Setting the Instantaneous Overcurrent Protection (I or ANSI 50)
Settings Guideline
Rules for Isd also apply to the Ii threshold.
|
Application |
Principle |
Usual value |
|---|---|---|
|
Secondary side of MV/LV transformer (switchboard main incomer) |
Selectivity with downstream circuit breakers |
Ii mode: OFF if other MasterPacT MTZ circuit breaker downstream (MicroLogic Active 5.0 and 6.0 only) Ii = 15 x In if ComPacT NSXm, ComPacT NSX, or PowerPacT P- and R-frame circuit breaker only downstream |
|
Feeder with selectivity with other MasterPacT MTZ, ComPacT NS or PowerPacT P- and R-frame circuit breaker downstream |
Same rule as for Isd |
Ii mode: OFF (MicroLogic Active 5.0 and 6.0 only) |
|
Feeder without selectivity with other MasterPacT MTZ, ComPacT NS or PowerPacT P- and R-frame circuit breaker downstream |
– |
Ii mode: ON Ii = 10-15 x In |
|
Primary side of LV/LV transformer |
– |
Ii mode: OFF (MicroLogic Active 5.0 and 6.0 only) |
|
Generators |
– |
Ii mode: OFF (MicroLogic Active 5.0 and 6.0 only) |
|
Power electronic (for example, uninterruptible power supplies, variable speed drives, photovoltaic inverters) |
Lower than minimum short-circuit or ground-fault at the end of the protected circuit. Lower setting possible as no selectivity or transient current is expected. |
Ii mode: ON Ii = 2 x In (MicroLogic Active 5.0 and 6.0) Ii = 1.5 x In (MicroLogic Active 2.0) |
|
Motor |
Lower than minimum short-circuit or ground-fault at the end of the cable. Lower setting possible above starting current. |
Ii mode: ON Ii ≥ 13 x Full load current of motor |
