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Earth & neutral connections

  1. Mar 5, 2006 #1
    can any body tell me what would happen if i took apart a computer power supply. connected the earth wire to the neutral wire. reassembled the power supply and connected it to an un earthed outlet having only live and neutral. (the two pin outlet)
  2. jcsd
  3. Mar 5, 2006 #2


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    Well if the hot and neutral wire of the outlet were reverse wired, you could kill yourself by touching the computer case (while your body is earth grounded).
  4. Mar 9, 2006 #3
    I didnt Ask About the Hot N the Neutral Wire
    I Asked About The "Earth And Neutral Wire"
    Please open ur ewyes And then reply
  5. Mar 9, 2006 #4


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    saad: He DID read your question, and he was giving a specific example of what MIGHT happen afterwards. He was saying that if you effectively eliminated the 3rd prong as you described, and reversed the remaining two prongs when plugging it in, then you have eliminated an important safety feature.

    dlgoff...why is there a danger when the two prong plug is plugged in with the reverse polarity? Can you elaborate please? Is it because "neutral" is always grounded to the device (casing) whereas you are earth grounded, and if you eliminate the third prong, your casing is NOT also earth grounded? Then I guess if you plugged it in the wrong way, neutral becomes hot, meaning your casing becomes high instead of neutral, and yet you are earth grounded, so touching your computer would...have an undesirable outcome!!! lol. Am I right?
    Last edited: Mar 9, 2006
  6. Mar 9, 2006 #5
    earth ground is ment to act as a shunt if the case goes live, neutral is a floating ground. if you reverse hot and neutral and you have a badly wired piece of equipment and touch something that is grounded your gonna wish you hadn't.
  7. Mar 9, 2006 #6
    Not really mugs. The only difference between ground and neutral is that one is meant to carry continuous current and the other is not. The neutral is in no way floating. The ground and neutral are hooked to the same place at the service entrance. There are exceptions such as mobile homes and sub-panels where the service entrance has an isolated bar for the neutral, but where trailer house is 'plugged in' the neutral and ground will end up connecting together.
  8. Mar 9, 2006 #7


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    I think what mugs was thinking is that you might find a potential on the neutral wrt earth groung. That is, since there is a little resistance in the current carrying neutral wire.

  9. Mar 14, 2006 #8
    what if u connect the case to a neutral wire? Wouldn't that protect you as if it is connected to a ground wire?
  10. Mar 14, 2006 #9


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    Why would you want to tear up your PS. Just get a "cheater" that is a 3 to 2 prong plug adapter. They generally have a screw for a separate ground wire but I have never used that feature and I am still alive.
  11. Mar 14, 2006 #10

    Ivan Seeking

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    btw, technically the difference is that a neutral is grounded but normally carries current. A ground only carries current in the event of a fault. Without a ground, the danger is that you could receive a dangerous or even deadly shock in the event of a fault. Yes, the neutral is grounded but it is live to the internal circuitry of the ps. So if you ground using the neutral, any break in the neutral wire between the ps and the breaker panel would result in a live case.
    Last edited: Mar 14, 2006
  12. Mar 14, 2006 #11


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    Saad, if you're going to mess around with this stuff, even just using the cheater that Integral suggested, I would seriously recommend that you install a Ground Fault Circuit Interruptor outlet either in place of the one that you're using or 'upstream' from it. They shut the current off in event of you trying to fry yourself.
  13. Mar 14, 2006 #12


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    It would still work. Single insulated ungrounded devices worked for years.
    Oh yeah, lots of people got electricuted, too.

    Any impedance between your PC and the ground at the service entrance would raise the potential of the case of your PC.
    If you lost the neutral connection, the case would be at the same potential as the input. If you touch it and you are grounded, it will fry your ass. :yuck:
    If you use an un-polarized plug and plug it in backwards (as dlgoff noted), the case will be hot right off the bat and, if you touch it and you are grounded, it will fry your ass. :yuck:

    Open your eyes and don't do this.
  14. Apr 14, 2006 #13
    Whenever I connected the white and green together, the GFI tripped and nothing worked. Of course, my cord (white, green and black wires) was coming through a GFI-protected outlet.
  15. Apr 16, 2006 #14

    I suspect you as asked about connecting the safety ground to the neutral because there's no green wire in your outlet. Like the other guys in this string said, if you connect the neutral to where the green was connected, it'll be tricky making sure you don't get a shock from the case, for example, if somebody wired the outlet wrong years ago. It'd probably be easier to just cut off the third prong on your power cord or don't connect the green-wire circuit to anything. That's the way it was years ago when I started in electricity. They also sell 3-to-2 prong converters that you could use to adapt your computer power to your 2-prong outlet.

    I had an experience one time with these 3-wire plugs on the water heater for my horses. In the winter I have to put a heater into the horse tank, otherwise, the water will freeze and my horses would be VERY unhappy. This one winter, I'd just bought "Fussin' Miz" a high-strung TB mare. She shared the water tank with "Spalding", a dutch warmblood gelding.

