WHY THREE PRONGS?

(C)1996 William Beaty

Also see below: WHY "GROUND" IS CONFUSING

QUESTION:
WITH AC POWER, AREN'T BOTH THE WIRES OF THE PAIR INTERCHANGABLE? WHY IS ONE WIRE CALLED "NEUTRAL?" WHAT'S ALL THIS STUFF ABOUT "GROUNDING?" WHY ARE THREE PRONGS NEEDED?

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ANSWER:
Yes, in an Alternating Current system there is no "plus" and "minus," so in theory the two wires should be interchangable. However, the real world is a bit more complex than the theory. Other issues crop up and cause trouble.

If you were to build your own electric power distribution system, you'd quickly discover some unexpected and strange effects. Sometimes your customers' appliances would fail for no apparent reason. And sometimes when you reached for a light switch, a foot-long spark would leap out to your hand and knock you senseless! What the heck?! It takes a huge DC voltage to make a foot-long spark. Why are high DC voltages appearing on your AC power lines?

The sparks occur because of a little-known fact: all the world is a gigantic electrostatic generator. There is a flow of charge going on vertically everwhere on earth. Thunderstorms pump negative charge downwards, and the charge filters upwards everywhere else on earth. Depending on the height of your circuitry above the earth's surface, depending on the area covered by your wires, and depending on whether there was a thunderstorm above you at the time, there might be a fairly huge DC charge on your electrical distribution system. This charge might be several hundred volts; enough to zap computers and delicate electronics. Or... it might be many tens of thousands of volts, enough to create enormous sparks which jump across switches and leap out of wall outlets, wall switches, across transformer windings, etc. Your electric power system is acting like a sort of capacitive "antenna" which intercepts the feeble current coming from the sky and builds up a huge potential difference with respect to the earth.

In addition to the above, you would find an unsettling phenomenon whenever lightning strikes your electrical distribution system. The lightning impulse-voltage spreads instantly throughout your whole network, which not only can explode every single appliance plugged in at the time, but can create lethal arcs many feet in length that reach out to "touch" your customers should they be anywhere near those wires within the walls.

There is a simple solution to these problems: connect your system to the earth. Drive some long metal rods into the earth, and connect them to your wires. That way, lightning currents will be directed into the earth rather than spreading throughout your power lines. Also, the clear-weather sky current can no longer build up a high voltage, if any excess charge immediately leaks into the earth.

Of course you cannot connect BOTH wires to ground, since that would also connect your wires to each other and short out the system. So, you must close your eyes and pick one wire. Connect that wire to ground. Do this at many points throughout your system of power lines, so if one part is disconnected for any reason, it won't present a lightning hazard or static discharge hazard. Now the clear weather sky-voltage will be discharged to earth, and during a lightning strike, the huge current will be diverted into ground at many points, and hopefully will find very few customers' bodies on its way into the earth.

The story isn't over. Since you've made a change to your system, Murphy's Law crops up and informs you that for every problem that you cure, another one is created. 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. This was a fairly rare occurrence. One single wire acted as if it was "safe," and it did not deliver shocks. If a miswiring inside an appliance caused one wire to accidentally touch the metal case of the device, your customers could still touch that metal case without danger. Curious kids might still stick their finger in a light socket and receive a shock, but the current was directed through the length of their finger and caused no danger of heart-stoppage.

Now that you've grounded your system, you'll find that suddenly your customers are occasionally dying! One wire of your system is now almost totally safe because it is connected to ground. But the other wire has developed a new hazard, because whenever the occasional customer comes into contact with it, that foolish customer is usually STANDING ON THE GROUND! By grounding half of your electric network, you've accidentally connected one entire half of your network indirectly to everyone's feet. Most of the time the floor is a pretty terrible conductor, so most of the time the hazard is small. However, when someone stands barefoot upon a damp floor, this electrically connects that person into the system. If they touch the grounded ("neutral") wire in the AC system, nothing happens. But if they touch the other, non-grounded wire, this applies the full AC voltage between their feet and finger. The current path within their body then includes the heart muscle, and the resulting AC current induces rapid, tail-chasing heartbeat waves called 'fibrillation' in their main blood pump. And so your new, half-grounded AC system has developed a lethal characteristic. Unfortunately, removing the ground connection causes even more danger, so you can't go back to a "floating" system where Hot and Neutral don't exist.

