Electric Motor FAQ - Common Questions & Expert Answers
Single Phase
What is the difference between Capacitor Start and Permanent Capacitor motors?
To wire a 3-phase motor, you must choose between Star or Delta based on your supply voltage and motor nameplate.Star (High Voltage): Links W2-U2-V2 together. Use this for 400V mains on a standard 230/400V motor.Delta (Low Voltage): Links U1-W2, V1-U2, W1-V2 in pairs. Use this for 230V inverter supply on a standard motor.Star (Y) Connection: Connects the three "finish" ends (W2, U2, V2) together. Used for 400V Supply on standard small/medium motors (up to 4.0kW).Delta (Δ) Connection: Connects the start of one phase to the end of the next (U1-W2, V1-U2, W1-V2). Used for 230V Supply (e.g., Single Phase Inverter) on small motors, OR 400V Supply on large motors (4kW+) marked 400/690V.Star Connection - Wiring DiagramDelta Connection - Wiring Diagram** STOP: Check your motor nameplate.If it says 230/400V: Star = 400V (Mains), Delta = 230V (Inverter).If it says 400/690V: Delta = 400V (Mains), Star = 690V.
Can I run a 3-phase motor on single-phase power?
To wire a 3-phase motor, you must choose between Star or Delta based on your supply voltage and motor nameplate.Star (High Voltage): Links W2-U2-V2 together. Use this for 400V mains on a standard 230/400V motor.Delta (Low Voltage): Links U1-W2, V1-U2, W1-V2 in pairs. Use this for 230V inverter supply on a standard motor.Star (Y) Connection: Connects the three "finish" ends (W2, U2, V2) together. Used for 400V Supply on standard small/medium motors (up to 4.0kW).Delta (Δ) Connection: Connects the start of one phase to the end of the next (U1-W2, V1-U2, W1-V2). Used for 230V Supply (e.g., Single Phase Inverter) on small motors, OR 400V Supply on large motors (4kW+) marked 400/690V.Star Connection - Wiring DiagramDelta Connection - Wiring Diagram** STOP: Check your motor nameplate.If it says 230/400V: Star = 400V (Mains), Delta = 230V (Inverter).If it says 400/690V: Delta = 400V (Mains), Star = 690V.
Three Phase
What is the difference between 2-pole, 4-pole, and 6-pole motors?
To wire a 3-phase motor, you must choose between Star or Delta based on your supply voltage and motor nameplate.Star (High Voltage): Links W2-U2-V2 together. Use this for 400V mains on a standard 230/400V motor.Delta (Low Voltage): Links U1-W2, V1-U2, W1-V2 in pairs. Use this for 230V inverter supply on a standard motor.Star (Y) Connection: Connects the three "finish" ends (W2, U2, V2) together. Used for 400V Supply on standard small/medium motors (up to 4.0kW).Delta (Δ) Connection: Connects the start of one phase to the end of the next (U1-W2, V1-U2, W1-V2). Used for 230V Supply (e.g., Single Phase Inverter) on small motors, OR 400V Supply on large motors (4kW+) marked 400/690V.Star Connection - Wiring DiagramDelta Connection - Wiring Diagram** STOP: Check your motor nameplate.If it says 230/400V: Star = 400V (Mains), Delta = 230V (Inverter).If it says 400/690V: Delta = 400V (Mains), Star = 690V.
Can I use a 3-phase motor with a Variable Frequency Drive (VFD)?
To wire a 3-phase motor, you must choose between Star or Delta based on your supply voltage and motor nameplate.Star (High Voltage): Links W2-U2-V2 together. Use this for 400V mains on a standard 230/400V motor.Delta (Low Voltage): Links U1-W2, V1-U2, W1-V2 in pairs. Use this for 230V inverter supply on a standard motor.Star (Y) Connection: Connects the three "finish" ends (W2, U2, V2) together. Used for 400V Supply on standard small/medium motors (up to 4.0kW).Delta (Δ) Connection: Connects the start of one phase to the end of the next (U1-W2, V1-U2, W1-V2). Used for 230V Supply (e.g., Single Phase Inverter) on small motors, OR 400V Supply on large motors (4kW+) marked 400/690V.Star Connection - Wiring DiagramDelta Connection - Wiring Diagram** STOP: Check your motor nameplate.If it says 230/400V: Star = 400V (Mains), Delta = 230V (Inverter).If it says 400/690V: Delta = 400V (Mains), Star = 690V.
