winding check with ohmmeter1.pdf

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PAGE 1 of 2 - How to check the Windings of a 3-Phase AC motor

There are several different AC motor types, each one with different operating and

mechanical characteristics. The most common type though is the -so called- squirrelcage rotor. It is called squirrel-cage, because it's rotor looks like the exercising wheelfound in squirrel or hamster cages.

A typical 3-phase squirrel-cage motor has six connection leads in the electricalconnection box for the three coils. If someone works with AC 3-phase motors, then itis important to know how to connect these motors in Star and Delta connection, andhow to detect an electrical problem. There are basically 4 problems that the motorwindings can suffer from:

Broken coil (infinite coil resistance)

Short-circuited coil (less than normal or zero coil resistance)

Leaking coil to ground (current leaking from one coil to ground/neutral)

Two or more coils short-circuited with each other (current leaking from one coil to another coil)All of the above problems can be detected with a simple Ohm-meter. First of all, you need to understand how thecoils are connected with the six motor leads that exist in the electrical connection box. Here is a photo from atypical electrical connection box:

As you can see, there are indeed six leads arranged in two rows. Since each coil has 2 endings, it is easy tounderstand that these six leads correspond can be separated in three pairs, and each pair is connected to one coil.It seems logical to separate these 3 pairs in a vertical pattern, but that is not correct. Instead, the pairs are incross-pattern like this:

How to check the Windings of a 3-Phase ACmotor with an Ohmmeter

AuthorGiorgos LazaridisJanuary 4, 2012

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Page 1 of 9How to check the Windings of a 3-Phase AC motor with an Ohmmeter

12-Sep-13http://www.pcbheaven.com/userpages/check_the_windings_of_a_3phase_ac_motor/index....


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You may now wonder, why the coils are connected in cross-pattern and not vertically... The answer is this: To easilybridge a permanent connection. A permanent connection is when the motor is connected in Star or Delta, and thisconnection cannot be changed. This is usually done if the motor is small (smaller than 3.5 KWatts) or the motor isdriven by an inverter or some kind of electronic driver. A permanent connection is usually accomplished with 2 or 3metallic bridges.

Suppose for example that the motor is connected in Star. In a star connection, each one of the 3 phases (R-S-T) isconnected at one end of each coil. The other ends of the coils are connected together in a common point. A starconnection can be easily accomplished simply by bridging one of the two horizontal rows in the connection box ofthe motor. The phases are then connected on the leads of the other horizontal row:

Suppose now that the motor is connected in Delta. In Delta connection, the end of each coil is connected with thestart of another coil. The 3 coils are then connected in a circle, creating thus 3 nodes. The 3 phases are then appliedon these nodes. A Delta connection is easily accomplished by bridging the 3 columns in the connection box

vertically:

There is one last thing to know: All 3 coils must have the same resistance. That is of-course easy to understand why,so there is no need to explain any further.

Checking the coils of an unconnected motor

Being a motor unconnected, means that there are no Star or Delta bridges on its leads. This is the most straight-forward case to understand. All you have to do is try to find the coil pairs in the electrical connection box. Let's givenumbers to the 6 leads:

This is why we call this type ofconnection "Star" (or Y)

A star connection is accomplishedsimply by bridging one horizontal

row in the connection box

This is a photo from the connectionbox of a motor connected in Star

This is why we call this type ofconnection "Delta" (from the

Greek letter )

A Delta connection is easilyaccomplished by bridging the 3columns in the connection box

vertically

This is a photo from the connectionbox of a motor connected in Delta

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Suppose that you start from lead 1 and you want to find it's pair. You connect the first probe of the ohm-meter to lead1, and then you connect the other probe of the ohm-meter to leads A, B, C, 2, 3 and ground (motor chassis).If themotor has no problem, then you must find infinite resistance between all leads and ground, except from one lead.This one cannot be lead A though, because -as we said- coils are connected in cross pattern.

Then, you repeat the same process but this time you connect the first lead of the ohm-meter to lead 2, and the secondlead to leads A, B, C, 3 and ground. Notice that you do not need again between 2 and 1 since you've measuredalready before. Again, you must find infinite resistance between all leads and ground, except from one lead. Thislead cannot be the one opposite to 2 (which is the lead B) and of course cannot be the lead that pairs with lead 1(found from the previous measurement).

Finally, you repeat the same process with the first probe on lead 3, and the second probe on leads A, B, C andground. Now, you know exactly which of these 3 leads pairs with lead 3. If for example you found that lead B pairswith 1 and lead C pairs with 2, then obviously lead A pairs with 3.

