Contactors are essential electromechanical switching devices used widely in industrial and commercial electrical systems. They are designed to make and break electrical circuits safely and reliably under load. To ensure proper selection and compliance, contactors are standardized by international electrical standards such as IEC 60947-4-1 and EN 60947-4-1.
Standards & Organizations For Contactors
Contactors are governed by international and regional standards that define performance, testing, and safety requirements.
|
Standard / Organization |
Focus Area |
Key Scope |
|
IEC 60947-4-1 |
Low-voltage contactors and motor starters |
Defines utilization categories, rated currents, voltages, making/breaking capacity and endurance tests for AC and DC applications. |
|
EN 60947-4-1 |
European equivalent of IEC 60947-4-1 |
Harmonized version used in EU markets. |
|
IEC 61095 |
Electromechanical contactors for household use |
Applies to smaller contactors used in household appliances up to certain current/voltage levels. |
|
NEMA (US) |
National Electrical Manufacturers Association |
Defines motor contactor sizes and performance for North American markets (not IEC categories). |
These standards ensure that contactors are tested and rated in a consistent, measurable way before they are used in real electrical systems.
What Are Electrical Parameters You Must Check?
When selecting a contactor, the key electrical parameters are:
-
Rated Operational Current (Ie)
Maximum current the contactor can carry continuously. -
Rated Operational Voltage (Ue)
Must match the supply system (e.g., 230 V, 400 V, 690 V). -
Utilization Category
AC1, AC3, etc., determining duty conditions. -
Making & Breaking Capacity
How much current the contacts can make or break at rated voltage under specified conditions. -
Electrical Endurance
Number of operations the contactor can perform under load before failure.
AC & DC Contactor Ratings Explained
|
Category |
Load Type |
Inrush/Running Current |
Typical Use |
|
AC1 |
Resistive |
Low peaks |
Heaters, resistive loads |
|
AC2 |
Slip-ring motors |
Moderate peaks |
Industrial motor starting |
|
AC3 |
Squirrel motors |
High peaks start |
Motor starters & pumps |
|
AC4 |
Frequent/Reverse |
Very high duty |
Jogging, reversing |
|
DC1 |
DC resistive |
Low |
DC heaters |
|
DC3 |
DC motors |
Higher |
Conveyor drives |
|
DC5 |
DC traction |
High |
Heavy DC applications |
What Is AC1, AC2, AC3, AC4 For Contactors?
Utilization categories (AC1, AC2, AC3, AC4) describe the type of load being switched and the severity of switching conditions. They are defined in IEC 60947-4-1 and indicate how much current and what kind of electrical stress a contactor must withstand during operation.
Most common utilization categories for industrial contactors include:
- AC1: AC1 rated contactors are used with non-inductive or slightly inductive AC loads, such as heaters or resistive circuits. These loads do not create high inrush currents.
- AC2: AC2 contactors are designed for slip-ring motor control, primarily where starting or stopping occurs with moderate inrush, but without heavy load stress during running.
- AC3: AC3 is the most common industrial contactor category. It covers starting and stopping of squirrel-cage induction motors where the motor is loaded and running when switched off.
- AC4: AC4 is for contactors that must withstand frequent operations like jogging, plugging and rapid reversing.
DC Categories — What Are Their Standards
DC contactor ratings are defined for direct current loads, which have different switching characteristics than AC loads (e.g., no current zero-crossing to extinguish arcs). IEC standards specify DC1, DC2, and DC3 categories, with no DC4 rating in mainstream industrial use.
|
DC Rating |
Core Application |
Key Characteristics |
Typical Loads |
|
DC1 |
Non-inductive/slightly inductive resistive loads |
No arc suppression required; steady current handling |
DC heaters, battery chargers, resistance banks |
|
DC2 |
Shunt motor control |
Handles moderate inrush; switches motor on/off during running |
DC shunt motors in conveyors, small machinery |
|
DC3 |
Series motor control |
Heavy-duty arc suppression; withstands frequent plugging/inching |
DC series motors in cranes, forklifts, traction systems |
DC contactors require specialized magnetic blowout or vacuum arc chambers to extinguish DC arcs, which are harder to break than AC arcs. This makes DC contactors bulkier than AC contactors with the same current rating.
How to Use Contactor Ratings to Choose a Contactor?
Choosing the right contactor means matching its utilization category to your load type and duty cycle, then verifying key electrical parameters to ensure compatibility. Wutai Electric’s contactor range covers all core AC (AC1-AC4) and DC (DC1-DC3) categories, fully compliant with IEC 60947-4-1 standards to handle harsh industrial environments.
Key Contactor Electrical Parameters Explained
|
Parameter |
Definition |
Practical Relevance |
|
Rated Operational Current (Ie) |
Maximum continuous current the contactor can carry at 40°C ambient temperature |
Must be ≥ load FLA + 25–50% safety margin (for AC3/AC4 motors) |
|
Rated Making Current |
Maximum current the contactor can safely close without damage |
For AC3, this is 6x Ie to handle motor startup inrush |
|
Rated Breaking Current |
Maximum current the contactor can safely open without damage |
For AC3, this is 1x Ie (motor running current); for AC4, it’s 8x Ie |
|
Coil Voltage (Uc) |
Voltage required to energize the contactor’s electromagnetic coil |
Must match control circuit voltage (24VDC, 110VAC, 230VAC) |
|
IP Rating |
Protection against dust/water ingress |
IP54 for factory floors; IP65 for outdoor HVAC or mining applications |
Common Mistakes to Avoid about Contactor Standards
1.Using AC1 Contactors for AC3 Motor Loads
AC1 contactors lack arc suppression for motor inrush, leading to welded contacts and equipment downtime. Always use AC3 for standard motors.
2.Oversizing Contactors Excessively
A 400A AC3 contactor for a 50A motor load will cause contact oxidation—larger contacts do not “wipe” properly with small currents, reducing connection reliability.
3.Ignoring Ambient Temperature Derating
A contactor rated for 40°C will have 10% lower current capacity at 50°C. Apply derating factors for hot environments like boiler rooms or outdoor enclosures.
FAQs about Electrical Standards For Contactors
What is the difference between AC1 and AC3 contactor ratings?
AC1 is for resistive loads (heaters) with no inrush current, while AC3 is for squirrel-cage motors that draw 5–7x FLA during startup. AC3 contactors have stronger arc suppression and higher making current capacity than AC1 models.
What is AC1, AC2, AC3, AC4 in contactor standards?
These are IEC utilization categories for AC contactors: AC1 (resistive), AC2 (slip-ring motors), AC3 (standard squirrel-cage motors), AC4 (heavy-duty squirrel-cage motors with frequent cycling). Each category has specific current handling and arc suppression requirements.
How to read a 3-phase contactor rating chart?
Start with your motor’s FLA (from the nameplate), then select a contactor with Ie ≥ 1.25x FLA and AC3 rating (for standard use) or AC4 (for frequent starts/stops). Match the contactor’s voltage rating to your 3-phase system (400V, 690V).
Can I use an AC contactor for DC loads?
No. AC contactors cannot extinguish DC arcs effectively, which will cause contact welding and safety hazards. Always use DC-rated contactors for DC loads.
What is the IEC standard for contactor utilization categories?
The core standard is IEC 60947-4-1, which defines all AC and DC contactor utilization categories, rated currents, and performance tests.
Post time: Jan-19-2026