Fun discovery of the day

[IanB]

So thanks to Matthias Wandel I discovered that there is a 20 A 120-0-120 V circuit wired to the socket in my kitchen where I plug in my electric kettle. The previous owner was confused by the wiring when he replaced the socket and only used one of the phases. His crap single phase pigtail job kind of explains why the socket was getting so warm...

I am so going to import a 240 V 3 kW electric kettle from England and install a NEMA 6-15 socket in the receptacle so I can run it :evil grin:

It's going to leave me with a problem of where to plug in my 120 V toaster, but I guess I will figure that one out.

[NiHaoMike]

Use an outlet that has a neutral connection. Then you can make an adapter for 120V.

[IanB]

But the sockets with neutral connections are for tumble driers and then I would have to make a bigger hole in the wall, and then the adapter for the toaster would be untidy. More likely I should just plug the toaster into a different socket. I could import a 240 V toaster from England too, but that would start getting silly. My existing toaster only needs 1 kW and it makes toast as fast as I expect it to. A quick check indicates toasters in England are about 1 kW as well--a 240 V toaster isn't going to make toast twice as fast. A 3 kW kettle will definitely boil water twice as fast though.

[NiHaoMike]

What about use a normal pair of 120V, 20A outlets with each one wired to each phase, then make a special plug for the kettle by gluing two 120V plugs together?

[sonicj]

put the toaster on a variac. 
-sj

[touchh]

I don't know if you know what this is called but it's a multiwire branch circuit. Typically the electrician in the kitchen will put the bottom and top outlets on different phases/breakers and there will be a total of about 3-4 outlets per a circuit. It saves wire this way, but you have to remember when you install new outlets to cut the cutout on the hot side.

I doubt this is the reason the outlet was getting warm, it was likely getting warm because the kettle has an overall high power draw. There are millions of kitchens in America with only one or two 20A circuits feeding the entire kitchen

[G7PSK]

Why not put a 120 volt socket along side the 240 volt socket, if you don't want to make holes in the wall use a surface mount.

[IanB]

They are also small and convenient, and every outlet automatically has sockets for two plugs. It's nice that the plugs are so compact too. Things are different over here, but you get used to it.

[vk6zgo]

Australian plugs are the best compromise I've seen between "big-n-clunky but extremely safe",like Brit ones,& "small & convenient  but a bit flimsy looking" like US ones.
Of course,you are really comparing apples & oranges .
American 240 volt plugs (or at least the 20A ones that I've seen) are big,clunky & over-designed,but look to be extremely safe.
An Australian 20A just looks like a big 10A one,but with a round earth pin!
Again,simple,easy to mass produce,safe,----do the job!

[IanB]

American 240 volt plugs (or at least the 20A ones that I've seen) are big,clunky & over-designed,but look to be extremely safe.

There's a difference between moulded on plugs and loose plugs you fit yourself. The loose plugs are much more clunky. Also the drier plugs are quite big and different from normal plugs.

[codeboy2k]

I am in Canada, we use the standard North American 3-prong plug and socket here.  I think they are compact, but extremely unsafe; the plugs are easy for kids to insert things into, so industry came up with little caps to fill the holes.  When a plug is inserted, it can become lose and the prongs are exposed. When you try to plug it in, you have to find the correct orientation. That's easy to do in the daylight, and when you can see the socket. However, put it behind a cabinet, or under a table, or in the dark, anywhere where you can't actually SEE the socket, and I challenge anyone to plug in a north-american plug in less than 5 minutes without getting electrocuted.

The best plug design I have seen is the German Schuko design.  It's a recessed socket, self-locating, safety-ground connects first. This is the ultimate plug and socket, I wish it was used worldwide. 

