As shown in the illustrated electronic overload relay, if the full load amp setting accurately represents the motor full load current of 4.5 amps and the definite time (D-time) setting is 25 sec. as shown, what statement is true assuming that the locked rotor current is 6 times the full load current. See illustration EL-0183.
• Definite time (D-time) setting on an electronic overload relay and what it controls • Relationship between full load amps (FLA) and locked rotor current (given as a multiple of FLA) • What current level an overload relay is intended to respond to vs. normal running current
• First, calculate the actual locked rotor current from the given motor FLA and the multiplier; then compare that value to each choice. • Ask yourself: Does an overload relay trip at exactly the motor full load current, or at some higher current above that value? Which options assume normal running current is something to trip on? • Look at the meaning of the D-time knob in the illustration: does it change the trip current or the trip time once the current exceeds the setpoint?
• Be sure you’ve correctly computed locked rotor current = (multiple) × (full load current) before judging the options. • Confirm in your mind that D-time controls time delay, not current magnitude; the current magnitude is set by the LOAD(A) or FLA setting. • Eliminate any answer that implies the relay should trip at normal full load current instead of an overload or locked-rotor condition.
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