As shown in figure "B" of the illustration, the self-test of the OCR performance is applied with a setting of 6 times the full load current and a trip time of 10 seconds is observed, which agrees with the manufacturers current/time characteristics. According to figure "C" of the illustration, under actual operation, how long would the trip time be if the motor was drawing 3 times the full load amperage due to a mechanical overload? See illustration EL-0172.
• Carefully read the current-time characteristic curves in figure C for different time settings (5 s, 10 s, 20 s). • Understand that the self-test at 6 × FLC with a 10-second setting is just one point on the 10-second curve. • Recognize that at a lower multiple of full-load current (like 3 × FLC), the same 10-second setting will trip more slowly according to the curve.
• On the 10-second curve in figure C, what happens to trip time as you move left from 6 × FLC down to 3 × FLC? • Roughly where does the 3 × FLC vertical line intersect the 10-second setting curve, and what time value does that correspond to on the vertical axis? • How do the times at 3 × FLC compare between the 5 s, 10 s, and 20 s curves—does that help you narrow down the closest answer choice?
• Be sure you are following the 10-second setting curve, not the 5-second or 20-second curve. • Confirm you are reading the horizontal axis as multiples of full-load current (× FLC) and the vertical axis as time (seconds and minutes). • Estimate the time at the intersection point carefully and compare it with the provided options to pick the closest value.
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