Motor Selection
How do I measure the frame size of an electric motor?
To confirm the frame size, measure the height from the centre of the motor shaft to the base of the foot, in millimetres. This measurement should correspond to standard frame designations like 71, 80, or 90. Most UK & European electric motors follow IEC frame standards.Locate the centre of the motor shaft.Using a ruler or measuring tape, measure straight down to the base of the foot.Round to the nearest 1mm (e.g. 71mm = Frame 71)Check your measurement with the motor nameplate to confirm (e.g. 71mm = AMAS SR 71G4)Frame size determines if the replacement motor is interchangeable with existing motor and has the shaft and mounting dimensions.Learn more about our complete range of [Motor Frames & Sizes].
What is the difference between IE1, IE2, and IE3 efficiency motors?
The Pitch Circle Diameter (PCD) is the diameter of the circle that passes through the centre of all the flange mounting holes.Measure the distance between the centre or two adjacent holes. This applies whether you have four, five, six or eight holes to measure between. Once you have the measurement between two studs, you can then work out the measurements.You use the PCD value to check the "M" dimension on the motor dimension sheet.In the below calculator, the measurement between two holes is value “S.”
Can I replace an aluminium motor with a cast iron motor?
Example Guide - Guide about how MM can supply motors with PT100 Sensors. Example Guide - Guide about how MM can supply motors with PT100 Sensors. Example Guide - Guide about how MM can supply motors with PT100 Sensors.
How do I read an electric motor nameplate?
The Pitch Circle Diameter (PCD) is the diameter of the circle that passes through the centre of all the flange mounting holes.Measure the distance between the centre or two adjacent holes. This applies whether you have four, five, six or eight holes to measure between. Once you have the measurement between two studs, you can then work out the measurements.You use the PCD value to check the "M" dimension on the motor dimension sheet.In the below calculator, the measurement between two holes is value “S.”
What does S1, S2, and S3 duty cycle mean?
B3 motors foot mounted motorsB5 Flange mounted motors
Can i replace a three phase motor with a single phase motor?
B3 motors foot mounted motorsB5 Flange mounted motors
Installation & Wiring
How do I wire a 3-phase motor in Star vs. Delta?
To wire a 3-phase motor, you must choose between Star or Delta based on your supply voltage and motor nameplate.Star (High Voltage): Links W2-U2-V2 together. Use this for 400V mains on a standard 230/400V motor.Delta (Low Voltage): Links U1-W2, V1-U2, W1-V2 in pairs. Use this for 230V inverter supply on a standard motor.Star (Y) Connection: Connects the three "finish" ends (W2, U2, V2) together. Used for 400V Supply on standard small/medium motors (up to 4.0kW).Delta (Δ) Connection: Connects the start of one phase to the end of the next (U1-W2, V1-U2, W1-V2). Used for 230V Supply (e.g., Single Phase Inverter) on small motors, OR 400V Supply on large motors (4kW+) marked 400/690V.Star Connection - Wiring DiagramDelta Connection - Wiring DiagramIf it says 230/400V: Star = 400V (Mains), Delta = 230V (Inverter).If it says 400/690V: Delta = 400V (Mains), Star = 690V.** STOP: Always consult the motor winding diagram on the terminal box cover. When in doubt, contact the manufacturer or a qualified electrician
What size cable do I need for my electric motor?
The size of the cable need for you electric motor installation depends on the motor power, voltage and the distance between the power source and the motor. A 2.2kW single phase motor would typically need a 1.5mm² cable, while a 2.2kW three phase motor would also need a 1.5mm².
How do I reverse the direction of a single-phase motor?
To wire a 3-phase motor, you must choose between Star or Delta based on your supply voltage and motor nameplate.Star (High Voltage): Links W2-U2-V2 together. Use this for 400V mains on a standard 230/400V motor.Delta (Low Voltage): Links U1-W2, V1-U2, W1-V2 in pairs. Use this for 230V inverter supply on a standard motor.Star (Y) Connection: Connects the three "finish" ends (W2, U2, V2) together. Used for 400V Supply on standard small/medium motors (up to 4.0kW).Delta (Δ) Connection: Connects the start of one phase to the end of the next (U1-W2, V1-U2, W1-V2). Used for 230V Supply (e.g., Single Phase Inverter) on small motors, OR 400V Supply on large motors (4kW+) marked 400/690V.Star Connection - Wiring DiagramDelta Connection - Wiring Diagram** STOP: Check your motor nameplate.If it says 230/400V: Star = 400V (Mains), Delta = 230V (Inverter).If it says 400/690V: Delta = 400V (Mains), Star = 690V.
