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# How to determine the pole number of an induction motor?

There are many much more interesting questions related to the pole number of induction motors, e.g.:
1. Does the induction motor supplied by the main grid (say, 50 Hz) increases its torque capability in "p" times with growing pole number "p" since its speed decreases in "p" time (like in a gearbox)?
2. Let's we have an induction motor with p=2 and feed it from 50 Hz grid. Then we re-connect the winding coils to arrange p=4 and feed if grow 100 Hz grid. Are performances of these two motors different or the same? Please note excluding frequency and inter-coil connections all remained the same.

It depends on the required speed. n (rpm) = (60 x f) / N where:- f = frequency and N = number of pole pairs. The 60 is there to convert from revolutions per second to revolutions per minute as the frequency is in cycles per second. Pole pairs is there because that any pole must be constructed in a pairs top and bottom / left right, so with one cycle it will move half the distance.

If you are using 50Hz and have a two pole motor 60 x 50 / 1 = 3000 rpm. The induction motor will run at a slight less speed due to "slip" which is what gives the motor its torque. For example 5.5kW, 400v, 2 pole motor will run at approximately 2880 rpm.

For a four pole machine, 60 x 50 / 2 = 1500 rpm so the same size motor at 5.5kW, 400v but 4 poles will have a nominal speed of 1500rpm but will run near 1455 rpm.

When selecting a three phase motor, the number of poles is chosen to achieve the speed of rotation that you require. Here are two tables, one for a 50 Hz power supply and one for a 60 Hz power supply:

The formula is n = 60 x f /p where n = synchronous speed; f = supply frequency & p = pairs of poles per phase. The actual running speed is the synchronous speed minus the slip speed.

For a 50 Hz three phase supply:

2 poles or 1 pair of poles = 3,000 RPM (minus the slip speed = about 2,750 RPM or 6 -7% n)
4 poles or 2 pairs of poles = 1,500 RPM
6 poles or 3 pairs of poles = 1,000 RPM
8 poles or 4 pairs of poles = 750 RPM
10 poles or 5 pairs of poles = 600 RPM
12 poles or 6 pairs of poles = 500 RPM
16 poles or 8 pairs of poles = 375 RPM

For a 60 Hz three phase supply:

2 poles or 1 pair of poles = 3,600 RPM (minus the slip speed = about 2,750 RPM or 6 -7% n)
4 poles or 2 pairs of poles = 1,800 RPM
6 poles or 3 pairs of poles = 1,200 RPM
8 poles or 4 pairs of poles = 900 RPM
10 poles or 5 pairs of poles = 720 RPM
12 poles or 6 pairs of poles = 600 RPM
16 poles or 8 pairs of poles = 450 RPM

To determine the number of poles, you can read the data plate directly or calculate it from the RPM stated on the data plate or you can count the coils and divide by 3 (poles per phase) or by 6 (pairs of poles per phase). Where the power of the induction motor is constant, the torque increases at the rate that the speed decreases.

With the advent of variable frequency drive (VFD), you can have any frequency / rated volts you desire. I often see name plates with things like 575VAC, 42.5 Hz etc. When these "specials" are made I usually see 6 pole machines - but that may be just a manufacturer's preference.

#### Leave your comment (Registered user only)

7/27/2020 3:17 PM
Hi.
I have a ac generator that has 328.5634 poles.
It's rpm is 3550 @60 htz
Output frequency is 9720 htz. Will carry over 100 amps.
Driven by a 100 HP motor on 3phase 220 volts
7/3/2020 7:13 PM
I have a 6pole motor single phase I want to rewind it into 4 poles to increas rpm it is possible?
5/31/2020 11:18 AM
very informative
5/25/2020 4:55 PM
any people contort my whats app number  03120025488
4/20/2020 2:56 AM
When a problem asks you to determine the synchronous speed of a 3 phase, 4 pole motor.  What is the # of poles that I should use in the formula?
3/31/2020 8:45 PM
Very Informative
3/5/2020 5:54 PM
A SINGLE PHASE INDUCTION MOTOR IS FOUR SPEED VARIABLE. ITS RESISTANCE OF HIGH CONNECTION IS 87 OHM, MEDIUM SPEED CONNECTION RESISTANCE IS 113.5OHM AND LOW SPEED CONNECTION RESISTANCE IS 130 OHM. CAPACITOR VALUE IS 4MICROFARAD.
NO.OF TURNS 266/126
NOW,CALCULTE TOTAL IMPEDANCE OF I.MOTOR ?
12/27/2019 11:27 AM
Just a Learner looking up on Induction motors and learning all about Ohms Law again from school about sixty years ago

Thanks for the page its' GREAT

Happy New Year to you all.

