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Why three prongs? (amasci.com)
578 points by xd 684 days ago | comments


gojomo 684 days ago | link

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?

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iliis 684 days ago | link

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?

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throwaway64 684 days ago | link

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

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stephengillie 684 days ago | link

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

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js2 683 days ago | link

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

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snowwrestler 681 days ago | link

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

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zdw 684 days ago | link

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.

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TazeTSchnitzel 684 days ago | link

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...

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sc00ter 684 days ago | link

" 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.

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TazeTSchnitzel 684 days ago | link

Oh, I notice the Earth pin is longer now that you mention it, you're right. Makes sense, considering it retracts the flaps.

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brudgers 684 days ago | link

It's simultaneous pressure on the two live prongs which allows the plug to enter the receptacle - a two pronged plug still works.

See: http://www.nfpa.org/itemDetail.asp?categoryID=1508&itemI...

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quarterto 683 days ago | link

We're talking about UK plugs here. It's impossible to insert a plug without the ground pin entering first. I've had a few double-insulated AC adaptor where the dummy plastic ground pin has broken off (in the socket!) rendering the plug unusable in most sockets.

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njs12345 683 days ago | link

If this happens and you don't want to replace the plug, you can get a pencil and put that in the ground hole to allow you to put the other two pins in.

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quarterto 682 days ago | link

I used another plug turned around along with some deftness.

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brudgers 684 days ago | link

Most receptacles [in the US] do not have flaps or any other mechanical part. If they had the sort of contraption described, ungrounded plugs would not work and there would be a significant risk due to failure.

The ground pin is longer because it is far safer to ground first before running current, and to continue to ground after disconnecting the current.

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ars 684 days ago | link

Not anymore. All new receptacles in the US have a protection that will not allow you to insert anything into just one side.

You have to insert prongs into both sides of the outlet at the same time in order for it to release.

http://en.wikipedia.org/wiki/NEMA_5-15#Tamper-resistant_rece...

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brudgers 684 days ago | link

The change is in NFPA 70 - 2008, also known as "The National Electrical Code."

The requirement only applies to dwellings (houses and apartments, not hotels or other commercial buildings), and only in jurisdictions which have adopted the 2008 NEC - the United States, unlike Canada does not have a national building code.

In addition, many jurisdictions have adopted the International Residential Code for One and Two Family Dwellings (aka, "IRC) which contains its own electrical requirements. While their is provision for tamper resistant receptacles in the 2009 IRC, many jurisdictions have remained on older versions of that code because the 2009 edition requires fire sprinklers in single family homes and therefore its adoption creates substantial political tension between building departments and the homebuilders whose fees fund those departments.

To put it another way, in the US, tamper resistant receptacles are not required in any non-residential structure, and because codes are adopted at the local or state level on an ad hoc basis, many dwellings are not required to conform with NEC 2008 or later versions.

Think of new editions of building codes like Windows, lots of people still use XP.

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marshray 684 days ago | link

I've never seen one of these things, not even at Home Depot.

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icarus_drowning 684 days ago | link

I live in an older home (1955), but when we bought it in 2010 we had the original owner do electric work that had failed inspection-- as a result (and due to the local laws here), this is the only kind of socket we have.

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ars 684 days ago | link

Look again - I had a hard time finding anything else last time I went.

They are labeled with "TR". (There is also WR for water resistant, and of course TR and WR together, sigh. Prices are going up since now stores need to stock 4 times as many types.)

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btgeekboy 684 days ago | link

They exist, but they sell them alongside the normal ones at an additional cost.

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btbuilder 683 days ago | link

Why would there be a significant risk of failure? Granted it would be more complex, but as the UK is a country of 65 million people I'd expect that if there were a lot failures the design would have changed by now.

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magic_haze 684 days ago | link

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?

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ricardobeat 684 days ago | link

The IEC 60906[1] standard was designed to replace BS1363 too, but the british requirement for fuses prevents it's adoption.

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

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ginko 684 days ago | link

Couldn't they just install the fuses in the sockets?

It seems terribly inefficient to require fuses in every plug even when the electrical wiring may not need them.

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ricardobeat 683 days ago | link

Their rules require different fuses according to the appliance's rated current and wire diameter, so no. I think you could make a smart outlet that switches fuses according to what's plugged in, but it would cost a fortune.

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tomfakes 684 days ago | link

In the UK, until fairly recently, it was illegal to sell a product with a plug attached. Consumers had to wire their own plugs to their electrical devices before use.

