Current–Based Protection Functions
There are four current–based protection functions provided by the overload relay :
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Thermal overload protection
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Phase loss protection
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Phase imbalance protection
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Ground–fault protection
Operation
The state of the auxiliary contacts of the overload relay changes, when a protection function triggers a tripping:
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NC 95/96 contact state changes from closed to open.
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NO 97/98 contact state changes from open to closed.
The trip state is latched and is indicated by the trip indicator on the front face of the overload relay . A reset action is required to acknowledge the trip condition and to release the auxiliary contacts.
The auxiliary contacts of the overload relay can be used as follows:
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the NC contact can be used to switch off the contactor and then stop the motor.
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the NO contact can be used to signal remotely the state of the overload relay .