Tom Bishop, P.E.
EASA Senior Technical Support Specialist
The markings on the external leads of a motor sometimes become defaced or are removed, which makes it necessary to identify and mark them before the motor can be properly connected to the line. This article will address lead identification of three-phase motors with 9 leads, based on the premise that none of the leads are marked. If some of the leads are marked, the process is the same, but may require fewer steps. Note: See the May 2008 issue of Currents for the article “Identifying Unmarked Leads Of 6-Lead Motors With 1 Or 2 Windings.”
Safety first
Make certain to follow all applicable electrical safe work practices during the tests described in this article. For each step of the test process, make certain that the motor is de-energized before making any connections. The motor will need to be started and stopped many times during this procedure, which may seem cumbersome. However, keep safety first and make certain that the power is off and the motor shaft has stopped rotating before making any connections.
The first step is to use an ohmmeter to identify whether the winding is wye or delta connected. If wye connected, there will be 3 circuits of 2 leads and 1 circuit of 3 leads. If delta connected, there will be 3 separate 3-lead circuits.
Wye connected motor
We will first address the case of a three-phase 230/460 volt wye connected 9-lead motor with no-lead markings. Testing for continuity with an ohmmeter or test light will indicate 4 independent circuits. There will be 3 circuits with 2 leads each and 1 circuit with 3 leads. To make it easier to identify each individual circuit, tie the leads of each of the 4 circuits together with a string or tie-wrap, about 3 inches (75 mm) from the end of each lead. Figure 1 illustrates the winding connections and test voltages related to this procedure.
Take the 3-lead circuit and randomly mark the leads T7, T8 and T9. Separate and tape off (electrically insulate) the other leads and connect T7, T8 and T9 to a de-energized 230 volt three-phase test supply. Start the motor and run it at no load. The motor should not make any unusual sounds and the currents should be balanced. De-energize the motor to make connections, and re-energize after safely reconnecting motor and voltmeter leads.
The next step is to identify the 2-lead circuits (1-4, 2-5, 3-6). To do this, connect 1 lead of any 2-wire circuit to T7 and the other lead to 1 side of an AC voltmeter which has at least a 500 volt scale. Connect the other voltmeter lead first to T8 and then to T9. (Tip: If two voltmeters are available they can be used to simultaneously perform these 2 tests.) There is a 1-in-3 chance of picking the right circuit the first time, so don’t be discouraged. If you pick a wrong 2-wire circuit, the readings will be unequal and you must try another 2-wire circuit. If the voltages to T8 and T9 are equal and about 350 volts, the 2-wire circuit and connection are correct. If the readings are equal and about 135 volts, reverse the leads of the 2-wire circuit, and the result should be about 350 volts to each lead. Following this, take the lead that is connected to T7 and mark it T4; and mark the lead on the voltmeter T1.
After completing the steps above, take another 2-wire circuit and connect one lead to T8 and the other lead to the voltmeter. As with the first circuit, when the correct lead connection is found there will be about 350 volts when connected to T9 or T7. Take the lead connected to T8 and mark it T5; and mark the other lead T2.
The third 2-lead circuit is tested in the same manner by connecting 1 lead of it to T9 and again testing for 350 volts when you connect to T7 or T8. Take the lead connected to T9 and mark it T6, and mark the other lead T3.
The next test is to confirm that the connection is correct for 460 volts. Connect T4 to T7, T5 to T8, and T6 to T9; then connect each of the other leads, T1, T2 and T3 to the supply lines. Run test the motor with no load at 460 volts. If the motor does not make any unusual sounds and the currents are balanced and at a level expected for no load, the markings are correct. See the February 2005 Currents article, “No-load Current Basics: Practical Guidelines For Assessment.”
The final test is to confirm that the connection is also correct for 230 volts. Connect T4, T5 and T6 together; then connect leads T1 and T7 together for one lead, T2 and T8 for the second lead, and T3 and T9 for the third lead. Run test the motor with no load at 230 volts. If the motor does not make any unusual sounds and the currents are balanced and at a level expected for no load, the markings are correct.
Delta connected motor
We will now consider a three-phase 230/460 volt delta connected 9-lead motor with unmarked leads. Begin by testing the leads for continuity with an ohmmeter or test light. With a delta connection there will be three circuits of three leads each. To make it easier to identify each individual circuit, tie the leads of each of the three circuits together with a string or tie-wrap, about 3 inches (75 mm) from the end of each lead. Next, label one circuit “A,” the next circuit “B” and the last circuit “C.” Figure 2 illustrates the winding connections and test voltages related to this procedure.
Connect each lead of circuit A to a de-energized 230 volt, three-phase test supply. Separate and tape off (electrically insulate) the other leads. Start the motor and run it at no load. The motor should not make any unusual sounds and the currents should be balanced. De-energize the motor to make connections, and re-energize after safely reconnecting motor and voltmeter leads.
Next, connect one lead of circuit A to one lead of circuit B. Then put the voltmeter from one of the other leads of circuit B to first one and then the other lead of circuit A. (Tip: If two voltmeters are available they can be used to simultaneously perform these two tests.) What is being sought are 2 leads that will result in a meter reading of approximately 460 volts. If the value is not 460 volts, repeat the test with the other lead of circuit A.
If the 460-volt reading is still not obtained, disconnect the two groups and connect groups A and B together with two different leads and repeat the test. This may take a lot of connecting and reconnecting; but between the two groups there will be a pair of wires, one from each group, that will result in a voltmeter reading of 460 volts. When these are found, mark the lead from circuit A T1 and the lead from circuit B T2. Next, mark the lead from circuit A that is connected to circuit B T4, and the lead that is connected to T4 mark as T7; then mark the third lead of circuit A T9, and the other lead of circuit B T5.
Disconnect circuit A from circuit B and connect 1 lead from circuit C to T9 of circuit A. Place one lead of the voltmeter on T1 and read the voltage between T1 and the other 2 leads of circuit C. The purpose is to find the 460 volt lead in circuit C. When this lead is found, mark it T3. Take the lead connected to T9 and mark it T6. Take the other lead of circuit C and mark it T8.
The next test is to confirm that the connection is correct for 460 volts. Connect T4 to T7, T5 to T8, and T6 to T9; then connect each of the other leads, T1, T2 and T3 to the supply lines. Run test the motor with no load at 460 volts. If the motor does not make any unusual sounds and the currents are balanced and at a level expected for no load, the markings are correct. See the February 2005 Currents article, “No-load Current Basics: Practical Guidelines For Assessment.”
The final test is to confirm that the connection is also correct for 230 volts. Connect T1, T6 and T7 together and use them as one lead. Use T2, T4 and T8 together as the second lead, and T3, T5 and T9 together as the third lead. Run test the motor with no load at 230 volts. If the motor does not make any unusual sounds and the currents are balanced and at a level expected for no load, the markings are correct.
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