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Schneider Electric Egypt×
In general hysteresis means - "a range" or "band width".
As for as our RM4 relay is concerned, It can be considered as the threshold for the reset function of RM4 series relay.
For example, in over voltage relay, if the over voltage threshold setting is 250 V and the hysteresis setting is 10% means - the relay will trip at 250V(with in the time delay) and it will reset at 250 - 25V(10%) = 225V.
The hysteresis is necessary for the relay to avoid continuous trip and reset.
If there is no hysteresis setting, the relay may trip at 250V and reset at 249V and again trip at 250V and reset at 249V, it means a small fluctuation in voltage will create nuisance trappings.