CR4 - The Engineer's Place for News and Discussion®

Previous in Forum: Convert 220 Volt German Plug To 220 Volt USA   Next in Forum: Effect Of Generator Frequency On Generator Efficiency And Voltage Output
Close

Comments Format:






Close

Subscribe to Discussion:

CR4 allows you to "subscribe" to a discussion
so that you can be notified of new comments to
the discussion via email.

Close

Rating Vote:







28 comments
Associate

Join Date: Mar 2012
Posts: 42

Three And Two Pin Power Sockets

05/09/2012 1:31 AM

Dear friends, I have a question about 3 and 2 pin sockets for domestic use. I live in Kenya and here we use 3 pin 240 V sockets, live, neutral and erath. While on a recent visit to USA, I found that two pin sockets are used at 110V. The two pin plugs do not indicate which pin is positive and which is negative. My question is: how is the polarity ensured? The plugs are the same and could be easily interchanged.

Register to Reply
Pathfinder Tags: Three Pin Power Sockets
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 9640
Good Answers: 523
#1

Re: Three and two pin power sockets

05/09/2012 1:50 AM

The left slot is slightly wider than the right slot....The wider slot is the neutral and the smaller right slot is hot...

__________________
Life is like riding a bicycle. To keep your balance you must keep moving. A.E.
Register to Reply
Guru
Hobbies - Musician - Engineering Fields - Chemical Engineering - New Member Engineering Fields - Control Engineering - New Member Engineering Fields - Instrumentation Engineering - New Member

Join Date: Jan 2007
Location: Kennewick, WA, USA, Thulcandra - The Silent Planet (C.S. Lewis)
Posts: 2824
Good Answers: 101
#2

Re: Three and two pin power sockets

05/09/2012 1:59 AM

The two conductors are (hot) live and neutral. This does NOT indicate polarity, since it is alternating current!

See SolarEagle's reply as to how the correct connections are ensured.

Note:

There are very few 2-conductor mains outlets in this day and age. For all I know, it may be a code violation. New installations require a ground pin as well. See SolarEagle's photo.

__________________
"I am enough of an artist to draw freely upon my imagination. Imagination is more important than knowledge. Knowledge is limited. Imagination encircles the world." -- Albert Einstein
Register to Reply
Guru

Join Date: Jun 2009
Location: South of Minot North Dakota
Posts: 5471
Good Answers: 492
#7
In reply to #2

Re: Three and two pin power sockets

05/09/2012 4:40 AM

Lots of two wire extension cords though.

__________________
"Posting information on the internet is rather like casting seeds to the wind. Once it leaves your hand you have little chances of getting it back and no control over where it may land or what may sprout from it in the future." tcmtech.
Register to Reply
Power-User

Join Date: Nov 2006
Location: Ontario, Canada
Posts: 146
Good Answers: 1
#13
In reply to #7

Re: Three and two pin power sockets

05/09/2012 10:55 PM

...and appliances.

__________________
Logic is the art of going wrong with confidence. -- Morris Kline
Register to Reply
Power-User

Join Date: Nov 2011
Location: New Hampshire
Posts: 176
Good Answers: 2
#20
In reply to #2

Re: Three and two pin power sockets

05/10/2012 8:53 AM

In the USA the only condition for a 2 prong outlet is in a "grandfathered" case. If an existing one has no ground at that outlet, you are required to replace it with a similar device (unless you install a ground conductor).

Register to Reply
Guru
Hobbies - Musician - Engineering Fields - Chemical Engineering - New Member Engineering Fields - Control Engineering - New Member Engineering Fields - Instrumentation Engineering - New Member

Join Date: Jan 2007
Location: Kennewick, WA, USA, Thulcandra - The Silent Planet (C.S. Lewis)
Posts: 2824
Good Answers: 101
#22
In reply to #20

Re: Three and two pin power sockets

05/10/2012 11:13 AM

I figured something like that! Thanks for the specific info.

__________________
"I am enough of an artist to draw freely upon my imagination. Imagination is more important than knowledge. Knowledge is limited. Imagination encircles the world." -- Albert Einstein
Register to Reply
Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Ketchikan, AK, USA
Posts: 15527
Good Answers: 607
#3

Re: Three and two pin power sockets

05/09/2012 2:05 AM

I think you found some older two-blade plugs (same size blades). There are also two-blade polarized plugs with one blade larger; they can be used on double-insulated devices. In the U.S., the most common receptacles nowadays are 3-blade, as in the previous photo.

