How to read a NEMA number
5-15P breaks down as: family 5 (125 V, two poles plus ground), rating 15 amps, P for plug (R is the receptacle). An L in front, as in L5-20P, means a twist-lock. The family number carries the voltage: 5 and L5 are 125 V, 6 and L6 are 250 V. Look at the outlet on the wall or the machine, read its designation off the face (it is moulded in), and order the matching plug.
The table
| Plug | Rating | Fits receptacle | Typical use | GFCI cords |
|---|---|---|---|---|
| 5-15P | 15 A, 125 V | 5-15R and 5-20R | the ordinary household and job-site plug | 5-15P GFCI cords |
| 5-20P | 20 A, 125 V | 5-20R only (one blade is turned) | 20 A tools, compressors, larger heaters on a 20 A circuit | GFCI hub (5-20P on request) |
| 6-15P | 15 A, 250 V | 6-15R and 6-20R | 240 V equipment: small machine tools, heaters, some air conditioners | GFCI hub (6-15P on request) |
| 6-20P | 20 A, 250 V | 6-20R only | 240 V, 20 A machines | GFCI hub (6-20P on request) |
| L5-15P | 15 A, 125 V | L5-15R | twist-lock 120 V where a cord must not pull out | L5-15P GFCI cords |
| L5-20P | 20 A, 125 V | L5-20R | twist-lock 120 V, 20 A | GFCI hub (L5-20P on request) |
| L6-15P | 15 A, 250 V | L6-15R | twist-lock 240 V machines | L6-15P GFCI cords |
| L6-20P | 20 A, 250 V | L6-20R | twist-lock 240 V, 20 A | L6-20P GFCI cords |
What fits what
A 20 A receptacle in the 5 family (5-20R) has a T-shaped neutral slot so that it accepts both the 5-15P and the 5-20P. The reverse is not true: a 5-20P will not go into a 5-15R, and that is deliberate, because the 15 A circuit behind it cannot feed a 20 A load. The 6 family works the same way. Twist-locks fit only their own designation. If a cord does not fit, do not file the blade; you are looking at the wrong cord.
Voltage and the GFCI device
The plug family also decides which GFCI you can use. A 5 or L5 plug carries one hot and a neutral at 120 V, and the GFCI compares those two. A 6 or L6 plug carries two hots and no neutral at 240 V, and the GFCI has to be a two-pole device that compares the two hots. They are different devices. A "120/240 V" user-attachable GFCI handles either; a 120 V device will not work on a 6 family plug, whatever adapter is in between. Guide 2 covers voltage in more depth.
Current: the plug is a promise
The plug's rating is the most current the cord should ever carry. Behind a 5-15P you want 14 AWG cordage for anything over about 25 ft, 12 AWG for 20 A plugs and long runs, and a GFCI device rated at least as high as the plug. A 15 A device on a 20 A cord is the wrong device (see guide 4). Tool nameplates give running amps; motors draw several times that for a moment at start.
Hospital grade and the green dot
A green dot on a 5-15P or 5-20P marks a hospital-grade plug tested to UL 817's extra requirements for grip, strain relief and abuse. It is the same pattern and fits the same receptacles. Where a facility specifies hospital grade, the GFCI cord needs the green-dot plug and the device rating to match.
The 30 A twist-locks and the 4-wire ones
L5-30P and L6-30P (30 A) and the four-wire L14 family (125/250 V, common on generators) exist and GFCI protection for them exists, usually as an in-line module or a GFCI at the generator receptacle rather than a plug-head device. Ask us for those; they are built to order.