Magnetic Contactor Sizing Pakistan | Amp Selection | CNC
Magnetic Contactor Sizing Guide Pakistan — How to Pick the Right Amp Rating
Updated: May 2026 • CNC Electric Pakistan
Magnetic Contactor — Pakistan Quick Answer (2026)
Pick the contactor whose AC3 amp rating equals or exceeds your motor’s full-load amps (FLA), and whose coil voltage matches your control circuit (220 V AC most commonly in Pakistan). For resistive loads (heaters, lights), use the AC1 rating instead — usually 1.5–2x the AC3 number on the same contactor.
CNC CJX2 / CJX2S magnetic contactor prices in Pakistan: 9 A from Rs.850, 25 A from Rs.1,650, 40 A from Rs.2,800, 65 A from Rs.4,500, 95 A from Rs.7,200. Browse the full CNC contactor range → or WhatsApp 0326-1111376 with your motor nameplate.
What Is a Magnetic Contactor?
A magnetic contactor is an electrically-operated switch designed to make and break heavy power circuits thousands of times without wearing out. Inside the contactor body, a small coil energises an electromagnet that pulls a movable armature carrying the main power contacts. Energise the coil → contacts close → load powers up. De-energise → spring opens the contacts → load drops.
You’ll find contactors at the heart of every motor starter, air conditioner outdoor unit, water pump panel, lift control board, and industrial heating circuit in Pakistan.
Why You Can’t Just Use a Big MCB Instead
An MCB or MCCB is designed for occasional manual switching plus automatic fault tripping. A contactor is designed for continuous duty switching — often hundreds of operations per day. The differences:
- Contactors carry the load through silver alloy contacts engineered for arc resistance.
- The coil provides remote control — you can switch a 95 A motor from any thermostat, PLC, push-button, or WiFi smart breaker using a 1 A control signal.
- Contactors interlock electrically and mechanically — two contactors can be physically prevented from closing simultaneously (essential for star-delta starters and reversing drives).
- Auxiliary contacts let you build complex control logic without separate relays.
AC Utilisation Categories — The Number That Actually Matters
Contactor amp ratings are NOT one number. Manufacturers publish ratings against IEC 60947 utilisation categories that reflect how harshly the contactor is used. The two you need:
| Category | Use Case | Why It Matters |
|---|---|---|
| AC1 | Resistive loads — heaters, incandescent lighting, capacitor banks, transformers at no-load | Low arc on open; the contactor handles ~1.5–2x its AC3 rating in AC1 |
| AC3 | Squirrel-cage induction motors, starting + running + occasional stopping under full load | The standard motor-duty rating — use this for almost every Pakistani motor application |
| AC4 | Plugging, reversing, inching, jogging of induction motors (lifts, cranes, hoists) | Heaviest duty; contactor handles only ~0.6x AC3 rating in AC4 |
So a contactor labelled “CJX2-2510” means 25 A in AC3 (motor service) and roughly 40 A in AC1 (heater service). The first digits are always the AC3 number.
Sizing Step-by-Step
Step 1: Identify the Load Type
Motor (3-phase / 1-phase induction)? Use AC3 rating. Heater, lighting, transformer? Use AC1 rating. Welding, lift, hoist with plugging? Use AC4 rating.
Step 2: Get the Load Current
For motors, read the nameplate FLA. For heaters / resistive loads, calculate I = P / V (where V is line-to-neutral for 1-phase and line-to-line / 1.73 for balanced 3-phase).
Step 3: Pick the Next Higher Standard Size
Contactors come in fixed sizes: 9, 12, 18, 25, 32, 40, 50, 65, 80, 95, 115, 150, 185 A (AC3). If your FLA is 22 A, pick the 25 A model — never run a contactor at 100% of its rated capacity continuously.
Step 4: Match the Coil Voltage
Standard Pakistani control voltages: 220–240 V AC 50 Hz (most common, single-phase main supply), 110 V AC 50 Hz (industrial control panels with dedicated 110 V control transformer), 24 V DC (PLC-driven systems), 380 V AC (rare, only specialty drives). Always confirm the coil voltage stamp before wiring.
Step 5: Check Auxiliary Contacts
Most CJX2 / CJX2S contactors ship with one NO + one NC auxiliary. If your control circuit needs more (sealing latch + interlock + run indicator + remote signal), specify a 2NO + 2NC auxiliary block.
