# Electric plugs/ Why Dual Sized Prongs ? **URL:** \ **Category:** Factual Questions\ **Created:** [April 9, 2009, 2:45am UTC](https://boards.straightdope.com/t/electric-plugs-why-dual-sized-prongs/492471 "2009-04-09T02:45:15Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![The\_Flying\_Dutchman](https://avatars.discourse-cdn.com/v4/letter/t/9fc348/32.png) [@The\_Flying\_Dutchman](https://boards.straightdope.com/u/The_Flying_Dutchman)\ **Post date:** [April 9, 2009, 2:45am UTC](https://boards.straightdope.com/t/electric-plugs-why-dual-sized-prongs/492471/1 "2009-04-09T02:45:15Z")
At some during my 58 years of life our society went to electric plugs with dual sized prongs (ignore the ground) instead of equal sized prongs . Presumably to ensure that the plug is inserted only one way. Given this restriction was never neccessary in the past, can anyone provide a reason for this fundamental change ? ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [April 9, 2009, 2:51am UTC](https://boards.straightdope.com/t/electric-plugs-why-dual-sized-prongs/492471/2 "2009-04-09T02:51:45Z")
The Wikipedia article on AC power plugs has a section on [polarisation](http://en.wikipedia.org/wiki/Domestic_AC_power_plugs_and_sockets#Polarisation). Basically it’s an added safety precaution. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [April 9, 2009, 2:57am UTC](https://boards.straightdope.com/t/electric-plugs-why-dual-sized-prongs/492471/3 "2009-04-09T02:57:31Z")
> [@](#): > > Initially, the plug’s prongs and the socket’s slots were the same height, so the plug could be inserted into the socket either way around. Modern[vague] plugs and sockets are polarised by means of a neutral blade/slot wider than the live blade/slot, so the plug can be inserted only the right way. Polarised type A plugs will not fit in unpolarised type A sockets, because both slots are narrow, but both unpolarised and polarised type A plugs will fit in polarised type A sockets and in type B sockets. Some devices that do not distinguish between neutral and live, such as sealed electronic power supplies, are still produced with unpolarised type A pins (both narrow). > **[AC power plugs and sockets](https://en.wikipedia.org/wiki/Domestic_AC_power_plugs_and_sockets#Types_in_present_use)** > > AC power plugs and sockets connect devices to mains electricity to supply them with electrical power. A plug is the connector attached to an electrically operated device, often via a cable. A socket (also known as a receptacle or outlet) is fixed in place, often on the internal walls of buildings, and is connected to an AC electrical circuit. Inserting ("plugging in") the plug into the socket allows the device to draw power from this circuit. > Plugs and wall-mounted sockets for portable applia... On Preview - beaten to the punch ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 9, 2009, 4:11am UTC](https://boards.straightdope.com/t/electric-plugs-why-dual-sized-prongs/492471/4 "2009-04-09T04:11:56Z")
Most things will function if plugged in the wrong way, but may not be as safe. For instance, a lamp should be wired so that the contact on the bottom of the socket is hot, and the one around the side is neutral, because you might be able to bump the side contact, and if it’s neutral, you’ll probably only get a very small shock, if at all. Kids, don’t try this at home, of course: If everything is done correctly, it’ll be safe, but the socket or the lamp might be wired wrong. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [April 9, 2009, 4:12am UTC](https://boards.straightdope.com/t/electric-plugs-why-dual-sized-prongs/492471/5 "2009-04-09T04:12:02Z")
> [@The\_Flying\_Dutchman](#): > > Given this restriction was never neccessary in the past, can anyone provide a reason for this fundamental change ? Actually it was necessary under certain conditions, to avoid electrical shock or hum in audio devices. ---
**Author:** ![Mongo\_Ponton](https://avatars.discourse-cdn.com/v4/letter/m/eb9ed0/32.png) [@Mongo\_Ponton](https://boards.straightdope.com/u/Mongo_Ponton)\ **Post date:** [April 9, 2009, 4:16am UTC](https://boards.straightdope.com/t/electric-plugs-why-dual-sized-prongs/492471/6 "2009-04-09T04:16:58Z")
I’m convinced it’s one of the 10,000 new methods to make sure my blood pressure never gets too low. Odds are you should be able to plug the cord in the right way 50% of the time but it doesn’t happen like that. More like 15% of the time. Unless of course you’re holding a bunch of things, balancing on one foot, and it’s dark, in which case the odds go down to 2 or 3%. ---
**Author:** ![Snnipe\_70E](https://avatars.discourse-cdn.com/v4/letter/s/b5a626/32.png) [@Snnipe\_70E](https://boards.straightdope.com/u/Snnipe_70E)\ **Post date:** [April 9, 2009, 4:21am UTC](https://boards.straightdope.com/t/electric-plugs-why-dual-sized-prongs/492471/7 "2009-04-09T04:21:04Z")
UL standard is to put the switch on the hot leg. A lamp should have the hot leg connected to the bottom contact. That is why plugs are polierized. ---
