EMR-5000
IM02602012E
Protective Elements
IOC Function
Elements:
IOC Function
Functional Description
The instantaneous overcurrent function (IOC) or 50P[x] is intended to protect in the event of a high-current fault. The
example IOC setting used in the Motor Protection Curve (see the Motor Protection Curve Examples in the Ultimate Trip
Current Section) is 12 times (1,200%) of FLA. In general, the instantaneous IOC should be at least 1.5 times LRC, well
above the locked rotor current normally seen at the moment of a start.
IOC should trip fast and therefore no run or pickup delay is provided. A start delay is set at a minimum of two cycles
(0.03 sec.), or more if needed to block IOC tripping on magnetizing inrush when the motor is first energized. An
additional IOC time delay setting is set at a default of zero seconds.
IOC Trip
L
evel
The IOC sets the instantaneous overcurrent trip limit in percentage of the FLA above at which the relay trips. This trip
type can be set to Inactive to deactivate this protective device element. For currents clearly above the setting, the IOC
function picks up in two power cycles or less.
The IOC setting must be below (1,130 * PCT/ FLA) or 1,600%, whichever
is less.
IOC Start Delay (IOCSD)
This setting sets the number of power cycles after a start is recognized until the IOC trip and alarm functions are
enabled. Use this delay to inhibit IOC tripping on a current peak caused by magnetic inrush when the motor is first
energized (usually two to three cycles).
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