Why three prongs?

by xd • 14 years ago

581 146 14 years ago

iveney• 14 years ago

Clears the mystery :)

xd• 14 years ago

Yeah, I dug this up when wondering why it mattered that the sensor for the wireless power usage meter I have could be clamped to either live or neutral but was told by the building manager that it had to go to live; yet I wasn't convinced.

Anyway, as you say .. mystery now clear.

danbmil99• 14 years ago

Been waiting 40 years for this explanation. Electricians have tried to explain it but their answers always ended up sounding circular and ill-founded.

tjic3• 14 years ago

An electrician explaining electricity is like a cop explaining the law.

They're hired to follow an instruction book. That doesn't mean that they have the least idea of the whys and wherefores of what's in the book.

Look at any of 1,000 videos of cops making up laws, falsely citing either the Patriot Act of 9/11, or explaining that parts of the Constitution and Bill of Rights don't apply in certain circumstances.

I'd rather listen to a cattle farmer talk about bovine genetics - he's likely to have some clue!

TazeTSchnitzel4• 14 years ago

Yep. The correct person to ask about electricity is a Physicist, or in your analogy's case, a lawyer.

ams6110• 14 years ago

How many electricians do you actually know?

rdl2• 14 years ago

For a random residential cable puller, sure. (there are good electricians who do small scale, but it isn't necessary to do most residential work; it's really more about knowing how to retrofit things in various eras of construction, techniques for opening walls/patching, etc. -- kind of general handyman stuff)

Commercial electricians. power engineers, etc. are quite smart.

To use your analogy, the residential cable puller is like a local street cop, but commercial electricians and power engineers are FBI, SWAT, or lawyers. EEs are judges and legislators. You wouldn't get a comprehensive view of the law by talking to only one.

(I took EE classes in college, although no power classes, and was really glad to know some commercial electricians when doing power systems for datacenters. It was all in unlicensed places, so there were no code/compliance issues, just performance and safety.)

ajross• 14 years ago

Electricians are the wrong people to ask. It's like asking an IT exchange admin to explain the the SMTP protocol.

bartwe• 14 years ago

Why don't Schuko plugs have this orientational bias ?

bmelton• 14 years ago

Schuko plugs expose some material on the sides to ground to their chassis. I personally think they're the better design, but if you look at this picture: http://upload.wikimedia.org/wikipedia/commons/2/23/Schuko_pl...

Number '2' is grooved out, and there is a receiving prong that sticks out to make contact to the groove-exposed metal, similar to how the contact chargers you're probably used to seeing on handheld phones (not cellular, but cell batteries are often similar) -- The important thing to note is that length-wise, 2 comes in contact to ground before either hot or neutral wires do (length-wise), so it's safer on paper than the traditional design.

kalleboo4• 14 years ago

That solves a different problem though - the problem of touching the prongs by mistake when fumbling with a plug.

I imagine there's no polarity in european plugs because the "use a third lead for grounding" solution was chosen right away instead of trying to patch things with forced polarity first (possibly with the prior knowledge of incidents from the U.S. - kind of like how PAL could avoid the issues inherent in NTSC)

edit: looks like my assumptions may be wrong - the Schuko patent predates the grounded NEMA plug patent by 2 years. But who knows how ideas like this spread back then... This is the kind of history I'd love to read a book on.

ralfd2• 14 years ago

There is also the Europlug.

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

davidw2• 14 years ago

As an aside, one of the things that's sorely missing from the day-to-day integration of the European Union is a standard for electrical plugs:

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

Here in Italy there are at least three kinds that are fairly common. Go north to Austria, and things change and you have to buy more adapters.

joelhaasnoot2• 14 years ago

I think day to day integration of voltages is worse. Not so much for gadgets since we have transformers for everything down to 5 volts, but anything else is a nightmare.

kalleboo4• 14 years ago

Really? Aside from white goods, it seems most things these days are multi-voltage. And even then, it's still mainly North America that strays more than 10% from the standard http://en.wikipedia.org/wiki/File:Weltkarte_der_Netzspannung...

gioele• 14 years ago

> Here in Italy there are at least three kinds that are fairly common.