    The day after I'd put in the heater, Miz was really "fussin". She was upset about the water; she wouldn't drink and kept running around the pen. While I was watching, Spalding (just like he was going to explain the situation to me) walk to the water tank, lowered his head as if to drink, but hesitated. Then raised his head a little, then plunged his nose into the water and began to drink. If the tank were slightly electrified, I could imagine that he'd be shocked only at the instant his muzzle touched the water; once submerged, the current density through his muzzle, body, etc. would be greatly reduced.

    So, I got a meter (back then it was a D'Arsonval-type). With one probe in the mud, one in the water I got a slight deflection on the most sensitive ac scale. That would be some micro-amps, which I suspect my very sensitive TB mare could feel.

    So, I took out the heater, and she drank--lots.

    The sheath of the heater (in contact with the water) is connected to the green wire. Neither the neutral nor the black wire are connected to the sheath, of course. (They are connected to resistance element.) In the electrical service to the barn, the green wire was connected to the neutral. I figure there must be some small amount of current passing through the soil at the club where the horses live. I believe overhead distribution lines can induce some current. Also, the poles that hold up the wires all have ground wires. These are connected to the neutral up on top of the pole, and to a ground rod at the base of the pole.

    In the winter, when lots of tank heaters are operating for the horses, there could be 30-40 amps in the overhead wires. Over a stretch of 5-600 feet, an IR drop of several volts could be developed.

    where: E = 1-10 volts
    I = 30 - 40 amps
    R = wire resistance (approx. 0.3 milli-ohms per ft.)

    This value of E, I'd expect, would be the Thévenin source term.

    I didn't feel any shock when I put my hand in the water, but the skin on a person's hand is a lot tougher that a horse's. Also, I was standing right near the tank; Miz was standing right near the tank too, but in this configuration her hind legs were several feet from the tank. In the distance between her hind feet and the tank the electric field in the soil (produced by the ground current) could develop plenty more potential than my body would.

    To fix the problem, I installed another ground rod near the tank and disconnected the green wire from the neutral in the service box. Then I connected the green wire of the heater to the ground rod--nothing else. That worked for many years. Eventually, I got "Salute", a thoroughbred gelding, and had the same problem. To fix it, I had to install another ground rod on the other side of the tank and connect it to the green wire which is connected to the original ground rod.

    Attached Files:

    Last edited: Apr 16, 2006
  16. Apr 17, 2006 #15
    I just have a problem seeing what's the difference between hot and neutral. After all, there's a reason it's called potential difference. Switching between hot and neutral just changes the phase of the AC by 90°. And the rectifier in a power supply doesn't care about phase. Neither does the filaments in your lighbulbs or your space heaters.

    I only know a few European countries (UK and France) where the plugs force you to put them into the outlet a certain way (due to earth prongs). Otherwise it fits in both ways, indiscriminate of hot and neutral position. This also goes for the earth plugs, as earth is connected through strips of metal on both sides of the plug.
  17. Apr 17, 2006 #16
    Wow. Now THAT'S alot of misinformation. The neutral is the center tap of a transformer. Each end of the transformer is what is referred to as each side of the line. It is neutral because it is 'central' on the transformers windings. 90 degree phase? I don't know where you get that. Phase always has a reference to another phase. Residential electrical service is single phase. You get 2 wires that have the voltage 180 degrees out of phase with each other, but it is still single phase. The center tap of the transformer is grounded.
    Last edited: Apr 17, 2006
  18. Apr 17, 2006 #17
    (I believe it's 180º between hot and neutral) Here in the US, at least, it's called "neutral" because its connected to the earth ground in the entrance service box. Therefore, you won't get a shock when you touch it (because it's already grounded). The other one (hot) will give you a shock.

    Besides France and UK, the outlets slots in the USA are different length, so "polarized" 2-prong plugs will go in only one way. (Polarized means one prong is wider than the other). Most cords in the US have three prongs, however: 2 for power and one for earth ground. When you look inside of the outlet box, you see three wires of different color. The color standard is: black=hot; white=neutral; green=earth ground.
  19. Apr 18, 2006 #18
    i agree with gschjetne. what's so significant about swapping hot and neutral
  20. Apr 18, 2006 #19
    Yeah, that's a good point. If someone wired your outlet incorretly, interchanging the black and white wires, nobody'd ever know.

    Two-wire cords are connected to double-insulated appliances, so you'd never get near either the hot nor the neutral. Three-wire cords have the earth ground connected to the case, so you wouldn't be shocked even if the "supposed" neutral shorted-out to the case.
  21. Apr 19, 2006 #20
    Belive me you would know. The polarized prongs on (for example) a lamp make sure that the larger part of the bulb contact (the screw cap) is attached to neutral. That means that if you change a bulb without unpluging the lamp all you will be able to touch while unscrewing the bulb is the neutral threaded metal bit. If the hot and neutral are backwards in the plug you coudl switch the lamp off and still touch live 120v because the outer screw in part of the bulb woudl be live.

    Same goes for the computer case. The neutal and hot are in such away that even if you really tried all you can touch is grounded or neutal metal. If you attach the neutral to ground but the receptical has hot and neutral switched you get the same senario as most of the other post have said. The case will be 120v above ground and the "hot" wire will be at 0v.

    I have seen this done and experience it, it's not safe or fun >_<. Call an electrician to give you a grounded receptical there, or you can MacGuiver it and use a 3 prong extention cord to the nearest grounded receptical.
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