Here is everything you will need to know about NEMA Connectors.
You will learn:
- What are NEMA Connectors?
- NEMA Plugs, Power Cords, and Receptacles
- NEMA Enclosures
- International Standards for Power Cords and Receptacles
- And much more…
Chapter One – What are NEMA Connectors?
NEMA, the National Electrical Manufacturers Association, sets the standards for electrical products sold in the United States with a focus on electrical connectors.
Electrical power connectors allow electronic devices to connect to power outlets. They can carry alternating current (AC) or direct current (DC). AC current is the typical current found in homes, offices, stores, or businesses. An example of DC current is electricity from a battery.
Though most of us are accustomed to the two or three pronged connectors commonly found in a home, there are hundreds of different connectors in industry and around the world. Each type has a different amperage and voltage.
Current ratings in the United States are 15 to 60 amps (A) with voltage ratings of 125 to 600 volts (V). Connectors, plugs and outlets, come in a wide variety of configurations with different blade widths, shapes, positions, and measurements. The different dimensions of connectors make them non-interchangeable with different combinations of voltage, current capacity, and groundings.
All manufacturers in the United States comply with the standards established by the NEMA, which has created consistency throughout the industry. NEMA standardization identifies the different pin positions of plugs and receptacles based on amperage and voltage.
As can be seen in the diagram, NEMA 2-20, NEMA 6-50, and NEMA 24-15 have different pin configurations and positioning. They are further differentiated by their amperage and voltage with 2-20 and 6-50 having 250V and 24-15 with 347 V.
Chapter Two – NEMA Plugs, Power Cords, and Receptacles
Electrical plugs and receptacles in the United States follow the quality standards of the NEMA. The two most common connectors are NEMA 1-15P and NEMA 5-15P, which have molded rubber bodies and prongs of steel or brass with a zinc, tin, or nickel coating. Other connectors have differently placed prongs and increased voltage.
Connectors are divided into locking and non-locking, where locking connectors have curved prongs that can be twisted, after being inserted, to be locked in place. Non-locking connectors have straight blades and are used for computers, appliances, and every day applications. The purpose of locking plugs and receptacles is to prevent the connector from being accidentally disconnected or dislodged.
The information below is a short overview of the types of NEMA connectors for home and industrial use.
Types of NEMA Connectors
Of the non-locking connectors, NEMA 1 and NEMA 5 are the most common. They have either two blades without a ground or two blades with a ground. In recent years, builders have been required to install receptacles with NEMA 5 ground plugs. The NEMA 1 series is slowly being phased out.
In the NEMA standardization system, the first number is the plug configuration, which includes the number of poles, wires, and voltage. The grounding type can be two pole three wire, four pole five wire, and on. Non-grounded connectors have the same number of wires as poles since they do not require a wire for grounding . The second number in the code is the amp rating, which is followed by “P” for plug and “R” for receptacle. For example, a NEMA 5-15R is a 125 V, two pole, three wire receptacle rated at 15 amps.
In the majority of cases, the ground pin is located up to avoid metal objects from making contact with the hot line. The up position of the grounding pin prevents falling objects from striking the neutral and conducting connections.
NEMA 1s have the typical two flat prong design. They are two pole two wire non-grounded rated for 125 V. Though this configuration has been popular for many years, it is slowly being phased out for grounded plugs. Pictured below is the most common of the NEMA 1 series, NEMA 1-15 P.
NEMA 2s is an obsolete series that is no longer manufactured. It was a two wire 250 V series.
NEMA 3s is a planned series that will have 277 V, two wires, and be ungrounded.
NEMA 4s is a series planned for the future to have 600 V, two wires, and be ungrounded.
NEMA 5s have two poles, three wires with two blades and a grounding pin with one of the blades wider than the other. They plug into NEMA 5 receptacles. NEMA 5-15, -20, and -30 are the most common varieties.
NEMA 6s has three wire grounding used for 208 and 240 V circuits. They are normally manufactured as commercial or industrial grade and come in various sizes with different pin configurations for the ground and hot pins. They have superior performance and reliability.