Additionally, you can compare the resistances between the pairs. If they are all equal, then you have a very wellmanufactured motor. A tolerance of 5% (and some times 10%) is generally accepted. If the difference is bigger, thiscould mean that some wires of the coil are short-circuited and the overall coil length is shorter. This is the mostdifficult problem to identify in such a motor. Usually, if the motor has short-circuited windings, it won't take longuntil this specific coil it is totally destroyed.

In short

You must find the same resistance between 3 pairs of leads ONLY

These pairs must be in cross-pattern as explained before

There must be absolutely no connection (infinite resistance) between all other combinations

There must be absolutely no connection (infinite resistance) between the leads and the ground

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At 24 July 2013, 0:15:50 userGiorgos Lazaridis wrote: [reply @ Giorgos Lazaridis]

@Shawn Hall Always talking about Y connection, between common and any terminal is the lowestresistance, between two terminals is the highest.

At 16 July 2013, 22:22:42 userJoseph Wilfred Unekwu wrote: [reply @ Joseph Wilfred Unekwu]

Thanks alot you just open my a new chapter to my knowledge.

At 12 July 2013, 8:02:01 userShawn Hall wrote: [reply @ Shawn Hall]

When testing the windings od a single phase motor,Technician #1 says that the common and the run terminals show the lowest resistance.Technition #2 says that the pair of terminals with the highest resistance will indicate that the otherterminal is the common.

Who is correct?A. Technician #1 only.B. Technitian #2 only.C. Both technicions #1 and #2.D. Neither technicions #1 or #2.

I think the answer is D?

At 14 June 2013, 23:32:38 userGiorgos Lazaridis wrote: [reply @ Giorgos Lazaridis]

@Robert Chadwick 3-phase AC induction motor Star connection? Then it is dead.

At 13 June 2013, 15:56:29 userRobert Chadwickwrote: [reply @ Robert Chadwick]

I have a 3 phase motor, and I am able to the 3 leads that go into the motor I get no resistance between 2of the leads, and 33 OHMS from either one of those to the third lead. what does that mean

At 3 June 2013, 10:43:16 userEswaran wrote: [reply @ Eswaran]

@samantha @samantha. if we change the connection RPM will not change. this 2 connections relatedfor voltage & current only. if the connection is star current will low sameas voltage should be costant415v. delta current will high but motor will start at littlebit low voltage also. RPM related only NO OFPOLES and Effeciency of motor




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At 3 June 2013, 6:50:17 userdanilo de vera wrote: [reply @ danilo de vera]

I had a 3 phase ac motor i want to to connect to power supply and the control was starting by star thendelta (6 leads) my problem is the si lead came from motor has no marking for the 1,2,3,4,5,6 i cantdetermine the 1,2,3 and the 4,5,6.please help me

At 11 May 2013, 5:03:24 userTim Rigsby wrote: [reply @ Tim Rigsby]

Will a fifty hz 415 .37kw work on 480 60hz.....?????,I

At 1 May 2013, 22:06:31 userGiorgos Lazaridis wrote: [reply @ Giorgos Lazaridis]

@kazi sahriar U1-V1-W1 goes to RST. U2-V2-W2 shorted all together for star connection.

At 29 April 2013, 0:41:01 userkazi sahriar wrote: [reply @ kazi sahriar]

dear sir,my problem is, I have a 3 phase motor which r 6 probe those r U1 V1 W1 & U2 V2 W3.so,how i canconnect those terminal.Plzz tell me sir.

At 22 April 2013, 23:22:16 userShelvindra Bali wrote: [reply @ Shelvindra Bali]

I want know if there is any type of book or software showing me all the connection daigrams of themotor. For example like 2star 2delta 3star 3delta 4star 4delta for different rpm and poles

At 16 April 2013, 9:38:23 userIdriss wrote: [reply @ Idriss]

That is a very clear explanation. I have read so many topics on this, but this is the first time I actuallyget it.

At 3 April 2013, 1:57:29 userRADHAKRISHNAN wrote: [reply @ RADHAKRISHNAN]

sir,

IN the Motor Winding end wire in 3 phase A1A2, B1B2, C1C2 connected thro RYB the motor will runBut if any changes in the terminal connection

A2A1 / B2B1 / C2C1 if the motor winding will get Abnormal heat.

Further, pleas give the diagram for the How to identify the A1, A2 B1, B2,C1,C2 by using TESTLAMP METHOD

At 21 March 2013, 23:53:42 userGeofry wrote: [reply @ Geofry]

Thanks for the info above. Its help me a lot.

