A Guide to NEMA Connectors

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.

Make sure you're using the correct power outlets in your project.

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:

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.

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 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.