Well, one of them is the Europlug (the "small" 2-pin variant) and that works everywhere in EU except UK.

The problem is that the two grounded versions are peculiar to Italy and not the standard ISO ones. Italy lost its chance to switch to the ISO sockets (compatible with the Europlug) sometimes in the 90s, when the EU forced the adoption of 230V (+-10V) from the previous 220V. The legislator failed to force the use of the ISO grounded plug and now it is not uncommon to see in Italy sockets that are compatible with Europlug, the 2 Italian grounded kinds of plugs, Schuko and type C. It is obvious that these sockets are both clumsy and expensive.

davidw2• 14 years ago

As somewhat of a neutral observer, I think the 3 pin Italian sockets are actually quite nice: it's easy to put a lot of them in a power strip, and they are a lot less big and clunky than the Schuko ones.

gojomo• 14 years ago

Even already knowing the gist of things, I enjoyed the description of the path-dependent incremental evolution here.

But, this sentence makes me wonder about something: "Also, the clear-weather sky current can no longer build up a high voltage, if any excess charge immediately leaks into the earth."

Have our region- and even continent-wide grounded electrical networks changed the expression of lightning storms, such that non-electrified areas are noticeably different?

throwaway64• 14 years ago

all manner of things can cause a build up of charge in what is essentially a massive network of thousand KM+ antennas: radio waves, the earth's magnetic field, cosmic rays, wind interacting with dust particles causing static charges, etc.

A bit of an interesting side note: it is possible to build a radio set passively powered by radio waves, requiring no external power:

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

stephengillie• 14 years ago

http://en.wikipedia.org/wiki/Radio-frequency_identification

js2• 14 years ago

http://news.ycombinator.com/item?id=3561321 (My foxhole radio)

iliis• 14 years ago

A very interesting idea! It's well known that storm create static electricity, but I've never thought of it the other way around. How does electricity shape the weather?

Thunderstorms are a highly complex system and I'm not an expert, so I can only speculate: A storm builds up a high electric potential between the clouds and the ground which results in a lightning strike if it gets strong enough. Now, what does the existence of grounded power-grids change? It basically makes the ground more conducting which may result in a more evenly distributed ground-charge. As this doesn't change the potential between ground and higher air masses, I don't think it directly influences a storm.

Maybe the weather is influenced by horizontal potential (Air from point A is attracted to differently charged air at point B), but I don't think this effect would be strong enough to notice.

While reading through the article, another idea sprang to my mind: Why don't we use all this electricity? Harnessing power from lighning seems rather impractical (extreme amounts of electcity in one unpredictable instant), but how about building a high tower or just laying a few long, ungrounded cabels an then slowly dischargin a thunderstorm?

snowwrestler• 14 years ago

Doesn't grounding the networks essentially return the atmospheric charge to the state it would be in if there were no networks?

lcargill99• 14 years ago

Never mind that yes, A/C can count on polarity and that you are isolated from the grid by one or more transformers.

The third prong is the "safety" ground, in case neutral fails. Go back to old guitar amps with "the cap of death" or a "ground" switch for one market in which this evolved. It's a fairly simple mod to make an old amp fully safe. Yes, they cover that in the "bad outlet" story, but it's easy to fix if you know how to run a meter and can find a ground.

The lead guitarist from Badfinger died from this.

I'd never heard about DC buildup on the grid - free power, maybe? :)

thought_alarm2• 14 years ago

Prior to the Ground Fault Interruptor sockets found in modern bathrooms, an isolating transformer was often used to protect bathroom outlets in the 60s and 70s. These are two-pin unpolarized sockets, usually with "Razors Only" stamped on the front (because if you plug in a 1000 W hair dryer you blow out the transformer).

