Identifying starting and running winding of single phase induction motor

Mostly in electrical technology students, a question is served in his mind about the single-phase motor and how to identify starting and running winding. Basically when we talk about single-phase motor wiring or installation connection. We always think about the start, run, and common wire or terminals. In one phase motor connection, we have three wire coming from the motor winding which is “start”, “run”, and “common”. As you know that we have two types of winding in a single-phase motor which we have known by the name of starting and running winding. The running winding is also called the main winding while the starting winding is better known by name of “auxiliary winding”. The point where both windings are connected is called the common point which we know better by name of “common connection of a one-phase motor” or “the common terminal of a single-phase refrigerator compressor”.

how to identify starting and running winding

How to Identify starting and running winding in a single-phase motor

If you open the single-phase motor, you will find out that your motor has two types of winding of which one is made from a thick wire gauge and one thin. the thick wire gauge winding is the main winding and the thin wire gauge winding is the starting winding.

But this Identification can be done when you open the motor but what you will do if don’t want the motor and just want to find out starting and running winding from the main connection plate or connection point?
(Basically to identify starting and running winding is just to find out the start, run, and common connection.)

In a single-phase motor we have three wires which come from both starting and running winding. Which we know with the name of common, start, and run connections.

To find out the common, start, and run wires or connections first read the connection plate diagram and notes to find out which one is common, which one is running, and starting.

In someone’s phase motor the common wire comes with a black colour wire, run as red, and starts as white colour. But is not important that the connection will come in the same colours.

Mostly these colours are changed. So the better and easy option to find out the run, start, and common wire or connection is to read the connection plate diagram or chart. And if you did not find any guide about the connection then follow the below step.

Use a Multimeter You can easily identify the common, starting, and running connection of a single-phase motor. In the single phase 3 wire motor we have a high resistance between the start and run connection or wire.

And if you find out that two wires have a high value of resistance showing on a multimeter or ohmmeter in three-wire then it means that these two wires are “start” and “run” connections and the other one is common. However, to completely understand, follow the below step-by-step guide


  • First of all, set your multimeter on ohm testing
  • Then check resistance between wire to wire in 3 wires
  • If you find out that two-wire have greater resistance between one another then it means that these are “start” and “run” and the 3rd one is common.
  • So you identify the common wire, so the next step to finding out which one is the “start” and “run” wire.
  • The method is easy, the resistance between the common and starting will be greater than the Resistance between the common and run wire. So the greater resistance between common and other wires will identify that this is starting, “starting connection”, or terminal. So you find out that starting connection. So it’s clear the other wire is run connection wire.
To identify starting and running winding’ i mean that you are searching about the starting and running and common identification in a single phase motor. So if you are searching for this then the above method is for you.
And if you want to identify the starting and running winding then the easy method is to open the motor internally. And see which winding wire is greater in size.
For example, if you find out two winding and one winding are made from 21 SWG and 2nd winding is made from 26 Then 21 SWG is greater in size which is running winding or main winding and 26 SWG winding is starting or auxiliary winding.
(Note That the above start, run, and common identification method you can use for any single-phase induction motor, like a ceiling fan, single-phase submersible water pump motor, A/C outdoor coiling fan, etc.)

I hope this post helps you find out how to identify starting and running winding or identification the start, run, and common terminals or connections is a single-phase motor. If the post helps you then kindly share this post. And if you have any questions then you can use the below comment section for asking you a question. I will try my best to give answer your questions.

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