__________________
In vino veritas; in cervisia carmen; in aqua E. coli.
Register to Reply
Guru
Popular Science - Weaponology - New Member Netherlands - Member - New Member Fans of Old Computers - Commodore 64 - New Member

Join Date: Sep 2007
Location: Japan
Posts: 2713
Good Answers: 37
#4

Re: Three and two pin power sockets

05/09/2012 2:24 AM

In Europe the 2 plugs are the same diameter as it is AC, you should stay away from live wires anyway.

Anyway AC input devices it doesn't matter which side the live or neutral is, as it goes to a transformer or rectifier.

DC on the other hand positive and negative side very important!

__________________
From the Movie "The Big Lebowski" Don't pee on the carpet man!
Register to Reply Off Topic (Score 5)
3
Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Ketchikan, AK, USA
Posts: 15527
Good Answers: 607
#5
In reply to #4

Re: Three and two pin power sockets

05/09/2012 2:28 AM

I'm sorry, but you very seriously do not know what you are talking about.

__________________
In vino veritas; in cervisia carmen; in aqua E. coli.
Register to Reply Good Answer (Score 3)
Guru
Hobbies - Automotive Performance - New Member Popular Science - Weaponology - New Member

Join Date: Oct 2008
Location: Want to be: 34° 34' 21.60" N, 92° 55' 42.28" W Really am in Arizona
Posts: 29284
Good Answers: 1096
#9
In reply to #5

Re: Three and two pin power sockets

05/09/2012 9:43 AM
__________________
Luck comes and goes. Skill is forever.
Register to Reply
Guru
Engineering Fields - Electrical Engineering - New Member United Kingdom - Member - New Member Engineering Fields - Electromechanical Engineering - New Member

Join Date: Aug 2010
Location: Under the Major Oak
Posts: 3605
Good Answers: 143
#8
In reply to #4

Re: Three and two pin power sockets

05/09/2012 6:39 AM

It's not very often we get the chance to hear absolutely pure unadulterated "Gibberish".

The film "Blazing Saddles" springs to mind.

__________________
Pessimists are rarely disappointed.
Register to Reply
Power-User

Join Date: Nov 2006
Location: Ontario, Canada
Posts: 146
Good Answers: 1
#11
In reply to #8

Re: Three and two pin power sockets

05/09/2012 10:47 PM

Reply #4 is not 'absolutely pure unadulterated "Gibberish"'.

There are actual English words in that garbage.

__________________
Logic is the art of going wrong with confidence. -- Morris Kline
Register to Reply Off Topic (Score 5)
Power-User
Engineering Fields - Control Engineering - Newby Member Long Time User Engineering Fields - Instrumentation Engineering - New Member

Join Date: Jun 2006
Posts: 171
Good Answers: 8
#10
In reply to #4

Re: Three and two pin power sockets

05/09/2012 10:09 AM

Doh!

Actually, it's very important which wire of an AC device goes to which plug (hot or return). Just as one example, for an ordinary household lamp, the base contact (the one that is hardest to reach when the bulb is removed) is designed for the hot wire. Connecting the threaded contact to the hot wire would make it too easy to touch when a bulb is removed.

Register to Reply Score 2 for Off Topic
Power-User

Join Date: Nov 2006
Location: Ontario, Canada
Posts: 146
Good Answers: 1
#12
In reply to #10

Re: Three and two pin power sockets

05/09/2012 10:54 PM

... or in some poorly designed, installed or maintained light fixtures or appliances, a tingle or a pop!

__________________
Logic is the art of going wrong with confidence. -- Morris Kline
Register to Reply Off Topic (Score 5)
Guru
Popular Science - Weaponology - New Member Netherlands - Member - New Member Fans of Old Computers - Commodore 64 - New Member

Join Date: Sep 2007
Location: Japan
Posts: 2713
Good Answers: 37
#16
In reply to #10

Re: Three and two pin power sockets

05/10/2012 12:53 AM

I know i should have worded it better, i was trying to convey the functionality, concerning safety yes, you are correct, but a lamp is the only thing i can think off that a user could come in contact with a live wire.

In Holland (or Japan) my TV works just fine evendo i turn my plug a 180degrees.

