A Guide to NEMA Connectors

Amol Patil
Author : Amol Patil
June 8, 2018
11 Minutes Read
  
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    The National Electrical Manufacturers Association (NEMA) is an industry authority in the USA, composed of more than 350 companies and with more than 700 standards and technical publications. Although NEMA is a USA-based organization, it has global recognition and its standards are used internationally. As you can imagine, power plugs and receptacles are among the electrical equipment categories covered by NEMA standards.

    Before presenting the NEMA classification for power plugs and receptacles, it is important to identify the two main types:

    1. Straight-blade, non-locking
    2. Curved-blade, twist-locking

    Non-locking connectors use plugs designed to be pulled in and out of receptacles freely, which is convenient but also means the plug can be easily disconnected by accident. Twist-locking connectors can be rotated once the plug is connected, causing them to latch in place and eliminating the risk of accidental disconnection.


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    Power plugs and receptacles manufactured according to NEMA standards come with an alphanumeric code that describes product features. This article will provide a guide on how to interpret such codes.

    Understanding NEMA Codes

    NEMA alphanumeric codes indicate four key pieces of information for power plugs and receptacles:

    CONNECTOR FEATURES

    DESCRIPTION

    Non-locking or twist-locking?

    If the NEMA code starts with the letter ‘L’, it's a twist-locking device.
    If the NEMA type is indicated directly without a letter, it's a non-locking device.

    NEMA type

    The NEMA type determines the construction features of a connector. It is indicated by a number, which is preceded by the letter ‘L’ in twist-locking devices, and followed by a dash.

    Current rating

    Indicated by a number after the dash, which represents the ampere rating of the device.

    Plug or receptacle?

    The NEMA code ends in ‘P’ for plugs and ‘R’ for receptacles.

    As an example, assume the NEMA code of a connector is L5-30R:

    • The letter ‘L’ indicates a twist-locking device.
    • The NEMA type is 5 (number before the dash).
    • The current rating is 30A (number after the dash).
    • The letter ‘R’ indicates a receptacle.

    On the other hand, a connector labeled as 2-15P would have the following features:

    • Since there is no letter ‘L’, it's a straight-bladed and non-locking device.
    • The NEMA type is 2.
    • The current rating is 15A.
    • The letter ‘P’ indicates a power plug.

    Twist-locking connectors are normally used in applications where accidental disconnection is likely and the consequences are significant, such as data centers or industrial locations.

    Note that power plugs and receptacles are designed for connecting the same NEMA types together; the angle between blades differs slightly among types to prevent accidental connection. For example, you cannot connect a 1-15P power plug to a 2-15R receptacle.

    powerplug

    NEMA Connector Types

    The following table describes the NEMA connector types, based on conductor properties and rated voltage. The types marked with an asterisk are only available in twist-locking versions, while the rest exist in both non-locking and twist-locking configurations.

    NEMA TYPE

    WIRES

    HOT

    NEUTRAL

    GROUND

    RATED VOLTAGE

    NEMA 1 / L1

    2

    1

    Yes

    No

    125V AC

    NEMA 2 / L2

    2

    2

    No

    No

    250V AC

    NEMA 5 / L5

    3

    1

    Yes

    Yes

    125V AC

    NEMA 6 / L6

    3

    2

    No

    Yes

    250V AC

    NEMA 7 / L7

    3

    1

    Yes

    Yes

    277V AC

    NEMA L8*

    3

    2

    No

    Yes

    480V AC

    NEMA L9*

    3

    2

    No

    Yes

    600V AC

    NEMA 10 / L10

    3

    2

    Yes

    No

    125/250V AC

    NEMA 11 / L11

    3

    3

    No

    No

    250V AC

    NEMA L12*

    3

    3

    No

    No

    480V AC

    NEMA L13*

    3

    3

    No

    No

    600V AC

    NEMA 14 / L14

    4

    2

    Yes

    Yes

    125/250V AC

    NEMA 15 / L15

    4

    3

    No

    Yes

    250V AC

    NEMA L16*

    4

    3

    No

    Yes

    480V AC

    NEMA L17*

    4

    3

    No

    Yes

    600V AC

    NEMA 18 / L18

    4

    3

    Yes

    No

    120/208V AC

    NEMA L19*

    4

    3

    Yes

    No

    277/480V AC

    NEMA L20*

    4

    3

    Yes

    No

    347/600V AC

    NEMA L21*

    5

    3

    Yes

    Yes

    120/208V AC

    NEMA L22*

    5

    3

    Yes

    Yes

    277/480V AC

    NEMA L23*

    5

    3

    Yes

    Yes

    347/600V AC

    NEMA 24 / L24

    3

    1

    Yes

    Yes

    347V AC

    NEMA TT-30

    3

    1

    Yes

    Yes

    120V AC

    NEMA TT-30 is a special type of connector used in recreational vehicles, where TT means travel trailer.

    You may have noticed that types 3 and 4 are skipped. NEMA 3 is for two-wire ungrounded 277V circuits, while NEMA 4 is for two-wire ungrounded 600V circuits. However, both connector types are reserved for future use by NEMA, and there are no commercial power plugs and receptacles using those designs.

    The ML series is a subtype of twist-locking connectors, where ML stands for “midget locking”. ML connectors are rated at 15 amperes and used in applications where normal twist-locking connectors don’t fit. There are three main types:

    • ML1: 2-pole, ungrounded, 125V.
    • ML2: 2-pole, grounded, 125V.
    • ML3: 3-pole (2 live conductors and neutral), ungrounded, 125/250V.

    Concluding Remarks

    Power plugs and receptacles are available in a large number of configurations, which provides great flexibility when specifying electrical installations. However, having many options also means there is a higher chance of selecting the wrong connectors for an application. By working with qualified electrical design engineers, you can make sure your electrical installations are property specified.

    Tags Electrical Engineering | Electrical Installation | NEMA Standards | Electrical Design

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