Electrical Reference Library · Measure & Identify

How to Identify a NEMA Plug or Receptacle

NEMA plugs and receptacles are identified by a configuration code that sets voltage, current rating and pin layout. This sheet shows how to find the code on a device and how to identify an unmarked one by its blade shapes.

Ref EL-0074NEMA WD 6

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

NEMA WD 6 defines the shape and spacing of plug blades and receptacle slots so that a plug fits only receptacles of the same rating. Each layout has a code, such as 5-15R or L14-30P. Straight-blade and locking devices have separate series. The full set of drawings is in the NEMA Receptacle Configuration Chart. For device types, see Receptacle Types and NEMA Configurations.

How to identify

Read the face or back of the device. Most are marked with the NEMA code and ratings in amps and volts.
If unmarked, note the blade style. Flat straight blades or curved locking blades.
Count the blades and pins. Note any round or U-shaped ground pin.
Note blade shapes and angles: parallel, tandem (in line), angled, T-shaped slot, or a bent blade.
Match to the chart. Compare against the NEMA Receptacle Configuration Chart drawings.

Reading the code

Part	Example	Meaning
L prefix	L14-30P	Locking (twist-lock) device; no prefix means straight blade
Number before the dash	14	Configuration family: voltage and wiring arrangement
Number after the dash	30	Current rating in amps
Suffix	P or R	P is a plug; R is a receptacle

Common configurations

Code family	Voltage	Arrangement
1	125 V	2-pole, 2-wire, no ground
5	125 V	2-pole, 3-wire grounding
6	250 V	2-pole, 3-wire grounding
10	125/250 V	3-pole, 3-wire, no ground (older dryer and range)
14	125/250 V	3-pole, 4-wire grounding
15	250 V three-phase	3-pole, 4-wire grounding

Key points

A 5-20R receptacle has a T-shaped slot and accepts both 5-15P and 5-20P plugs.
Locking devices are not interchangeable with straight-blade devices of the same family.
The rating on the device is the device rating. Circuit protection and wire size come from the NEC.
Replacing a 10-series receptacle with a 14-series may require a new grounding conductor and cord. Follow the NEC.
Industrial devices may also carry IEC 60309 pin-and-sleeve configurations, which are a separate system.

Common mistakes

Reading the amp number as the configuration.
Forcing an adapter between configurations.
Mixing up P and R when ordering.
Assuming two locking devices with the same amp rating fit each other.

Governing standards: NEMA WD 6 (wiring device configurations); NEC Article 406 (receptacles and attachment plugs); UL 498 (attachment plugs and receptacles).

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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