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ben's avatar

What does grounding an electrical plug actually do (and why do we ignore it)?

Asked by ben (8006 points ) December 17th, 2009

Take a look at Apple laptop plugs: The two different ends plug into the exact same adapter, but one has three prongs and one has two. And anyone can buy those two-to-three converters that seemingly unground the third prong.

What’s going on here? How does it work, and why is it both important enough to be kept as a standard, yet no one ever thinks twice about ignoring it?

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19 Answers

nope's avatar

I’m not an electrical expert by any means, but my understanding is that if something does go wrong in your connection (a short circuit or something), then the ground gives the outgoing electricity another place to go…sort of like when on a dam they open the floodgates to prevent flooding when there’s too much water. This can help prevent a fire. At the end of the day, the ground is essentially connected to the same place as the neutral wire.

jrpowell's avatar

My brother in law is a licensed electrician. I asked him a similar question.

Basically, stuff is grounded in the event that a wire touches the case. Like in a computer. The metal case will zap you if a wire comes loose and hits the case. Grounding that will not hurt you. Ungrounded and you will get a shock.

Plastic stuff is different. It simplifies things. Electricity isn’t going to transfer through the plastic housing.

I’m sure that he dumbed it down for me. But that was the jist.

global_nomad's avatar

I don’t think the third prong has anything to do with something being grounded. All I know is that everything in the States is grounded. Washing machines, dish washers, dryers etc…If they are not, you will know, trust me you’ll know. We used to live somewere where nothing was gorunded and if you did not wear rubber-soled shoes or slippers while opening the dish washer you would get a nasty shock. Jesus, it made my whole arm go numb for a bit. I learned never to open that thing, along with the washer and dryer, barefoot again.

jerv's avatar

@global_nomad Not everything is automatically grounded. For instance, most handheld power tools are not, so without that ground plug you could get a nasty shock from, say, a power drill. Had that dishwasher of yours been grounded properly, you might’ve gotten a tingle but not a full-on 120-twitch. Trust me, I’ve done the 60-cycle-shuffle quite a few times ;) (US Navy ships are wired a little differently than a house is.)

@johnpowell Exactly correct!

engineeristerminatorisWOLV's avatar

The advantages of grounding are,
1.It helps to ground the leakage current.
2.Helps in better voltage regulation.
3.Protects shock hazards during short circuits
4.Grounding lightning strikes
5.Provides safety to human lives and material.
The basic reason of grounding the plug or using the 3 pin plug is,to ground the leakage current in case of a short or open circuit and provide safety from electrical shock.When the hot wire get’s connected to any metal body part of the equipment due to insulation failure,you have all chances of getting your head shaken off for a moment.It might land you in more severe trouble when you touch the part that is charged.In that case, your body will ground the charge and no need to ask how it feels at that moment.The third wire is connected to the body of the equipment with tight connection.Hence,whenever the equipment get’s charged,the charge is grounded through the ground wire.
Ground wire provides better voltage regulation to your equipment and might increase it’s longevity.Securing your life with an extra ground pin is not a bad deal at all.Make sure that happens or else, make sure the equipment body is grounded.

jerv's avatar

@engineeristerminatorisWOLV Some people are more worried about convenience than safety though. Yanking out the grounding plug to use something in a 2-prong outlet is pretty easy, but so is getting in your car and driving off without fastening your seat belt. Both are perfectly safe as long as you don’t have an accident. However, if something does go wrong, you have a better chance of avoiding injury/death by using stuff as-designed.

sndfreQ's avatar

I’ll try and add to @engineeristerminatorisWOLV‘s explanation. Now keep in mind, I got this explanation from ART SCHOOL, so don’t fault me if it’s not totally accurate!

“Ground” or “Earth” as it’s called in the UK, is the path back into the earth (literally), which is an alternate (and shorter) path from the circuit back to the source that created it (the power plant). In theory, when electrons flow through a closed circuit, some electrons that are unspent by the load have “no place” to go, but back to the source (completing the circuit). When they do, they will always find the quickest physical path back to the source.

The ground plug (the 3rd pin) in a house is wired to a common wire ground that actually is wired to a copper spike next to your electrical service; that spike is driven into the earth a couple of feet, and provides that “shorter” path back into the earth, back to the source. As electrons have no speed limit (well, basically the speed of light), what happens with the ground is that the “extra electrons” not used more readily flow into the ground pin, and down to the ground spike, and back to the source of the power, if they are unexpended by the “load.”

When there is a short circuit, the extra electrons don’t flow into the ground, they remain in the system and “charge” the metal surfaces and electrify them. When you touch that surface, you create an additional “load” and your body becomes part of that circuit (because flesh/water is a good conductor of electricity). The exit path out of your body goes down to the earth, which in turn goes through the earth back to the source of the energy (the power plant).