NEMA 7s are two-pole, grounded connectors rated for 277 V. The NEMA 7-15 plug and receptacle have current carrying pins at angles to each other and a U-shaped ground.
NEMA 8s is a proposed design that will have three-wires, two-poles, and be grounded with a rating for 480 V.
NEMA 9s is planned to be similar to NEMA 8 with a rating of 600 V.
NEMA 10s are obsolete and have been replaced by NEMA 14-30 and NEMA 14-50.
NEMA 11s are three-wire, three-pole, and ungrounded for three phase 250 V usage. They come in 20, 30, and 50 amp versions.
NEMA 12s is planned for future introduction to be three-wire, three-pole, and ungrounded for three phase and 480 V use.
NEMA 13s is similar to NEMA 12 and is planned for future introduction. Unlike NEMA 12, NEMA 13 will be rated for 600 V.
NEMA 14s are four-wire and grounded with 15 to 60 amps and a 250 V rating. They can be used for charging electric vehicles and supplying power to electric ranges.
NEMA 15s is like NEMA 14 but is three phase without a neutral conductor.
NEMA 16s is planned for future introduction to be four-wire, three-pole, grounded, and three phase with a 480 V rating.
NEMA 17s is similar to NEMA 16 with a 600 V rating.
NEMA 18s is another version of NEMA 14 and NEMA 15. It is 120Y208V three-phase ungrounded.
NEMA 19s is for future introduction. 277/480Y four-wire, three-pole, ungrounded.
NEMA 20s is similar to NEMA 19 but is 247/600Y ungrounded.
NEMA 21s is for future introduction and is 120/208Y, five-wire, three-pole with neutral, three phase and grounded.
NEMA 22s is similar to NEMA 21 for 277/480Y usage.
NEMA 23s is similar to NEMA 21 and 22 for 347/600Y usage.
are two-pole and ground with a 347 V rating and are mainly used in Canada.
Travel Trailer Connector – NEMA TT-30:
NEMA TT-30s are 120 V and 30 A designed for recreational vehicles.
Locking connectors ensure that connectors fit securely together and stay connected. The plugs of locking connectors have curved blades that allow them to be turned when inserted into the receptacle.
The majority of locking connectors are designed for commercial and industrial use. There are miniature or midget locking connectors that are identified by “ML”. They are used where the larger type of locking connectors will not fit. They come in three varieties.
- two-pole, ungrounded, 125 V rating
- two-pole, grounded, 125 V rating
- three-pole, ungrounded, 125/250 V rating
Locking connectors are differentiated from other NEMA connectors by an “L” placed before the series number as in NEMA L6, NEMA L7, or NEMA L10.
NEMA L1 are single-pole plus neutral, two-wire, ungrounded with a 125 V single phase. They are designed for 15 amp applications.
NEMA L2 are two-pole, two-wire, ungrounded single-phase with a 250 V rating designed for 20 amp applications.
NEMA L3 and L4:
NEMA L3 and L4 were never developed or specified.
NEMA L5 are two-pole and grounded rated for 125 V. They are used at marinas, campsites, and RV parks.
NEMA L6 are 250 V rated with a two-pole, three-wire design for voltage ratings of 208 or 240 without a neutral connection. The phase configuration varies with the voltage. They are used for technical applications such as servers and UPS units.
NEMA L7 are grounded two-pole rated for 277 V for commercial lighting.
NEMA L8 are two-pole grounded connectors rated for 480 V. Intended for three-wire circuits.
NEMA L9 has the same configuration as NEMA L8 with a 600 V rating.
NEMA L10 are two-pole plus neutral, three-wire, ungrounded, single-phase rated for 125/250 V and is deprecated.
NEMA L11 are three-pole, three-wire, ungrounded, 250 V, and three-phase. They come in 15, 20, and 30 amps.
NEMA L12 has the same configuration as NEMA L11 with a 480 V rating.