__________________
From the Movie "The Big Lebowski" Don't pee on the carpet man!
Register to Reply Off Topic (Score 5)
Guru
Popular Science - Weaponology - New Member Safety - ESD - New Member Hobbies - Fishing - New Member

Join Date: Sep 2006
Location: Near Frankfurt am Main, Germany. 50.390866N, 8.884827E
Posts: 14939
Good Answers: 161
#19
In reply to #10

Re: Three and two pin power sockets

05/10/2012 7:51 AM

In most of Europe (not the UK, the lamps usually have two contacts on the bottom, though Edison screw has even got there as well I am told nowadways!) the metal base is hidden from making contact with fingers by an insulating "belt"....just for that reason as the live can be on either contact....

This picture shows that clearly:-

__________________
"Better to remain silent and be thought a fool than to speak out and remove all doubt!"
Register to Reply Off Topic (Score 5)
Guru

Join Date: May 2006
Location: Placerville, CA (38° 45N, 120° 47'W)
Posts: 3080
Good Answers: 113
#23
In reply to #19

Re: Three and two pin power sockets

05/10/2012 11:26 AM

We have sockets that look something like that here in the USA as well. They are used for lamps that have a low, medium, and high setting (using one, the other, or both filaments). This particular one is a 'mogul' size (1.5" screw OD), but they also exist in standard Edison size.

This one looks like a good quality unit, with ceramic insulation (needed for that 750W rating); it's in an antique floor lamp.

In the European ones like you show, are there really 3 contacts, or is one of them a tab that disconnects the center contact unless a bulb is in place?

__________________
Teaching is a great experience, but there is no better teacher than experience.
Register to Reply Off Topic (Score 5)
Guru
Popular Science - Weaponology - New Member Safety - ESD - New Member Hobbies - Fishing - New Member

Join Date: Sep 2006
Location: Near Frankfurt am Main, Germany. 50.390866N, 8.884827E
Posts: 14939
Good Answers: 161
#24
In reply to #23

Re: Three and two pin power sockets

05/10/2012 11:32 AM

As far as I am aware, we do not have multifilament bulbs for the house, nor do we have that useful safety device either, when a bulb is missing.

__________________
"Better to remain silent and be thought a fool than to speak out and remove all doubt!"
Register to Reply Off Topic (Score 5)
Guru

Join Date: May 2006
Location: Placerville, CA (38° 45N, 120° 47'W)
Posts: 3080
Good Answers: 113
#25
In reply to #24

Re: Three and two pin power sockets

05/10/2012 11:48 AM

Then what purpose does the third contact serve?

__________________
Teaching is a great experience, but there is no better teacher than experience.
Register to Reply Off Topic (Score 5)
Guru
Popular Science - Weaponology - New Member Safety - ESD - New Member Hobbies - Fishing - New Member

Join Date: Sep 2006
Location: Near Frankfurt am Main, Germany. 50.390866N, 8.884827E
Posts: 14939
Good Answers: 161
#26
In reply to #25

Re: Three and two pin power sockets

05/10/2012 2:44 PM

Its actually only 2 contacts, one is the same as the metal thread......its a particular manufacturer...

I picked only because it showed the insulated part to stop accidently making contact with the bulb screw thread.

__________________
"Better to remain silent and be thought a fool than to speak out and remove all doubt!"
Register to Reply Off Topic (Score 5)
Anonymous Poster #1
#6

Re: Three and two pin power sockets

05/09/2012 3:59 AM
Register to Reply
Associate

Join Date: Jan 2012
Location: Halmahera Island Indonesia
Posts: 46
#15
In reply to #6

Re: Three and two pin power sockets

05/10/2012 12:25 AM

Yes there is quite an amount of "dangerous" gibberish on this discussion. AC does indeed have polarity, called active and neutral, possibly also known as hot and return. Most modern countries use a system called Multiple Earthed Neutral which means the neutral and earth are directly bonded to each other.

Most modern plugs are 'polarised' which means they can only be inserted one way into the socket. if this polarity is reversed you run the risk of making the exposed parts of the device at full mains volage These exposed parts should be at earth potential to protect the user.

Even double insulated devices which do use an earth wire need to have the correct polarity.