Now that is inefficient!

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jrockway 684 days ago | link

Citation needed.

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tomfakes 684 days ago | link

I may have had it a little wrong. I can't find older legislation about this subject that confirms my supposition.

This 1994 legislation made it the law that plugs must be fitted to certain consumer devices: http://www.legislation.gov.uk/uksi/1994/1768/contents/made

Before that time, almost everything (certainly everything I purchased) came without a plug and you had to buy a plug and wire it yourself. Probably because these things are expensive, and costs could be reduced by leaving them out.

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shabble 683 days ago | link

I have a suspicion you have it exactly backwards. It's now a requirement for some|many devices to have non-removable moulded plugs (although they still have replaceable fuses).

I'm not certain on the exact motivation, but I think it's a mix of preventing people doing it wrong, and better mechanical properties (especially strain-relief) of moulded plugs.

It's also required now that the live/neutral pins be partially insulated (the 1/3rd closest to the plug or so) to prevent shock hazards to people curling their fingers around the plug when inserting or removing.

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FuzzyDunlop 683 days ago | link

It wasn't uncommon for us to have spare cord and plugs either, although the change of law to require moulded plugs obviated the need for any of it.

I remember us having to wire up kettles, lamps, and irons when I was a kid. And you'd sometimes go to antique (or second hand) shops and come across old appliances that had no cord attached. Anecdotally, we bought an old style telephone that we then had to wire back up.

That being said, I can't corroborate any claim that this was backed by legislation.

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DanBC2 684 days ago | link

It's a huge lump, but it handles 240 v at 13 amp and does so without burning down houses or killing people who plug it in.

I have no idea how many sockets are installed in UK houses and how many plugs are fitted to UK equipment but a new plug / socket design would have to be God-Tier to justify the cost of replacement.

Also, I've seen people wiring plugs and it's sometimes scary, so anything that avoids the need for many people to botch a new plug onto their equipment is a good thing. And I guess this is where most improvement has happened - plugs that can be built quickly, cheaply and safely in Chinese factories for use in UK. You can change the fuse, but the plug is molded and you can't take it apart.

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magic_haze 684 days ago | link

you misunderstand my intent: I was merely interested in finding out if there were any new ideas in plug design than what was indicated in the wiki article.

The IEC 60906-1 design linked by ricardobeat above, for example, can handle 250V at 16A and is way smaller and more compatible with other european standards. It was designed in the mid 80s, taking advantage of the new injection molding processes popularized in the late 70s.

I was wondering if there were any other designs that took advantage of the newer technologies since: I seem to recall a concept plug designed by an art student that was on HN a few years back that folded up rather neatly: does anyone know what happened to that?

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DanBC2 684 days ago | link

Oh! That was posted here very recently. It's going into production with a few small changes.

(http://news.ycombinator.com/item?id=4033328)

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protomyth 683 days ago | link

The sad part is even with all the AC plugs, there are multitudes more DC plugs. I guess USB is kind of a universal standard, but I really wish Apple had licensed their MagSafe to everyone to make a world DC standard wall plug.

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kalleboo 684 days ago | link

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.

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lmm 684 days ago | link

True, but you learn after the first time, and it's pretty non-lethal (I think? It doesn't seem sharp enough to do serious damage, but for something to hurt that much your body must think something's up). The real problem with British electrical standards is the nutty "ring main" system.

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jdietrich 684 days ago | link

We'll be laughing when copper hits $20,000 a ton - the ring main is very close to the most economical possible design.

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ars 684 days ago | link

The ring main makes wifi much more difficult, and encircles the building with a strong (and varying) magnetic field causing problems for many devices.

It induces current in all metal near it, which causes sensitive devices to fail.

And it was only economical when you assumed a small number of high current devices. But these days when every outlet has something plugged into it the benefits are nill (since you have to have enough capacity for all the outlets, not just a small number of them).

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ricardobeat 684 days ago | link

Then we'll switch to copper clad steel/aluminum :)

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dfc 684 days ago | link

What is the "ring main" system?

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DanBC2 684 days ago | link

It's a circuit layout used mostly in the UK.

Wikipedia has a nice explanation.

(http://en.wikipedia.org/wiki/Ring_circuit)

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ricardobeat 684 days ago | link

So THAT's the reason for the damn fuses. Thanks!

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ricardobeat 684 days ago | link

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

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swah 684 days ago | link

And we have our own exclusive design because no other was good enough. Also, so that using imported products its harder :)

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ricardobeat 684 days ago | link

It's based on an international standard. The different plug diameter is an annoyance (why shave .5mm?), but it's still backwards-compatible with the spec, and the standard plugs will probably fit anyway.