NEMA L13 are three-pole, three-wire, ungrounded, rated for 600 V, and three-phase.
NEMA L14 are three-pole, grounded, rated for 125/250 V. They are used for three-pole, four-wire neutral ground circuits with voltages of 240 or 208 and 120 V neutral. They can be found on household generators and on racks for amplifiers in large audio systems.
NEMA L15 is a 250 V 30 A four pronged connector. It has a one piece grounding system with polarized and water resistant plugs and connectors.
NEMA L16 are three-pole, ground, rated for 480 V for three-phase circuits.
NEMA L17 has the same configuration as NEMA L16 with a 480 V rating.
NEMA L18 are four-pole, ungrounded, rated for 120/208 V for three-phase four-wire circuits.
NEMA L19 are three-pole, four-wire, ungrounded connectors for three-phase 277/480 V usage. They come in 20 or 30 amp versions.
NEMA L20 is the same as NEMA L19 with a voltage rating of 347/600 V.
NEMA L21 are four-pole, grounded with a 120/208 V rating. They are designed for dusty, damp, and wet environments and have a watertight seal.
NEMA L22 are four-pole, grounded, and rated for 277/480 V for three-phase four-wire circuits with neutral and ground. The middle pin is ground, and the right angle blade on the tab is neutral.
NEMA L23 has the same configuration as NEMA L22 with a 347/600 V rating.
The chart below is a graphic representation of NEMA plug and receptacle configurations.
NEMA PLUG AND RECEPTACLE CONFIGURATIONS
NEMA Power Cords
As with every aspect of electricity transfer, there are a wide variety of power cords that are designed to meet several voltage and amp requirements. The purpose of a power cord is to transfer current from a power source to a receiving device.
In general, power cords are made of copper wire enclosed in an insulating material that is covered with a protective non-conductive material, which can be seen in the diagram below. Every power cord has a plug, socket, and cord. Critical power cords may have a locking mechanism on the plug to prevent accidental disconnection.
Power cords are rated by voltage or kilovolts, which determines the amount of power it can transfer. The amperage rating is a function of the cord’s wiring, number of current carrying conductors, and the length of the cord. When a cord has three current carrying conductors or is over fifty feet, there is a decrease in amperage.
The wire gauge rating is determined by the American Wire Gauge (AWG) standard numbering system. A 12 AWG is a 120 volt cord with 12 gauge wire to be used with 120 volt outlets. In the AWG system, the lower the number the thicker the wire.
The image below is a 6 AWG with 4 conductors and grounding for 45 amps.
The longer a power cord is the greater is its voltage drop. The lower capacity is due to the amount of power lost from the connector to the end of the cable. A very long cord of over 50 feet may have a high AWG because of the length of the cord and extreme voltage drop.
Voltage or power drop generates heat. Too much heat buildup can damage a wire or the power cord. The example below shows the amount of power drop in a 100 foot power cord set.
Chapter Three – NEMA ENCLOSURES
Electrical enclosures are a cabinet or box designed to protect electrical equipment and prevent electrical shock. They are made from plastic, steel, stainless steel, or aluminum and are rated for their protection against hazards and other environmental conditions. Part of the function of an enclosure is to protect electronic equipment from electromagnetic (EMI) and radio frequency (RFI) interference.
The NEMA has thirteen types of enclosures that are rated by where they can be used and the types of protection they offer. Listed below is six of the most common types.
Types of Enclosures
A type 1 enclosure is a general purpose enclosure for indoor use and designed to provide protection against dirt and prevent contact with people. It is used in standard factory environments.
Type 3R enclosures are for protection against rain, sleet, and damage from ice. They are designed for outdoor use, are made of galvanized steel, and are mainly used as meter cabinets, filtered fans, and utility boxes.
A type 4 enclosure is constructed for indoor or outdoor use to provide protection against accidental contact with equipment, dirt, rain sleet, snow, windblown dust, and water as well as damage from ice. The door clamps on three sides to provide a watertight seal. Type 4 enclosures are used in industrial applications such as wiring enclosures, hydraulic controls, and operator consoles.
