3-Phase Contactor Pakistan: DOL Star-Delta Wiring

3 Phase Contactor Pakistan — Wiring Star-Delta, DOL & Reversing Diagrams Guide

Updated: May 2026 · CNC Electric Pakistan

Pattern 1 — DOL (Direct-On-Line) Starter

The simplest 3-phase motor starter. Single contactor switches all three phases simultaneously. Motor sees full voltage immediately and accelerates to running speed.

Power circuit wiring

1. 3-phase supply R + Y + B → upstream MCCB (sized to 1.25× motor FLA)
2. MCCB outputs → contactor power input terminals L1, L2, L3
3. Contactor power outputs T1, T2, T3 → thermal overload relay input
4. Thermal overload outputs → motor U, V, W terminals

Control circuit wiring (220 V)

1. 220 V control supply (Live) → STOP push button (NC) → START push button (NO) → contactor coil A1
2. Contactor coil A2 → 220 V control supply (Neutral)
3. Contactor auxiliary NO contact wired across the START button (the "seal-in" contact)
4. Thermal overload trip contact (NC) in series with the contactor coil — opens when overload trips, drops the coil

How it operates

Press START → coil energises → main contacts close, all 3 phases reach motor → motor runs. Seal-in contact closes, keeping the coil energised after START is released. Press STOP → coil drops → contacts open → motor stops. Thermal overload on sustained current = trip → opens → coil drops → motor stops.

When to use DOL

• Motors up to 10-15 HP where starting inrush (6-8× FLA) is acceptable
• Standard pumps, fans, compressors with no special starting requirements
• Light commercial applications where simplicity matters more than start current

Pattern 2 — Star-Delta Starter

Reduces starting current by initially connecting the motor windings in STAR (each winding sees line voltage / √3 = 220 V), then switching to DELTA (each winding sees full line-to-line voltage = 380 V) once the motor is at speed. Reduces starting inrush from 6-8× FLA to 2-3× FLA.

Three contactors required

• K1 (Main / Line) — feeds the motor's start of windings (U1, V1, W1)
• K2 (Star) — shorts the ends of the windings (U2, V2, W2) together at the star point
• K3 (Delta) — connects the ends of one winding to the start of the next (creating delta configuration)

Sequence (typical 8-10 second star, then transition to delta)

1. Press START: timer starts, K1 + K2 energise → motor in STAR. Motor accelerates to ~70-80% of synchronous speed.
2. Timer expires: K2 drops first (delay typical 50-100 ms transition), K3 energises → motor in DELTA. Motor reaches full speed.
3. Mechanical and electrical interlocks: K2 and K3 must NEVER be closed simultaneously (would short the supply). Hard mechanical interlock + auxiliary NC contacts wired in series with each other's coils.

When to use Star-Delta

• Motors 15-50 HP where DOL inrush would trip upstream breakers or cause WAPDA voltage sag
• Loads with low starting torque requirements (centrifugal pumps, fans) — high-torque loads can stall in star
• Industrial environments with reliable, repeatable operation

Required components

• 3× contactors (matched, sized to motor FLA — for 30 HP use 65 A series)
• 1× timer relay (8-12 second range, with delta-output contact)
• 1× thermal overload (set to motor delta-run FLA)
• Mechanical interlock between K2 and K3
• Standard START + STOP push buttons

Pattern 3 — Reversing (FWD/REV) Starter

Allows motor to run in either direction. Achieved by swapping any TWO of the three phases — typically R and B exchange. Two contactors with mechanical and electrical interlocks ensure both phases can never close simultaneously (which would short two phases together).

Power circuit

• K-FWD contactor: feeds motor as R, Y, B
• K-REV contactor: feeds motor as B, Y, R (swap of L1 and L3)
• Both contactors feed into the same thermal overload, then to the motor terminals

Control circuit

1. STOP push button (NC) — breaks both coil circuits simultaneously
2. FORWARD push button (NO) → through K-REV NC auxiliary (interlock) → K-FWD coil A1
3. REVERSE push button (NO) → through K-FWD NC auxiliary (interlock) → K-REV coil A1
4. Seal-in contacts on each contactor's NO auxiliary across the corresponding START button

Interlock logic

If FWD is running, K-FWD's NC auxiliary is OPEN — blocking the K-REV coil. To reverse, operator must press STOP first (drops K-FWD, closes its NC auxiliary), THEN press REVERSE. Hardware logic prevents the operator from accidentally shorting two phases together.

When to use Reversing

• Lifts and elevators (cabin goes up and down)
• Conveyor belts that need to clear jams in reverse
• CNC machinery with bidirectional tool feeds
• Pumps with reverse-flow cleaning cycles

Common Wiring Mistakes Across All Three Patterns

• Skipping the seal-in auxiliary contact. Motor only runs while START button is held — release and it stops. Add the NO seal-in contact across the START button.
• Skipping thermal overload. Contactor handles short-circuit (via upstream MCCB) but NOT sustained overload — that's the thermal relay's job. Without it, a stuck pump overheats the motor and burns the windings.
• Wrong coil voltage. Wiring a 110 V coil to 220 V supply burns it out in seconds. Always check the coil voltage stamp.
• Forgetting the interlock in reversing or star-delta. Without interlocks, two contactors can close simultaneously — short-circuiting the supply.
• Sizing the contactor on starting current instead of running. The AC3 amp rating handles starting inrush — size to motor FLA, not 6× FLA.
• No control fuse or MCB. A fault on the 220 V control circuit can damage the contactor coil and create fire risk. Use a small 2 A fuse or MCB on the control supply.