**Author:** ![whitetho](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whitetho/32/1059_2.png) [@whitetho](https://boards.straightdope.com/u/whitetho)\ **Post date:** [April 9, 2009, 9:20am UTC](https://boards.straightdope.com/t/electric-plugs-why-dual-sized-prongs/492471/8 "2009-04-09T09:20:30Z")
A Straight Dope Classic from Cecil’s Storehouse of Human Knowledge: [I can’t plug in these new plugs! What’s the deal?](http://www.straightdope.com/columns/read/170/i-cant-plug-in-these-new-plugs-whats-the-deal) ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [April 9, 2009, 9:48am UTC](https://boards.straightdope.com/t/electric-plugs-why-dual-sized-prongs/492471/9 "2009-04-09T09:48:38Z")
> [@The\_Flying\_Dutchman](#): > > At some during my 58 years of life our society went to electric plugs with dual sized prongs (ignore the ground) instead of equal sized prongs . Presumably to ensure that the plug is inserted only one way. > > Given this restriction was never neccessary in the past, can anyone provide a reason for this fundamental change ? Well, a lot of things were never necessary in the past, including seatbelts in cars and even electricity itself up to recently in history. Not to mention cell phones and computers. They keep inventing things which make life better. At least that is what they claim. Now concentrating on polarized plugs, it has already been explained why it is a good thing so I won’t go into that but I will note that in Europe, where voltage is 230 V and therefore more dangerous, plugs are all non polarized. Europeans have not found any advantage in using polarized plugs, something which pretty much costs nothing and yields some safety. I favor polarized plugs. ---
**Author:** ![wmdkitty](https://avatars.discourse-cdn.com/v4/letter/w/e19adc/32.png) [@wmdkitty](https://boards.straightdope.com/u/wmdkitty)\ **Post date:** [April 9, 2009, 12:00pm UTC](https://boards.straightdope.com/t/electric-plugs-why-dual-sized-prongs/492471/10 "2009-04-09T12:00:16Z")
On the topic of plugs, why aren’t ground prongs universal on outlets? With the near omnipresence of computers these days, you’d think you’d find the standard three-prong outlet _everywhere_, but NO! (I actually have to go out and hunt down an adapter!) ---
**Author:** ![StinkyBurrito](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@StinkyBurrito](https://boards.straightdope.com/u/StinkyBurrito)\ **Post date:** [April 9, 2009, 12:37pm UTC](https://boards.straightdope.com/t/electric-plugs-why-dual-sized-prongs/492471/11 "2009-04-09T12:37:17Z")
> [@wmdkitty](#): > > On the topic of plugs, why aren’t ground prongs universal on outlets? With the near omnipresence of computers these days, you’d think you’d find the standard three-prong outlet _everywhere_, but NO! (I actually have to go out and hunt down an adapter!) Switching to polarized plugs simply requires changing out the socket. Switching to 3 prongs (and actually making it work) means rewiring the whole house in most cases. Chances are that if your outlets are only two slots, then there are only two wires running to the outlet and the third wire to carry the ground was never installed (if it was, they probably would have installed the corresponding 3 prong outlets at the same time). ---
**Author:** ![Ludovic](https://avatars.discourse-cdn.com/v4/letter/l/7ab992/32.png) [@Ludovic](https://boards.straightdope.com/u/Ludovic)\ **Post date:** [April 9, 2009, 12:40pm UTC](https://boards.straightdope.com/t/electric-plugs-why-dual-sized-prongs/492471/12 "2009-04-09T12:40:03Z")
> [@whitetho](#): > > A Straight Dope Classic from Cecil’s Storehouse of Human Knowledge: [I can’t plug in these new plugs! What’s the deal?](http://www.straightdope.com/columns/read/170/i-cant-plug-in-these-new-plugs-whats-the-deal) Which of course contains my number one favorite Cecil quote:Shaking hands with Jesus! ---
**Author:** ![wmdkitty](https://avatars.discourse-cdn.com/v4/letter/w/e19adc/32.png) [@wmdkitty](https://boards.straightdope.com/u/wmdkitty)\ **Post date:** [April 9, 2009, 12:40pm UTC](https://boards.straightdope.com/t/electric-plugs-why-dual-sized-prongs/492471/13 "2009-04-09T12:40:05Z")
> [@StinkyBurrito](#): > > Switching to polarized plugs simply requires changing out the socket. Switching to 3 prongs (and actually making it work) means rewiring the whole house in most cases. Chances are that if your outlets are only two slots, then there are only two wires running to the outlet and the third wire to carry the ground was never installed (if it was, they probably would have installed the corresponding 3 prong outlets at the same time). ::sigh:: Damn, it had to be complicated. I don’t understand why they don’t just, you know, change the wiring codes to _require_ three-prong wiring – it would be so much _easier_! ---
**Author:** ![StinkyBurrito](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@StinkyBurrito](https://boards.straightdope.com/u/StinkyBurrito)\ **Post date:** [April 9, 2009, 12:50pm UTC](https://boards.straightdope.com/t/electric-plugs-why-dual-sized-prongs/492471/14 "2009-04-09T12:50:16Z")
> [@wmdkitty](#): > > ::sigh:: Damn, it had to be complicated. I don’t understand why they don’t just, you know, change the wiring codes to _require_ three-prong wiring – it would be so much _easier_! That is the code. But it wasn’t always that way. So now people with oder wiring have only two prongs/wires and some people with more modern wiring have the 3 prongs. ---