[M. András]

there could be a unified socket design all over the world, it would stop the need for another power cable things which are ripoff to use a different socket style device in another country with the same line voltage etc. i wonder which one would be the best, i like the iec sockets which are used for the ups systems you cant touc any of the terminals uniform etc

[IanB]

I am in Canada, we use the standard North American 3-prong plug and socket here.  I think they are compact, but extremely unsafe; the plugs are easy for kids to insert things into, so industry came up with little caps to fill the holes.  When a plug is inserted, it can become lose and the prongs are exposed. When you try to plug it in, you have to find the correct orientation. That's easy to do in the daylight, and when you can see the socket. However, put it behind a cabinet, or under a table, or in the dark, anywhere where you can't actually SEE the socket, and I challenge anyone to plug in a north-american plug in less than 5 minutes without getting electrocuted.

Valid points. Some of it is down to quality. There are some very cheap (read under $1) sockets on the market and they wear out quickly. I had one socket that was so loose plugs would just fall out under the weight of the cable. These cheap sockets are of course very attractive for builders to install. Consequently I have been going round my house and replacing all the sockets with new better quality ones.

There are shuttered sockets available now that prevent anything but a plug being poked in the holes. Though I have to say the risk window is very small here and education remains the best safeguard. By the time a child is, say, two the curiosity to poke things in a socket is matched by the ability to defeat the shuttering system.

As for inserting a plug when you can't see clearly, I have installed sockets with recessed guides like the ones below. This helps guide the plug into the socket without having to fuss around trying to line it up.

http://www.legrand.us/passandseymour/receptacles/straight-blade-receptacles/duplex-receptacles-back-side-wire/construction-grade/crb5262.aspx

[codeboy2k]

Yes, the recessed guides can help. You will still need a finger on the ground plug to find that hole, before the other 2 can be found.

BTW, I noticed in the the link you included, the pictures of the 3 receptacles shown (brown, black, white) are all photographed with the earth-ground plug UP, and I have mostly seen receptacles installed with the ground plug DOWN (showing the happy face )

I like ground UP for safety reasons, but ground DOWN for looks and aesthetic reasons.  But safety trumps aesthetics.  Which do you prefer, and have you ever been told to install it a specific way UP or DOWN?

[G7PSK]

The Ceeform plugs and sockets are probably the best one's out to date as they have the greatest tracking distance of any of the other plugs and sockets on the market making them splash proof or even water proof, further they are color coded  for voltage. I use them exclusively in my work shop other than the odd standard 13 amp. The shuko is also very good for having a longer tracking distance than any other domestic design and really ought to become the European standard including here in the UK. The Ceeform and others can be seen on the Wikipedia link.   
http://en.wikipedia.org/wiki/Industrial_and_multiphase_power_plugs_and_sockets


 http://en.wikipedia.org/wiki/Mains_electricity_by_country

[IanB]

I have installed them with the ground pin down because nearly every device I have that is orientation sensitive (especially flat or right angle plugs) is designed to be plugged in that way round with the cable hanging downwards. If I installed them with the ground pin upwards then I would be plugging everything in upside down. As far as I can tell there is a de-facto industry standard that the neutral pin goes on the left and the hot or live pin on the right.

[IanB]

...really ought to become the European standard including here in the UK

That can never happen because of the huge safety implications. Millions of moulded on BS plugs would have to be cut off and rewired with schuko plugs. Moulded on plugs were originally mandated because people can't be trusted to wire their own plugs.

[G7PSK]

...really ought to become the European standard including here in the UK

That can never happen because of the huge safety implications. Millions of moulded on BS plugs would have to be cut off and rewired with schuko plugs. Moulded on plugs were originally mandated because people can't be trusted to wire their own plugs.

We had a complete change in the past of plug type so we can again much equipment these days has the IEc plug on the other end or figure 8 or clover leaf the rest could be changed fairly easily in much the same way that we had the original plugs changed and the the switch to natural gas where every appliance to be converted and more recently the change over to digital TV it could be done and should be done. One of the original reasons for the choice of the 13 amp plug was ease of wiring now we are told we cannot be trusted to do it ourselves so there is no reason to continue with it. 

