Three Phase Electric Motor Wiring Diagrams: Complete Guide (3, 6, 9, & 12-Lead)

Wiring a three-phase electric motor correctly is one of the most critical steps in any motor installation. Get it wrong, and you risk burned windings, tripped breakers, or worse — a safety hazard. Get it right, and your motor will run efficiently for decades. This guide covers every common three-phase motor configuration — 3-lead, 6-lead, 9-lead, and 12-lead — with wiring diagrams, voltage explanations, wire sizing tables, and the real-world tips that come from over 50 years of helping people run three-phase equipment.

Understanding Three-Phase Motor Leads

Three-phase motors use either 3, 6, 9, or 12 wire leads coming out of the motor housing. The number of leads determines how the motor can be configured:

Voltage Basics: 230V vs. 460V and Why Dual Voltage Matters

Most three-phase motors in the United States are rated for dual voltage — typically 230V and 460V (sometimes labeled 208-230/460V). Understanding the difference is essential before you wire anything:

• 230V (Low Voltage): The motor windings are connected in parallel. This draws more current but requires a lower supply voltage. Most shops with single-phase utility power use a phase converter to generate 230V three-phase — making this the most common configuration for small to mid-size operations.
• 460V (High Voltage): The motor windings are connected in series. This draws roughly half the current of the 230V configuration. Used where utility three-phase power is available at 480V. Less common in residential or small shop settings.

Why does dual voltage matter? Flexibility. A dual-voltage motor can be installed in either a 230V or 460V facility. If you move your shop or upgrade your electrical service, you can reconfigure the motor instead of replacing it. It also means you can run the motor on a rotary phase converter at 230V even if the motor nameplate shows 460V — just wire it for low voltage.

Three-Phase Motor Wiring Diagrams

Below are standard wiring connections for each lead configuration. The lead numbers (T1, T2, T3, etc.) follow NEMA standards. Your motor's nameplate diagram is always the final authority.

3-Lead Motor Wiring

A 3-lead motor is the simplest to wire. It has three leads — T1, T2, and T3 — and operates at a single fixed voltage. There is no high/low voltage option. You simply connect the three motor leads to the three power supply lines (L1, L2, L3).

  L1 ────── T1
  L2 ────── T2
  L3 ────── T3

  That's it. Single voltage, single configuration.
  To reverse rotation: swap any two line leads (e.g., swap L1 and L3).

Rotation: If the motor spins the wrong direction, swap any two of the three line connections. For example, move L1 to T3 and L3 to T1.

6-Lead Motor Wiring

A 6-lead motor has two sets of three windings that can be connected in series (high voltage) or parallel (low voltage). Leads are typically numbered T1–T6.

6-Lead — Low Voltage (230V) — Parallel Connection

  L1 ────┬──── T1
         └──── T6

  L2 ────┬──── T2
         └──── T4

  L3 ────┬──── T3
         └──── T5

  Connect together:     L1+T1+T6    L2+T2+T4    L3+T3+T5

6-Lead — High Voltage (460V) — Series Connection

  L1 ────── T1          T4 ──┐
  L2 ────── T2          T5 ──┤── Connect T4+T5+T6 together
  L3 ────── T3          T6 ──┘

  Line connections:     L1→T1    L2→T2    L3→T3
  Join together:        T4 + T5 + T6 (insulate this splice)

9-Lead Motor Wiring (Most Common)

The 9-lead motor is the most common dual-voltage three-phase motor you'll encounter in industrial and shop settings. Leads are numbered T1–T9. It can be wired in either wye (star) or delta configuration, depending on the motor's design — check the nameplate.

9-Lead Wye (Star) — Low Voltage (230V)

  L1 ────┬──── T1
         └──── T7

  L2 ────┬──── T2
         └──── T8

  L3 ────┬──── T3
         └──── T9

  Join together:  T4 + T5 + T6 (this is the internal star point — insulate it)

  Summary:
    L1 → T1 + T7
    L2 → T2 + T8
    L3 → T3 + T9
    Together: T4 + T5 + T6

9-Lead Wye (Star) — High Voltage (460V)

  L1 ────── T1          T4 ──── T7
  L2 ────── T2          T5 ──── T8
  L3 ────── T3          T6 ──── T9

  Summary:
    L1 → T1        T4 → T7
    L2 → T2        T5 → T8
    L3 → T3        T6 → T9

9-Lead Delta — Low Voltage (230V)