TazeTSchnitzel4• 14 years ago

I always wondered why it said "Shavers Only". Luckily the worst thing I ever stuck in was an American phone charger.

texec• 14 years ago

Current installations use Residual-Current Devices instead of individual breakers, at least in Europe. This requires three way wiring up to the distribution. In Germany RCDs are required for all outlets in new installations.

sc00ter4• 14 years ago

Or rather both - individual circuits have a current limiting circuit breaker in addition to a master RCD across multiple circuits.

brudgers5• 14 years ago

In the US, it is relatively common to use circuit breakers in new construction but in no way universal - protection at the receptacle is still very common and can be significantly cheaper since only the first receptacle in a series needs to be GFCI type...of course this creates an issue of finding the tripped device for a person unfamiliar with the wiring scheme.

lostlogin• 14 years ago

RCDs are required throughout the house in New Zealand now (used to be bathroom only). They work. I tried angle grinding a metal bar, and it's link to the extension cord fell in a puddle I was standing in. Power clicked off thank god, and I became ok with the re-wiring cost. RCDs are the best.

ajasmin• 14 years ago

Does that mean the output of the transformer have no difference of potential relative to the ground? Why is that?

It must be for the same reason that an electric shock from an ungrounded AC circuit doesn't travel through your feet as the article mention.

But I'm having difficulties understanding this concept. My (admittedly naive) understanding of electricity is that when one terminal has more electrons than another you can wire both terminals to a light bulb and it will light up. i.e. electron travel through the light bulb from one terminal to the other.

If my understanding was correct it would mean that one terminal from the input circuit of the isolation transformer (the neutral wire and the ground it is connected to) would always have the same number of electrons than either terminal of the transformer output.

Since the reason we have an isolation transformer is to prevent electrons from traveling between the transformer output and the ground, both outputs and the ground need to have the same number of electron. i.e. zero voltage. Right?

Is there really no voltage at all between the two circuits? I find this confusing.

jakobe• 14 years ago

You must understand the concept of capacity: Capacity describes the amount of charge (number of electrons) needed to create a potential difference (voltage) across a gap. The capacity between ground and shaver circuit is tiny, so only a really tiny number of electrons travels through you to put the shaver circuit on the same potential as ground.

The important thing here is that as soon as you ground the shaver circuit by touching it, there is a (tiny) static discharge, and then there is no force that restores any potential difference between ground and shaver circuit. The only force is the transformer, creating a potential difference between the two ends of the shaver circuit. But since that circuit is open, and again has a low capacity, barely any electrons need to move in order to create that potential difference.

andrewreds• 14 years ago

Ummm....

Essentially electrons must travel around in a circuit. Sort of like a racing car. Electrons can't teleport from one location to another, and the number of electrons in a circuit will never change.

If touching you touch a wire, and you don't make a circuit (a complete loop) then you will receive no current (electrons can't move in a circuit), thus there is no voltage (since V = IR)

Usually when you touch the active wires in a powerpoint a circuit is made:

from the powerplant to the powerpoint, from the powerpoint to you, from you to the floor you are standing on, from the floor back to the powerplant.

A transformer works by having two coils of wires, and when electrons flow through one coil, it excites the electrons in the other coil, and they start to move too. (This is done through magnetism).

A transformer is usually used to change the voltage of an AC source, but in the case of the "Isolation transformer" the voltage on the input side and the output side are the same.

In a transformer, the two coils of wire aren't actually connected to each other. So if you touch one of the output wires, you don't make a circuit, as the electrons need to get back to the other output wire for a circuit to be formed.

The same thing happens with a battery. Unless you are touching both terminals, there will be no current flow.

zdw• 14 years ago

Ever wonder why, in some buildings (mainly commercial properties), the plugs are installed so that the ground is at the top of the outlet?

I asked an older electrician/installer about this once, and the reason he gave was that if a wire fell in between the gap between the plug and outlet it could short easily.

Having the ground on the top makes it so that if something does land in this way, it will be at an angle and more likely to fall off the shorting outlet.

Plugs in other countries, specifically european or british plugs aren't susceptible to this because they're designed not to expose hot wires during insertion.

TazeTSchnitzel4• 14 years ago

British plugs[1] have a pretty clever design. There's 3 prongs arranged in a triangle, each of equal length, but they are rectangular prisms, not cuboids, so you can only plug it in one way up. The lower 2 "live" holes only open if there's a prong in the top earth hole. Because of this, double-insulated appliances still have a plastic prong on the plug.

