AC Induction Motor Star and Delta Connections Explained

Introduction

Most dual-voltage AC induction motors are supplied with a terminal box containing six connection points. These terminals can be linked in different ways to match the motor to the available power supply.

The two connection types are:

Star (Y) – used for higher voltage
Delta (Δ) – used for lower voltage

Important: The connection method is not a choice for performance—it must match your supply voltage. Incorrect wiring can damage the motor and create a safety risk.

Typical UK & European Motor Voltages

In the UK and Europe, the standard three-phase supply is 400V. Motors are commonly rated as follows:

Up to 3kW: 230V / 400V → Connect in Star for 400V supply
4kW and above: 400V / 690V → Connect in Delta for 400V supply

Always check the motor nameplate before making any connections.

Star Connection (Y)

Star connection is used when the motor is connected to the higher voltage shown on the nameplate.

Ensure the earth (ground) connection is securely connected.

Star (Y) connection diagram for AC induction motor

Delta Connection (Δ)

Delta connection is used when the motor is connected to the lower voltage shown on the nameplate.

Ensure the earth (ground) connection is securely connected.

Delta (Δ) connection diagram for AC induction motor

Motor Links Explained

AC induction motors are typically supplied with three brass linking bars (links) used to configure the terminals.

If the motor is pre-configured in Star, you may only see two links at first glance. One terminal will usually have two links fitted, allowing easy conversion to Delta if required.

Safety Advice

Always isolate the power supply before working on motor terminals
Verify the supply voltage matches the motor nameplate
Ensure all terminal screws are tight and secure
Check correct earthing before operation
If unsure, consult a qualified electrician