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
• Dual-voltage nine-lead motor internal connections (compare the delta vs wye diagrams on the right side of EL-0134). • In a wye connection, three winding ends join at a common point; in a delta connection, the windings form a closed triangle with no single common junction of three leads. • What an ohmmeter continuity check really shows when three leads are tied together versus when they are only connected through separate windings.
• On each of the two motor diagrams (delta and wye) on EL-0134, which specific three lead numbers are physically joined together at a single junction point inside the motor? • If you removed all external jumpers and line leads, which group of three leads would still remain connected together in the wye motor, and would any such group exist in the delta motor? • When you place the ohmmeter between any pair of those three leads, what reading would you expect if they all meet at a common point, compared with leads that are only connected via separate windings around the triangle?
• Be sure you can point to the common junction point (star point) in the wye diagram and read the exact lead numbers attached there. • Confirm from the delta diagram whether any three leads share a single common junction, or whether all junctions are only between two leads at a time. • Before choosing, match each answer choice to what the ohmmeter would see: direct common tie of three leads (wye) vs no three-way common tie (delta).
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