Motor HP to Contactor Size — Pakistan Quick-Pick Table
| Motor HP | Motor kW | FLA @ 380V 3Φ | Contactor Size (AC3) | CNC Model | PKR Price 2026 |
|---|---|---|---|---|---|
| 0.5 HP | 0.37 kW | 1.1 A | 9 A | CJX2-0910 | Rs.850 |
| 1 HP | 0.75 kW | 2.0 A | 9 A | CJX2-0910 | Rs.850 |
| 2 HP | 1.5 kW | 3.7 A | 9 A | CJX2-0910 | Rs.850 |
| 3 HP | 2.2 kW | 5.0 A | 12 A | CJX2-1210 | Rs.1,150 |
| 5 HP | 3.7 kW | 8.5 A | 18 A | CJX2-1810 | Rs.1,400 |
| 7.5 HP | 5.5 kW | 12 A | 18 A or 25 A | CJX2-2510 | Rs.1,650 |
| 10 HP | 7.5 kW | 16 A | 25 A | CJX2-2510 | Rs.1,650 |
| 15 HP | 11 kW | 23 A | 32 A | CJX2-3210 | Rs.2,300 |
| 20 HP | 15 kW | 30 A | 40 A | CJX2-4011 | Rs.2,800 |
| 25 HP | 18.5 kW | 37 A | 50 A | CJX2-5011 | Rs.3,500 |
| 30 HP | 22 kW | 45 A | 65 A | CJX2-6511 | Rs.4,500 |
| 40 HP | 30 kW | 60 A | 80 A | CJX2-8011 | Rs.5,800 |
| 50 HP | 37 kW | 73 A | 95 A | CJX2-9511 | Rs.7,200 |
Contactor + Thermal Overload Relay — The Complete Motor Starter
A contactor alone doesn’t protect the motor against gradual overload (clogged pump, jammed fan). For motor circuits, always pair the contactor with a thermal overload relay matched to the motor FLA. The combination is called a Direct-On-Line (DOL) motor starter:
- MCCB at the top — short-circuit protection + isolation.
- Contactor — switching duty.
- Thermal overload relay (OL) bolted to the contactor outputs — trips contactor coil on sustained overload.
- Motor.
Set the OL dial to the motor’s FLA (not to the contactor amp rating). Pair with a Start / Stop push-button + sealing-in auxiliary contact for classic DOL control.
Common Sizing Mistakes
- Sizing on AC1 for a motor. A 25 A AC1-rated “contactor” will weld shut after a few months of motor switching. Always check AC3.
- Undersizing for inrush. Motors draw 6–8x FLA on start. The contactor handles this for the short start period, but only if you sized to the correct AC3 amp class.
- Wrong coil voltage. Wiring a 110 V coil to 220 V will burn it out in seconds. Always read the stamp.
- No thermal overload relay. The contactor doesn’t protect the motor against gradual overload — only against fast short-circuits (and that’s really the MCCB’s job).
- Forgetting auxiliaries. A reversing starter needs interlocked auxiliaries on both contactors so they can never close together. Skipping this fries motor windings and creates a fault.
Pairing With WiFi Smart Breakers for Smart Control
A modern combination Pakistani electricians are using: a WiFi smart breaker drives the contactor coil. The smart breaker handles the 1–2 A coil current effortlessly and gives you phone-app control + scheduling + energy monitoring — while the contactor switches the heavy 30–95 A motor or heater. Cost ~Rs.10,000 in parts; saves you a dedicated PLC or smart relay.
Frequently Asked Questions
What is the difference between a contactor and a relay?
A relay switches small loads (typically below 10 A) for control or signal circuits. A contactor switches heavy power loads (9 A to 600+ A) for motors, heaters, and industrial equipment. Contactors have larger silver-alloy contacts, arc chutes for safe interruption, and are designed for hundreds of thousands of operations under load.
What does AC3 mean on a contactor?
AC3 is the IEC 60947 utilisation category for switching squirrel-cage induction motors during normal start / run / stop. The AC3 amp rating tells you the contactor’s safe motor-duty current. For Pakistani motor applications, ALWAYS size from the AC3 number, not from any other rating on the label.
What is the coil voltage of a CNC CJX2 contactor in Pakistan?
CNC CJX2 and CJX2S contactors are stocked with 220–240 V AC 50 Hz coils as standard for Pakistan, since that’s the universal single-phase mains voltage. Other coil voltages (110 V, 24 V DC, 380 V) are available on order for industrial control panels.
Can I use a contactor to switch a heater?
Yes — heaters are resistive loads, so use the AC1 rating, which is typically 1.5–2x the AC3 rating on the same contactor. A 25 A AC3 contactor handles roughly 40 A AC1 of heater load.
How do I wire a contactor for a single-phase motor?
For a 1-phase 220 V motor: live in → one main pole → motor live. Neutral straight through. Earth to motor body. Coil terminals A1 (live) + A2 (neutral). Add a thermal overload between the contactor and the motor for proper protection.
What size contactor for a 10 HP motor in Pakistan?
A 10 HP (7.5 kW) 3-phase 380 V motor draws roughly 16 A FLA. Use a 25 A AC3-rated contactor (CNC CJX2-2510) with a thermal overload relay set to 16 A. Always size one step above FLA — never run a contactor at 100% of its rated current.
How long do magnetic contactors last?
A correctly-sized AC3 contactor typically delivers 1–3 million electrical operations in motor service. At 50 operations per day that’s 50–150 years — you’ll retire the equipment before the contactor fails. Mechanical life (no current switched) is 10–30 million operations.
Need the right contactor for your motor?
Send us your motor nameplate (HP/kW, FLA, voltage) and load type (pump, fan, compressor, heater) — we’ll size the contactor + thermal overload in 5 minutes.