Type 4X enclosures are similar to type 4 enclosures with the added feature of being corrosion and rust resistant. They provide protection where equipment may be hosed down and are found in marine environments, paper manufacturing applications, industrial food processing, oil and gas drilling, refining and processing, and water treatment.
Type 12 enclosures can be mounted or freestanding. They are non-corrosive and may or may not have knockouts. They are made from 14 gauge steel with welded seams and are designed to protect against flowing liquids.
Type 7 enclosures are for use in hazardous locations as defined by National Electrical Code (NEC) Articles 500 to 506. They are sometimes referred to as explosion-proof and are intended for indoor use in Class I, Groups A, B, C, and D hazardous environments as defined by the NEC. Class I, Groups A, B, C, and D environments contain flammable gases or other potentially explosive materials.
When discussing the protection of components, fixtures, or enclosures, ingress protection (IP) ratings are also used. The IP Rating system is primarily used to measure the ingress of water and solid particles. In some cases, electrical components will contain a NEMA rating and an IP rating.
Though they are dissimilar in their rating scale, they can provide guidance regarding the quality and protection of electrical components. Below is an abbreviated version of IP classifications.
Chapter Four – International Standards for Power Cords and Receptacles
The United States, as demonstrated by the NEMA standards, has a wide variety of plugs and sockets to accommodate the requirements of appliances, machines, heavy duty equipment, and unusual electrical needs. With all of those different types, it may be assumed that there are a sufficient number of alternatives to meet the needs of other countries.
Unfortunately, regardless of the many plugs and receptacles that are found in North America, there are several more found in various countries around the world, with different voltage and amp requirements. To simplify the understanding of international plugs and receptacles, the United States Department of Commerce International Trade Administration has assigned letters from A to O to the different types of connectors, which can be seen on the map below.
With the rise in international travel and the dependence on electronic devices, manufacturers have developed adapters to accommodate the needs of every country. Though standardization and uniformity would make things more convenient, it is very unlikely we will see that in the near future.
International Plugs and Receptacles
The first two types of international plugs, A and B, are used in the United States, Canada, Mexico, and Japan. They are the common ones that we use every day. As can be seen in the two diagrams, the plugs and receptacles used in other countries are somewhat unlike what we are accustomed to.
Type A –
The United States, Canada, Mexico, and Japan – two pins and ungrounded
Type B –
The United States, Canada, Mexico, and Japan – three pins and grounded
Type C –
Europe, South America, and Asia – two pins and ungrounded
Type D –
India – three pins and grounded
Type E –
France, Belgium, Poland, Slovakia & Czechia – two pins and grounded
Type F –
Europe & Russia, except the United Kingdom & Ireland – two pins and grounded
Type G –
The United Kingdom, Ireland, Malta, Malaysia & Singapore – three pins and grounded
Type H –
Israel, the West Bank & the Gaza Strip – three pins and grounded
Type I –
Australia, New Zealand, China & Argentina – two pins and ungrounded or three pins and grounded
Type J –
Switzerland & Liechtenstein – three pins and grounded
Type K –
Denmark & Greenland – three pins and grounded
Type L –
Italy & Chile – three pins and grounded
Type M –
South Africa – three pins and grounded
Type N –
Brazil and South Africa – three pins and grounded
Type O –
Thailand – three pins and grounded
Below is the international plug chart from Webber Electronics in North Ridge, OH.
Chapter Five – IEC vs NEMA
When electronics began to flourish, at the beginning of the 20th Century, manufacturers saw the need to establish standards and requirements for electrical components for safety and uniformity. The International Electrotechnical Commission (IEC) was formed in 1906 as a non-profit and non-governmental organization to create standards for electrotechnical devices.
In the United States, the Electric Power Club and the Associated Manufacturers of Electrical Supplies merged in 1926 to form the National Electrical Manufacturers Association for the standardization of electrical equipment for the safety of consumers. NEMA provides standards exclusively for North America.
