3-Phase Motor Wiring Diagram: 6-Wire Star and Delta Connection

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A 6-wire three-phase motor wiring diagram shows how the six leads (U1, V1, W1, U2, V2, W2) in the terminal box are linked to configure the motor for star (Y) or delta (Δ) operation on two different supply voltages.

A dual-voltage three-phase induction motor has six external leads brought out to the terminal box. These leads correspond to the beginning and end of each of the three stator windings. IEC standard terminal designation uses U1, V1, W1 for the winding starts and U2, V2, W2 for the winding ends. NEMA designation uses T1–T6 or T1–T9 for nine-lead motors; on a six-lead motor these often appear as T1/T4, T2/T5, T3/T6.

The motor nameplate specifies two voltages, for example 230/400 V or 380/660 V (IEC) or 208–230/460 V (NEMA). The lower voltage uses delta connection; the higher voltage uses star (wye) connection. This is because in star, each winding sees phase voltage (supply voltage divided by √3), while in delta, each winding sees full line voltage.

Star (wye) connection — high-voltage configuration: Link the three winding ends together to form the star point: connect U2, V2, and W2 together with a jumper link. Supply line conductors L1, L2, L3 connect to U1, V1, W1 respectively. Each winding operates at V_line / √3.

Delta connection — low-voltage configuration: The end of each winding connects to the start of the next: connect U1 to W2, V1 to U2, W1 to V2. Supply line conductors L1, L2, L3 connect to the U1/W2 junction, V1/U2 junction, and W1/V2 junction respectively. Each winding now operates at full line voltage.

Star-delta starting: To reduce starting current (which can be 6–8 times full-load current in direct-on-line starting), many motors are started in star configuration then switched to delta at approximately 75–80% of full speed, using a star-delta starter. In this case all six terminals must be individually accessible and a dedicated starter controls the contactor arrangement.

Phase rotation and direction: Swapping any two supply leads (e.g., L1 and L2) reverses the direction of rotation regardless of whether the motor is connected star or delta. Always verify rotation direction before connecting to a load.

Most modern low-voltage motors are designed for delta connection on 230/400 V systems and star connection on 400/690 V systems, enabling use on either European 400 V or higher-voltage networks.

How to wire 3 phase motor wiring diagram 6 wire

Read the motor nameplate and identify the required connection Note the voltage ratings (e.g., 230/400 V Δ/Y), confirm the supply voltage, and determine whether star or delta connection is required. Also note full-load current, frequency (50 or 60 Hz), and power rating.
Isolate the supply and verify dead Disconnect and lock out the supply. Apply lockout/tagout at the isolator or drive. Use a calibrated voltage tester to confirm no voltage is present on all three phases at the motor terminal box before opening it.
Open the terminal box and identify all six leads Locate terminals U1, V1, W1, U2, V2, W2 (or T1–T6 in NEMA notation). Check for any existing jumper links and remove them if reconfiguring the connection. Photograph the existing configuration before making changes.
Install jumper links for star connection (high-voltage supply) Bridge U2, V2, and W2 together using the supplied jumper bar or appropriate rated copper links. Connect supply phases L1, L2, L3 to U1, V1, W1 respectively. Tighten all terminal screws to the torque specified in the motor manual.
Install jumper links for delta connection (low-voltage supply) Connect U1 to W2 (L1 supply here), V1 to U2 (L2 supply here), W1 to V2 (L3 supply here). Three separate jumper links are required. Ensure the motor winding voltage matches the supply line voltage exactly before energising.
Verify phase rotation before connecting to load Connect supply and run the motor uncoupled from the load. Observe shaft rotation direction. If rotation is wrong, de-energise, verify dead, then swap two supply conductors. Re-check before coupling.
Close terminal box and commission Replace terminal box lid and tighten all cable gland entries to the appropriate IP rating. Restore power via isolator and starter. Measure running current on all three phases with a clamp meter and compare to nameplate full-load amperage.

Specifications

IEC terminal designation (6-lead motor)	U1, V1, W1 (winding starts); U2, V2, W2 (winding ends) per IEC 60034-8
NEMA terminal designation (6-lead motor)	T1, T2, T3 (line terminals in delta/wye connection); T4, T5, T6 (internal winding ends)
Star point winding voltage (relative to line voltage)	V_line / √3 ≈ 0.577 × V_line (e.g., 230 V winding on 400 V supply)
Delta winding voltage (relative to line voltage)	V_line (e.g., 400 V winding on 400 V supply)
Starting current reduction — star-delta vs DOL	Star-delta start reduces starting current to approximately 1/3 of DOL starting current
Applicable IEC standard for motor terminal markings	IEC 60034-8 (rotating electrical machines — terminal markings)
Typical direct-on-line starting current (induction motor)	6–8 × full-load current (FLA)

