Power plug orientation and usability

Question

I was wondering what advantage is gained by modeling a power plug after the lower design. These are American power plugs, and they both exist.

Perhaps the only consumer-based effect gained by using the upper plug is that the plug can be put in upside down, which is helpful when using big, bulky wall warts.

enter image description here

I know that electricity-wise, the orientation really doesn't matter, and that the options below don't matter if there is a ground pin. The ground pin will limit the orientation to the upright position.

However, I can't really think of a solid advantage gained by the lower option.

Also, why are there sometimes holes in the end of the plug? I think that they may exist to save metal.

As always, thanks for your input.

I don't really understand what you're asking here. It appears you've designed a new plug, yet can't think of any advantages to using it? Why have you proposed this new design then? Can you also describe what is different between the two designs - it looks the same but the lower one has a larger end to one of the pins (or is it the same size, but the stem of it is thinner?) It's all a bit unclear really. — , Aug 21 '13 at 07:49
They exist already. I didn't make them up. The lower design has a taller left pin (that is the only difference) to accommodate the taller slot in a power socket on the left side. Anyway, I made the picture better. When you have the chance, can you check this out? Thanks. — Blue Ice, Aug 21 '13 at 13:08
And, no, the bottom design does not have pins that are closer together. — Blue Ice, Aug 21 '13 at 13:11
You can fit a padlock in the little hole at the end so other people in your home can't use the device. — jippie, Aug 21 '13 at 15:20
It's for safety. See Anindo Ghosh's answer for a more detailed look. — Shamtam, Aug 21 '13 at 15:24
For interesting insights into the "why do the blades have holes" part of the question, see this other question: [NEMA 5-15P blade holes](http://electronics.stackexchange.com/q/11495/14004) — Anindo Ghosh, Aug 21 '13 at 15:24
@AnindoGhosh oh come on, do you really buy stories on that question? The hole is for a padlock, a padlock I tell you. To prevent your home mate from using your ... whatever ;o) — jippie, Aug 21 '13 at 15:37
possible duplicate of [Why are some AC outlets and plugs polarized?](http://electronics.stackexchange.com/questions/15228/why-are-some-ac-outlets-and-plugs-polarized) — JYelton, Aug 21 '13 at 17:14

score 10 · Accepted Answer · edited Apr 13 '17 at 12:32

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In some applications, polarity matters because there is typically a policy of having switches and fuses all in the "hot" path (from the fusebox right through to appliance internals).

enter image description here

The holes are for locking the plug to certain types of receptacle (maybe)

The world's smartest man says "Engineers have been sticking holes in the prongs of plugs for so long that they have forgotten why they started."

You leftpondian householders seem to have a baffling array of outlets to understand.

enter image description here
^{from Z-tronix}

The National Electrical Manufacturers Association (NEMA, USA) has set standards for configuration that differ depending on current rating (15, 20, 30, 50 or 60 A) and electrical potential (120, 208, 240, 277, 480 or 600 V)*. This has resulted in more than 35 different straight blade configurations (various grounding systems included).

From Museum of plugs and sockets

The system rules out accidental intermating of devices and related risks.

If you look at the DIY SE site you'll find several questions where leftpondians are having trouble changing plugs on appliances to fit their outlets, or rewiring outlets to suit new appliances.

Luckily for rightpondians, their homes have exactly one type of outlet (two if you have a shaver outlet in bathroom) so life is a lot simpler. Anything over 3.1 kW gets hardwired by an electrician.

edited Apr 13 '17 at 12:32

Community

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answered Aug 21 '13 at 15:06