The IEC is an international organization with over 80 member countries, including the United States. Its standards are created by thousands of electrical and electronics experts. The numbers for IEC standards begin at 60000 and go to 79999, which are written in the form of IEC 60548. Below is a sampling of some IEC standards.
- IEC 60027 Letter symbols to be used in electrical technology
- IEC 60028 International standard of resistance for copper
- IEC 60034 Rotating electrical machines
- IEC 60038 IEC Standard Voltages
- IEC 60041 Field acceptance tests to determine the hydraulic performance of hydraulic turbines, storage pumps and pump-turbines
- IEC 60044 Instrument transformers
- IEC 60045 Steam turbines
- IEC 60050 International Electrotechnical Vocabulary
- IEC 60051 Direct acting indicating analogue electrical measuring instruments and their accessories
- IEC 60052 Voltage measurement by means of standard air gaps
- IEC 60055 Paper-insulated metal-sheathed cables for rated voltages up to 18/30 kV (with copper or aluminium conductors and excluding gas-pressure and oil-filled cables)
- IEC 60059 IEC standard current ratings
- IEC 60060 High-voltage test techniques
- IEC 60061 Lamp caps and holders together with gauges for the control of interchangeability and safety
- IEC 60062 Marking codes for resistors and capacitors
- IEC 60063 Preferred number series for resistors and capacitors
- IEC 60064 Tungsten filament lamps for domestic and similar general lighting purposes – Performance requirements
Listed below are samples of NEMA standards. Prior to the number on the code is EWS, MG, or ICS, which indicate water service (EWS), motors and generators (MG), and industrial control systems (ICS). There are several other letter combinations that indicate the specific area where the code would be used.
- NEMA EWS 1 Increasing Energy Efficiency in Urban Water Systems: Summary Report
- NEMA EWS 1.1 Market Potential for Electricity Efficiency in Urban Water Systems
- NEMA EWS 1.2 Use of Performance Contracts for Advancing Efficiency in Water Infrastructure
- NEMA EWS 1.3 Glossary of Terms Used in the Water Sector
- NEMA EWS 1.4 Literature Review
- NEMA EWS 1.5 U.S. Water-Related Infrastructure Needs and Potential Funding Opportunities
- NEMA MG 1 Motors and Generators
- NEMA MG 1 Condensed
- NEMA MG 2 Safety Standard for Construction and Guide for Selection, Installation and Use of Electric Motors and Generators
- NEMA MG 10 Energy Management Guide for Selection and Use of Fixed Frequency Medium AC Squirrel‑Cage Polyphase Induction Motors
- NEMA MG 11 1977 Energy Management Guide for Selection and Use of Single‑Phase Motors
- NEMA MG SET
- NEMA ICS 1 Industrial Control and Systems: General Requirements
Though the goals of the IEC and NEMA are similar, there are distinct differences between them. A few of the differences are listed below.
NEMA is designed for ease of selection. All you need to know is the horsepower and voltage of the application. The IEC requires more details.
NEMA products have broader applications. IEC products are smaller and less expensive with closely defined operating conditions.
NEMA products are sold fully assembled, while IEC products have a modular design.
NEMA products have an open design and require safety covers. IEC contactors are finger safe.
The NEMA does not certify products but works with the National Institute of Standards and Technology (NIST) and ASTM International. IEC works closely with several certifying organizations such as the System for Conformity Testing and Certification of Electrotechnical Equipment and Components (IECEE) and the International Organization for Standardization.
There are benefits from using the guidelines of the IEC and NEMA, depending on your needs. The chart below describes some of the major differences.
|Less expensive||More expensive|
|Less versatile; designed to meet life/current requirements in specific applications||More versatile; ratings are broad and apply to many different applications|
|More compact device||Larger sized device|
|Caters to global market||Specific to North American market|
|Reacts faster to overloads||Better at withstanding short circuits|
|Finger safe||Requires safety covers|
Chapter Six – Safety Features
All of the items that we use require easy access to electricity. We are surrounded by electronics from the kitchen to the bedroom. The IEC, NEMA, and other regulatory agencies were organized to provide standards and guidelines for safe use of electricity. Described below are a few of the safety devices that have become standard requirements for providing power to electrical devices.