Safety warnings

All wiring of three-phase motor circuits is fixed electrical work and must be carried out by a licensed electrician in compliance with the applicable wiring standard: NEC/NFPA 70 (USA), BS 7671 (UK), AS/NZS 3000 (Australia/NZ), IEC 60364 (international). Always verify which standard applies in your jurisdiction.
Always isolate the supply, apply lockout/tagout, and verify all three phases are dead with a calibrated voltage tester before opening the motor terminal box. Three-phase voltages are lethal.
Never connect a motor in delta on a voltage rated for star connection. The winding voltage will be √3 times the rated value, causing immediate overheating, insulation breakdown, and potential fire.
Verify the phase sequence before coupling the motor to any mechanical load. Connecting a pump, fan, or compressor in reverse can cause mechanical damage, flooding, or pressure reversal. Test rotation uncoupled first.
Set the overload relay to the motor's nameplate full-load amperage (FLA). An incorrectly set overload relay will either nuisance-trip or fail to protect the motor from overheating damage.

Tools needed

Calibrated multimeter (AC voltage, resistance, continuity)
Non-contact voltage tester
Clamp meter (for phase current measurement during commissioning)
Phase rotation meter / phase sequence tester
Insulated screwdrivers and spanners
Torque screwdriver or torque wrench (for terminal torque compliance)
Lockout/tagout kit
Cable gland tools and crimping tool

Common mistakes

Connecting the motor in delta when star is required for the supply voltage (or vice versa), causing immediate over-voltage or under-torque conditions.
Incorrectly identifying terminals when nameplate or terminal markings are worn or non-standard, leading to open-circuit or incorrect winding connections.
Failing to verify phase rotation before coupling to a load, resulting in mechanical equipment running backwards.
Setting the overload relay to the star current but then switching to delta operation, causing nuisance tripping (delta FLA is √3 times the star FLA at the same power).
Tightening terminal screws without meeting specified torque, leading to loose connections that arc and overheat under load.
Using a star-delta starter without ensuring all six leads are individually accessible; linking any two terminals together in the terminal box defeats the starter's function.

Troubleshooting

Motor runs but draws unbalanced current on the three phases: Cause: A loose or open terminal connection, a damaged winding in one phase, or a missing jumper link has created an unbalanced winding circuit Fix: De-energise and lock out. Check all six terminals for tightness to specified torque. Measure winding resistance between all terminal pairs (U1-U2, V1-V2, W1-W2) and compare; they should be equal within approximately 5%. Investigate any open or high-resistance measurement further.
Motor will not start and overload relay trips immediately: Cause: Motor may be connected in wrong voltage configuration (delta on star-rated voltage), single-phasing (one supply phase missing), or a mechanical jam Fix: Verify supply voltage on all three phases. Confirm terminal connections match the nameplate configuration. Check that all three supply phases are reaching the motor terminals. Disconnect from the load and retest to eliminate mechanical causes.
Motor runs in the wrong direction: Cause: Supply phase sequence does not match the intended rotation direction Fix: De-energise, lock out, and verify dead. Swap any two of the three supply conductors (e.g., L1 and L2) at the motor terminal box or at the starter. Restore supply and re-verify rotation before coupling to the load.
Motor overheats in normal operation: Cause: Motor connected in star on a delta-rated voltage (under-voltage), incorrect overload setting, inadequate ventilation, or sustained overload from the driven equipment Fix: Confirm connection configuration matches nameplate voltage. Measure phase currents and compare to nameplate FLA. Check ventilation clearances and fan cover for blockage. Investigate mechanical load for overload condition.

Frequently asked questions

How do I know whether to connect my 6-wire motor in star or delta?

Read the motor nameplate. It states two voltages (e.g., 230/400 V Δ/Y). Connect in delta for the lower voltage and star for the higher voltage. If your supply is 400 V, use the star configuration as specified. Never connect in delta on a voltage rated for star — windings will be over-volted and the motor will fail.

What is the purpose of a star-delta starter with a 6-wire motor?

A star-delta starter reduces the starting current by initially connecting the motor in star, which applies only 58% of line voltage to each winding. Once near full speed, the starter switches to delta for rated operation. This reduces starting current to approximately one-third of direct-on-line delta starting current, lowering mechanical and electrical stress.

What do U1, V1, W1, U2, V2, W2 mean on the terminal board?

These are IEC 60034-8 terminal designations. U1, V1, W1 are the start (supply-end) of the three stator windings. U2, V2, W2 are the finish (opposite) end of the same three windings. In star connection, U2/V2/W2 are linked together. In delta, U2 connects to V1, V2 to W1, and W2 to U1.

Can I run a 6-wire motor on a variable frequency drive (VFD)?

Yes. Connect the motor in delta for low-voltage drives or star for higher-voltage drives, matching the drive output voltage to the motor winding voltage. Link unused terminals correctly and do not use a star-delta starter with a VFD — the VFD controls starting directly. Always follow both the VFD and motor manufacturer's instructions.

How do I reverse a three-phase motor?

Swap any two of the three supply conductors (e.g., swap L1 and L2 at the terminal box or at the supply contactor). The internal star or delta connection does not affect how reversal is achieved. Never reverse a motor by altering the internal winding links. Always de-energise and verify dead before accessing terminals.

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