RedGrittyBrick

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+1, bizarre, I always wondered why some people insert utensils and other objects into power points but now see it may be the only practical way to get interoperability in some places. – PeterJ Aug 21 '13 at 15:15
Very rarely do you see anything besides the 1-15R and 5-15R in any house in the US, short of a couple 250V sockets for an electric range or a dryer, both of which are never used. I've only seen a couple of those other ones in industrial applications. – Shamtam Aug 21 '13 at 15:21
"You leftpondian householders seem to have a baffling array of outlets to understand." Don't worry, none of us actually understand. – The Photon Aug 21 '13 at 15:30
@Shamtam, electric ranges and dryers certainly are used, especially in homes that don't have gas plumbing. – The Photon Aug 21 '13 at 15:31
What is the source of your chart? They seem to have 6-20P mirror-imaged so it looks like 5-20P. (not picking at your fine answer) – Tut Aug 21 '13 at 15:55
@Tut: I'm suitably in awe. I don't recall where the image came from, I just Googled and picked the most humungously confusing image I could find. Probably came from [here](http://www.anderson-bolds.com/brands/shock_shield.htm) – RedGrittyBrick Aug 21 '13 at 16:13
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@Tut: Image in answer replaced. – RedGrittyBrick Aug 21 '13 at 16:19
@RedGrittyBrick Just to prove your point of how baffling our "leftpondian" array of outlets and plugs are, the z-tronix image has shown a 5-15P plug in place of a 5-20P plug. Probably not worth fixing again. – Tut Aug 21 '13 at 16:50
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Once Starfleet is formed, all humankind will finally agree on a single standard... – JYelton Aug 21 '13 at 17:18
@RedGrittyBrick Actually there are some interesting plugs on in some places on the right side too. For example, my electrical thermal storage heater has a polarized 3-phase, ground and neautra plug and is actually 3.5 kW. There are also other models for up to 6 kW which use same type plug. Here we call them 3-phase plugs, but I don't know if they have an international name, since I was unable to find any non-local references to them. – AndrejaKo Aug 21 '13 at 17:54
@AndrejaKo: I'd guess you have one of the many varieties of [IEC 60309](http://en.wikipedia.org/wiki/IEC_60309) that UK mainly reserve for use in industrial settings - does your plug look like those? – RedGrittyBrick Aug 21 '13 at 19:44
@Jyelton: When starfleet personel relocate appliances doesn't it usually involve ripping off wall panels, throwing them on the floor and using something like an arc welder to create showers of sparks? – RedGrittyBrick Aug 21 '13 at 19:47
@RedGrittyBrick No, it's in no way similar. It looks more like a shuko plug. Actually, here are the photos of the [plug](http://img580.imageshack.us/img580/5862/4da6.jpg) and the [receptacle](http://imageshack.us/a/img20/5148/o732.jpg). – AndrejaKo Aug 21 '13 at 20:24
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Uh...I live in the leftpondian domain, and I have never seen anything but the 5-15R receptacle in a household. 5-20 is encountered in some commercial construction, but is compatible with 5-15P. L5-30R is common in data centers, where [tripping on the cord](http://xkcd.com/908/) would be bad. I'd bet good money that your average householder isn't even aware other plugs and receptacles exist; the only variation encountered by 99% of people is a grounding pin (5-15), or no grounding pin (1-15), either of which is compatible with a 5-15R. – Phil Frost Aug 21 '13 at 20:44
I work in a building designed in Belgium, we have 3 kinds of outlets out hardware plugs into based on rating, all by Euro standards, not leftpondian standards. – Kortuk Aug 21 '13 at 21:28
@ThePhoton I mentioned that in my comment. Short of a couple 250V plugs, you don't ever see anything besides the 5-15R or 1-15R in common use. And even those 250V plugs aren't really _used_ (by used, I mean encountered on a day-to-day basis ie. plugging and unplugging appliances/devices from them), because you don't move a dryer or electric range very often... Phil Frost shares my sentiments – Shamtam Aug 21 '13 at 21:30
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@Shamtam, fine, but that's like saying lots of Americans aren't aware that their car has a fanbelt. It's true, but only because most people don't pay much attention to what's going on around them. Anybody who pays attention will see those 220 V receptacles pretty regularly --- anywhere there's an electric dryer, range, or water heater. I do agree that everything else is pretty much restricted to industrial uses, not household use. – The Photon Aug 21 '13 at 22:52
Until "recently" (for certain values of recently), British appliances were shipped with bare wires! You selected the correct plug and wired it. I haven't seen that in the last 10 years, but it wasn't always so standardised. – david Aug 22 '13 at 04:26
I think it was around 1994/5 when it became a legal requirement that electrical products for domestic use had to come with a plug fitted. (Voted for a good answer, but an upvote was deserved for "leftpondian" alone!). – John Aug 22 '13 at 07:45
Also there's a third outlet type that you see in the UK (though not very commonly) - the BS546 5A type, with 3 round pins. – John Aug 22 '13 at 07:51