  L1 ────┬──── T1
         ├──── T7
         └──── T6

  L2 ────┬──── T2
         ├──── T8
         └──── T4

  L3 ────┬──── T3
         ├──── T9
         └──── T5

  Summary:
    L1 → T1 + T6 + T7
    L2 → T2 + T4 + T8
    L3 → T3 + T5 + T9

9-Lead Delta — High Voltage (460V)

  L1 ────── T1          T4 ──── T7
  L2 ────── T2          T5 ──── T8
  L3 ────── T3          T6 ──── T9

  Summary:
    L1 → T1        T4 → T7
    L2 → T2        T5 → T8
    L3 → T3        T6 → T9

12-Lead Motor Wiring

12-lead motors provide the most wiring flexibility. They have four sets of three windings, allowing wye or delta connections in both series (high voltage) and parallel (low voltage) configurations. Leads are numbered T1–T12.

12-Lead Wye — Low Voltage (230V)

  L1 ────┬──── T1
         └──── T7

  L2 ────┬──── T2
         └──── T8

  L3 ────┬──── T3
         └──── T9

  Join together:  T4 + T5 + T6 + T10 + T11 + T12

  Summary:
    L1 → T1 + T7
    L2 → T2 + T8
    L3 → T3 + T9
    Together: T4 + T5 + T6 + T10 + T11 + T12

12-Lead Wye — High Voltage (460V)

  L1 ────── T1          T4 ──── T7
  L2 ────── T2          T5 ──── T8
  L3 ────── T3          T6 ──── T9

  Join together:  T10 + T11 + T12

  Summary:
    L1 → T1        T4 → T7
    L2 → T2        T5 → T8
    L3 → T3        T6 → T9
    Together: T10 + T11 + T12

12-Lead Delta — Low Voltage (230V)

  L1 ────┬──── T1
         ├──── T7
         ├──── T6
         └──── T12

  L2 ────┬──── T2
         ├──── T8
         ├──── T4
         └──── T10

  L3 ────┬──── T3
         ├──── T9
         ├──── T5
         └──── T11

  Summary:
    L1 → T1 + T6 + T7 + T12
    L2 → T2 + T4 + T8 + T10
    L3 → T3 + T5 + T9 + T11

12-Lead Delta — High Voltage (460V)

  L1 ────── T1          T4 ──── T7       T12 ──── T6
  L2 ────── T2          T5 ──── T8       T10 ──── T4
  L3 ────── T3          T6 ──── T9       T11 ──── T5

  Correction — standard 12-lead delta high voltage:

  L1 ────── T1          T7 ──── T6       T12 ──── T4  (wait — not right)

  Use your motor nameplate for 12-lead delta high voltage.
  The standard NEMA connection is:

    L1 → T1        T6 → T7        T12 → connect per nameplate
    L2 → T2        T4 → T8        T10 → connect per nameplate
    L3 → T3        T5 → T9        T11 → connect per nameplate

Note: 12-lead delta high-voltage connections vary more between manufacturers than other configurations. Always follow your motor's specific nameplate diagram for this connection.

Wire Sizing Reference for Three-Phase Motors

Proper wire sizing prevents overheating, voltage drop, and fire hazards. The table below shows recommended copper conductor sizes for typical three-phase motor circuits at 230V, based on NEC Table 430.250 full-load current values and 75°C-rated conductors. For 460V motors, current is approximately half — you can often use wire one or two sizes smaller.

These are general guidelines based on NEC Table 430.250 and 310.16. Actual requirements depend on ambient temperature, conduit fill, conductor length, and local code. Breaker sizing per NEC 430.52 allows up to 250% of FLA for inverse-time breakers on motor circuits. Always consult a licensed electrician or your local AHJ (Authority Having Jurisdiction) for your specific installation.

Common Three-Phase Motor Wiring Mistakes

After 50+ years in the phase converter business, we've seen every wiring mistake in the book. Here are the ones that keep coming back:

1. Wiring for the Wrong Voltage

This is the #1 killer. Someone wires a dual-voltage motor for 230V (parallel) and then connects it to 480V utility power. The motor might run for a few seconds before the windings burn. Always verify your supply voltage before touching a single wire.

2. Mixing Up Lead Numbers

On a 9-lead motor, confusing T7 with T4 puts windings in the wrong configuration. The result: unbalanced currents, excessive vibration, overheating, and premature failure. Use a multimeter to verify lead identification if the markings are worn or unclear.

3. Poor Connections

Loose wire nuts, corroded lugs, or undersized connectors create high-resistance joints. These show up as hot spots, voltage drops, and intermittent tripping. Use properly rated connectors, torque lugs to specification, and apply anti-oxidant compound on aluminum conductors.

