numbered and connected for the voltage desired. This is accom-plished by connecting internal windings in series or in parallel. Theinternal connections of the motor may be connected wye or delta,but wye is the most used.

A schematic of a three-phase squirrel cage induction motor isshown in Figure 30-9. This is delta-connected. The internal andexternal connections for a dual-voltage, delta-wound motor areillustrated in Figure 30-10.

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ROTOR

DENOTES CONTINUITY ASREAD ON OHMETER

STATOR

Figure 30-9 Delta-connected induction motor.

Figure 30-10 Connections for a dual-voltage delta-connected motor.

322 Chapter 30

Figure 30-11 illustrates the internal windings and external con-nections for a dual-voltage wye-wound motor.

Figure 30-11 Connections for a dual-voltage wye-connected motor.

An easy way to remember how to connect the leads of a dual-voltage motor, connected for wye, is shown in Figure 30-12. Firstdraw the arrangements of wye windings. Then, starting at onepoint, draw a spiral so that it connects in order with all six coils.Begin at the starting point and number from 1 through 9 as youprogress around the spiral. From this it is easy to see how to seriesor parallel coils as needed.

The following description is a method of determining the correctwiring sequence of a three-phase motor that for some reasondoesn’t have the leads from the motor numbered. You don’t need todisassemble to find the proper numbering of the motor leads.

Step 1: Number the nine leads arbitrarily so that you have astarting point.Step 2: With an ohmmeter or similar device, find the variouscoil sets and make a record of these coil sets, using the num-bers that you originally assigned to the leads; assuming themotor is wye-connected, only three leads will show continuityto all of the thru leads. These three leads are the internally

connected wye. The remaining six leads belong to the threeisolated sets of coils. See Figure 30-9.Step 3: If the motor is Y connected, follow this procedure:

(a) Apply reduced voltage (40–100 volts) across one of thesets of coils that is in the internal, not in the wye. UseFigure 30-9A as an example, and put voltage across 6 and7. Read the voltages across the internal wye that you havelocated (from 3 to 4, 4 to 5, and 3 to 5). Pick the lowest ofthese voltages. (Let us assume that this is between 3 and 4.)(b) The terminal of the wye that the voltmeter is notattached to when the lowest voltage is read is the terminalthat should be connected to the energized coil. In the exam-ple, since the voltmeter is connected across 3 and 4 whenthe lowest voltage is read, terminal 5 should be connectedto coil 6 or 7.(c) It now remains to find out whether 6 or 7 should beconnected to 5 for correct operation of the motor. First

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Figure 30-12 Easy method for remembering the proper connections for a dual-voltage wye-connected motor.