Difference Between NEMA and IEC Motor Starters & Contactors

Electrical Technology

Comparison Between NEMA and IEC Contactors, Controllers and Motor Starters

Motor starters, controllers, and contactors are essential components used to control electric motors in industrial, commercial, and general electrical systems.

A motor starter is a device designed to control the flow of electric power to a motor, enabling its starting, stopping, and forward/reverse operations. In simple terms, a motor starter (also called a motor controller) is a combination of a contactor and a thermal overload relay in a single unit used to control the ON/OFF operation and protect the motor from overload.

A contactor is an electrotechnical switch used to turn a circuit ON or OFF. It is an advanced form of a relay but does not provide protection against motor overload conditions.

According to NEC – Article 100 – Definitions, A motor controller is a device or switch used to start or stop the motor by making or breaking the motor circuit current. Motor controllers are extensively covered in NEC Article 430 – Part VII.

A thermal overload relay is used to protect the motor from overload conditions, particularly those caused by high starting (inrush) currents. When a thermal overload relay is combined with a contactor, the assembly is referred to as a motor starter or motor controller.

Good to Know:

Contactor is a device used to switch ON or OFF a circuit
Thermal Overload Relay is used to protect the motor from high inrush current.
If a contactor and thermal overload relay is combined in a single unit, it is known as motor starter or controller.

Two of the most widely recognized global standards for classifying and designing motor starters and contactors are NEMA (National Electrical Manufacturers Association) and IEC (International Electrotechnical Commission). Both standards serve the same core purpose but differ significantly in design, sizing, characteristics, and application.

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What is a NEMA Motor Starter?

NEMA starters are motor control devices designed and built according to standards set by the National Electrical Manufacturers Association (NEMA). These starters are widely used in the United States, Canada, and some parts of Latin America. These starters are known for their robust construction, durability, and ability to withstand harsh conditions.

NEMA contactors and starters are built for durability and can typically withstand higher levels of mechanical and electrical stress. These starters are classified and sized standard types categories (e.g., Size 00, 0, 1, 2, etc.) rather than by precise current ratings. Selecting a NEMA starter is generally easier, as the sizing is standardized and application-specific.

Due to conservative design and robust construction, NEMA starters tend to be physically larger than their IEC counterparts. Additionlly, they may be more expensive initially due to their rugged build and broader safety margins. Overall, with wide safety margins, rated NEMA starters are can operate reliably under adverse conditions.

NEMA starters and controllers are generally used in Industrial plants, manufacturing environments, oil & gas sectors, and other harsh or demanding environments with dust, moisture, and vibration or where reliability and long life-span is considered as a priority.

What is an IEC Motor Starter?

IEC starters comply with International Electrotechnical Commission (IEC) standards. As IEC is adopted in Europe and other parts of the world, IEC contactors and starters are widely used in Europe, Australia, Asia, Africa, and other global regions. These starters are compact, application-specific, and designed for efficiency.

Starters designed according to IEC standards focus on compactness and efficiency, optimized for specific motor protection and switching requirements. Component ratings are selected based on the motor’s actual full-load current (FLC), duty cycles, and operational characteristics.

Featuring a modular and configurable design, these starters are built for easy integration with other control and protection devices. As they are optimized for space-saving installations, IEC starters are generally smaller in size and more economical than NEMA starters. They also offer greater flexibility for fine-tuning overload protection, trip settings, and coordination.

IEC starters are generally less expensive than NEMA starters, particularly for light to medium-duty operations. However, compared to NEMA starters, IEC starters are designed for a specific service life and may require more frequent replacement in heavy-duty applications.

IEC starters and contactors are commonly used in OEM equipment, commercial and light industrial applications, HVAC systems, pumps, and conveyors, control panels, machinery manufacturing, commercial installations, and other applications where space-saving and modular designs are a priority.

Sizing and Rating of NEMA and IEC Starters

One major difference between NEMA and IEC starters is how they are rated and sized. Sizing the NEMA and IEC starters are explained in the previous article with solved examples.

NEMA

The table below, based on NEMA ICS 2-2000, shows motor starters categorized by standard frame sizes: 00, 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. These NEMA sizes indicate the maximum continuous current, in amperes, that a starter can safely carry for switching purposes. This sizing corresponds to the motor’s horsepower (HP) rating and the operating voltage.

NEMA Size	Continuous AMP Rating	HP at 230V-AC	HP at 480 AC
00	9	1.5	2
0	18	3	5
1	27	7.5	10
2	45	15	25
3	90	35	50
4	135	50	100
5	270	100	200
6	540	200	400
7	810	300	600
8	1215	450	900
9	2250	800	1600

IEC

On the other hand, IEC motor starters are rated and sized according to the “Utilization Category,” which specifies the type of application and duty cycle for which the starter is designed. The table below, based on IEC standard 60947-4-1, shows the types of contactors categorized by service and application. Keep in mind that AC-3 and AC-4 are the most common utilization categories used for squirrel cage induction motors in industrial applications.