score 3 · Answer 2 · answered Aug 21 '13 at 15:15

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The only NEMA plugs and sockets I could find (here is a chart) that fit the description in the question are the NEMA 1-15 (15 Ampere) and 2-30 (30 Ampere) formats:

NEMA 1-15:

NEMA 2-30:

_(source)

Both formats are designed for the second type of plug described in the question:

Plug

This ensures that the "hot" or "live" line is correctly connected to the "hot" or "live" side within the appliance, not that it should matter for a 2-wire AC mains connection.

The non-polarized version of this plug works in either orientation, so it'll still fit the polarized socket, but without "hot" guaranteed to go to some hypothetical "hot" inside the device:

Plug

Since low-power 2-wire equipment often works under the assumption that neutral is equivalent to building earth, the polarity affects only such applications where such a "neutral" being exposed to touch is a concern.

For typical household equipment that uses an isolating power adapter / isolated switch mode power supply, this polarity issue becomes moot, hence the convenience of a plug that works in either orientation simply saves some aggravation when plugging an appliance in, in a dark room or in a hurry. I can see the merit of that.

answered Aug 21 '13 at 15:15

Anindo Ghosh

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Aww, I was hoping for inclusion of a synopsis of the reason for the holes. – JYelton Aug 21 '13 at 17:19
@JYelton Others far wiser than me have beaten that (w)hole topic to death already, as I noted in [this comment](http://electronics.stackexchange.com/questions/79670/power-plug-orientation-and-usability/79672?noredirect=1#comment155964_79670) – Anindo Ghosh Aug 21 '13 at 17:21
... and now I'll wait for someone to say "*far wiser than I*" ;-) – Anindo Ghosh Aug 21 '13 at 17:22
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Well that's just it, I saw your link but I was expecting a brief version of it in your answer. :) – JYelton Aug 21 '13 at 17:23
Oh, my bad. I thought you had linked to a NEMA PDF, not another SE question. Sorry. – JYelton Aug 21 '13 at 17:24

score 2 · Answer 3 · answered Aug 21 '13 at 15:26

The difference in blade width is for polarity. The wider blade is for ACN (neutral) and the narrower blade for ACH (hot). Wikipedia AC power plugs and sockets in the section for "North American and IEC 60906-2, NEMA 1-15 (15 A/125 V unearthed) (Type A)" states:

Initially, both blades were the same width, so the plug could be inserted into the socket either way around. Plugs manufactured since the 1950s are polarized; the neutral blade is wider than the line blade, so the plug can be inserted only one way. Polarized NEMA 1-15 plugs will not fit into unpolarized sockets, which possess only narrow slots. NEMA 1-15 plugs will fit NEMA 5-15 earthed sockets, which have a wider slot for the neutral blade. Some devices that do not distinguish between neutral and line, such as internally isolated electronic power supplies, are still produced with unpolarized narrow blades.

Regarding the holes, according to HowStuffWorks They are to help maintain the grip in the socket, allow a plastic "lockout tie to be inserted at the factory", and to save metal.

score 2 · Answer 4 · answered Aug 22 '13 at 07:21

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About the holes in the prongs. The socket will have a dent in its contacts which falls in the whole, making it harder to retract the plug. This way they reduce the risk of the plug simply "falling out" of the socket.

answered Aug 22 '13 at 07:21

Johan.A

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Power plug orientation and usability

4 Answers4