One solution would be to insist that all customers wear dry, insulating footwear, never walk on wet floors, never sit in bathtubs, etc . This guarantees that they are not connected to one half of your system, and it makes the other half of the system act safe again should they touch it. Professional electricians might enjoy the challenge of learning all these rules, but your new requirements would cause some negative repercussions in selling your service to non-experts. To say the least. Some other solution is needed.

The solution: guarantee that no one touches the non-grounded wire. Get into the schools and pound into everone's mind that AC wires are dangerous. Teach all electricians and technical people that one of the wires is now to be called "Hot", and that this wire can be lethal if touched. Choose differing colors for the two wires (black is "hot" in the US, brown is "hot" most everywhere else.) Force manufacturers to treat the wires differently inside appliances, designing with careful wire positioning and adding extra insulation to the "hot" wire.

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. But economic concerns prevent making massive, instant changes. You can't force a recall of half the appliances in the entire world, and you can't force manufacturers to instantly redesign all their products. The economic upheaval from this would wreck far more lives than the dangerous circuitry does. So instead you decide to change the power outlets of all new homes, as well as changing the plugs of all new appliances, in order to force customers to always stick the plug in the "right" way. Manufacturers must use the new types of cords, but at least they don't have to redesign all of their products. For appliances with one wire connected to the metal case, this connects the case to the grounded or "neutral" side instead of to the "hot" side. Now make one slot of the two-slot electric outlet longer than the other. Do the same with the appliance plugs. Choose the neutral side to be the long slot, the hot side to be the shorter slot. Apply legal pressure to get manufacturers to stop connecting their metal cases to the power wires. Make electricians preserve the polarity of the wiring when they install outlets in new homes. Thus we enter the "Age of the Electrical Outlet with One Long Slot."

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Things now seem much improved, but there are still problems. If an appliance is dropped into water, and if that water is touching a grounded container (such as a bathtub, a kitchen sink, or even a basement floor or a standing pool outdoors) then any human sticking more than one appendage into the water will be in serious trouble. Humans are salt water, and they present a low-resistance path for current, which preferentially directs it through their bodies rather than through the water. Another thing: sometimes an appliance with a metal case will suffer internal wear or damage, and then the "hot" wire will wiggle around inside and end up touching the metal case. Anyone standing on wet ground will feel pain and death if they should grab that metal case.

Some unnamed genius realizes that if we could somehow permanently connect all the metal cases of appliances to the "neutral" wire, then if the "hot" wire should ever accidentally touch the case, a short circuit would blow the fuses in the building and quickly remove the electrical connections, and the hazard. However, this is not entirely safe. 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.

The idea works! Like magic the faulty metal-cased appliances start blowing their fuses to indicate trouble. And power tools dropped into water will create a current path to the metal case rather than to nearby humans standing in the puddle. We've entered the "Age of Electrical Outlets Having a Little Face and Different Sized Eyes."

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But still, every once in a while a Customer will get a really nasty shock from a cheap plastic appliance that's wet. Or perhaps an electric hair dryer will fall into the bathtub, but the short-circuit current in the water won't be enough to blow the fuses in the house, and the bathtub water will become lethal. In theory there is a way to prevent this. These Customer shocks are happening because the customers' bodies offer a path for current between the appliance and the lightning-safety earth grounds. During the shocking event, some of the flowing charge is going in (and out) of the "hot" wire, but it is NOT going back into (and out of) the "neutral" wire as it's supposed to. Instead, it's going through the human, and also going into the grounded pipes of the plumbing.