(Legally) imported products must conform to the local standards and pass inspection anyway :)

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swah 683 days ago | link

I'm also from Poa :)

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ricardobeat 683 days ago | link

Hey, hit me up on LinkedIn/twitter. You should add some contact info to your HN profile :)

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gcb 684 days ago | link

Last time i checked the middle plug was optional, so no, not polarized.

granted, the last time i looked at the paper was 2,5 years ago and there was still a lot of allowances for transition.

And i'm certain the Nokia adapters sold via local phone operators only have two plugs.

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ricardobeat 683 days ago | link

Not every appliance needs grounding[1], in those that do the ground pin is mandatory and so the plug is polarized.

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

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gcb 683 days ago | link

Remember that the idea,of polarization is,because cost cuttings in products. A product opting to use 2 prongs and grounding the chassis would cause problems. Yes it's forbidden, but may happen and (and products may be repaired by not so perfect techs) and the current system will offer you no precaution.

And don't even get me started on adapters for international products... Which btw, are the vast majority of brazil consumer gadgets.

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kika 684 days ago | link

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

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jevinskie 683 days ago | link

Exactly. Is there another design that shares the same features but in a smaller (more in line with US plugs) size?

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speleding 682 days ago | link

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?

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Fizzadar 684 days ago | link

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

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swah 684 days ago | link

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...)

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ricardobeat 684 days ago | link

Cut them up and replace the plug. You wouldn't want an adapter the size of a brick attached to your outlet anyway.

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swah 684 days ago | link

I just buy replacements from DealExtreme, because they're just USB hubs in the end... (but the Apple and Amazon versions have great build quality).

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rdl 684 days ago | link

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).

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kevindication 684 days ago | link

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.

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dfc 684 days ago | link

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.

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dpitkin 684 days ago | link

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

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sc00ter 684 days ago | link

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.)

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X-Istence 684 days ago | link

This isn't for in the wall, but outside of it...

For example you plug in a drill but it slowly works its way out, you are working with a screw driver against the wall and accidentally drop it, at this point the screw driver can come to rest on the live pins of the drill that is plugged partially into the wall. With the ground pins up the screw driver will pick a side and fall off...

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dubya 684 days ago | link

You can try it yourself by dropping a bit of pencil lead across the prongs a slightly unplugged plug. You get a flash and it hops away, but I don't know that a piece of metal would break contact. I don't recall this ever even tripping a breaker, but be careful.

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X-Istence 683 days ago | link

If you want a nice flash, take some low resistance half watt or even quarter watt resistors, place in power strip, plug power strip in ...

Ah, so awesome.

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brudgers 684 days ago | link

[for the US]

The longer ground pin at the top provides a mechanical advantage when a downward force is applied to the plug. Since this is the most common accidental force (e.g. something dropped or a cord on the ground dragged) it slightly reduces the risk of disconnect.

In addition, the ground at the top allows for a better view of the pin and receptacle hole.

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ars 684 days ago | link

The other way around. Plugs always fall out of ground up receptacles to the point that I will rewire them if I have any in my house.

They hold nicely in ground down receptacles though.

The insertion force of the one ground pin is lower than the two live ones. So when force is allied downward the plug pivots out of the receptacle.

In a ground down orientation the plug will pivot into the wall. Since the ground pin moves easier than the other two, it moves into the wall instead of out.

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bhousel 684 days ago | link

This story of a kid dropping a tape measure down on a partially plugged in device seems somewhat credible: http://www.electriciantalk.com/f12/1st-hand-ground-down-stor...

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bburky 683 days ago | link

I once had a metal 18" ruler that fell off the back of a desk, and fell perfectly flush with the wall catching the top two prongs of an outlet. A spark, blackened the ruler and took a small notch out of it.

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thought_alarm 684 days ago | link

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).

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ajasmin 684 days ago | link

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.

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jakobe 683 days ago | link

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.

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andrewreds 683 days ago | link

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.

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TazeTSchnitzel 684 days ago | link

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

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texec 684 days ago | link

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.

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brudgers 684 days ago | link

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.

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lostlogin 683 days ago | link

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.

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sc00ter 684 days ago | link

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

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colanderman 684 days ago | link

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?

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DenisM 684 days ago | link

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.

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danbmil99 684 days ago | link

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

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tjic 684 days ago | link

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!

