Next on the list of things-to-grasp is the subject of connectors: receptacles and plugs. Don't under-estimate this portion of the puzzle. If you don't know the cryptic NEMA "WD 6" published standard, you'll have a real fun time trying to communicate with an electrician or UPS vendor about your requirements. I've had to deal with ordering outlet installations from the electricians in the past, and so I made a blog entry which lists the NEMA outlet/plug types and explains their labeling system. (In English, it's a page explaining all the power plug labeling and having links to lots of labeled pictures of connector types.) Thankfully, clues were contributed by grateful people, so I'm going to recap the pith of the content here in a (hopefully) more useful manner.

What the heck is NEMA? And what are they doing giving all of our wall plugs and outlets these funky, indecipherable names such as L5-30, 6-15 and P6-20? And who the heck knew that there were dozens and dozens of standard types of American plugs and wall outlets? Not me. I was short on clues.

I had dig up some charts with pictures of various types of NEMA standard plugs so I could communicate properly with a vendor who supplied a UPS (uninterruptible power supply) to us with the wrong type of wall plug. Thankfully, the vendor clued me in on how to decipher the NEMA naming system.

NEMA (National Electrical Manufacturers Association) is the standards organization that names all of our (American) outlet and plug types. Unfortunately their website is pretty useless when it comes to locating meaningful information. I found it very difficult to even grasp their site layout, let alone dig up the details I was looking for. Anyhow, here's how to decipher the NEMA naming scheme:

Say you have an L5-30P connector. It is deciphered as

• L = Locking. This means it's the type of connector where the plug is rotated into the socket, locking it in place so that it can't accidentally be yanked (with ease)
• 5 = rated for handling 120 volt power (up to 150 volts)
• 30 = rated for handling up to 30 amps
• P = Plug (as opposed to R, which would be receptacle)

I'm no electrician by any means. So if I've worded any of this wrong, feel free to correct me. You get the idea though. It's pretty simple. For you Linux geeks out there, the GNU --help line might read the syntax as:
[X]nn-aa[Y]

Where:

• 'X' is an optional modifier, sometimes having a value of 'L' for 'Locking'.
• 'nn' is a number (most commonly 5 or 6, for 125v (120v power) or 250v (208v power), respectively) which states how many volts the connector (receptacle or plug) can handle. This number can be a number between 1 and 24 (though 3 and 4 are not used). The number represents a certain combination of voltage, # of poles, # of wires, and whether it is a grounding type plug or not.
• 'aa' is a number stating how many amperes the connector or plug can handle.
• 'Y' is either a 'P' or an 'R', which tells you whether the connector is a plug (male) or rreceptacle (female/socket).

The following chart shows some of the NEMA codes with their corresponding outlet shapes. When communicating with your electrician you would append 'P' to the codes for plugs or 'R' to these codes for receptacles. Letters used here are:

• L = Locking
• A = Amps
• V = Volts
• P = Poles (?)
• W = Wires

NEMA No.	Config	Rating
L5-15		15A, 125V 2P, 3W
L5-15 5-15		15A, 125V 2P, 3W
L6-15		15A, 250V 2P, 3W
L7-15		15A, 277VAC 2P, 3W
L5-20		20A, 125V 2P, 3W
L6-20		20A, 250V 2P, 3W
L7-20		20A, 277VAC 2P, 3W
L8-20		20A, 480VAC 2P, 3W
L5-30		30A, 125V 2P, 3W
L6-30		30A, 250V 2P, 3W
L7-30		30A, 277VAC 2P, 3W
L8-30		30A, 480VAC 2P, 3W
L14-20		20A, 125/250V 3P, 4W
L15-20		20A, 250V 3ø 3P, 4W
L16-20		20A, 480V 3ø 3P, 4W
L14-30		30A, 125/250V 3P, 4W
L15-30		30A, 250V 3ø 3P, 4W
L16-30		30A, 480V 3ø 3P, 4W
L21-20		20A, 120/ 208V 3/Y 4P, 5W
L22-20		20A, 277/ 480V 3/Y 4P, 5W
L23-20		20A, 347/ 600V 3/Y 4P, 5W
L21-30		30A, 120/ 208V 3/Y 4P, 5W
L22-30		30A, 277/ 480V 3/Y 4P, 5W
L23-30		30A, 347/ 600V 3/Y 4P, 5W

NEMA No.	Config	Rating
5-15		15A, 125V 2P, 3W
5-20		20A, 125V 2P, 3W
6-15		15A, 250V 2P, 3W
6-20		20A, 250V 2P, 3W
5-30		30A, 125V 2P, 3W
5-50		50A, 125V 2P, 3W
6-30		30A, 250V 2P, 3W
6-50		50A, 250V 2P, 3W
14-30		30A, 125/250V 3P, 4W
14-50		50A, 125/250V 3P, 4W
14-60		60A, 125/250V 3P, 4W

Note that I found this chart elsewhere (from someone who in turn found it elsewhere on a site which no longer exists) and reformatted it for use on my site here.

I have found charts of the plug/outlet types which are more comprehensive at the links listed below, complete with illustrations of the pin layouts:

• Non-locking (straight blade) connectors
• Twist-lock connectors

The same site has a collection of useful and relevant references on power plugs, connectors and receptacles.

While researching I came across an interesting page which gives clues on the quality of plug terminators and indications of failure or poor construction (obviously pitched with the vested interest of peddling their wares, but informative none-the-less).

Another piece of lingo I came across during my recent UPS shopping run was the phrase "three-wire" in reference to an equipment's input power connector type. The English translation of this phrase is, "you need to contact an electrician to wire this directly into your breaker panel".

A few quick notes on attaching a plug to your component's power cable:

• Green screw goes to the (green) ground wire's terminator.
• Silver screw goes to the (white) neutral wire's terminator.
• Copper screw goes to the (black) positive wire's terminator.