Ha!Ha! No I'm not a robot.
11/24/2019 2:23 PM
how to calculated the number of poles in induction motor?
10/15/2019 9:15 AM
What is the RPM of 50 Hz, 4-pole, Single phase Synchrounus induction motor...?
7/7/2019 10:31 PM
how much ram does a 4 pole vs a 2 pole take?
5/2/2019 6:53 PM
7200 constant divided by RPM = # of poles

# of poles x 3 phase = # of groups

# of slots / # of groups = # of coils in each group
4/18/2019 9:31 AM
how to find kw, if data given 4pole,415 V,1450 rpm?
1/12/2019 5:40 AM
if we want to make 375 rpm 16 poles how many slots in this stator what is winding detail .
1/10/2019 3:30 AM
how to select a motor that will use in machines?
11/29/2018 3:20 PM
13,200 Volts motor, 356 RPM, 60 Hz. How many poles?   18?
5/24/2018 2:42 AM
600KW INDUCTION MOTOR,50HZ,4 POLE HOW MUCH RPM
2/28/2018 1:29 PM
i am a robot
2/3/2018 1:04 PM
I need to convert 5.5 kW with current 960 RPM into 3000 RPM, please tell me the winding formula
9/23/2017 9:29 AM
A question says a three phase 60hz induction motor runs at 715 r/min at no load and at 670r/min at full load. How many poles does this motor have,,, and the answer is 10 poles why?
5/10/2017 1:59 PM
I read this hoping to find out "how to determine the pole number", but I just found out how to calculate the rpm from the pole number.  Let's say I have 14 magnets on rotor and 12 coils on stator. What is the pole number? How do I determine how fast will this motor turn?
4/29/2017 2:09 AM
the question states no frequency.
How can I determine number of pole in induction motor?
Eg. A three-phase 60 hz induction motor runs at 715 r/min and at 670 r/min at full load. How many poles does this motor have?
4/26/2017 6:01 AM
That'll be alright!
B. Melon
4/12/2017 1:40 AM
How can we determine the no. Of pole in 3 phase induction motor .if we have 3 slot per pole . I means what is in 3 phase motor no. Of pole are different from 6  or not.?
4/8/2017 12:41 PM
how to calculate no of poles of a synchronous motor , if frequency & RPM are given. my email is vvengineer@gmail.com ..can anyone support me please.. 8000 RPM & 50 Hz are given value to find out no of poles .
As well as how to slip percent ?....
awating kind cooperation ..
3/12/2017 7:32 AM
Whats the RPM ?
If we got a 400v ,50Hz 4 pole ...?

3/9/2017 4:57 PM
6% slip in a 3,600rpm motor would lead to a rotation of 3384rpm, not 2,750rpm. 2,750rpm would be an unacceptable amount of slip.
2/8/2017 5:53 PM
nice
2/2/2017 10:15 PM
what is the formula for calculating rev/min using f,  V , I , poles and pairs of poles
2/1/2017 5:16 PM
Your document is straightforward and quite simple to apply.
My  point is  we should surely have a formula relating the following:-
No of turns / coils per pole to No to No of poles.
In fact I have a 1750 and 420 rmp 19.3 Hp . 48 slots Two speed ac motor. The 420 rmp winding has been stripped off with no trace it.
Does your  Easy formula apply in this case?
No of coil set in 3phase Ac motor=no of poles X NO of Phase.                              Quite confusing "coil set" and " no of turns per pole"
Anyway thanks for to consider my case.  Regards Farook.
1/5/2017 7:11 PM
If i have 2 poles generator, how can i justify how much RPM do i need for an induction motor?
1/5/2017 7:09 PM
If i don't know pole number, how can i know RPM???
1/3/2017 6:12 AM
If I don't know rpm than how can I known
Number of pole ?
12/30/2016 6:30 PM
I want make a ac alternator with low rpm
How much pole i need
12/17/2016 1:35 PM
I don't understand what's described
11/28/2016 9:40 AM
Im new to this but if I want to mae a PMG at 130 rpm 500 w at 48 v how many poles and how many stators do I need ?
10/31/2016 5:39 PM
Easy Formula
No of coil set in 3phse AC Motor
=no of poles×no of phase.
10/15/2016 2:11 PM
So the name of the article is "how to determine the number of poles of an induction motor" i read the whole article still don't know how to determine the number of poles on an induction motor
9/29/2016 8:26 AM
Is no. of poles equal to no. of phases used in stator winding?
8/26/2016 11:05 AM
all is right but if we want to make 375 rpm 16 poles how many slots in this stator what is winding detail .