4. Undersized Wire

Running a 10 HP motor on 14 AWG wire is a fire waiting to happen. Motor circuits must be sized at 125% of the full-load amperage per NEC 430.22. Refer to the wire sizing table above and always round up, not down.

5. No Overload Protection

A breaker protects the wire, not the motor. Motors need dedicated overload relays (thermal or electronic) sized to the motor's nameplate FLA. Without overloads, a jammed shaft or single-phasing event will cook the windings before the breaker trips. NEC Article 430 Part III covers motor overload protection requirements.

6. Ignoring the Ground

Every motor installation requires an equipment grounding conductor per NEC 250.4 and 430.12. The motor frame must be bonded to the grounding system. This isn't optional — it's what keeps people alive in a fault condition.

7. Not Checking Rotation Before Connecting the Load

Wire the motor, bump the start button, and verify rotation before coupling it to the load. Running a compressor or pump backward can cause serious damage. Swapping any two of the three line leads reverses rotation.

Running Three-Phase Motors on Single-Phase Power

Here's the reality for most home shops, farms, and small businesses in the US: your utility only provides single-phase power. But the best industrial equipment — CNC machines, lathes, milling machines, air compressors, dust collectors — runs on three-phase motors. So what do you do?

You use a rotary phase converter.

A rotary phase converter takes your single-phase 230V power and generates a true third leg, producing balanced three-phase power that motors love. Unlike static converters or VFDs (which have limitations), a rotary phase converter delivers clean, balanced power across all three legs — identical to utility three-phase.

How to Size a Phase Converter

The general rule: match the phase converter HP rating to your largest motor's HP rating. If you're running multiple motors simultaneously, add up the HP of everything that runs at the same time.

Wiring a motor to a phase converter follows the exact same diagrams above. The phase converter output gives you L1, L2, and L3 — you connect them to the motor leads just as you would with utility three-phase power. Wire the motor for low voltage (230V) since phase converters operate at 230V single-phase in / 230V three-phase out.

Why Phoenix Phase Converters?

Phoenix Phase Converters has been building rotary phase converters in the USA for over 50 years. Every unit comes with a lifetime warranty and is built to industrial standards. Our founder, Daniel Floreancig, designed these converters for real-world shop use — they're not lightweight consumer products. They're built to start hard loads, run all day, and last a lifetime.

NEC Code References for Three-Phase Motor Installations

For those who want to do it by the book (and you should), here are the key NEC articles that apply to three-phase motor wiring:

• NEC Article 430 — Motors, Motor Circuits, and Controllers (the big one)
• NEC 430.6 — Use nameplate amperage for overload protection, but use NEC Table 430.250 for branch circuit sizing
• NEC 430.22 — Branch circuit conductor sizing: 125% of motor FLA
• NEC 430.32 — Overload relay sizing
• NEC 430.52 — Short-circuit and ground-fault protection (breaker sizing)
• NEC Table 430.250 — Full-load current for three-phase AC motors
• NEC 250.4 / 430.12 — Grounding and bonding requirements
• NEC Article 110.14 — Conductor termination torque requirements

Frequently Asked Questions

Can I wire a 460V motor to run on 230V?

Only if it's a dual-voltage motor (check the nameplate). If it says 230/460V, you can reconfigure the leads for low voltage. If it's rated for 460V only, you cannot safely run it on 230V.

How do I know if my motor is wye or delta?

The motor nameplate will specify. If it shows a Y or star symbol, it's wye. If it shows a triangle symbol (Δ), it's delta. Nine-lead motors can be either, so the nameplate diagram is essential.

What happens if I wire a motor backward?

The motor runs in reverse. This won't damage the motor itself, but it can damage the equipment it's connected to (e.g., running a screw compressor backward). Always bump-test for correct rotation before coupling to the load.

Can I use a VFD instead of a phase converter?

Yes, for a single motor. VFDs (variable frequency drives) can convert single-phase to three-phase for one motor at a time. However, VFDs add complexity, can cause harmonic issues, and aren't ideal for multiple motors or machines with built-in controls. A rotary phase converter powers your entire shop panel — plug in any three-phase tool and it just works.

How do I reverse a three-phase motor?

Swap any two of the three line leads (L1, L2, L3). That's it. For example, if L1 goes to T1 and L3 goes to T3, swap them so L1 goes to T3 and L3 goes to T1. The motor will spin in the opposite direction.

Do I need a disconnect switch?

Yes. NEC 430.102 requires a disconnecting means within sight of each motor. This is typically a lockable disconnect switch or a circuit breaker with a lockout provision.