NEMA WD 6 · Plugs & receptacles

How to read NEMA plug & receptacle numbers

What the number, dash rating, L prefix, and P/R suffix mean, how to identify a receptacle on site, and the mix-ups that fry equipment or fail inspection.

Anatomy of a NEMA designation — using L14-30R

Part	Example	What it tells you
Leading letter	L	Locking (twist-lock). No letter = straight blade
Number before the dash	14	The configuration family: voltage rating, number of poles, number of wires, and whether there is a ground pin
Number after the dash	30	Ampere rating of the device
Trailing letter	R	R = receptacle, P = plug (connector bodies are also marked)

Our own summary of the NEMA WD 6 naming scheme, not the standard itself. Confirm ratings on the device and manufacturer data, and install per the NEC edition adopted by your AHJ.

Worked identifications

Designation	Decoded	Where you see it
5-20R	125 V, 20 A, 2-pole 3-wire grounding, straight blade	Commercial and kitchen receptacle circuits
6-50R	250 V, 50 A, 2-pole 3-wire grounding (no neutral)	Welders, some EV chargers
14-50R	125/250 V, 50 A, 3-pole 4-wire grounding (hot-hot-neutral-ground)	Ranges, RV hookups, EV chargers
L14-30R	125/250 V, 30 A, 3-pole 4-wire grounding, locking	Portable generators and generator inlet boxes
L21-30R	120/208 V three-phase wye, 30 A, 4-pole 5-wire grounding, locking	Three-phase PDUs, event power

Five examples to teach the decoding, not a full catalog. Our own summary of the NEMA WD 6 naming scheme, not the standard itself. Confirm ratings on the device and manufacturer data, and install per the NEC edition adopted by your AHJ.

Identifying a receptacle in the field

Check	What to look for
Read the face or back	Most devices are stamped with the NEMA designation, voltage, and amp rating — start there
Count the openings	Separate the ground opening (round or U-shaped) from the current-carrying slots; hots + neutral = poles, all openings = wires
Look for a neutral	A neutral slot means the device can serve 120 V loads; hot-hot-ground only means straight 208/240 V
Slot shape	Curved slots that turn and lock = L-series. A T-shaped or L-shaped slot is a keying feature that tells higher-amp devices apart
Check the circuit	Confirm the breaker and wire match the device rating before plugging anything in — the receptacle label is not proof of the circuit

Our own summary of the NEMA WD 6 naming scheme, not the standard itself. Confirm ratings on the device and manufacturer data, and install per the NEC edition adopted by your AHJ.

Common mix-ups

Mix-up	What to do instead
Treating same-amp devices as interchangeable (e.g., 6-50 vs 14-50)	Match the full designation — the family number decides whether there is a neutral
Counting the ground pin as a pole	Poles are current-carrying contacts only; the ground adds a wire, not a pole
Assuming a straight-blade and locking device with the same numbers are the same part	Electrically similar, mechanically different — an L14-30 plug won't fit a 14-30 receptacle
Installing a 3-wire dryer or range receptacle on new work	New dryer and range circuits need an equipment grounding conductor — a 4-wire configuration
Sizing the circuit to the device rating for a continuous load	Continuous loads like EV charging are sized at 125% — the load may need to be turned down to fit the receptacle

Our own summary of the NEMA WD 6 naming scheme, not the standard itself. Confirm ratings on the device and manufacturer data, and install per the NEC edition adopted by your AHJ.

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Decoding any NEMA designation

NEMA configurations are defined in ANSI/NEMA WD 6, a published standard; this page explains the naming logic in our own words. The scheme is built so a plug only fits a receptacle with the same voltage and amp rating. The number before the dash is the family — it fixes voltage, poles (current-carrying contacts), wires, and whether there’s a ground pin. The number after the dash is the amp rating. An L in front means twist-lock, and P or R at the end means plug or receptacle.

Worked identification. You find a receptacle stamped 14-50R in a garage. Family 14 means 125/250 V with two hots, a neutral, and a ground — 3-pole, 4-wire. The 50 is 50 A. So it needs a 50 A, 2-pole breaker and conductors rated for 50 A; per the NEC 310.16 ampacity chart, 6 AWG copper at 75 °C (65 A) covers it, and the 250.122 EGC chart gives 10 AWG copper for the ground on a 50 A device.

EV charger example. A customer wants to plug a 48 A charger into that 14-50. EV charging is continuous, so the circuit must be 125% of the charger rating: 48 × 1.25 = 60 A — too much for a 50 A receptacle. Turn the charger down to 40 A (40 × 1.25 = 50 A) or hardwire it on a larger circuit.

Picking the breaker behind the receptacle? See the standard breaker sizes guide and the wire size & breaker chart, and record each circuit on the panel schedule template. For outdoor or washdown device covers, see NEMA enclosure types.

FAQ

How do you read a NEMA plug number?+

The number before the dash is the configuration family, which sets voltage, poles, wires, and grounding. The number after the dash is the amp rating. A leading "L" means twist-lock, and a trailing "P" or "R" means plug or receptacle. For example, L14-30R is a 125/250 V, 30 A, 3-pole 4-wire grounding locking receptacle.

What is the difference between a NEMA 14-50 and a 6-50?+

Both are 50 A. A 14-50 is 125/250 V, 3-pole 4-wire: two hots, a neutral, and a ground, so it can serve 120 V loads. A 6-50 is 250 V, 2-pole 3-wire: two hots and a ground, no neutral — for equipment that only needs 240 V, like welders.

What does "3-pole 4-wire grounding" mean?+

Three current-carrying contacts (two hots and a neutral) plus a separate equipment ground, for four wires total. The ground pin is counted as a wire but not as a pole.

Can I plug a 48 A EV charger into a 14-50?+

No. EV charging is a continuous load, so the circuit must be rated at 125% of the charger setting: 48 A × 1.25 = 60 A, which is more than a 50 A receptacle. Set the charger to 40 A (40 × 1.25 = 50 A) or hardwire it on an appropriately sized circuit.

Is 125 V the same as 120 V?+

For practical purposes, yes. NEMA ratings are device voltage ratings (125 V, 250 V), while system nominal voltages are 120 V, 208 V, and 240 V. A 250 V-rated device is used on both 208 V and 240 V circuits.

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