Single Phase Motor Capacitor Start

We have had a look at motor testing on the three phase motors and I think we should also have a quick look at the single phase connection diagram. There are a number of single phase motors on various pieces of equipment and what I will try to do here is to explain it as easily as possible.

Let’s start with the basic diagram of the motor connection. Now you will see people will draw this in all sorts of methods but I will show you a very simple way of doing it.

To understand the circuit, you need to know how to find the two windings of the motor. These are your starting winding and the running winding. The way to determine which is which, is to measure the resistance of the winding. Use your multimeter and set it to the ohm scale. Now measure the resistance of each winding and write it down. The highest reading you obtained is the starting winding and the lower reading is the running winding.

Now look at the connection based on the diagram below:

You will see that one end of the run winding and one end of the capacitor is connected to the Active or “Live”

The other side of the capacitor is connected to one end of the start winding

The other end of both the start and run windings now gets connected to the Neutral

All done, you can now run the motor.



So now the motor runs but in the wrong direction. How do we change that?


Again, there are two ways of doing that. You can change either the starting OR running winding connection around. Never do them both or the motor will still be running in the wrong direction!


In the sketch below I show how to swop the start winding around. As a habit, I always do the start winding but you may choose your own way of doing it.


You will note the sketches are drawn pretty rough but the result is what we are after. This is typically the sketch I would make when having to connect a single phase motor.

And again, as always, I hope you find this useful and remember to always think before you do! There is no substitute for SAFETY!


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