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Setting Alarms
Notice: It is the customer's responsibility to decide whether to set alarms or not and to
decide what thresholds to set alarms at, as this will depend on the customer's operational
priorities and risk philosophy. However, here are some guidelines that may prove helpful in
deciding what threshold values to use:
Alarm summary
This table summarises all the alarms that can be set in terms of contact wear monitoring.
Threshold values
Arcing time
In the absence of any other value, a maximum arcing time of one complete power cycle
should be set (20ms for 50Hz in Europe/Asia, 17ms for 60Hz in NAM). This gives two
chances for the arc to be extinguished when the current crosses the zero point.
Contact wear
Contact electrical wear thresholds T1 and T2 should be entered in accordance with the
arcing contact manufacturer's recommendations and based on the operational planning
lead-time required to purchase new ones and go replace them:
- T1 - approaching contact wear limit - for example 120 KA
- T2 - contacts need to be replaced - for example 150 KA
When installing on an already operational CB, we may need to enter during setup an
estimate of the cumulative electrical wear to date. This is very tricky to do and should be
avoided if possible as an incorrect guess may lead to an incorrect assumption as to the
status of the contacts:
However, if the number of operations already performed is small and the history of
interrupted fault currents is known from the relays and fault recorders, you can rebuild the
history and calculate the starting contact wear value.
If not monitored
If this function is not being monitored and no sensors are present, then the threshold values
should be set very large so as to avoid any erroneous alarm:
MA-037 - CB Watch 3 Operating Manual
Figure 105 – Contact wear alarm summary
v7.0 - May 2020
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