Frequently Asked Questions

Related Collections & Guides

• CNC Magnetic Contactors (CJX2 / CJX2S)
• Push Buttons & Selector Switches
• MCCBs (upstream protection)
• Timer Relays (for star-delta)
• Phase Sequence Relays
• Magnetic Contactor Wiring Guide
• Contactor Sizing Guide
• Push Button Switch Guide
• CNC Pakistan 2026 Price List

⚠ Panel fire safety reminder: Any DB or panel that runs motors, capacitors, VFDs, or batteries should have an in-panel aerosol fire-suppression cylinder. Read our complete Electrical Panel Fire Extinguisher Pakistan guide — covers BS/EN ISO 14520, NFPA 12/2010 standards, cylinder sizing per panel volume, and 2026 Pakistani pricing.

Magnetic Contactor Wiring — Pakistan-Specific Diagrams

The most common wiring questions Pakistani electricians ask about magnetic contactors:

1. Single-phase contactor + push-button START/STOP (most common home application)

  L1 ━━━━━━━━━━━━━━━━━━━┳━━━━━━━━━━━━━━━━━━━━━ Motor L1
                         ┃
                         ┃    [STOP-NC]
                         ┃     ┃ ┃
                         ┃     ┃ ┃    [START-NO]
                         ┃     ┃ ┗━━━━━┓ ┃
                         ┃     ┃       ┃ ┃
                         ┃     ┃     [A1] [Aux NO 13-14]
                         ┃     ┗━━━━━━━┻━━━━━━━━━━━━━ Coil + Hold-in
                         ┃                              ┃
                         ┃                            [A2]
                         ┃                              ┃
  N  ━━━━━━━━━━━━━━━━━━━┻━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┻━ Motor N

Key wiring rules: STOP button is normally-closed (NC) — broken wire = motor stops (fail-safe). START is normally-open (NO), held in by the contactor's own auxiliary contact (13-14). Coil terminals are A1+A2; coil voltage must match supply (230V AC most common in Pakistan).

2. 3-Phase DOL (Direct On-Line) Starter Wiring

  L1 L2 L3                              U V W (Motor)
   ┃  ┃  ┃                               ┃ ┃ ┃
   ┃  ┃  ┃                               ┃ ┃ ┃
  [Contactor main: 1-2 / 3-4 / 5-6 / N-N]
   ┃  ┃  ┃                               ┃ ┃ ┃
   ┃  ┃  ┃                               ┃ ┃ ┃
  [Overload Relay: 95-96-97-98 (trip aux)]
   ┃  ┃  ┃
   ┃  ┃  ┃ Control circuit (drawn from L1 + N or separate 24V)
   ┃  ┃  ┃     ┏━━[STOP-NC]━━[START-NO]━━┓
   ┃  ┃  ┃     ┃                          ┃
   ┃  ┃  ┃     ┃         [Aux 13-14]──┐  ┃
   ┃  ┃  ┃     ┃                       ┃  ┃
   ┃  ┃  ┃     ┃                      [A1] ┃
   ┃  ┃  ┃     ┗━━━━━━━━━━━━━━━━━━━━━━━━━━┛
   ┃  ┃  ┃                              [A2]
   ┃  ┃  ┃                                ┃
   ┃  ┃  ┃                       Overload NC 95-96
   ┃  ┃  ┃                                ┃
  L1 (or N if 24V control)

Critical detail: the overload relay's 95-96 NC trip contact MUST be wired in series with the contactor coil. When overload trips, coil de-energises and motor stops. Without this, the overload relay does nothing useful.

3. Reversing Contactor (Forward / Reverse swap)

  [Forward Contactor K1]: L1→U, L2→V, L3→W
  [Reverse Contactor K2]:  L1→W, L2→V, L3→U   (swap L1 and L3)

  Mechanical interlock between K1 and K2 — physical bar that prevents both
  from closing at once. Required to avoid L1-L3 short circuit.

  Electrical interlock:
    K1 coil   ━┳━[FWD button NO]━[K2 aux NC 21-22]━[A1 of K1]
    K2 coil   ━┻━[REV button NO]━[K1 aux NC 21-22]━[A1 of K2]

Both must STOP before reversing direction (typically 1-2 sec delay via timer). Direct fwd→rev without stop will burn out motor windings on most induction motors.

4. Star-Delta Starter Wiring (DOL for motors > 5HP)

3 contactors required: Main (KM), Star (KS), Delta (KD). Sequence:

1. Start: KM closes + KS closes simultaneously → motor windings in star configuration (1/3 voltage per winding = 1/3 starting current)
2. Transition (after 6-12 sec, timer-controlled): KS opens, KD closes → motor windings reconnected in delta (full voltage)
3. Run: KM + KD stay closed; KS is open. Motor runs at full speed.

Use a dedicated star-delta timer (CNC AH3-3 with 2 outputs + transition time) — never wire star-delta logic from raw contactors and pushbuttons.

Common Pakistani Contactor Brands & CNC Equivalents

Pakistani Brand	Model	CNC Equivalent
Chint	NXC-9 / 12 / 18 / 25 / 32 / 40	CNC YC1-09 / 12 / 18 / 25 / 32 / 40
Schneider	LC1D09 / D12 / D18 / D25	CNC YC1-09 / 12 / 18 / 25
ABB	AF09 / AF16 / AF26	CNC YC1-09 / 18 / 25
Siemens	3RT2017 / 3RT2023 / 3RT2025	CNC YC1-12 / 18 / 25
Mora	LC1-D09 / D18 / D32	CNC YC1-09 / 18 / 32