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Fyrius's avatar

Can a plug be plugged in upside down?

Asked by Fyrius (14555points) November 19th, 2010
15 responses
“Great Question” (2points)

This question may be limited to Europeans. We seem to have different plugs.

If I understand correctly, a plug has one “plus” and one “minus” pin, both of which are required for the electric current to run through it. That implies the right pin must go into the right hole in the socket, since the “plus” current would be unable to transfer into the “minus” pin and vice versa.
But when I plug in an appliance with the plug upside down, so each pin is in the other hole, it still seems to work, as far as I can tell.
What’s up with that?

(I have a hypothesis, but I’d rather hear the experts first. :) )

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Seelix's avatar

Just to clear up any confusion, in North America, plugs made recently (seems to be within the last 30 years or so) have one prong that is larger than the other, making it impossible to plug something in upside down. Also, some plugs have a grounding prong that requires a socket with 3 holes rather than two. Older plugs have two prongs of the same size, but it doesn’t seem to matter whether you insert them “right side up” or not.

I’m not an expert by any means, so please excuse my (lack of) terminology :)

Fyrius's avatar

Thanks for the background info. :)

European plugs have two identical round pins. They look like this or this, and they go into a socket like this.

El_Cadejo's avatar

that seems annoying. Cant just go pluggin shit in in the dark without checking which side is pos or neg
assuming this question says you cant that is :P

misstrikcy's avatar

In the UK, our plugs have 3 pins so it would not be possible to plug them in upside down.
I’d show you a picture but, shamefully, i dont really know how to do that.
However if you wish to google UK Plugs you’ll be able to see.

El_Cadejo's avatar

@misstrikcy its really quite easy. Just find whatever image you want to link then you could just straight paste it in here, or you can make it look pretty like this

To do that you just put quotes around the word followed by a colon and then the link so like ” this ”: and just take away the spaces

misstrikcy's avatar

@uberbatman aw.. thank you. I’ll give it a whirl…

ragingloli's avatar

You can. I have done it many times.

Paradox's avatar

I’m not familiar with European outlets or residential voltages. I’m not sure if that’s a 120 volt, 210 volt or 230 volt outlet. The short answer is because it’s ac or alternating current and not direct current. There is no set polarity in ac voltage as there is in dc voltage. Alternating current is always changing it’s polarity between the + and – peaks of the sine wave every 50 or 60 hertz (frequency) which means + or – sine wave cycles per second. If this was a dc appliance trust me the device you would be plugging in would not work. I’m not great at explaining things over the internet but I hoped this helped. I used sine waves here because that is what’s generated to supply power to homes, businesses and industries.

Fyrius's avatar

No worries, your post is very helpful. :)
I think I understand now. But now I’m wondering why people invented alternating current electricity networks. I suppose there’s one obvious enough advantage; you can plug stuff in both ways.

So electric currents take the form of wave patterns? What sort of waves are they? Are they electromagneitc waves like radio waves and visible light?

Maybe I should just take my curiosity to Wikipedia. But it’s more interesting when a human being explains it. :)

Paradox's avatar

@Fyrius Well the term “electricity” can have many variables such as potential, field, charge, current, ect. I think the best way to answer your question is to know what causes electrical potential. All atoms have a nucleus that consist of protons (positively charged particles) and neutrons (no charge) and electron/s that orbit around the nucleus. When atoms lose electrons this creates electrical potential and when these electrons move from atom to atom this is called electrical current (amperage). Opposites attract so the atoms that lose their electrons want new electrons to replace the lost ones to balance them out for stability. Charged atoms are called ions. An atom can be positively charged (when they lose their electrons) and the unbalanced electrons are considered to be a negative charge.

These electrons are measured in “waves” depending on how they are generated. You can see these waves with an oscilloscope. Because the unbalanced atoms want to stablize themselves so their electrons and protons are in equal amounts this is what is considered positive and negative potential. Depending on how this electrical potential is generated it will come up in different waveforms. Sinewaves are generated usually from a rotating alternator. Squarewave ac can be made from using a digital means to oscillate from dc to ac such as in digital electronic circuits or using solid state components such as transistors and such. There is even a modified “stepwave” which is similar to a sinewave.

Electricity is basically nothing more than the motion of electrons moving through conductors such as copper, aluminum, silver, etc because these materials atoms have electrons that are loosely attached to their nucleus. This is why some materials make better conductors than others.

The best way to picture the original question you’ve asked is look at each of your two prongs on the plug. When one prong has a positive potential the other prong has a negative potential and this polarity changes about 50 to 60 times a second. In a dc circiut each prong would stay with one potential without changing polarities. DC can only induct one time so it usually has to be pulsed. AC can travel much further distances than DC and it’s cheaper to generate as well. AC can be transformed very easily.

gasman's avatar

Designating the phases of power as “plus” and “minus” (which I never heard of in the US) is misleading, because the potential difference between phases is constantly flipping polarity. Switching the leads of an AC circuit should not affect the circuit operation; voltage and frequency don’t change. Switching the leads only matters from the standpoint of electrical safety.

I remember (late 50s – early 60s) when US plugs were 2-prong & not polarized. Radios & TVs were manufactured using a so-called “hot chassis”. This means that the metal structure was used as a common ground, similar to automobiles. One of the power leads connected to the dc power supply & the other to the chassis. You could plug it in either way, so there was a 50–50 chance the chassis was at 120 volts instead of neutral / ground. Either way the device itself worked the same.

As a lad I got shocked while tightening antenna screws on the back of our tv set, using a metal implement while standing barefoot. On another occasion the kid next door told me touch the metal screw on the back of his radio—shocked again. Cue Beavis & Butthead laugh. Btw in both cases a modern GFI would have protected me, even with the non-grounded systems of the day.

