How to determine polarity on three phase motor?
How to determine polarity on three phase motor?
(OP)
Is there a procedure for determining how to properly identify the leads on a 6 wire 3 phase motor? The motor leads are unidentifiable. The nameplate only shows T1, T2 and T3 connections. This is a 460v, 150hp motor. Any direction would be greatly appreciated.





RE: How to determine polarity on three phase motor?
Usually, identifying which lead is which is not important. Usually, all that matters is phase rotation -- that is, A-B-C or B-C-A or C-A-B are usually all acceptable -- they all lead to rotation in the same direction.
There's only two choices for rotation, clockwise or counterclockwise. Reverse phase rotation will make your motor spin the wrong way. You've got a 50-50 chance of getting it right the first time.
So then, the usual procedure, so far as I know, is to take a guess at wiring the motor, see if it spins the right way by "bumping" it (momentary energization -- don't continuously energize it or some motor designs might be damaged), and if it turned out it was wired the wrong way, you switch two of the leads.
Hope that helps. Others might have additional insights.
RE: How to determine polarity on three phase motor?
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: How to determine polarity on three phase motor?
It reads like you need to identify 6 leads, Are you asking for connection of 6 wires externally or just three? If just three the previous post got it covered, if not does it need to be connected Wye or delta?
The more info you can supply will help get you a better answer. I like to bump or jog the motor w/no load.
Chuck
RE: How to determine polarity on three phase motor?
EG A1, A2; B1, B2; C1, C2.
Spin the motor up to speed with another motor.
Energise A1, A2. For use 480 volts and fuse for about 75% of nameplate current. If the fuse blows repeatedly the motor is probably intended for wye operation. Ruduce the voltage to 240 volts and continue. The motor is now running as an induction generator and we can use the voltages output on the windings to easily determine the connections.
Connect B1 to A2. Read the voltage from A1 to B2. If it is equal to the applied voltage it is connected correctly.
If the A1 to B2 voltage is approximately 1.73 times the applied voltage one of the windings is reversed. Reverse B1 and B2.
Now connect C2 to A1. Check the voltage from C1 to B2. If it is zero or close to it the connections are correct. If the voltage is approximately twice applied voltage reverse the "C" winding connections. When the voltage between the free ends of the "C" wionding and the "B" winding are zero or close to it, you can connect them and the motor is now wired in delta.
Now if any of the windings have been reversed, make sure the labels have also been reversed. Your connections should be A2 with B1, B2 with C1, C2 with A1.
To change to a wye connection, connect power to A1, B1, C1, and connect A2, B2, and C2 together.
Nema motors are often star-delta start and use the delta connection for the high voltage or rated voltage connection.
IEC motors are often dual voltage and use the wye or star connection for the higher voltage.
yours
RE: How to determine polarity on three phase motor?
To have a better idea of your problem and a possible solution check and report the following:
1- Asign arbitrary numbers from 1 to 6
2- Check for continuity bettween the six cables you have.
3- Measure resistance in Ohms between the terminals that showed continuity.
RE: How to determine polarity on three phase motor?
RE: How to determine polarity on three phase motor?
The Waross method sound good but the matter is how you coupled the prime mover to the motor?? what happened with large and high voltage motors??
Adding to the aolalde comments I will suggest:
1. Random to three wires Asign arbitrary numbers from 1 to 3
2. Check the continuity between the no marked and marked wires: Continuity with 1 is marked like 4, continuity with 2 is marked like 5 and continuity with 3 is marked with 6.
3. You could use the surge tester, and find the lead combination that gives the correct pattern (1-6, 2-4, 3-5).
4. Check the right name plate connection (wye or Delta)
5. Check Insulation and start the motor.
RE: How to determine polarity on three phase motor?
If the motor can not be turned with another motor, try single phasing it. Connect some capacitors in series with one winding and connect the second winding in parallel with the first winding. Use a switch so that when the motor starts you can disconnect the connection to the capacitors and leave the motor running single phase on one winding, with another winding connected on one end and free on the other end. Apply voltage and try to start the motor with single phase. You may have to reverse the leads of one of the windings to get the motor to start. When you get it running on one phase, open the switch and follow the procedure for checking the voltage at the open end of the winding.
respectfully
RE: How to determine polarity on three phase motor?
RE: How to determine polarity on three phase motor?
RE: How to determine polarity on three phase motor?
A NEMA motor is probably delta for star delta starting.
An IEC motor is probably Star for dual voltage use.
A delta motor connected star will be underpowered and slow starting. The slip will be excessive.
A Star motor connected delta will probably blow the fuses because of overvoltage saturation. I would be aware of this and use appropriate fuses and monitor the current the first time starting an unknown motor in delta.