If we could measure the current that's taking the "wrong" path, maybe we could detect the problem and turn off the power before anyone dies. We can't measure the current in the plumbing, but we can measure it in the "hot" wire, measure the current in the "neutral" wire, then subtract them. This tells us what level of current was escaping via the "illegal" path through the human to ground. The subtraction should normally give a zero result, since there never should be a current path to ground that isn't using the neutral wire. If we amplify the subtraction's result and use it to trip a circuit breaker, we'll have a new type of appliance which turns itself off immediately when a human gets into the electrical path. These devices are now required in wet areas of homes (bathrooms.) They're called Ground Fault Interrupters. And so we've finally entered modern times, the "Age of the Electric Outlet with the Little Red Button Which Pops Out!"

- Bill Beaty

STUPID BILL B. VIDEOS!				educational too. But no less stupid!
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MORE ABOUT "GROUNDING" AND "EARTH"

In electrical circuits, the word "ground" can be very confusing. The word has several different meanings. Your instructor might know which meaning he or she is using in any spoken sentence. But this spreads confusion, because students aren't even aware of the multiple meanings. Or even when students know that "ground" is a multi-facted term, they may lack skill in connecting each definition. It's better to ban use of the word "ground" in the classroom. That forces everyone to use less confusing words.

The word "ground" means:

A 'common' connection, but not connected to Earth.

A connection to the power supply (usually to the negative terminal)

A connection to the inside of a shielded metal box

A connection to a metal stake driven into the earth (or a connection to a metal water pipe which extends out of the house into dirt.)

Only number four is actually connected to ground!

What Is "Electricity"?

SEE ALSO:

Scientist's definition of Electricity
Electricity is not Energy
What is electricity, REALLY?!

What is electricity? This question is impossible to answer because the word "Electricity" has several contradictory meanings. These different meanings are incompatible, and the contradictions confuse everyone. If you don't understand electricity, you're not alone. Even teachers, engineers, and scientists have a hard time grasping the concept.

Obviously "electricity" cannot be several different things at the same time. Unfortunately we have defined the word Electricity in a crazy way. Because the word "electricity" lacks a distinct meaning, we can never pin down the nature of electricity. In the end we are forced to declare that there's no such stuff as "electricity" at all! Here's a quick example to illustrate the problem.

Do generators make electricity? To answer this question, consider the household light bulb. In a lamp cord the charges (electrons) sit in one place and wiggle back and forth. That's AC or alternating current. At the same time, the waves of electromagnetic field move rapidly forward. The wave energy does not wiggle, instead it races along the wires as it flows from the distant generators and into the light bulb. OK, now ask yourself this: is an electric current a flow of "electricity?" If so, then we MUST say that the "electricity" sits inside the wires and vibrates back and forth. It does not flow forward. Next, ask yourself if electricity is a form of energy. If it's energy, then "the electricity" DOESN'T wiggle back and forth within the wires, instead it's made of EM fields and it races forward at high speed. But it cannot do both! Which one is "the electricity", the wiggling electrons, or the high-speed EM field energy? The reference books give conflicting answers, so there *is* no answer.
If someone asks whether generators make electricity, it exposes a great flaw in the way we talk about "electricity". If we can repair this flaw, perhaps our explanations will finally make sense.

Below are the most common meanings of the word Electricity. Which one do you think is right? Think about it carefully. If one of these meanings is correct, all the others must be wrong! After all, no "science term" must ever have several conflicting definitions. Unfortunately dictionaries and encyclopedias have all of these contradictions. (Click the links to find out more about each one.)

1. The scientist's definition: "Electricity" means only one thing: it's the electrons and protons, the electric charge.: Examples: CURRENT OF ELECTRICITY. QUANTITY OF ELECTRICITY. COULOMBS OF ELECTRICITY.

2. The everyday definition: "Electricity" means only one thing: the electromagnetic field energy sent out by batteries and generators.: Examples: PRICE OF ELECTRICITY. KILOWATT-HOURS OF ELECTRICITY.

3. The grade-school definition: "Electricity" means only one thing: it refers to the flowing motion of electric charge.: Examples: "CURRENT" ELECTRICITY. AMPERES OF ELECTRICITY.