Today metal chassis are seldom used, or when used then—for safety— it’s connected directly to the ground pin on the power cord, which is electrically connected to true ground at the service panel. So if you touch an appliance’s metal case while in contact with (say) a cold water pipe, no current will flow & no electric shock occurs.

Not all electrical appliances require this precaution. In many cases power first goes to a transformer such as a “wall wart” or a lamp socket or other device that’s electrically isolated from the user on both sides of the alternating voltage. There’s no path for current to take even if the user is grounded. Electrical code dictates which appliances are safe for which kind of power plug.

Note on terminology: ground in US is the same as earth in UK. Power is mains.

ragingloli's avatar

DC involves the actual transport of electrons over the conducting line, which is the reason it became so infeasible over greater distances, requiring lines of massive diametres and repeater stations throughout the distance covered.
AC does not actually transport electrons, it just moves the already existing electrons in the conducting material back and forth.

Paradox's avatar

@ragingloli Actually there are voltage drops for both AC and DC voltage. The voltage drops are the same for both using Ohm’s Law. This is in my line of work, I’m no engineer but I do have to know these basics because I actually physically do this stuff for a living and my line of work requires me to make these types of estimations. The real reason AC is used for long range power transmission is because it can be easily stepped up to the high voltages necessary to make up for the overall impedence of the long range cables. AC can easily be transformed to step up or down. DC can only induct one time through a transformer or other type of inductor. Because AC is nothing more than DC changing polarities at a set frequency it can be easily transformed. DC can be transformed for the record but it must be pulsed. On a side note there is debate now as to whether the moving electron theory is even entirely accurate but I’m not on that end of it, I troubleshoot electrical problems in a hands-on manner for a living. I will leave the physicists and engineers battle that one out.

@Fyrius Perhaps the best way to explain the term “electricity” is by describing different concepts of it. This is hard to explain and even many electricians can’t accurately explain it and I’m not saying I’m great at it either but I will try. First there are magnetic fields which are the invisible force which surrounds a permanent magnet. Second there is a phenomenon known as an “electric field” which is related but different from a true magnetic field. They are both similar because both forces have lines of flux and can attract/repel objects. Electrical fields are not magnetism but voltage.

Think of voltage like this: Voltage starts/or is nothing more than a generated e-field. Voltage is way of using numbers to measure an electrical or electrostatic field (e-field) such as volts per centimeter. A stronger e-field has more volts per centimeter than a weaker field. Think of the e-field as a hill and voltage being different elevations on the hill. Voltage & e-fields are the same thing basically. The term “electro” used in the word “electromagnetism” really means “voltage” or voltage current since the flow of electromagnetic energy (from the e-field) in a conductor is half current and half voltage. An object by itself does not have voltage. Voltage is all about measuring distance from an e-field or power source. You can have a 12 volt car battery and at the + terminal you would have 0v but at the – terminal you would have -12 volts and vice versa.

As far as describing electrical potential energy what this really means is the potential for energy and not the e-field or voltage itself. You need electrical charges before you can electrical potential to begin with. Remember the hill I mentioned above? Entire hill=e-field/different elevations on the hill=voltage and think of potential as being the boulder on top or other set point on the hill. The boulder would be say the – and the bottom of the hill (or lower point) would be the +.

Now about current, one thing to remember here is that current is not voltage. You can have current with a lack of voltage, example: short out a battery or coil. You can also have voltage without current, example: an unused battery or an unused outlet has a live e-field or voltage but no current because there is no load. Voltage or the e-field can be compared to hydraulic pressure in a line because there can be pressure without flow. Electrical current is comparable to the flow of the volume of flowing hydraulic fluid. The pressure used in mechanical terms however is still not the same as electrical pressure which doesn’t really exist but voltage charges repelling/attracting one another. Electrical pressure is really nothing more than a hypothetical term used to describe charged electrical fields. The stronger the e-field there will be more voltage per centimeter which in turn will allow for a greater electrical potential.

As far as radio waves go they are nothing more than electromagnetism that is generated by an e-field source on a set frequency. You can get shocked from radio waves as well if you touch the antenna or emmiter or even by being near but not physically touching the radio wave source itself if the e-field is strong enough. I’ve already had my jaw twitch and such just from being near the radio waves when working on top of material silos with radio wave sensors. I hope this helped you understand the basics but I’m not great on writing or explaining what I know. Hope it wasn’t confusing.

Fyrius's avatar

Again, thanks, that was very helpful.
I think I understand now. :)

gasman's avatar

@ragingloliDC involves the actual transport of electrons…” There’s a common misconception that electrical current is the same as movement of electrons, when in fact they are separate phenomena. Electrons, as freely mobile negative charge carriers in metals, actually do move through wires when current is flowing, but only at a slow drift rate on the order of a few centimeters per second. Electric current, on the other hand, represents the flow of charge through the wire, which occurs at close to the speed of light. A voltage applied to one end of a wire appears at the other end nearly instantaneously—traveling almost 186 miles each millisecond.

There’s an analogy comparing the speed of sound with wind speed. Sound waves are carried by collisions of air molecules moving very fast, while the bulk flow of air molecules (which we call wind) is much slower. In the case of electrons (unlike air molecules) electric charge is a property distinct from the electron’s other quantum properties such as position or momentum.

While AC is more efficient in general for power transmission, I’ve heard that above some (high) voltage then DC is more efficient over long distances. I’m not sure, but this might be due to radiation loss along the length of the line that occurs with AC but not DC.

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