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Can someone please clarify something about below statement.

"For motors that are prone to locked rotor, instantaneous overcurrent relays, adjusted to pickup at 200 to 300% of rated motor current, are used. Their contacts are connected in series with the inverse time overcurrent relay contacts to automatically trip the motor breaker. High-reset instantaneous relays should be used to make sure they will reset when the current returns to normal after the inrush of starting current has subsided"

My understanding is that in addition to inverse time overcurrent relay there is also instantaneous overcurrent relay connected to it in series, and this relay will be energized if motor current reaches > 200% of rated design, thus tripping the breaker.

However, what is "high-reset"? How can motor keep running even after breaker is tripped? There shouldn't be any current if breaker trips.

Thank you for clarification.

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    \$\begingroup\$ Can you post a link to those products? I had never heard about High-reset instantaneous relays and instantaneous overcurrent relays, only motor circuit breaker which is set to 1:1 to the nominal motor current. \$\endgroup\$ Mar 13, 2021 at 10:01

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The quoted statement does not seem to completely describe the use of the "high-reset instantaneous current relays." The objective seems to be to shut down the motor in the event of a sudden severe overload "locked rotor" while running. However the same level of current must be allowed during starting. That would require an instantaneous over-current trip that would automatically reset as soon as the current returns to normal. It would also require the trip to be ignored during starting and shut the motor down only after the initial start. There are probably some standard ways to accomplish that.

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An AC motor may draw 5x to 8x the rated max and reduces as speed builds up so after this period the trip level is reset rapidly so if the motor is overloaded and continues to draw >2x rated current, it will break and at 3x rated current even faster. This is carefully timed for the expected rating and inertia of the system and power rating to prevent heat rise damage.

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