Register to Reply Score 1 for Good Answer
Guru

Join Date: Jan 2008
Posts: 1756
Good Answers: 59
#14

Re: Three And Two Pin Power Sockets

05/10/2012 12:20 AM

The two pins connector indicates a device with double insulation. I will expand on it, if anybody interested. The two pins ARE interchangeable, as they go to a transformer's primary. Epke was correct for the european/export design. The US wide/narrow blade is something I use, but do not trust. I saw too many times a mixup. Ground Fault Interrupter is a must, with them, IMHO.

Register to Reply
Guru

Join Date: May 2006
Location: Placerville, CA (38° 45N, 120° 47'W)
Posts: 3080
Good Answers: 113
#17
In reply to #14

Re: Three And Two Pin Power Sockets

05/10/2012 12:58 AM

"The two pins ARE interchangeable, as they go to a transformer's primary."

Not necessarily! I suspect the OP is talking about a portable electric hand saw, commonly referred to here in the USA as a skill saw, no matter what company made it. There is no transformer in such a saw; the current goes directly through the power switch to the motor. If there are only two pins, and the two pins are identical, either in Germany or here, then by law it must be double-insulated, and the two pins are indeed interchangeable, whether or not there is a transformer.

If the two pins are NOT identical, then the two pins are NOT interchangeable. Normally the larger or wider pin is ground.

__________________
Teaching is a great experience, but there is no better teacher than experience.
Register to Reply
Power-User

Join Date: Nov 2011
Location: New Hampshire
Posts: 176
Good Answers: 2
#27
In reply to #17

Re: Three And Two Pin Power Sockets

05/11/2012 10:45 AM

Be careful how you describe this. "Ground" in not the same as neutral. The neutral conductor is on the silver screw on the duplex receptacle. The ground conductor is on the green screw. Connecting it otherwise will create a current path on the "ground" conductor. Not a good condition.

Register to Reply
Guru

Join Date: May 2006
Location: Placerville, CA (38° 45N, 120° 47'W)
Posts: 3080
Good Answers: 113
#28
In reply to #27

Re: Three And Two Pin Power Sockets

05/11/2012 12:42 PM

In modern wiring, you are correct; the neutral (white in the USA) and the ground (bare, green, or green with yellow in the USA) are required to be separate wires, even though they commonly connect to the same point at the supply panel.

I was discussing the old 2-pin sockets. My home was built at a time (early '60s) when only those outlets near water (kitchen, bath, laundry) were required to be 3-pin. The rest were 2-pin. I have replaced a few of the 2-pin outlets, adding the separate ground wire and 3-pin sockets, but there are still several of the old 2-pin ones left. On these, the narrow socket hole could be called neutral, but it is in fact ground. I have indeed checked every outlet in the house, as I have more than once found outlets wired incorrectly in other buildings.

__________________
Teaching is a great experience, but there is no better teacher than experience.
Register to Reply
Guru
Hobbies - CNC - New Member United States - Member - New Member

Join Date: Feb 2008
Location: Mid-West USA
Posts: 502
Good Answers: 28
#18

Re: Three And Two Pin Power Sockets

05/10/2012 7:04 AM

An electrician friend told me a simple rule to follow when working with 120V residential AC.

Black on brass will save your ass.

Black wires to brass colored screws. White wires to silver colored screws. Green wire to green colored screw.

Register to Reply
Guru

Join Date: Feb 2006
Posts: 1775
Good Answers: 6
#21

Re: Three And Two Pin Power Sockets

05/10/2012 10:35 AM

In 2pin plugs you will note one blade is extended on tip not to fit in revese and the same way socket has one smaller hole than the other.

While 3pin plug has both blades similar

Though it is not "N" and "L" as in other countries because the Distribution in USA is not "Y" with N [4wire] but in Delta [3wires] and a single phase [220V] center-tapped gives 2 x 11oV supplies;

Register to Reply
Register to Reply 28 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

Andy Germany (3); Anonymous Poster (1); BDThompson (1); dkwarner (4); Epke (2); GordieGii (3); Haajee (1); leveles (1); lyn (1); Mikerho (2); Munster (2); philphy (1); SolarEagle (1); tcmtech (1); The Mechanic (1); TonyS (1); Tornado (2)

Previous in Forum: Convert 220 Volt German Plug To 220 Volt USA   Next in Forum: Effect Of Generator Frequency On Generator Efficiency And Voltage Output

Advertisement