And yes, we have insulation on both "live" prongs.

Plus, it's the only kind of plug that's both Grounded, Polarised, Fused and has Insulated Pins[2]

[1] http://en.wikipedia.org/wiki/BS_1363

[2] http://en.wikipedia.org/wiki/AC_power_plugs_and_sockets#Comp...

kalleboo4• 14 years ago

It's also the only plug that'll wake the neighbors when you step on it going to the loo in the middle of the night.

kika• 14 years ago

And the only kind of plug the size of the aircraft carrier :-)

magic_haze2• 14 years ago

After an hour-long detour through Wikipedia's various power plugs articles (shocking how many of them there are), I have to ask this: historical reasons aside, isn't there any kind of consensus on which is the "best" plug/socket system (in purely objective terms)? The comparison table in [2] would have us believe BS1363 has the most features, but surely, there must have been more improvements in plug design since that huge lump was designed in the 1940s?

sc00ter4• 14 years ago

" There's 3 prongs arranged in a triangle, each of equal length"

No, the earth pin is noticeably longer. This serves two purposes - first, to ground the device being plugged in before it is live; second, to retract the mechanical barriers that are ordinarily across the entrance to the power pins, in order that the plug can be inserted, but stray fingers, paperclips, keys, or other conductive items cannot (without some effort and intent).

As an aside - as a result of the mechanical barrier across the power pins, the plastic socket safety inserts that parenting stores sell are completely redundant, and arguably a scam.

ricardobeat10• 14 years ago

The new standard plug in Brazil[1] is both grounded, polarised and has insulated pins, plus it's obligatorily recessed and connects earth first.

And you don't get hurt or break anything if you step on it :)

[1] http://en.wikipedia.org/wiki/IEC_60906-1

swah4• 14 years ago

I hate those plugs because I can't find adapters to usethem in Brazil (while european/US ones can go directly into our (now replaced with 3-pin version) outlets: http://www.osetoreletrico.com.br/web/images/stories/Edicao59...)

Fizzadar• 14 years ago

I love the British design; I've always found two pronged cables wobblier in the socket/not to mention buying-forgetting-rebuying many adapters of course

speleding• 14 years ago

The UK plugs are over engineered for their task though. It's occasionally useful that you can use the same outlet that you use for your 4.5W iPhone to use for 6000W welding torch but IMHO the Euro plugs that are a third the size and a third the price are a better use of resources.

When you imagine there are hundreds of millions of these plugs that bit of over-engineering really adds up. Really, when was the last time you plugged in anything above 2KW?

dpitkin• 14 years ago

It looks like only the 30 Amp plus NEMA connectors require ground to be on top. It does appear technically "safer".

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

sc00ter4• 14 years ago

Nope - the diagram on that page shows every current rating of NEMA plug with an earth pin at the bottom.

I call bullshit on the whole "earth pin position as a safety measure" debate anyway. Copper wiring of any substance is physically to rigid to move, even if completely free of other mechanical constraints, so isn't going to "drop onto the live pins" no matter what, even if the internal arrangement of a socket facilitated it. (They - don't they're insulated, shrouded, separated etc.)

dfc2• 14 years ago

The upside-down / ground on top installation is a requirement in hospitals because of the danger of a scalpel falling between the plug and wall.

rdl2• 14 years ago

This was in the NEC a few versions ago, but removed. It was very common in hospitals, and then got used elsewhere, added to NEC, and then people complained (due to some plugs, like transformer wall warts, not working as well in this orientation). Of course the NEC isn't itself law, it's just an industry standard which is sometimes incorporated into local code (which is law).

kevindication• 14 years ago

Kind of not law. Most local codes will have a few items that they consider special and worth mentioning, and then it will tell you to refer to the County code (assuming you were at the city level). Then the County code will add some things and refer you to the State code. The State code may add a few more and then ultimately tell you that the NFPA 70 (NEC) is law.

