Question 310Electricity & Electronics - Assistant Engineer

70% to pass

Suppose it is desired to connect a dual voltage three phase squirrel-cage induction motor for low volts, but it is undetermined whether the nine-lead motor is internally configured for wye or delta configuration. Using an ohmmeter, the motor itself with leads disconnected, and the illustration as a guide, what statement is true? Illustration EL-0134

Diagram for USCG Electrical Assistant: Suppose it is desired to connect a dual voltage three phase squirrel-cage...
AIf leads "4", "5", and "6" have continuity across each other, the motor is "wye" configured. Without continuity, the motor must be "delta" connected.
BIf leads "4", "5", and "6" have continuity across each other, the motor is "delta" configured. Without continuity, the motor must be "wye" connected.
CIf leads "7", "8", and "9" have continuity across each other, the motor is "wye" configured. Without continuity, the motor is "delta" configured.
DIf leads "7", "8", and "9" have continuity across each other, the motor is "delta" configured. Without continuity, the motor is "wye" connected.
AI Explanation

The correct answer is C. If leads "7", "8", and "9" have continuity across each other, the motor is "wye" configured. Without continuity, the motor is "delta" configured. This is because in a wye-connected three-phase motor, the three windings are connected in a wye configuration, and the neutral point (center of the wye) is connected to leads "7", "8", and "9". Therefore, if these leads show continuity, it indicates a wye configuration. Conversely, in a delta-connected motor, the windings are connected in a closed loop, and there is no neutral point, so the leads "7", "8", and "9" would not show continuity. The other options are incorrect because they involve checking the wrong set of leads to determine the configuration.

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Official Resources
46 CFR Electrical Engineering 46 CFR Machinery & Electrical USCG National Maritime Center
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