[Kremmen]

[...]
The best plug design I have seen is the German Schuko design.  It's a recessed socket, self-locating, safety-ground connects first. This is the ultimate plug and socket, I wish it was used worldwide.

I am of course biased because the German system is standard in Finland. For some smaller devices the original plug is a bit clunky, but fortunately there is the Europlug. I snapped a photo of the sockets behind my desk. As you se it is possible to cram 2 sockets into a standard size module without too much trouble.
There used to be the plain round variant without grounding, permitted for "safe" installation conditions but nowadays the code does not permit that anymore. Additional to grounding, all outlets need RCDs nowadays, with a few specific exceptions (electric sauna heaters being one of those - and there is at least one in every house ).
@G7PSK & IanB: Funnily enough, connecting a plug to a mains cable is one of the few electrical "installation" jobs permitted for everyone here. It is specifically allowed in the code. Same thing with the ceiling plugs for light fixtures. Nobody died yet...

P.S. I also use the CEE 3 phase and 1 phase connectors in my workshop, in addition to the regular schukos. The red 3 phase CEE connector is nowadays the only one you ever see any more. It has completely replaced all previous domestic standards that were usually metal housings. Scary things when old beat up connectors were handled outdoors.

[XynxNet]

One problem of the schuko plug is, that it's ground contacts are exposed. I saw a lot of flats where some idiot didn't tape the power sockets before renovating and somehow coated the gound contacts with paint.

[Kremmen]

Sure, that can happen if one is careless or challenged in the thinking department. Generally it is inadvisable to paint over your outlets;  that's what masking tape is for. The newer modular socket systems are easy - just undo 2 screws and remove the whole front face, mask over, paint, remove tape and replace front. The socket itself stays put (it has its own fixings to the mounting box). Quick and easy.

[Jeff1946]

Typical US sockets have push in holes and screw on lugs.  Had quite a few plugs fail and of course those downstream due to push in connector failing.  Killer was our vacuum which has high startup current.   No big deal to wire the plugs using the lugs.  Have probably done this to about half the plugs in the house.

[Kremmen]

Very common nowadays, the spring loaded quick connects. Never had a failure in one of those, but then my house is mainly done with screw connects. Springs have the advantage of not loosening over time as some types of screw connect might. Still, i trust the screws more.
Is it so that in the US the higher power appliances like dryers are 240 VAC? If so then the spring failure is not explained by the higher current needed for the power.
While on the subject, how is the 3 phase power generated in the US if as i understand the distribution is center tapped 240V?

[IanB]

No, the springs definitely loosen over time. In some of the sockets I have replaced (all spring connect) the wires have just fallen out of the holes. (The heat from high current loads passing through a high resistance contact point can destroy the springiness of the brass.)

There is no mechanical benefit to the push-fit design, it is done purely as a convenience so electricians can shave a few seconds of the installation time when wiring a house. You have a small contact area and little mechanical pressure. Also they are only designed for one wire gauge, so if someone tries to use the wrong size wire you will get a poor connection.

Tumble driers have a special 240 V socket designed for them that I don't think uses spring connects. You can't plug a drier into a normal outlet. There will be just one drier hookup point in a home with the special 240 V socket installed there.

Three phase power is distributed just as you would expect. The centre tapped 240 V is just for final delivery. In the traditional configuration the three phase power at a few thousand volts is run along the top of wooden poles and single phase transformers ("pole pigs") are hung off the poles with the primary connected between one of the phases and ground. The secondary is then the 120-0-120 arrangement for feeding to consumers. In newer installations the cables are buried and compact transformers are installed in boxes at ground level. This helps to remove "pole blight".

[G7PSK]

The spring loaded push in connectors only make a point contact with many of the designs on the market so high loads cause heating which weakens the spring which leads to more heating and then arcing, they should be banned.