Oh and by the way, did you want to know what the NFPA 70 actually says, since it's you know, law? Up until a few years ago that cost you a pretty penny. In recent times you can read it for free through their special online viewer.

tjic3• 14 years ago

> Another problem springs up. At present, some appliance manufacturers INTENTIONALLY connect the outside of their metal products to one of the power wires. This must be stopped.

I disagree with this.

If one side is tied to ground (and it is), then tying the chassis of a piece of equipment to that same line is the same as tying it to ground...a ground that you're already standing on.

Am I missing something?

dattaway• 14 years ago

Voltage drop across the neutral side can and does happen. Also, loose connections often happen on the neutral side supplying the plug. This could give you the full voltage across your chassis.

mturmon4• 14 years ago

"Voltage drop across the neutral side can and does happen."

This is true. Even though the neutral conductor is grounded at the panel box, loading elsewhere in the circuit can cause the neutral conductor to have a potential above ground.

That is, there is a small resistance of the copper wire as it goes from the electrical outlet back to the panel box. If something in the circuit is drawing significant current, this small resistance can cause a voltage to appear in the grounded ("neutral") conductor.

If your home uses "shared neutral" wiring (two opposite-phase 120V hot lines sharing a single neutral wire for the return), then even throwing the circuit breaker on a given circuit can leave a potential in the neutral wire. This is because the paired hot conductor can be carrying current, causing the shared neutral wire to have potential.

This can be surprising.

harpastum• 14 years ago

From my reading, the reason it was unacceptable was that since the wires were previously identical, the manufacturers attached an arbitrary wire to the case, so 50% of the time it wasn't the neutral one.

So, once we switched the polarized plugs, some of the appliances would always have a hot chassis; unless we made sure appliance-makers always attached neutral to the chassis.

fshaun• 14 years ago

If everything is wired and functioning correctly I believe you are correct; the article mentions the case of electricians mixing up hot and ground wires. Presumably an appliance manufacturer could also have a mistake, but assembly lines are more consistent than humans -- if UL or CE tests a device it's likely all devices of that model are OK.

Sidnicious• 14 years ago

Keep reading. At that point outlets aren’t polarized and the case might end up connected either to ground or to the hot wire depending on how you plug it in. Even when outlets are polarized…

> “Occasionally an electrician will accidentally wire an outlet backwards. This can't be helped, because Perfect Electricians are far more expensive than the normal human variety. And so we cannot intentionally wire appliance cases to the Wide Prong of the plug, since it would cause a lethal hazard if the appliance was plugged into a miswired wall outlet. Miswired outlets look exactly the same as the normal ones.

> “The solution? Why, add a Third Prong! Connect this prong to the neutral side of the network, but do it only in one place in the circuit, and run a new third wire out to all of the wall-outlets. Give this wire a new color, one which is different from the other two. Give this this third prong a very different shape as well, so even Highly Imperfect Electricians will rarely connect the special prong to the wrong wire. Inside metal-cased appliances, insist that manufacturers connect this third wire to the case.”

excuse-me2• 14 years ago

And if there is any current flowing in the circuit and you have a finite resistance in the neutral wire there will be a (small) potential difference between the case and ground.

HarrietTubgirl• 14 years ago

This is an awesome article. Here's an example of the usual non-explanation:

http://electronics.howstuffworks.com/everyday-tech/question1...

This is how it was always explained to me. Yes, neutral and ground are the same thing. Why can't you just connect the case to neutral? Because you connect it to the ground plug. Huhh???

bpowah3• 14 years ago

Wonderfully entertaining to read. I was once told by a certified electrician (and physicist) that you don't even need a neutral wire and many rural services only have one "hot wire" and use the earth as the neutral "return" circuit (which really just need to have capacitance. I think the author could have started with a "one slot" age. More info: http://en.wikipedia.org/wiki/Single-wire_earth_return

cynicalkane• 14 years ago

You still need two slots, unless all of your appliances happen to rest on copper stakes hammered into the ground.

bpowah3• 14 years ago

or have some capacitance of their own.

bpowah3• 14 years ago

Now would somebody please tell me what the little holes are for in the end of the plug prongs!? http://www.worldofstock.com/slides/BEN2097.jpg

pndmnm• 14 years ago

Many sockets have little bent-wire brackets that pop into those holes when the plug is fully inserted in order to help hold it in place.

sc00ter4• 14 years ago

A tangential use (but not the original design intent) is to put a padlock on the plug to prevent it being plugged for safety reasons. (Think power tools, high temperature devices etc).

ars8• 14 years ago

http://www.straightdope.com/columns/read/579/why-are-there-h...

jrockway3• 14 years ago

Do we need grounded sockets now that we have GFCIs?

