming may not be practical when the load has an increasing resistance with temperature
(such as self-regulating cables).
• Use of the LOW RESISTANCE ALARM assumes that the controller power is derived from
the same circuit as the tracing power (either by direct connection or through a step-down
transformer).
• No LOW RESISTANCE ALARMS will be generated if the measured voltage is below the LOW
VOLTAGE ALARM setpoint, regardless if the LOW VOLTAGE ALARM is enabled. This stops
an alarm from being generated when the circuit power is turned off. If the LOW VOLTAGE
ALARM is disabled, ensure that the LOW VOLTAGE setpoint is set to a relevant level
otherwise no LOW RESISTANCE ALARMS will occur.
• LOW RESISTANCE ALARMS will only be generated if the output switch is on.
5.5.13 LOW RESISTANCE ALARM FILTER TIME SETTING
Purpose: The LOW RESISTANCE ALARM FILTER will prevent LOW RESISTANCE ALARMS
from being indicated until a low resistance condition has existed for the duration of the LOW
RESISTANCE ALARM FILTER time.
Range: 0 to 12 seconds
Procedure: Adjust the LOW RESISTANCE ALARM FILTER time to the desired value. Note that
the LOW RESISTANCE ALARM must be enabled in order to adjust the LOW RESISTANCE
ALARM FILTER time.
IMPORTANT:
• If an alarm condition appears and then disappears before the alarm filter time has expired,
the filter timer is reset and the alarm condition must exist again for the entire alarm filter
time before the corresponding alarm will be indicated.
• If the user resets an alarm while the alarm condition is still exists, then the alarm will not be
indicated again until the entire alarm filter time has expired.
5.5.14 HIGH RESISTANCE ALARM
Purpose: Alarms heater resistance levels that have increased from the NOMINAL RESISTANCE
setting by more than the selected amount. The HIGH RESISTANCE ALARM may be used to
indicate an open or a high resistance connection or, when using constant wattage parallel
cables, may indicate the failure of one or more heating zones. It may also be used to monitor
a failed series-type cable or connection in three-phase applications while minimizing nuisance
alarms created by voltage fluctuations.
Alarm Mask: ENABLE or DISABLE
Range: 1% to 250% (deviation from NOMINAL RESISTANCE)
Procedure: Adjust the HIGH RESISTANCE ALARM level to the desired value. Note that the
HIGH RESISTANCE ALARM must be enabled in order to adjust the HIGH RESISTANCE deviation.
IMPORTANT:
• Using the LOW CURRENT ALARM feature to ensure that unexpected decreases in current
consumption by the heating cable are alarmed is a reliable method of monitoring the integrity
of series-type heating cables. When using parallel-type heaters (zoned constant wattage or
self-regulating) or in three-phase installations, the LOW CURRENT ALARM setting must be
chosen as close to the lowest expected current as possible to detect failed zones, or cable
degradation,