What is a Split Phase Induction Motor & Its Working

There are different kinds of power systems available like single phase, three phases, etc. At present, we use a 1-phase power system for different purposes like domestic, commercial & industrial. As compared with three phases, single-phase has more benefits like economical & the requirement of this power system in most of the applications are shops, houses, offices, etc. To activate a single-phase induction motor, the supply of the stator can be split into two phases to generate a revolving magnetic field to turn the motor. So this kind of motor is named as a split-phase induction motor. This article discusses an overview of split phase induction motor, design, theory, working, advantages, disadvantages & its applications.

What is Split Phase Induction Motor?

An alternate name of the this motor is resistance to start the motor. This motor has a single-phase along with a stator as well as a rotor with a single cage. The stator of this type of induction motor includes two windings like main & an auxiliary or starting winding. The arrangement of these two windings can be done with 90°separately in space. These motors are available in different types like resistance split-phase, capacitor split-phase, capacitor start, and permanent capacitor.

Split-phase Induction Motor
Split-phase Induction Motor

The working principle of a split-phase induction motor is related to a polyphase induction motor. But the main disparity is, in single phase motor, it does not generate a rotary magnetic field whereas the polyphase generates simply a pulsating filed. Therefore, phase splitting can be done to generate the rotary magnetic field for self-starting and to run the motor like a two-phase induction motor for starting.

Split Phase Induction Motor Theory

The Split phase induction motor diagram is shown below. The following diagram can be built with main winding resistance (Rm), main winding inductive resistance (Xm), series resistor (Ra), inductive reactance with auxiliary winding (Xa), relay or centrifugal switch (S). In this motor, the main winding has less resistance & high inductive reactance whereas the auxiliary winding has less inductive reactance and high resistance.

Construction Diagram
Construction Diagram

In the above diagram, both the resistor & the auxiliary winding are connected in series. The flowing current in the windings cannot be equal consequently the rotary field is not consistent therefore, the initial torque is little. At the beginning of the motor, the two windings are allied in parallel.

Working of Split Phase Induction Motor

Once the motor gets the 70 to 80 % of the synchronous speed then the starting winding can be detached automatically from the mains supply. If this motor is rated with 100 Watt or above then a centrifugal switch is utilized for disconnecting the starting winding. Similarly, if the motor has less rating then a relay is utilized to detach the winding by connecting in series with main winding.


Once the current flow through the circuit, the relay gets closed. So, the starting winding is within the circuit & when the motor gets the fixed speed, then the flowing current within the relay will start reducing. Thus, the relay opens & the auxiliary winding can be detached from the mains supply to make the motor run on the main winding simply.

The current in the main winding (IM) can be lagged behind the supply voltage ‘V’ almost by the 90-degrees of angle. The current in the auxiliary winding IA is approximately in phase with the line voltage. Thus, there exists a time difference between the currents of the two windings. The time phase difference ϕ is not 90 degrees, but of the order of 30 degrees. This phase difference is enough to produce a rotating magnetic field.

Phasor Diagram

The split phase induction motor phasor diagram is shown below. The flow of current within the IM (main winding) can be lagged after the voltage supply approximately through the 90 degrees angle. Here, IA is the flow of current within the auxiliary winding can be around in phase through the line voltage. Therefore, the time disparity among the two windings current can exist. The phase difference of time ‘ϕ’ is not 90 degrees, but 30 degrees. So to generate the rotating magnetic field, this phase difference is sufficient.


The advantages of a split phase induction motor include the following.

  • The motor is economical & can be changed once it wears out before trying to reverse it.
  • These are available in different frame sizes so that they can be placed effortlessly in most of the machines.


The disadvantages of a split phase induction motor include the following.

  • These motors have less starting torque, so not suitable for above 1 KW.
  • The disadvantage of this motor is power output and efficiency. As compared to a 3-phase motor, these are unsuccessful while changing the energy from electrical to working.
  • These motors rely simply on the different resistance & inductance of the starting winding.
  • These are used where high starting torque is mandatory like an air compressor.
  • These are suitable for the loads which start easily such as fans, grinding wheels, etc.


The applications of split phase induction motor include the following.

  • The applications of this motor include in different loads which are used for general purpose. Generally, these loads are AC, grinders, lathe machine, drilling, washing machines, AC fans, drill presses, Centrifugal pumps, floor polishers, blowers, mixer grinder, heating blowers with belt-driven and conveyors with tiny belt-driven.
  • This motor is used where the distribution of the three phases is not required.
  • This motor does not give lots of starting torque, thus the load should be quite small, and where mechanical gain can be used to assist the motor to begin.

Thus, this is all about an overview of the split phase induction motor that includes its function, working principle, and its applications. The basic concept of an induction motor with single-phase mainly includes the second set of windings which are connected using a capacitor to generate the rotary magnetic field. This magnetic field is essential to run the motor. Subsequently, the split-phase induction motor mainly includes two sets of windings which are built differently to make the phase distinction necessary for the rotary magnetic field. Here is a question for you, what are the different types of induction motors available in the market?

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