X-Istence3• 14 years ago

Yes. We still want device manufacturers to ground their cases, and using a third wire that is most likely not mounted the wrong way round is preferable.

marshray2• 14 years ago

I agree. It would be a bad idea to have a stack of metal equipment all plugged into floating outlets. You'd be likely to get all kinds of weird voltages between the metal cases.

The electrocution hazard was just one way it was the bad old days. It also sucked for other kinds of signals, hi fi, radio, etc. I would not want to try to have a home office full of computer equipment that weren't sharing a common ground.

Did you ever have one of those 17"+ CRT monitors? Recall how they would make the hair on your arm stand on end when you turned them off or on? Without a dedicated ground for those things, guess where all that charge is going to go? Into your computer, via the ground on the signal cable.

keenerd2• 14 years ago

Do you absolutely 100% trust the GFCI breaker? They do require a small imbalance to trip, so something bad could happen in that brief time. Or maybe stopped working one day.

But technically yes, ungrounded GFCI will still protect you. Doing it intentionally is a bit like not buckling up because you have 100% faith in your air bags.

For the non electrical people: GFCI works by measuring the current in vs the current out. Normally these should be perfectly equal. But if you drop your hairdryer in the bathtub, maybe 10 amps comes in (through the plug), 9.9 amps goes out (through the plug) and 0.1 amps goes out (through the bathtub, killing you). GFCI notices that 10 != 9.9 and shuts down. The trick is detecting 0.01% differences and shutting it down in milliseconds, fast enough to save someone's life.

GCFI is way more complicated than a ground wire, and you'd be a fool to not have a cheap, passive and redundant safety system.

ars8• 14 years ago

Actually, it's totally legal. If you have an outlet without a ground wire, you can use a three prong GFCI and put a sticker on it that says "No Equipment Ground" and it's totally legal and to code.

You are over exaggerating how useful the ground is - a GFCI is far more effective, the ground pin hardly does anything at all.

jrockway3• 14 years ago

Or maybe stopped working one day.

I believe this is why they are labeled "test monthly". This is a lot more frequently than I check that neutral is not accidentally wired to hot or that the ground wire actually goes to the ground and not some random piece of plumbing that was removed in a renovation. (I live in a building that was built in the 1860s, and plumbing and wiring are being redone all the time.)

anologwintermut• 14 years ago

Can anyone confirm the articles assertion that " Before you 'grounded' your system, the AC voltage in general acted pretty safe for your customers. The only way they could get a shock was if they touched both wires at the same time?"

It seems that if I stick my finger in the hot socket, there is still a path via me to 0 voltage (the ground). I will still get shocked.

DanBC24• 14 years ago

> It seems that if I stick my finger in the hot socket, there is still a path via me to 0 voltage (the ground)

Over-simplified, but you need a complete circuit. In your example you say that voltage is across you - live at a finger and earth at your feet. But earth is not connected to the circuit, so there's no complete path. That's why the article talks about sticking rods into the Earth to create a ground connection. Now there is a complete circuit. (And this would be across your heart - the current flows through a finger, your arm, your heart, down your leg, and to Earth. This is especially dangerous, and is the reason you see test engineers working with one hand in their pocket. Not having two hands connected to live equipment means it's harder for a voltage across the heart.)

