nvent 910 Series Installation, Operating And Maintenance Instructions page 43

5.5.20 CIRCUIT BREAKER LIMITING STATUS (SSR ONLY)
Purpose: The circuit breaker limiting feature is always enabled when using an SSR output
switch and is intended to prevent the circuit breaker immediately upstream of the controller
from tripping during a temporary overcurrent condition. Enabling this alarm will only inform the
user that circuit breaker limiting is currently active.
Alarm Mask: ENABLE or DISABLE
Procedure: Adjust the CIRCUIT BREAKER CURRENT RATING setting to the heating circuit
breaker size (i.e. 15.0 or 20.0 Amps). Enable or disable the alarm as required. Note that
the CIRCUIT BREAKER LIMITING ALARM does not have to be enabled in order to adjust the
CIRCUIT BREAKER CURRENT RATING setting.
IMPORTANT:
• This is a non-latching alarm.
• This alarm may be considered an advisory alarm. If the measured current exceeds the level
that would cause the upstream circuit breaker to release, the HTC will begin to switch the SSR
ON and OFF rapidly to limit the average current to an acceptable level.
5-5-21 POWER LIMITING STATUS (SSR ONLY)
Purpose: The power limiting feature is always enabled when using an SSR output switch and is
intended to limit the average amount of power that is applied to the trace circuit. The controller
measures the voltage and current of the tracing circuit and will vary its output switch to limit
the amount of power applied to the trace to the value set by the MAXIMUM POWER setting.
Enabling this alarm will only inform the user that power limiting is currently active.
Alarm Mask: ENABLE or DISABLE
Procedure: Adjust the MAXIMUM POWER setting to the desired value. Enable or disable the
alarm as required. Note that the POWER LIMITING ALARM does not have to be enabled in
order to adjust the MAXIMUM POWER setting.
IMPORTANT:
• This is a non-latching alarm.
• This alarm may be considered more appropriately an advisory alarm and is normally
disabled. It will be active if the MAXIMUM POWER setting is set below the power output level
required for temperature maintenance. In other words, if the circuit demands the maximum
power allowed and the alarm is enabled, then this alarm will be indicated and the output
switch will pulse ON and OFF to limit the average power output to a value approximately
equal to the MAXIMUM POWER setting.
5.5.22 SWITCH LIMITING STATUS (SSR ONLY)
Purpose: The switch limiting feature is always enabled when using an SSR output switch and
is intended to provide protection for the output switch. Enabling this alarm will only inform
the user that switch limiting is currently active and an excessively high current condition is
present. The controller pulses its output switch for a small number of cycles and reads the
resulting current. If the measured current exceeds the SWITCH RATING setting, then the duty-
cycle of its output switch will be varied so that an average current not exceed- ing the SWITCH
RATING setting is maintained.
Alarm Mask: ENABLE or DISABLE
Procedure: Adjust the SWITCH CURRENT RATING setting to the actual current rating of the
SSR. Enable or disable the alarm as required. Note that the SWITCH LIMITING ALARM does not
have to be enabled in order to adjust the SWITCH CURRENT RATING setting.
IMPORTANT:
• This is a non-latching alarm.
• This alarm should normally be enabled. Currents in this range cannot be considered normal
and should be investigated.
5.5.23 CONTACTOR COUNT ALARM
Purpose: Generates an alarm if the number of off-to-on transitions of a contactor reaches or
exceeds the CONTACTOR COUNT ALARM setting. This serves as a method to perform pre-
ventative maintenance on the contactor before a failure is likely to occur.
Alarm Mask: ENABLE or DISABLE
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