How do you connect a 3 phase motor in star?

For a standard 6-terminal motor, connect L1 to U1, L2 to V1, L3 to W1 and link U2, V2 and W2 together as the star point.

How do you connect a 3 phase motor in delta?

For a common IEC terminal layout, make three links: U1 to W2, V1 to U2 and W1 to V2. Then connect the supply lines to the three joined pairs.

Can every motor use star delta starting?

No. Star-delta starting is normally used only when the motor has six accessible terminals and is rated to run in delta at the supply voltage, for example 400V delta / 690V star on a 400V system.

Star Delta Motor Terminal Diagram | Wiring Reference

Star Delta Motor Terminal Diagram

A practical reference for 6-terminal three-phase motor star and delta wiring, including U1 V1 W1 / U2 V2 W2 terminal links, contactor sequence, overload placement and common nameplate checks.

⚠️ Important: Star-delta starting is suitable only when the motor can run in delta at the supply voltage. On a 400 V supply, the motor nameplate is usually expected to show 400 Δ / 690 Y. Check the motor nameplate before wiring.

🔌 Visual terminal box reference: Star vs Delta links

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Item	Connection / Meaning	Group	Practical note
Star supply	L1 → U1, L2 → V1, L3 → W1	STAR	Supply goes to the start ends of the three windings.
Star point	Link W2 + U2 + V2 together	STAR	The three lower terminals are shorted as one common star point.
Delta links	U1-W2, V1-U2, W1-V2	DELTA	These three vertical links form the delta winding loop.
Delta supply	L1, L2, L3 feed the three linked pairs	DELTA	In normal run, each winding sees full line-rated phase voltage.
Starter sequence	Main + Star ON → open transition → Main + Delta ON	CONTROL	Star and delta contactors must be electrically and mechanically interlocked.
Timer	Star time usually a few seconds, then transfer to delta	CONTROL	Set just long enough for the motor to accelerate near rated speed.
Overload relay	Line-side or inside-delta depending on panel design	CONTROL	Inside-delta overload setting is typically 0.58 × motor FLA.
Nameplate check	400 Δ / 690 Y is typical for 400 V star-delta use	SAFETY	Do not run a 230 Δ / 400 Y motor in delta on a 400 V supply.
Rotation	Swap any two incoming phases to reverse direction	SAFETY	Verify rotation before coupling pumps, fans, conveyors or compressors.

Step 1

Main + Star

starting period

Step 2

Open gap

transition delay

Step 3

Main + Delta

normal running

✅ In a standard open-transition star-delta starter, the delta contactor should never close while the star contactor is still closed. Use both mechanical and electrical interlocking.

⚠️ Too-short star time causes high current during transition. Too-long star time can make the motor run weakly, overheat, or fail to accelerate under load.

Good for 400 V star-delta

Nameplate400 Δ / 690 Y

Supply400 V

RunDelta

Not for 400 V delta run

Nameplate230 Δ / 400 Y

Supply400 V

RunStar / VFD check

Terminal requirement

Motor leads6 terminals

LabelsU1 V1 W1 / U2 V2 W2

Starter3 contactors

❌ If the motor has only three accessible terminals, a conventional star-delta starter cannot change the winding connection externally.

📋 Quick Reference

⭐ Star links

SupplyU1 V1 W1

Common linkW2-U2-V2

🔺 Delta links

Link 1U1-W2

Link 2V1-U2

Link 3W1-V2

⚙️ Current / torque

Star line current≈ 1/3 DOL

Star torque≈ 1/3 DOL

Delta runfull voltage

📚 Field Notes

Terminal layout matters Many IEC motors use top row U1 V1 W1 and bottom row W2 U2 V2, but always confirm the terminal box diagram.

Star-delta reduces torque Starting torque is also reduced, so it is not ideal for heavily loaded starts such as loaded conveyors or compressors.

Overload setting depends on location A line-side overload is normally set to motor FLA. Inside-delta overload often uses 0.58 × FLA.

Check alternatives For frequent starts, heavy loads or smooth acceleration, compare with a soft starter or VFD.

Star Delta Motor Terminal Diagram

This star delta wiring reference explains how to connect a six-terminal three-phase induction motor in star for starting and delta for normal running. It shows the common U1, V1, W1, W2, U2 and V2 terminal layout used in many motor terminal boxes.

How star delta starting works

In star mode, the motor windings receive reduced phase voltage, so starting current and starting torque are lower than direct-on-line starting. After the motor accelerates, the starter opens the star contactor and closes the delta contactor for normal full-voltage running.

❓ Frequently Asked Questions

Connect L1 to U1, L2 to V1, L3 to W1, then link U2, V2 and W2 together as the star point.

For the common IEC terminal layout, link U1-W2, V1-U2 and W1-V2. Connect the three supply lines to those three linked pairs.

Usually a motor marked 400 Δ / 690 Y is suitable for star-delta starting on a 400 V supply because it runs in delta at 400 V.

Normally no. A 230 Δ / 400 Y motor is designed to run in star on 400 V, not in delta on 400 V.

Common causes include wrong terminal links, wrong phase sequence, too-short acceleration time, heavy load, contactor overlap, low voltage, mechanical jamming or wrong overload setting.

There is no universal value. It is usually set long enough for the motor to reach near rated speed before transfer, often a few seconds depending on load inertia.

It may be installed in line or inside delta depending on the panel design. The setting changes with the location, so follow the wiring diagram and relay manual.

Yes, line starting current is typically reduced to about one-third of DOL, but starting torque is also reduced to about one-third.