Ground fault circuit interrupter (GFCI)
A GFCI protects against electric shock by measuring the current flow from hot wire to the neutral wire. When it detects a variation as small as 4 milliamps, it shuts off the power supply.
Tamper resistant receptacles (TR)
TR receptacles prevent electricity from energizing anything stuck into the receptacle, reduce the potential of electrical shock, and are an effective way to protect against the dangers of electricity. They have spring-loaded shutters to close off the contact openings, or slots, of the receptacle. The shutters only open when both shutters are pressed at the same time.
Arc fault circuit interrupters (ADCI) receptacles
An arc fault is an unintended arc created by current flowing on an unplanned path. It creates high intensity heat at the point of the arc, which can ignite surrounding materials. An AFCI is designed to detect arcing to reduce the potential of an electrical system from igniting a fire. GFCI and AFCI are similar in appearance, as can be seen in the image below, but have different functions. While GFCI protects against electrical shock, AFCIs protect against fires.
Surge protector receptacles
Surge protectors reduce energy surges of voltage that can damage electronics, such as TVs, computers, and smart appliances. A voltage surge can last for microseconds but can reach 1000 volts. A surge protector blocks or shortens the current flow.
When normal electrical current flows through the circuit, choke coils or capacitors, connected to the hot wire, move it through the device. When voltage spikes or surges happen, it is sent into the green ground wire, shown in the diagram, to prevent it from damaging the power outlet and connector.
Weather resistant receptacles
Weather resistant receptacles are able to withstand rain, snow, humidity, ice, and any form of moisture. They protect the outlet from damage from corrosion or hazardous conditions. Weather resistant receptacles can be identified by the “WR” printed on the face plate, as seen in the example below.
Leakage current detection and interruption (LCDI)
In an electrical connection, some current flows through the ground conductor to ground, which is called leakage. Most current leakage flows in the insulation around the conductors and the protective filters. When leakage is undetected, it can cause a GFCI to trip. A leakage detector can identify the source of the leakage. It is clamped on a conductor and reads the value of the current.
Wiring for AC and DC power is color coded for easy identification. The IEC has wiring color codes for AC branch circuits. The chart below describes common color codes used in the United States. Since they are not standardized, there may be variations depending on the region or area of the United States.
|Function||Label||Common Color||Alternate Color|
|Ground||PG||bare, green, or green-yellow||green|
|Line, single phase||L||black or red (2nd hot)|
Black Electrical Wires –
Black Electrical Wires are used to transfer power and can be used as switch legs.
Red Electrical Wires –
Red Electrical Wires are secondary live wires and can be used as switch legs. They are used to connect hardwired smoke detectors to the power system.
Blue and Yellow Electrical Wires –
Blue and Yellow Electrical Wires are not used in outlet wiring. Blue and yellow wires are used as live wires pulled through conduits. Yellow wires can be switched legs to ceiling fans, structural lights, and outlets paired with light switches. Blue wires are used as travelers for three or four-way switches.
White and Gray Electrical Wires –
White and Gray Electrical Wires are neutral wires with white being the most used.
Green Electrical Wires –
Green Electrical Wires are groundings for electrical circuits and connect to the grounding terminal. They act as a failsafe for electricity to escape.
- Electrical power connectors allow electronic devices to connect to power outlets.
- Electric power connectors carry alternating current (AC) or direct current (DC).
- Electrical enclosures are a cabinet or box designed to protect electrical equipment and prevent electrical shock.
- NEMA provides standards exclusively for North America. The IEC creates electrical standards used by over 80 nations.
- The most common wiring devices in the United States have current ratings of 15 to 60 amps (A) with voltage ratings of 125 to 600 volts (V).