**Author:** ![gaffa](https://avatars.discourse-cdn.com/v4/letter/g/e68b1a/32.png) [@gaffa](https://boards.straightdope.com/u/gaffa)\ **Post date:** [April 9, 2009, 5:04pm UTC](https://boards.straightdope.com/t/electric-plugs-why-dual-sized-prongs/492471/15 "2009-04-09T17:04:49Z")
> [@sailor](#): > > I will note that in Europe, where voltage is 230 V and therefore more dangerous, plugs are all non polarized. Europeans have not found any advantage in using polarized plugs, something which pretty much costs nothing and yields some safety. It should be pointed out that the various European plug designs I’ve encountered all have a much safer basic design than any US plug. For instance, the two pin UK plug used to be two metal pins, but is now mostly plastic with metal only at the end. This means that the plug doesn’t make contact with the current until it is almost entirely in the socket. You can’t shock yourself by a stray finger accidentally touching a prong. Couple that with the switch beside each outlet, and you have a much safer system. ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [April 9, 2009, 5:30pm UTC](https://boards.straightdope.com/t/electric-plugs-why-dual-sized-prongs/492471/16 "2009-04-09T17:30:46Z")
> [@wmdkitty](#): > > ::sigh:: Damn, it had to be complicated. I don’t understand why they don’t just, you know, change the wiring codes to _require_ three-prong wiring – it would be so much _easier_! Easier by requiring every home and building built before the new requirement to be rewired? Often requiring walls to be opened up? I sympathize with your irritation, but I think you misjudge what a huge task bringing every old-code structure up to a new code can be. ---
**Author:** ![GreasyJack](https://avatars.discourse-cdn.com/v4/letter/g/df705f/32.png) [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)\ **Post date:** [April 9, 2009, 5:33pm UTC](https://boards.straightdope.com/t/electric-plugs-why-dual-sized-prongs/492471/17 "2009-04-09T17:33:18Z")
I’ll add some hearsay. The electrician I used to work with said that it was because European light sockets were designed differently and didn’t have the big pieces of exposed metal. Consequently, it didn’t matter which way you plugged it in and so they didn’t need polarized outlets. However, he didn’t mention exactly _how_ they’re different and I’ve been having some trouble finding something along the lines of a field guide to world light sockets. Those electricians can be a wily bunch, so I don’t know… ---
**Author:** ![gaffa](https://avatars.discourse-cdn.com/v4/letter/g/e68b1a/32.png) [@gaffa](https://boards.straightdope.com/u/gaffa)\ **Post date:** [April 9, 2009, 5:53pm UTC](https://boards.straightdope.com/t/electric-plugs-why-dual-sized-prongs/492471/18 "2009-04-09T17:53:17Z")
The Wikipedia article on electrical plugs around the world is [a masterpiece of nerdish obsessiveness](http://en.wikipedia.org/wiki/AC_power_plugs_and_sockets). The British plug I mentioned above has [one solid metal ground pin](http://upload.wikimedia.org/wikipedia/commons/8/86/G_plug.png), but the neutral and hot pins are plastic for half their length. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [April 9, 2009, 8:25pm UTC](https://boards.straightdope.com/t/electric-plugs-why-dual-sized-prongs/492471/19 "2009-04-09T20:25:26Z")
> [@gaffa](#): > > It should be pointed out that the various European plug designs I’ve encountered all have a much safer basic design than any US plug. For instance, the two pin UK plug used to be two metal pins, but is now mostly plastic with metal only at the end. This means that the plug doesn’t make contact with the current until it is almost entirely in the socket. You can’t shock yourself by a stray finger accidentally touching a prong. Couple that with the switch beside each outlet, and you have a much safer system. This is true but European grounded plugs are bulkier and more uncomfortable to use. British plugs are ridiculously big for some thin cable used with some small appliance. As far as I know ever country in Europe uses the [Edison screw - Wikipedia](http://en.wikipedia.org/wiki/Edison_screw) lightbulbs and the sockets are similar to American sockets. ---
**Author:** ![GreasyJack](https://avatars.discourse-cdn.com/v4/letter/g/df705f/32.png) [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)\ **Post date:** [April 9, 2009, 8:38pm UTC](https://boards.straightdope.com/t/electric-plugs-why-dual-sized-prongs/492471/20 "2009-04-09T20:38:03Z")
It sounds like maybe he was thinking of [bayonet terminal](http://en.wikipedia.org/wiki/Bayonet_mount) sockets. It doesn’t sound like they’re all that common, though. [Next page](https://boards.straightdope.com/t/electric-plugs-why-dual-sized-prongs/492471.md?page=2)