At 16 March 2013, 5:15:37 usertanveer shah wrote: [reply @ tanveer shah]

sir many regards

kindly send me any post notification as to be more informative and conscious about my related field.thanx a lot

At 15 March 2013, 8:01:50 userGiorgos Lazaridis wrote: [reply @ Giorgos Lazaridis]




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@Vasilis Caravitis This is the worst case scenario... Star-Delta switches though have schematics how toconnect them. You have to consult this schematic. There are 6 connectors, RST and UVW. Youconnect the first row of motor connectors to R-S-T and the second row to U-V-W

At 10 March 2013, 21:34:37 userVasilis Caravitis wrote: [reply @ Vasilis Caravitis]

Hi, My problem is that I need to replace the Star-Delta change-over switch. The existing 5-position

(broken) switch allows also reverse rotation, but I only need one direction of rotation. The rplacementis intended for single direction operation and has a different terminal pattern. How can I determinewhich cable goes where?

At 5 March 2013, 12:13:07 userGiorgos Lazaridis wrote: [reply @ Giorgos Lazaridis]

@Decker auto electric This motor must be connected in star probably (i may be mistaken though).Connect the 3 poles on one side all together, and then apply RST to the other 3 opposite poles

At 4 March 2013, 14:04:59 userDecker auto electric wrote: [reply @ Decker auto electric]

I got this electric motor that i can notFigure out how to connect the internal

Wires coming out of the motor..Could anybody help me on it???

24 slot. 2 pole lapwinding 2 coils per group6 groups. 295 rounds per coil. Pitch 1 to 11

440/220 volts 3 ph 3200 rpmThere are only 6 leads coming out of motorBut just can't get the motor runningThank a lot

At 16 February 2013, 8:33:43 userkevin wrote: [reply @ kevin]

Hi does anyone have any ideas about wiring a six wire motor to use on a rotary phase converter becauseive tried a few different ways but im getting nowhere, any help is appreciated.

At 6 January 2013, 13:00:17 userGiorgos Lazaridis wrote: [reply @ Giorgos Lazaridis]

@samantha none, both will give you the same rpm. Delta will give you (if motor permits) more torque.

At 6 January 2013, 11:10:14 usersamantha wrote: [reply @ samantha]

pls tel me which connection is giving more RPM? (star or delta)

At 2 January 2013, 0:35:49 userGiorgos Lazaridis wrote: [reply @ Giorgos Lazaridis]

@Abbas musa there is no formula. It depends on the wire thickness and length.

At 1 January 2013, 18:28:13 usergeoffwrote: [reply @ geoff]

Well presented explanation. This is a good site for electrical mechanics.

At 1 January 2013, 7:42:05 userAbbas musa wrote: [reply @ Abbas musa]

helo... Am 4rm Nigeria.please, what is the formula used for calculating the winding resistance of a.casynchronous motor using the volt-ampere method?




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At 19 December 2012, 18:16:37 userJohn Romano wrote: [reply @ John Romano]

Six wires are not a problem. I have a motor that I looked at today that had 9 wires, and two ways to setup. The first is high voltage and the other is low voltage. What is the correct way to check the motor for

proper connection?

At 13 December 2012, 7:46:52 userKHALID wrote: [reply @ KHALID]

GOOD EXPLANATION, I LEARN TOO MUCH FROM THIS TOPIC.

At 12 December 2012, 12:36:44 userThamir Kareem wrote: [reply @ Thamir Kareem]

Dear Sir,I would like to know the connection (star star/star) two speed three phase squirel cage motor also theconnection (star/-star) that i saw those connection in ASIA type motors and supporting your answering

by drawings(line voltage is 380vac)thankyou

At 23 November 2012, 3:43:56 userAamir mehmood wrote: [reply @ Aamir mehmood]

I like very much improve knoldge my selfthanks

At 12 November 2012, 8:54:39 usermahroof.o wrote: [reply @ mahroof.o]

it'S EASY TO UNDERSTAND............

At 3 November 2012, 12:04:58 userjonas hamata wrote: [reply @ jonas hamata]

This is good and clear

At 31 October 2012, 0:27:30 userGiorgos Lazaridis wrote: [reply @ Giorgos Lazaridis]

@atish kumar read 'Checking the coils of an unconnected motor"

At 28 October 2012, 4:29:59 useratish kumar wrote: [reply @ atish kumar]

I have the same doubt that..How would you go about testing the start & end of each motor winding prior to powering up the motor,either by the use of a multimeter or a battery and a volt meter. I understand that one could power up themotor and check the current being pulled by each phase, if there is a serios unbalance on a singlewinding, then turn that winding around, BUT I would like clarity on how to sort out the windings startand end before power up.