Do I need a motor starter or overload protection?
To wire a 3-phase motor, you must choose between Star or Delta based on your supply voltage and motor nameplate.Star (High Voltage): Links W2-U2-V2 together. Use this for 400V mains on a standard 230/400V motor.Delta (Low Voltage): Links U1-W2, V1-U2, W1-V2 in pairs. Use this for 230V inverter supply on a standard motor.Star (Y) Connection: Connects the three "finish" ends (W2, U2, V2) together. Used for 400V Supply on standard small/medium motors (up to 4.0kW).Delta (Δ) Connection: Connects the start of one phase to the end of the next (U1-W2, V1-U2, W1-V2). Used for 230V Supply (e.g., Single Phase Inverter) on small motors, OR 400V Supply on large motors (4kW+) marked 400/690V.Star Connection - Wiring DiagramDelta Connection - Wiring Diagram** STOP: Check your motor nameplate.If it says 230/400V: Star = 400V (Mains), Delta = 230V (Inverter).If it says 400/690V: Delta = 400V (Mains), Star = 690V.
Troubleshooting
Winding Failures
To wire a 3-phase motor, you must choose between Star or Delta based on your supply voltage and motor nameplate.Star (High Voltage): Links W2-U2-V2 together. Use this for 400V mains on a standard 230/400V motor.Delta (Low Voltage): Links U1-W2, V1-U2, W1-V2 in pairs. Use this for 230V inverter supply on a standard motor.Star (Y) Connection: Connects the three "finish" ends (W2, U2, V2) together. Used for 400V Supply on standard small/medium motors (up to 4.0kW).Delta (Δ) Connection: Connects the start of one phase to the end of the next (U1-W2, V1-U2, W1-V2). Used for 230V Supply (e.g., Single Phase Inverter) on small motors, OR 400V Supply on large motors (4kW+) marked 400/690V.Star Connection - Wiring DiagramDelta Connection - Wiring Diagram** STOP: Check your motor nameplate.If it says 230/400V: Star = 400V (Mains), Delta = 230V (Inverter).If it says 400/690V: Delta = 400V (Mains), Star = 690V.
Why is my electric motor humming but not starting?
To wire a 3-phase motor, you must choose between Star or Delta based on your supply voltage and motor nameplate.Star (High Voltage): Links W2-U2-V2 together. Use this for 400V mains on a standard 230/400V motor.Delta (Low Voltage): Links U1-W2, V1-U2, W1-V2 in pairs. Use this for 230V inverter supply on a standard motor.Star (Y) Connection: Connects the three "finish" ends (W2, U2, V2) together. Used for 400V Supply on standard small/medium motors (up to 4.0kW).Delta (Δ) Connection: Connects the start of one phase to the end of the next (U1-W2, V1-U2, W1-V2). Used for 230V Supply (e.g., Single Phase Inverter) on small motors, OR 400V Supply on large motors (4kW+) marked 400/690V.Star Connection - Wiring DiagramDelta Connection - Wiring Diagram** STOP: Check your motor nameplate.If it says 230/400V: Star = 400V (Mains), Delta = 230V (Inverter).If it says 400/690V: Delta = 400V (Mains), Star = 690V.
Why does my motor keep tripping the circuit breaker?
To wire a 3-phase motor, you must choose between Star or Delta based on your supply voltage and motor nameplate.Star (High Voltage): Links W2-U2-V2 together. Use this for 400V mains on a standard 230/400V motor.Delta (Low Voltage): Links U1-W2, V1-U2, W1-V2 in pairs. Use this for 230V inverter supply on a standard motor.Star (Y) Connection: Connects the three "finish" ends (W2, U2, V2) together. Used for 400V Supply on standard small/medium motors (up to 4.0kW).Delta (Δ) Connection: Connects the start of one phase to the end of the next (U1-W2, V1-U2, W1-V2). Used for 230V Supply (e.g., Single Phase Inverter) on small motors, OR 400V Supply on large motors (4kW+) marked 400/690V.Star Connection - Wiring DiagramDelta Connection - Wiring Diagram** STOP: Check your motor nameplate.If it says 230/400V: Star = 400V (Mains), Delta = 230V (Inverter).If it says 400/690V: Delta = 400V (Mains), Star = 690V.