There's another thing to mention though: Imagine wearing rubber boots, on a dry wooden floor, and jabbing a metal rod into the socket. That's still risky, because your body will act like a capacitor and the charge can be fatal.

thought_alarm2• 14 years ago

In an isolated or ungrounded system there is no electric potential between the socket and ground, so the current has nowhere to go but back into the socket. Therefore, you only get shocked when touching both pins.

no_more_death• 14 years ago

I recall moving a water dispenser that leaked, as a child, stepping on the wet spot barefoot, and plugging in a two-pronged vacuum cleaner. It was a shock.

colanderman• 14 years ago

I thought the primary reason for a separate ground was because neutral was a current return path and thus could develop a voltage on it due to resistance of wires, whereas a true ground carries no current and thus will not develop a voltage?

DenisM• 14 years ago

I remember there are two reasons for the third prong, and neither is mentioned in the article.

The first reason is the one you have outlined - the larger the current, the bigger the differential between the actual ground via and the neutral wire in the appliance.

The second reason is that if you're using a transformer to change the voltage, the output of the transformer is not connected to the input, and thus can have arbitrary large voltage differential with the ground due to charge accumulation, and so it needs to be grounded. Now I'm getting fuzzy here, but I think there is a reason why you can't connect one of the transformers inputs to one of it outputs (the neutral one) to provide the "grounding" this way, so the third wire is used. I've noticed that devices which do not need to provide voltage conversion usually lack the ground prong, e.g. heaters.

gcb4• 14 years ago

heh, in brazil they just finished a mandatory replacement of all the plugs.

previously we had a plug with a flat face like the US, but the connectors were like "d b" meaning a US flat in the middle with round ones right out. using the same metal connector for both formats in the middle. clever, cheap, worked with everything. (US, Japan, Swiz, ...all except UK and australia as far as I know)

now, they have mandatory round plugs only, slightly larger so they can't fit the old ones by one or half milimiter, and a recessed insert like the new Switzerland type J, and an optional ground.

It serve the purpose of solving NONE of the mentioned issues in the article, but help lots of people that manufacture the new plugs.

ricardobeat10• 14 years ago

You could be a little more proud of your country - it's among the first to implement an international standard that is safer, simpler and more reliable. The new plug solves real problems (including all those mentioned in the article) and it does fit the old european-style outlets when groundless - if it has a ground pin or is the 20A variant it should not be plugged into a standard outlet anyway.

gcb4• 14 years ago

Remember that polarized plugs are not to protect against properly designed products. And with the vast amount of international electronics in Brazil (heck, i think i had only a electric shaver that had national plugs, everything else required adapters) the cheap adapters null all the benefits.

CUR10US• 14 years ago

I love the amasci website (I don't mean the design; I have no idea about what it looks like in a graphical browser; I only mean what there is to read- lots of text! I just extract the text for viewing on 80x25). If only all websites could have this much information density. Long live sites like amasci!

ajb• 14 years ago

This is a great article.

As an example of innovation in this space, some Chinese company has devices a socket which accepts many international plugs: http://www.bbc.co.uk/news/magazine-18266022 This appears to be the company: http://www.europlugs.com/

It's not clear to me that they have managed to fulfil all the safety requirements. I guess it would take some effort to really be sure, but can anyone see any obvious bloopers?

toddh• 14 years ago

If there's so much DC energy available can we store it?

BigTuna• 14 years ago

That site is an absolute gold mine.

nroman• 14 years ago

In college I lived in an old apartment building that had been updated to have 3-prong outlets. One day I was wiring up some audio equipment for a party. As I hooked my computer to a a receiver in another room the audio cable immediately started sparking and the rubber insulation melted off. I yanked it out of my computer. Luckily the only real damage done was the sound card for my computer and the destroyed cable.

Later I did some investigation. First I bought one of those standard outlet testers. It seemed to suggest that everything was fine with the outlet. Then I did some more investigation. I got a volt-meter and started measuring the voltage from the different prongs. Finally I measured the voltage compared to a copper pipe in the house.

Turns out that both the neutral and ground wires were actually hot (as measured against the grounded pipe), and the "hot" wire was the ground. The outlet in the other room had been wired correctly. The shielding on the cable was grounded so suddenly it sent 120 volts down the audio cable when I plugged it in—destroying it in seconds.

The electrician didn't believe me when he came in to fix it, but was finally convinced when he checked against a pipe.

Just goes to prove that you can't make any system fully fool-proof.

Why three prongs?

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