IEC Utilization Categories for Contactors and Starters
Contactor Type	Typical Applications
AC-1	Non-inductive or slightly inductive loads (e.g., heaters, resistive loads)
AC-2	Slip-ring motors (starting, plugging, inching)
AC-3	Squirrel-cage motors (starting, stopping during running)
AC-4	Squirrel-cage motors (starting, plugging, inching, rapid stops)
AC-5a	Switching of electric discharge lamps (e.g., HID, mercury vapor)
AC-5b	Switching of incandescent lamps
AC-6a	Transformer switching
AC-6b	Capacitor bank switching
AC-7a	Slightly inductive household loads (e.g., mixers, fans)
AC-7b	Motor loads for household appliances (e.g., washing machines)
AC-8a	Hermetic refrigerant compressor motors (manual reset)
AC-8b	Hermetic refrigerant compressor motors (auto reset)
AC-12	Control of resistive, solid-state load with O/C isolation
AC-13	Control of solid state loads with T/F isolation
AC-14	Control of small electromagnetic loads
AC-15	Control of AC electromagnetic loads
AC-20	Connecting/disconnecting under no-load
AC-21	Switching of resistive load
AC-22	Switching of mixed inductive and resistive load
AC-23	Switching of motor load and other highly inductive load

Comparison Between NEMA and IEC Starters and Controllers

Design and Sizing:

NEMA: NEMA starters are designed with a more robust, “one-size-fits-all” or “general purpose” approach. They are categorized into broad “sizes” (e.g., Size 00, 0, 1, 2, 3, through 9) that cover a wide range of motor horsepower and current ratings. This often results in NEMA starters being somewhat oversized for a specific application, offering a built-in “service factor” or reserve capacity to handle occasional overloads. This simplifies selection, as you typically only need to know the motor’s horsepower and voltage.
IEC: IEC starters are designed to be more application-specific and precise. Instead of broad sizes, they use “utilization categories” (e.g., AC-1, AC-3, AC-4) to rate devices based on the specific type of load and duty cycle (e.g., normal starting of squirrel-cage motors, frequent jogging/plugging). This allows for a more compact and cost-effective design, as the starter is precisely matched to the application’s needs. However, it requires a more in-depth understanding of the motor’s duty cycle and operating parameters.

Installation:

NEMA starter comes in enclosed unit and designed for panel mounting.
NEMA starter are modular and designed for DIN rail mounting.

Size and Cost:

NEMA: Due to their robust and oversized design, NEMA starters are generally larger and heavier than their IEC counterparts for similar current ratings, especially below 100A or 50HP. This can lead to larger enclosure requirements and higher material costs.
IEC: IEC starters are typically more compact and lighter, making them ideal for applications where space is limited, such as within original equipment manufacturer (OEM) designs. They are generally less expensive upfront, particularly for smaller sizes.

Interchangeability and Replaceability:

NEMA: NEMA components are highly standardized across different manufacturers within the NEMA framework. This means that parts like overload heater elements are often interchangeable, simplifying maintenance and reducing downtime. NEMA devices are generally considered more serviceable and repairable.
IEC: IEC components are more modular and often supplied as individual components to be assembled. While this offers flexibility, interchangeability across different manufacturers might be less straightforward than with NEMA. Below 100A, IEC devices are often considered “disposable” rather than repairable.

Overload Protection:

NEMA: NEMA starters typically come with Class 20 overload relays. It indicates they will trip within 20 seconds at 600% of the full load current. They are designed to handle short circuits effectively.
IEC: IEC starters commonly use Class 10 overload relays, which trip faster (within 10 seconds at 600% of the full load current). IEC standards emphasize quicker response times to overloads, enhancing safety and reliability. They also often provide single-phase detection.

Application:

NEMA: Predominantly used in North America (USA, Canada, Mexico) and some parts of South America. NEMA starters are favored in heavy-duty industrial applications, process industries, and situations where operating parameters might be less precisely defined or subject to frequent overloads.
IEC: Widely used globally, especially in Europe, Asia, and other international markets. IEC starters are popular in OEM applications, commercial buildings, and light industrial settings where cost, space, and precise application matching are critical.

Safety and Construction:

NEMA: NEMA starters often have an “open design,”. It means, safety covers may need to be purchased separately or added in the field to protect against accidental contact with live parts.
IEC: IEC devices are often designed to be “finger-safe” or “touch-proof” inherently. Hence, it minimize the risk of electrical shock without additional covers

Network Integration:

IEC: IEC devices generally offer more options for networking components into distributed control systems using open fieldbus standards, which is increasingly important in modern automated plants.
NEMA: While NEMA devices can be integrated, they may offer fewer native options for advanced networking compared to IEC.

The following table shows the key differences between IEC and NEMA starters

Feature	NEMA Starters & Contactors	IEC Starters & Contactors
Standard	NEMA (North America)	IEC (International)
Construction	Heavy-duty, rugged and conservative	Compact and lightweight
Sizing	Standardized sizes (00, 0, 1, 2, etc.) based on Horsepower (HP)	Current, voltage, and utilization category-based
Size	Larger	More compact
Installation	Designed for panel mounting	Designed for DIN rail mounting
Durability	Highly durable, robust, and mechanical endurance	Adequate for the application, less rugged and moderate lifespan
Service Factor / Safety Margin	High	Lower (closer to actual motor ratings)
Selection	Simplified by size	Requires detailed calculation
Lifespan	Longer mechanical and electrical life	Shorter lifespan under similar conditions
Maintenance	Less frequent	More frequent depending on duty cycle
Initial Cost	Higher	Lower
Unit Type	Enclosed Unit	Modular Type
Preferred Regions	USA, Canada, parts of Latin America	Europe, Asia, Africa, globally
Applications	Heavy industry, oil & gas, mining, harsh environments	OEMs, HVAC, commercial, machinery manufacturing