Respectfully
RE: How to determine polarity on three phase motor?
For Wye: L1--- 1 L2--- 2 L3--- 3 and 4-5& 6 Together
Delta: L1-- 1&6 L2-- 2 & 4 L3-- 3 & 5
Regards
Petronila
RE: How to determine polarity on three phase motor?
Are you sure that this motor is not a part-winding start?
Bigbillnky,C.E.F.....(Chief Electrical Flunky)
RE: How to determine polarity on three phase motor?
Are you sure that this motor is not a part-winding start?
Bigbillnky,C.E.F.....
Actually, I do not know. How would it matter?
RE: How to determine polarity on three phase motor?
If there is continuity between two leads in three groups it may be a wye delta motor.
respectfully
RE: How to determine polarity on three phase motor?
RE: How to determine polarity on three phase motor?
Looks like a typo? Three groups of three would be 9 wires. I understood you had 6 wires. I understood that there were three groups of two leads but I am not sure.
High current may indicate:
1> One winding is reversed. (Either star or delta)
2> Voltage is not right for the connection.
The load is stalling the motor.
Can you run the motor free or is it coupled up to a machine?
Can you describe your breaker?
Have you been able to measure the motor amps?
Can you give us a make and model of the motor?
respectfully
RE: How to determine polarity on three phase motor?
RE: How to determine polarity on three phase motor?
I checked the siemens web site and it appears that your motor is a wye-delta start motor.
It appears that you have one winding reversed.
There are two ways to go;
One way is to spin the motor up.
The other way is to trip the breaker a few more times.
Start on the wye connection. This is the normal starting connection and the current and the stresses on the motor will be less with this connection.
1> Identify the leads from each winding.
2> Connect one lead from each winding together and insulate or make safe.
3> apply three phase 480 volts to the remaining thre leads.
4> if the motor starts go to part two.
5> If the current is excessive, reverse the connections of one winding.
6> If the motor starts go to part two.
7> If the current is excessive, return the connections that you reversed to the original connection and reverse another set.
8> If the motor starts go to part two.
9> If the current is excessive, return the connections that you reversed to the original connection and reverse another set.
If you are not able to start the motor by now, inspect the motor for damage and check that the load is not stalling the motor.
You should have the motor running on the star connection.
Part Two
Delta connection.
1> Mark the three line leads 1, 2, and 3.
2> Mark the other end of "1" as "4".
3> Mark the other end of "2" as "5".
3> Mark the other end of "3" as "6".
Your connections for 480 volt delta are:
Line 1, 1 and 6
Line 2, 2 and 4
Line 3, 3 and 5
respectfully
RE: How to determine polarity on three phase motor?
respectfully
RE: How to determine polarity on three phase motor?
1> Tools Needed---One old Simpson Multimeter, a 6 volt lantern battery,some gator clip jumpers and a book of tape on numbers.
2> Proceedure---Identify the three pair of leads with the resistance function of the Simpson. Wrap a piece of tape around each pair just so you don't get lost.
Take the lantern battery and connect the negative post to one lead from one pair.Use a Gator Jumper.
Connect the Simpson to one of the remaing pairs. Select the meter to read dc voltage (50v range)
With another gator jumper attach one end to the positive terminal of the battery.Then just touch the jumper to the other motor lead of the first pair.
Observe the meter when you touch the lead. You will see a deflection (forward or reverse). Remove the the jumper and you should see another deflection in the opposite direction.Do this several times to get the feel.
What we are looking for is a forward deflection when you take the jumper off.
Reverse the meter leads if needed to to achieve this.
Mark the first pair [Batt(+)=T1 Bat(-)=T4]. Second pair [Meter (+)=T2 Meter (-)=T5].
Connect the meter to the third pair and repeat the same proceedure as before leaving the battery on the first pair.
Reverse the meter leads if needed.
Mark the third pair [Meter (+)=T3 Meter(-)= T6].
3> Now that you have identified the the T leads, determine from the name plate if this a dual voltage motor or not.
If it is dual voltage, tie T4, T5, and T6 together for the lower voltage.[wye or star]
Tie T1 to T6, T2 to T4, and T3 to T5 for the higher voltage.[delta]
If the motor is a single voltage, connect T4,T5,and T6 together and insulate. Line on T1-T2-T3.
This method is used to determine the polarity of a current transformer.It worked for me in motor applications as well.
Lots of luck!
I hope you gained some useful info.
wt
RE: How to determine polarity on three phase motor?
You should convert your post to a FAQ!
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: How to determine polarity on three phase motor?
RE: How to determine polarity on three phase motor?
We do appreciate the feedback. Thanks
respectfully