The National Electrical Manufacturers Association (NEMA) is an industry authority in the US, made up of more than 350 companies and with more than 700 standards and technical publications. Although NEMA is a US-based organization, it has global recognition and its standards are used internationally. As you might imagine, power plugs and receptacles are among the electrical equipment categories covered by NEMA standards.
Before presenting the NEMA rating for power plugs and receptacles, it is important to identify the two main types:
- Straight blade, no locking
- Curved blade, twist lock
Non-latching connectors use plugs designed to be pulled in and out of receptacles freely, which is convenient but also means the plug can easily be accidentally disconnected. Twist lock connectors can be rotated once the plug is connected, causing them to lock in place and eliminating the risk of accidental disconnection.
Make sure you use the correct electrical outlets in your project.
Power plugs and receptacles manufactured to NEMA standards come with an alphanumeric code that describes the product's characteristics. This article will provide a guide on how to interpret these codes.
Understanding NEMA Codes
NEMA alphanumeric codes indicate four important pieces of information for power plugs and receptacles:
|
CONNECTOR FEATURES |
DESCRIPTION |
|
No locking or twist locking? |
If the NEMA code starts with the letter 'L', it is a twist locking device. |
|
NEMA type |
The NEMA type determines the construction characteristics 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 ranking |
Indicated by a number after the dash, which represents the amperage of the device. |
|
Plug or receptacle? |
The NEMA code ends in 'P' for plugs and 'R' for receptacles. |
As an example, suppose the NEMA code of a connector is L5-30R:
- The letter 'L' indicates a twist locking device.
- NEMA type is 5 (number before the dash).
- Current rating is 30A (number after dash).
- The letter 'R' indicates a receptacle.
On the other hand, a connector labeled 2-15P would have the following features:
- As there is no letter 'L', it is a straight blade, non-locking device.
- NEMA type is 2.
- The current rating is 15A.
- The letter 'P' indicates a power plug.
Twist lock connectors are typically used in applications where accidental disconnection is likely and the consequences are significant, such as data centers or industrial sites.
Note that power plugs and receptacles are designed to connect to the same NEMA types; the angle between the blades differs slightly between types to avoid accidental connections. For example, you cannot connect a 1-15P power plug to a 2-15R receptacle.
NEMA Connector Types
The following table describes the types of NEMA connectors, based on conductor properties and voltage rating . Types marked with an asterisk are only available in twist-lock versions, while the remainder exist in non-lock and twist-lock configurations.
|
NEMA TYPE |
WIRES |
WARM |
NEUTRAL |
FLOOR |
RATED VOLTAGE |
|
NEMA1/L1 |
two |
1 |
Yes |
No |
125 Vac |
|
NEMA2/L2 |
two |
two |
No |
No |
250 Vac |
|
NEMA5/L5 |
3 |
1 |
Yes |
Yes |
125 Vac |
|
NEMA 6/L6 |
3 |
two |
No |
Yes |
250 Vac |
|
NEMA7/L7 |
3 |
1 |
Yes |
Yes |
277 Vac |
|
NEMA L8* |
3 |
two |
No |
Yes |
480 Vac |
|
NEMA L9* |
3 |
two |
No |
Yes |
600 Vac |
|
NEMA 10/L10 |
3 |
two |
Yes |
No |
125/250 Vac |
|
NEMA 11/L11 |
3 |
3 |
No |
No |
250 Vac |
|
NEMA L12* |
3 |
3 |
No |
No |
480 Vac |
|
NEMA L13* |
3 |
3 |
No |
No |
600 Vac |
|
NEMA 14/L14 |
4 |
two |
Yes |
Yes |
125/250 Vac |
|
NEMA 15/L15 |
4 |
3 |
No |
Yes |
250 Vac |
|
NEMA L16* |
4 |
3 |
No |
Yes |
480 Vac |
|
NEMA L17* |
4 |
3 |
No |
Yes |
600 Vac |
|
NEMA 18/L18 |
4 |
3 |
Yes |
No |
120/208 Vac |
|
NEMA L19* |
4 |
3 |
Yes |
No |
277/480 Vac |
|
NEMA L20* |
4 |
3 |
Yes |
No |
347/600 Vac |
|
NEMA L21* |
5 |
3 |
Yes |
Yes |
120/208 Vac |
|
NEMA L22* |
5 |
3 |
Yes |
Yes |
277/480 Vac |
|
NEMA L23* |
5 |
3 |
Yes |
Yes |
347/600 Vac |
|
NEMA 24/L24 |
3 |
1 |
Yes |
Yes |
347 Vac |
|
NEMA TT-30 |
3 |
1 |
Yes |
Yes |
120 Vac |
NEMA TT-30 is a special type of connector used on recreational vehicles, where TT stands for travel trailer.
You may have noticed that types 3 and 4 have been ignored. NEMA 3 is for two-wire ungrounded 277V circuits, while NEMA 4 is for two-wire ungrounded 600V circuits. However, both types of connectors are reserved for future use by NEMA, and there are no commercial power plugs and receptacles that utilize these designs.
The ML series is a subtype of twist lock connectors, where ML stands for “dwarf lock”. ML connectors are rated at 15 amps and used in applications where normal twist lock connectors will not fit. There are three main types:
- ML1: 2 poles, ungrounded, 125V.
- ML2: 2 poles, grounded, 125V.
- ML3: 3 poles (2 live conductors and neutral), ungrounded, 125/250V.
Final Observations
Power plugs and receptacles are available in a large number of configurations, which provides great flexibility in specifying electrical installations . However, having too many options also means there is a greater chance of selecting the wrong connectors for an application. By working with qualified electrical design engineers you can ensure that your electrical installations are property specified.
