NEMA connectors are the standardized plugs and receptacles used for North American line-voltage power. The system looks like a wall of cryptic numbers — 5-15, 6-50, 14-50, L14-30 — but it follows one consistent rule, and once you know the rule, you can read any of them at a glance and know exactly what they carry.
Reading the designation
Every NEMA name splits into two parts around a dash, with optional prefix and suffix letters:
- The number before the dash is the configuration — it encodes the voltage and the number of poles and wires.
- The number after the dash is the current rating in amps: 15, 20, 30, 50, 60.
- An
Lprefix (as in L14-30) means it is a locking twist-lock connector. - A trailing
RorPdistinguishes the Receptacle (outlet) from the Plug — same configuration, opposite halves.
The common configurations
The number before the dash is the part worth memorizing. These are the ones you will actually meet:
| Config | Voltage | Wires | Typical use |
|---|---|---|---|
| 1 | 125 V | 2-wire, no ground | Old 2-prong outlets (obsolete) |
| 5 | 125 V | 3-wire grounding | Standard household outlet (5-15) |
| 6 | 250 V | 3-wire grounding | 240 V tools, AC, welders, EV (6-50) |
| 10 | 125/250 V | 3-wire, no ground | Legacy dryers & ranges (pre-1996) |
| 14 | 125/250 V | 4-wire grounding | Modern dryers, ranges, EV, RV |
| TT | 125 V | 3-wire grounding | RV 30 A shore power (TT-30) |
| L5 / L6 / L14 | varies | locking | Generators, transfer switches, stage gear |
3-wire vs 4-wire: the dryer/range split
This is the single most important — and most misunderstood — distinction in the chart. Before the 1996 National Electrical Code, electric dryers and ranges used 3-wire connectors (10-30 and 10-50): two hot legs and a neutral, with the appliance frame bonded to the neutral. Since 1996, new circuits must use 4-wire connectors (14-30 and 14-50) that add a separate equipment ground, so the neutral no longer doubles as the safety ground.
The practical consequences:
- A new dryer ships with a 4-wire cord. An older home may have a 3-wire 10-30 outlet.
- You change the cord to match the outlet, and reconfigure the appliance's neutral/ground bonding strap accordingly — you do not force-fit a 4-wire plug into a 3-wire receptacle.
- If you are rewiring or building new, install the 4-wire 14-series. It is what code requires and it is safer.
EV and RV charging
For EV charging, the workhorse outlet is the NEMA 14-50 — 120/240 V, 50 A. On a properly sized dedicated circuit it delivers up to 40 A continuous (the 80% rule for continuous loads), which covers most Level 2 home charging. The 6-50 (240 V, 50 A, no neutral) is the other common choice and is shared with welders.
For RVs, two connectors dominate: the TT-30 (120 V, 30 A) for smaller trailers, and the 14-50 (240 V, 50 A) for larger rigs with two air conditioners. The dangerous trap is that TT-30 and the 240 V "30 amp" connectors are all called "30 amp" — but TT-30 is 120 V only. Using the wrong adapter to feed a TT-30 RV from a 240 V source can put 240 V into 120 V electronics.
Twist-lock (L) connectors
Locking connectors use curved blades that rotate to latch, so they cannot vibrate loose or be pulled out accidentally. That makes them standard for portable generators (L5-30, L14-30), manual transfer switches, RV shore power, and stage/AV equipment. The numbering logic is identical to the straight-blade types — L14-30 is the locking version of the 120/240 V 4-wire configuration at 30 A — just with a mechanically different, lockable face.
A word on safety
The genius of the NEMA system is mechanical keying: a 240 V plug physically will not fit a 120 V outlet, and a 50 A cord will not seat in a 30 A receptacle. But the chart identifies connectors; it does not size circuits. The breaker rating, wire gauge, and grounding all have to be correct for a connector to be safe, and a receptacle is only as trustworthy as the wiring behind it. Verify questionable outlets with a tester, and have a licensed electrician size and install anything you are unsure about.
Frequently asked questions
What do the numbers in a NEMA plug mean?
A designation like 14-50 has two parts. The number before the dash is the configuration — it sets the voltage and the number of poles/wires (5 = 125 V grounding, 6 = 250 V grounding, 14 = 120/240 V 4-wire, and so on). The number after the dash is the amp rating (15, 20, 30, 50, 60). An L in front means it is a locking/twist-lock version.
Is a 10-30 the same as a 14-30?
No. A 10-30 is a 3-wire connector (two hots + neutral, no separate ground) used for dryers before the 1996 NEC. A 14-30 is 4-wire (adds a dedicated ground). New installations require the 4-wire 14-series, and the two are not directly interchangeable — converting safely is a wiring change, not just a new plug.
What outlet do I need for an EV charger?
The most common is a NEMA 14-50 (120/240 V, 50 A), which supports up to 40 A continuous charging. NEMA 6-50 (240 V, 50 A, no neutral) is also widely used. The circuit, breaker, and wire gauge must be sized for the load by a licensed electrician.
Why does my 20-amp outlet have a sideways T-slot?
The T-shaped neutral slot on a 5-20 or 6-20 receptacle lets it accept both 15 A and 20 A plugs. A true 20 A plug has one blade rotated 90°, so it only fits the T-slot — preventing a 20 A appliance from being plugged into a 15 A circuit.
What is the TT-30 RV plug — is it just a 30-amp 120-volt outlet?
Yes. TT-30 ("travel trailer") is 120 V, 30 A, 3-wire grounding. It is frequently confused with the 240 V 10-30/L5-30 connectors because they are all "30 amp," but TT-30 is 120 V only. Plugging a TT-30 RV into a 240 V outlet via the wrong adapter can destroy its electronics.
Does the plug shape guarantee the voltage is correct?
The shapes are keyed so incompatible voltages cannot cross-connect, but the wall outlet is only as correct as its wiring. On older or DIY installations, verify with a meter or outlet tester before trusting the receptacle.