What causes an electric motor to overheat?
To wire a 3-phase motor, you must choose between Star or Delta based on your supply voltage and motor nameplate.Star (High Voltage): Links W2-U2-V2 together. Use this for 400V mains on a standard 230/400V motor.Delta (Low Voltage): Links U1-W2, V1-U2, W1-V2 in pairs. Use this for 230V inverter supply on a standard motor.Star (Y) Connection: Connects the three "finish" ends (W2, U2, V2) together. Used for 400V Supply on standard small/medium motors (up to 4.0kW).Delta (Δ) Connection: Connects the start of one phase to the end of the next (U1-W2, V1-U2, W1-V2). Used for 230V Supply (e.g., Single Phase Inverter) on small motors, OR 400V Supply on large motors (4kW+) marked 400/690V.Star Connection - Wiring DiagramDelta Connection - Wiring Diagram** STOP: Check your motor nameplate.If it says 230/400V: Star = 400V (Mains), Delta = 230V (Inverter).If it says 400/690V: Delta = 400V (Mains), Star = 690V.
How do I test a motor capacitor with a multimeter?
To wire a 3-phase motor, you must choose between Star or Delta based on your supply voltage and motor nameplate.Star (High Voltage): Links W2-U2-V2 together. Use this for 400V mains on a standard 230/400V motor.Delta (Low Voltage): Links U1-W2, V1-U2, W1-V2 in pairs. Use this for 230V inverter supply on a standard motor.Star (Y) Connection: Connects the three "finish" ends (W2, U2, V2) together. Used for 400V Supply on standard small/medium motors (up to 4.0kW).Delta (Δ) Connection: Connects the start of one phase to the end of the next (U1-W2, V1-U2, W1-V2). Used for 230V Supply (e.g., Single Phase Inverter) on small motors, OR 400V Supply on large motors (4kW+) marked 400/690V.Star Connection - Wiring DiagramDelta Connection - Wiring Diagram** STOP: Check your motor nameplate.If it says 230/400V: Star = 400V (Mains), Delta = 230V (Inverter).If it says 400/690V: Delta = 400V (Mains), Star = 690V.
Maintenance
How often should I grease electric motor bearings?
To wire a 3-phase motor, you must choose between Star or Delta based on your supply voltage and motor nameplate.Star (High Voltage): Links W2-U2-V2 together. Use this for 400V mains on a standard 230/400V motor.Delta (Low Voltage): Links U1-W2, V1-U2, W1-V2 in pairs. Use this for 230V inverter supply on a standard motor.Star (Y) Connection: Connects the three "finish" ends (W2, U2, V2) together. Used for 400V Supply on standard small/medium motors (up to 4.0kW).Delta (Δ) Connection: Connects the start of one phase to the end of the next (U1-W2, V1-U2, W1-V2). Used for 230V Supply (e.g., Single Phase Inverter) on small motors, OR 400V Supply on large motors (4kW+) marked 400/690V.Star Connection - Wiring DiagramDelta Connection - Wiring Diagram** STOP: Check your motor nameplate.If it says 230/400V: Star = 400V (Mains), Delta = 230V (Inverter).If it says 400/690V: Delta = 400V (Mains), Star = 690V.
What is the typical lifespan of an industrial electric motor?
To wire a 3-phase motor, you must choose between Star or Delta based on your supply voltage and motor nameplate.Star (High Voltage): Links W2-U2-V2 together. Use this for 400V mains on a standard 230/400V motor.Delta (Low Voltage): Links U1-W2, V1-U2, W1-V2 in pairs. Use this for 230V inverter supply on a standard motor.Star (Y) Connection: Connects the three "finish" ends (W2, U2, V2) together. Used for 400V Supply on standard small/medium motors (up to 4.0kW).Delta (Δ) Connection: Connects the start of one phase to the end of the next (U1-W2, V1-U2, W1-V2). Used for 230V Supply (e.g., Single Phase Inverter) on small motors, OR 400V Supply on large motors (4kW+) marked 400/690V.Star Connection - Wiring DiagramDelta Connection - Wiring Diagram** STOP: Check your motor nameplate.If it says 230/400V: Star = 400V (Mains), Delta = 230V (Inverter).If it says 400/690V: Delta = 400V (Mains), Star = 690V.