4. "Electricity" means only one thing: it refers to the amount of imbalance between quantities of electrons and protons.: Example: "STATIC" ELECTRICITY. DISCHARGE OF ELECTRICITY.

5. "Electricity" is nothing other than the classes of phenomena involving electric charges.: Examples: BIOELECTRICITY, PIEZOELECTRICITY, TRIBOELECTRICITY, THERMOELECTRICITY, ATMOSPHERIC ELECTRICITY ...ETC.

6. Other less common definitions:: "Electricity" refers to the flowing motion of electrical energy (electric power, Watts of electricity); "Electricity" really means the electric potential or e-field (Volts of electricity); "Electricity" only means the glowing nitrogen/oxygen plasma (sparks of electricity); "Electricity" is nothing but a field of science (Basic Electricity, Advanced Electricity)

ELECTRICITY, n.
The power that causes all natural phenomena not known to be caused by something else.
(Ambrose Bierce, The Devil's Dictionary, 1911)

If we wish to agree on a single correct definition of "electricity," which definition should we choose? Well, maybe we don't need to choose just one. Suppose we ignore all these contradictions and instead pretend that ALL of the above definitions are true. Below is the "clear" and "simple" description of electricity that results:

Electricity is a mysterious incomprehensible entity which is invisible AND visible BOTH AT THE SAME TIME. Also, it's both matter and energy. It's a type of low-frequency radio wave which is made of protons. It is a mysterious force which looks like blue-white fire, and yet cannot be seen. It moves forward at the speed of light... yet it vibrates in the AC cord without flowing forwards at all. It's totally weightless, yet it has a small weight. When electricity flows through a light bulb's filament, it gets changed entirely into light. Yet no electricity is ever used up by the light bulb, and every bit of it flows out of the filament and back down the other wire. College textbooks are full of electricity, yet they have no electric charge! Electricity is a class of phenomena which can be stored in batteries! If you want to measure a quantity of electricity, what units should you use? Why Volts of electricity, of course. And also Coulombs of electricity, Amperes, Watts, and Joules, all at the same time. Yet "electricity" is a class of phenomena; it's a type of event. Since we can't have an AMOUNT of an event, we can't really measure the quantity of electricity at all... right?
Heh heh.

Does my description above sound stupid and impossible? You're right. It is. The word "electricity" has contradictory meanings, and I'm trying to show what happens when we accept more than one meaning. Electricity is not both slow and fast at the same time. It is not both visible and invisible.

Instead, approximately ten separate things have the name "electricity." There is no single stuff called "electricity." ELECTRICITY DOES NOT EXIST. Franklin, Edison, Thompson, and millions of science teachers should've had a long talk with Mrs. McCave before they decided to give a variety of independent science concepts just one single name.

Mrs. McCave was invented by Dr. Seuss. She had twenty three sons. She named them all "Dave."

Whenever we ask "WHAT IS ELECTRICITY," that's just like asking Mrs. McCave "WHO IS DAVE?" How can she describe her son? There can be no answer since the question itself is wrong. It's wrong to ask "who is Dave?" because we are assuming that there is only one Dave, when actually there are many different people. They all just happen to be named Dave. Who is Dave? Mrs. McCave cannot answer us until she first corrects our misunderstanding.

For the same reason, we will never find a simple answer to the question "what is electricity?" because the question itself is wrong. First we must realize that "electricity" does not exist. There is no single thing named "electricity." We must learn that, while several different things exist in wires, people wrongly all of them by a single name.

So never ask "WHAT IS ELECTRICITY". Instead, discard the word "electricity" and instead use the correct names for all the separate phenomena. Here are a few of them:

What is electric charge?

What is electrical energy?

What are electrons?

What is electric current?

What is an imbalance of charge?

What is an electric field?

What is voltage?

What is electric power?

What is a spark?

What is electromagnetism?

What is electrical science?

What is electrodynamics?

What is electrostatics?

What are electrical phenomena?

The above questions all have sensible answers. But if you ask WHAT IS ELECTRICITY?, then all of the answers you'll find will just confuse you, and you'll never stop asking that question.