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12 Lead I.D. for Three Phase Generators & Motors

Steve Dawkins

Subscriber
Last Subscription Date
07/04/2016
Occasionally, we need to identify the leads for generators or motors, and don't have a schematic diagram of the windings available. Here is a handy way to remember how the windings are labeled. All you will need is a pen/pencil and paper.

- Draw a Y with each "leg" of the Y broken into two segments. You will have a total of six segments. Each segment represents one winding. Don't connect the center of the Y.
- Starting at the 10 o'clock position, label the outmost end of that winding "1".
- Pretend like you are drawing a spiral in a clockwise direction, and consecutively number each outermost end as you pass by it. The attached sketch will explain this easier.
- If labeled correctly, the bottom leg of the Y will read 3-6-9-12. (Just remember multilples of 3)

NOTES:
- The two windings on each segment of the Y are installed on the same poles of the stator. They will be the same phase. If the generator or motor is wired for low voltage such as 208 volts, these two windings will be in parallel. If the generator or motor is wired for high voltage such as 480 volts, the same two windings will be wired in series.
- Most small 3 phase motors in the US are 9 lead motors. For these, 10-11-12 are connected internally in the windings.

Hopefully this method of identification will help if you need to ring out the windings, or if the wire marking is missing on a couple of the leads.
 

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armandh

Registered
Last Subscription Date
09/02/2010
ringing them out

use an ohm meter to identify winding pairs

use a low voltage AC transformer to energize one pair

of the other 5, 4 will meter a similar voltage the fifth a bit higher
that higher one is in the same phase relationship as the powered winding

energize one of the 4 similar from the first cull
2 will have a similar voltage and one higher
again that higher one is in the same phase as the energized one

you now have 3 groups of pairs

you can check the pair phases by connecting in series and powering one
the other will be less, the total a sum [correct] if the difference flip one winding
repeat for each windings pair

tentatively connect in a high Y and energize one pair at a time
meter from point to point for similar results [correct]
uneven one pair is flipped try tentative Y connection again

or maybe I was just lucky
 
Last edited:

Mark Dieckmann

Registered
use a low voltage AC transformer to energize one pair

you can check the pair phases by connecting in series and powering one
the other will be less, the total a sum [correct] if the difference flip one winding
repeat for each windings pair

tentatively connect in a high Y and energize one pair at a time
meter from point to point for similar results [correct]
uneven one pair is flipped try tentative Y connection again

The timing of this thread is amazing. I have an old generator that I need to identify the leads on soon. Thanks for the above procedures. I have a few questions. You said to use a low voltage transformer. Any suggestions on voltage or wattage. I was thinking we a furnace control transformer. 24 volt 40VA, am I on the right track? Also could you expand upon the procedure to get the pairs in sync with each other. Thanks again.
 

armandh

Registered
Last Subscription Date
09/02/2010
24 is a-ok I used a 5V ac wall wart
anything 10 v doorbell xf

the idea is some less than lethal voltage [an old train xf not HO which are DC]
 

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