At 24 September 2012, 7:30:09 userganesh wrote: [reply @ ganesh]

may be ur ohm meter problem.

At 19 September 2012, 20:03:18 userkaac.perera wrote: [reply @ kaac.perera]

i like this web site

At 24 August 2012, 0:16:52 userGiorgos Lazaridis wrote: [reply @ Giorgos Lazaridis]




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@marcus usually 3-phase motors with 3 wires are internally Y or delta connected. It must be on theplate.

At 23 August 2012, 22:23:58 usermarcus wrote: [reply @ marcus]

and if your three phase motor only has three wires not six - what way do you test it then?

At 21 August 2012, 14:29:29 userT.Sethuram kumar wrote: [reply @ T.Sethuram kumar]

Today i got different problem what actually happen one motor got tripped continually so i checked themotor amps its high 12A so i checked the name plate there full load current 12A so that i removed theload and checked after that also same current 12A how it's i confused because with load 12A withoutload also 12 A so that i checked the winding resistance that is ok 3phase equally, after that i checked

bearing that also good winding also good then how this it's happen anybody knows kindly reply me

At 18 July 2012, 1:19:57 userFrancisco Gavina wrote: [reply @ Francisco Gavina]

(Portugal) Great tutorial. I am 51 years old, I am self taught. I'm unemployed. I like learning things ofquality. I like to diversify knowledge. It will not let me grow old. Thank you. Gavina.

At 21 May 2012, 4:30:55 userGiorgos Lazaridis wrote: [reply @ Giorgos Lazaridis]

@Ian Ellis there are 6 connectors on a 3-phase squirrel cage motor. You can test them with multimeter,ohm-meter or battery by following the instruction if the first page of this theory, at the bottom(Checking the coils of an unconnected motor)

At 19 May 2012, 22:29:49 userIan Ellis wrote: [reply @ Ian Ellis]

How would you go about testing the start & end of each motor winding prior to powering up the motor,either by the use of a multimeter or a battery and a volt meter. I understand that one could power up themotor and check the current being pulled by each phase, if there is a serios unbalance on a singlewinding, then turn that winding around, BUT I would like clarity on how to sort out the windings startand end before power up.

At 6 January 2012, 11:43:50 userKammenos wrote: [reply @ Kammenos]

@George excellent! I am working on a simple coil checker tool (that is why i uploaded this theory afterall). I will check this link and see if i can add it as a function. ;) thanks.

At 5 January 2012, 15:42:46 userGeorge wrote: [reply @ George]

one other thing.

NEVER WORK ON AC system by yourself, ALWAYS have another person there as the SAFETYperson. To switch off the power, and/or save your butt/ life if anything goes seriously wrong

At 5 January 2012, 15:39:19 userGeorge wrote: [reply @ George]

@Paul - there are two methods for checking phase of windings mentioned oncr4.globalspec.com/thread/71498

One uses a push button DC voltage and a galvanometer .

The other uses live AC voltage on 1 winding against the other 2 windings connected in series to see ifthere is a net 0V AC or double the test winding Voltage, BUT beware YOU ARE WORKING WITHLIVE AC POWER. So make sure that you have tested for earth faults. [A multimeter is not really thegreatest here a megger would be better] AND DO NOT TOUCH ANYTHING WHEN LIVE - useINSULATED PROBES




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At 5 January 2012, 8:17:57 userKammenos wrote: [reply @ Kammenos]

@Paul :D :D i'll tell you a little secret. The motor that is the photos, is a repaired motor that had aburned coil. The (not so good) technician that repaired the coils connected one of them the oppositedirection. I tried hard to find a way to measure that problem, but had no luck with simple instruments.You connect it in the supply and if it makes noise and does not rotate, or rotate with no torque, thenchange connection...

At 5 January 2012, 8:03:36 userPaul wrote: [reply @ Paul]

Just wonderin...

Some time ago I also had to figure out how to connect a 1.5KW three phase motor but on this motorthere was not such a nice board for connecting the wires. It basically had 6 loose wires dangling from it.

A big problem would be if one of the phases is connected backwards relative to the other 2.

How do you check for that?In the end I just (sort of) guessed, but I took some extra precautions to prevent destroying a perfectlygood motor.I guessed right but didn't feel happy about it.

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