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In general if I look at a 3 phase AC motor outlet wires there are six wires that comes out of motor, three of them are marked to show coils end and other three are not marked which show coils other end.

Sometimes what happens these marks are worn out due to the reason that motor is rewinded and winder guy forgot to mark the coil ends or due to other reasons.

Six wires also comes out of a star-delta motor starter, now how would I correctly identify outlet wires which are coming out of motor so that I can configure the star-delta connection correctly?

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  • \$\begingroup\$ There is a reason that they are marked of course!!! \$\endgroup\$ – Andy aka Dec 20 '14 at 23:14
  • \$\begingroup\$ @Andyaka i know the reason but what if those marks are worn out and you have to connect motor to star-delta starter correctly. What is the way out to identify correct coil ends? \$\endgroup\$ – dev gr Dec 21 '14 at 2:09
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I had this problem once with a motor which losses is terminal block and solved it following these steps,

  1. Identify the coils, measuring continuity.

  2. Connect the motor in delta style using six cables or use a star-delta starter as power of motor dictates.

  3. Test all the combinations in one of the ends of the coils, left the other side fixed. There are only two possibilities.

You must try uvw-uwv-vuw-vwu-wvu-wuv, skipping the ones who puts the same phase at the ends of the same coil, you could test this with a voltmeter.

If the sequence is wrong and you have a star-delta starter, the motor will starts up always correctly in star an showns an anormal response at delta changeover, stops or severely losses torque.

I followed this procedure with a 15Kw motor and a star-delta starter.

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In this case try measuring conductivity between the ports with a tester/multimeter, i.e. when you get conductivity with the ports 1 and 5, then they are part of the same coil, different coils are galvanic isolated. Once you have identified each coil ports, then injecting a small voltage (in comparison with the rated one) on each coil/motor phase, identify the direction of the motor rotation and assign the phase names that are more convenient for you. For this part you just have to set one coil as phase T and interchanging the other two phases will set the rotation of the motor on the opposite direction. Hope it helps. Sorry for the bad English.

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I suspect you could test it like a transformer. Apply 12 volt ac to one coil pair and look at the waveform on that coil and another coil using a two channel oscilloscope. If the second coil is in phase with the first coil mark the two wires that the probe tips connect to. Move the second probe to the 3rd coil pair and repeat the marking procedure.

This should ensure that the marked ends of the three coils are all having the same phase relationship.

I will add that you should use a low voltage ac compared to the rated running voltage because the rotor winding is acting like a shorted turn in this test and it could cause several amps to be taken from the ac test supply.

I'd be interested to hear what you measure.

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  • \$\begingroup\$ I don't have a two channel oscilloscope so I can not do this, any other idea without using such instruments. \$\endgroup\$ – dev gr Dec 22 '14 at 4:33
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I use this method to find correct polarity of the coils: With all six end loose, use a continuity meter to pair up each of the coils two ends.

Use a controlled DC supply across each coil and inject a small DC current. Then take a simple magnetic compass and place it near each of the three coils.

If the direction of current flow is the same through each coil, the magnetic compass should give the same pole(north or south)near each coil. You can decide which of each end is start and finish end of the coils. Credit to A.Mizzi

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    \$\begingroup\$ This is very interesting but the procedure is unclear. (1) Do you power all three coils simultaneously? (2) Where do you hold the compass? (3) Does this work with the motor fully assembled? \$\endgroup\$ – Transistor Jul 22 '17 at 18:38
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Connect meter (analogue volts) across a winding..dab a 6/12v battery across another winding to induce a forward flick of meter...take into concide ration 180 deg phase shift..Mark up and repeat for other win ding. ..job done

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    \$\begingroup\$ It's three-phase. The windings are 120° apart - not 180°. Ding ... job not done. Have you used your technique? Can you give a bit more detail? \$\endgroup\$ – Transistor Oct 27 '17 at 22:48
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We took two coils and combined two terminals and give supply at one uncombined terminals and combined terminal,if we check the voltage across the uncombined terminals if it's more than supply voltage than its terminal are in correct position otherwise if less than wrong one thus we can check

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    \$\begingroup\$ A series of diagram would be a big help. The talk of combined and uncombined terminals will cause confusion. There is a schematic button on the editor toolbar. Use the inductors and node symbols to represent your motor coils. Welcome to EE.SE. \$\endgroup\$ – Transistor Jan 28 '18 at 13:57
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Take one winding mark a1 and a2,take 6v or 12 v battery.connect multimeter in dc v smaller range to other winding terminals,assume b1 and b2.

connect multimeter to b1 and b2. Just touch 12 v battery positive to a1 and negative to a2,dont connect permenant. observe multimeter makes a positive kick,then assumed polarity b1 and b2 is correct,make permanent marking. same way connect battery positive to b1 and negative to b2 just touch battery terminals. connect multimeter to other leftout terminal,multimeter makes positive kick the assumed terminal is c1 and c2. if the multimeter makes negative kick then the assumed connections become reverse like c2 anc1. like this repeat this for all the three windings.

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We can also check the polerty by using a series testing lamp First of all make a series testing lamp .Now touch any two terminal of motor with lamps both terminal ,if lamp will glow then that both terminal of motor is in same polerty.

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    \$\begingroup\$ Welcome to EE.SE. (1) Your post is poorly worded, has bad punctuation and some spelling mistakes. We can make allowances and correct it if English is not your first language but your profile gives no clue. (2) What is "a series testing lamp"? (3) How does touching a series testing lamp to "both terminal of a motor" demonstrate polarity? \$\endgroup\$ – Transistor Jul 22 '17 at 18:35

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