In plugs with only 2 conductors, there is no “extra” dedicated path into the earth, so the free flowing electrons stay in the system of the two wires, and eventually find their way back to the source via those two wires. In the case of 2-to-3 pin adapters, as in the power supplies of computer adapters, the 2-pin plug is sheilded (meaning, there are two wires for hot and neutral, but they are wrapped by a shield that is usually a foil wrapper around both wires). The foil wrapper then gets wired into the ground plug and then you have a complete path to ground.

Ground lift adapters defeat the path to ground, resulting in the two-pin scenario; if any metal in the housing/chassis of the appliance touches the wires, then you have a case where the device’s surfaces can be electrified again, which is why it’s not recommended to break off or defeat the purpose of a 3-pronged plug with those adapters. You’ll notice that the ground lift adapters often have a little hang-tag at the bottom; that metal tag is intended to be wired to the junction box of your outlet, as most J-boxes are connected to the house ground.

engineeristerminatorisWOLV's avatar

@jerv : I’d agree upon that.People are more bothered about convenience and just a way to reduce cost on the cost of their lives.

@sndfreQ :You are absolutely correct on that one.Many a times charges also stay in the system as a result of induction or due to eddy currents.It happens incase of equipments that have a transformer connected in series with it.In Power lines we also have a ground switch.Even opening the circuit breakers and isolating the lines is not safe enough.You have to close the ground or the Earth switch so that the extra charge due to inductance drains to the ground.A 220KV power line stores enough charge due to it’s inductanec that’s lethal enough to burn a full grown elephant into ashes when the power supply is not there.Grounding is equally important during generation,transmission,distribution as well as during consumer usage.

sndfreQ's avatar

@engineeristerminatorisWOLV burn an elephant to ashes? Holy $hite! I guess what fascinates me just as much is the fact that the electrons flow into the earth, and move at the speed of light back to their source of origin (the power plant)...that factoid still baffles me to this day!

You hear that Ben?!! Don’t f- with those ground plugs!

The context for learning this for me was the fact that in audio electronics those free flowing electrons manifest themselves as noise-white noise and 60-cycle hum, in particular…bad bad bad for Audio!

engineeristerminatorisWOLV's avatar

Indeed,
Check this out.
http://www.youtube.com/watch?v=D7rVT83wPG8
See what happens when they suddenly open the isolator without closing the breaker.Charges travelled in air for a moment.Could you imagine the potential that could discharge ions in air and that too through such a large gap?
Electricity is a killer beast and we need to take it the right way out.
.

Another advantage of grounding is,It reduces noise in RF communication systems.

sndfreQ's avatar

W-O-W that is both terrifying and impressive! Lurve to you @engineeristerminatorisWOLV

engineeristerminatorisWOLV's avatar

Thanks,sndfreQ.Lurve to you too.

cornbird's avatar

It is to provide a way for excess fault current to travel safely.

jerv's avatar

@engineeristerminatorisWOLV There is this electric dragster called White Zombie. One time, the controller stuck so that it was at full power so the driver had to pull the emergency disconnect after leaving a pair of 550-foot skid-marks that wore flat spots on the front tires . Well, at upwards of 2000 amps (yes, two thousand), you can guess what sort of light show happened when he pulled the plug!
However, it’s nothing compared to the story of how John Wayland earned his nickname “Plasm Boy’.

engineeristerminatorisWOLV's avatar

@cornbird.:Exactly

@jerv : Thanks for the link.Just gone through the it and I’m impressed by it’s specifications.Don’t know if we could get that off the race track and make it hit the freeways.

jerv's avatar

@engineeristerminatorisWOLV The White Zombie is street-legal. That license plate is not for show; it’s a vanity plate with valid tabs. However, like many race cars, it makes a few sacrifices for the sake of performance; range, upholstery, back seat…
BTW – Have you taken a look at the Tesla Model S ?

engineeristerminatorisWOLV's avatar

Yes,I like the Teslas and have read a lot about these,but looking at this model that’s shown in the link,it’s hard to believe that it’d be a 7 seater one.It looks like at max 5 to me.How do they accomodate 7 in that.Do they open the rear lid to stuff in some kiddos out there?

jerv's avatar

@engineeristerminatorisWOLV I have seem some station wagons with rear-facing seats in the rear “cargo” area in the past so I imagine that that is how they handle the third-row seating. And with a second “trunk” under the hood, I think you could fit more than 2 ;)

engineeristerminatorisWOLV's avatar

@jerv : Got it now. Thank you.

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