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rdl 684 days ago | link

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.)

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ams6110 684 days ago | link

How many electricians do you actually know?

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tjic 683 days ago | link

Three. One I walk dogs with daily.

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TazeTSchnitzel 684 days ago | link

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

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DougBTX 684 days ago | link

As a physicist*, I would suggest speaking to an electrical engineer.

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K2h 683 days ago | link

As an EE, I say ask one specific branch of the Electrical Engineering profession.

see [1], here there are 3 specific sub disciplines you can test in, and all are considered "EE"

computer

electronics

power

you want to talk to an expert in the power arena, but from what I remember when studying for the exam, the content was mostly things way above residential (which is what this discussion has been about) and more of power gen and conversion. Y, delta configurations and conversions, power angles and factors, etc. the kind of thing you come out really knowlegable in one very small area and still clueless on the NEMA power plug.

[1] http://www.pels.ca.gov/applicants/refs.shtml

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mturmon 684 days ago | link

But, conversely, be careful about asking a physicist to wire your home. They may not be conversant with the codes, which contain a lot of practical wisdom.

I once tried to convince a physicist friend to not use just solder on his ground connections. He thought that by using solder he was going above-and-beyond the code.

But actually, ground connections are required to be pressure-fit, not just soldered, to ensure that heating during a current spike does not allow the connection to separate.

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ars 684 days ago | link

Sorry, but that's not true. For your solder joint to fail it would have to be hot enough to cause a fire.

Pressure type connectors are simply cheaper and easier, and were not initially allowed because soldered connections are better.

http://www.justanswer.com/electrical/18vcb-not-allowed-solde...

Soldered (sweated) fittings are not allowed on gas lines for this reason though: If there was a fire you don't want the gas lines to leak after the solder melts.

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mturmon 683 days ago | link

What I said is correct according to the NEC. In fact, the relevant part of your link says:

"Soldered splices shall first be spliced or joined so as to be mechanically and electrically secure without solder and then be soldered."

So, the joint has to be totally secure, mechanically and electrically, without the solder.

My friend was relying on solder and tape, with an inadequate mechanical connection that relied partly on the solder to hold it together. His installation was therefore not compliant with the NEC, although he did not want to admit it.

If you read the explanatory note related to the code, it gives the rationale I gave. Maybe it's BS, but it's the NEC.

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ars 683 days ago | link

> relied partly on the solder to hold it together

You are not ever supposed to do that. I was assuming he wrapped the wires together securely first. http://en.wikipedia.org/wiki/Western_Union_splice or even http://en.wikipedia.org/wiki/Rat-tail_splice

I was just saying you don't have to use a pressure type connector - you can use a wrap splice, then solder it. (Electrical tape is not sufficient insulation, but you said this was a ground.)

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mturmon 683 days ago | link

The NEC is even more restrictive with equipment grounding conductors, actually. You are not allowed to use solder-only connections on grounds. I don't want to go farther down the road, since we're only talking to each other, but here is a link FYI:

http://www.ecmag.com/?articleID=8721&fa=article

The relevant part is:

"Connection of Grounding and Bonding Equipment. Grounding conductors and bonding jumpers shall be connected by exothermic welding, listed pressure connectors, listed clamps, or other listed means. Connection devices or fittings that depend solely on solder shall not be used."

You really cannot just twist-and-solder for a ground. It is specifically forbidden by the NEC.

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ajross 684 days ago | link

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

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davidw 684 days ago | link

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.

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gioele 684 days ago | link

> 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.

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davidw 683 days ago | link

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.

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joelhaasnoot 684 days ago | link

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.

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kalleboo 684 days ago | link

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...

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joelhaasnoot 683 days ago | link

Ok, so it has gotten a little better, but having lived in close proximity to Americans in Africa and so buying their appliances second hand, etc, there were all to many cases of people accidentally switching plugs. PC Power supplies used to also be manually switcheable - no autodetect (atleast the ones we had access to in Africa), guessing that's changed. The dangerous examples were cords that didn't have the right end or had changed ends so that you could hook a 110V appliance to a 220 outlet.

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ralfd 684 days ago | link

Interesting effect: http://upload.wikimedia.org/wikipedia/commons/f/f5/Weltkarte...

Never cared about this svg file format, but how does it work? If I make a reload on the link the countries are drawn individually as the file is loaded (relatively slow network connection). Like a puzzle.

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kalleboo 684 days ago | link

Try view source and you can see how it's built. Simplified, SVG could be described as "like HTML only with shapes".

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