You know you need a new electric motor for your equipment, but when it comes to identifying an option that will meet your performance requirements, you’re not sure what you need. Maybe you have an old motor that must be replaced, but you don’t know how to identify a comparable unit for your update.

Before you contact an electric motor manufacturer to buy a motor, you’ll save time and be more likely to gain optimal performance if you have some familiarity with basic electric motor terms and parameters.

Motor Type/Current

Current will define the type of motor as one of two types: AC (alternating current) or DC (direct current). An AC motor runs on AC power and a DC motor runs on DC power via a commutator or electronic servo system. One of the simplest ways to identify whether a motor is AC or DC is to check the NEMA or IEC nameplate that’s affixed to most standard motors. The other method is to open up the motor and look for a commutator, which is present on brushed DC motors and located on the end of the armature shaft. Although it’s sometimes possible to deduce a motor’s type based on its application, this isn’t always reliable. While AC motors are the most widely used type, DC motors are still a prominent option in industrial and commercial equipment.

In general, AC motors have lower start-up demands, can deliver more torque, are easier to control in terms of acceleration, and provide more options and flexibility for their operational capacities. DC motors have a stronger start-up and more responsiveness and are better suited for continuous motion and long duty cycles.


Motor voltages are a standard that will vary based on the motor’s phase and type. In general, the higher the voltage, the more efficient and the greater power/torque capacity of the motor. It’s very important that motors are constructed, implemented, and operated in a way that over-voltage or voltage stress does not occur. This can happen when the supply voltage exceeds the motor’s rated voltage, which can cause the motor to burn out.


Motor phases mainly concern AC motors, which are categorized as single-phase or three-phase. The number of phases a motor has will determine how the electric load is distributed during a motor’s operation and how much power it outputs as a result.

In a single-phase electric motor, the motor uses two wires to simultaneously change supply voltage. In a three-phase motor, three alternating currents pass through three condor wires while a fourth wire is the neutral wire. Single-phase motors don’t deliver as much power as three-phase motors but they do not require as much insulation. Three-phase motors are mainly used for high-power industrial applications and single-phase electric motors are used in household and lower-power systems.


Motor frequency is measured in Hz cycles. It is the operational frequency of the motor’s input current. Most standard motors will operate at either 50 or 60 Hz. Motors used in systems aboard aircraft, ships, and in defense or mil-spec applications will use 400 Hz motors as a standard. Not all AC motor manufacturers will build 400 Hz motors, but those that serve military and aerospace OEMs will usually offer such products.


A motor’s speed refers to the RPMs of the motor’s shaft, which determines the rotational rate of the motor. This is not to be confused with torque, which is the rotational force of the motor.


A motor’s insulation is the type of protective coating that’s used to protect the motor’s windings. Standard-duty motors will usually have a simple epoxy-resin varnish, which is sufficient for improving the rigidity of the stator assembly and protecting it possible contaminants. Heavy-duty and high-performance motors will have special encapsulation as insulation.

Motor insulation is defined by class, which is determined by a maximum operational temperature. For example, class A motor insulation will be adequate for motors that do not need to operate in excess of 221 degrees F and class H motor insulation is suitable for motors that must operate as high as 356 degrees F. Electric motor parts manufacturers that cater to industrial, defense, and aerospace customers will be more likely to offer motors with class F and class H insulation.


A motor’s horsepower is determined by the combination of its speed and torque. It can be determined by multiplying the motor’s speed and its torque. Horsepower can also be determined by multiplying the motor’s voltage, current, and efficiency and dividing the total by 746.