Shorting neutral to Earth confusion

  1. what will happen if i short neutral ac outlet wire with earth? please see the figure if you have any confusion.
     

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  2. jcsd
  3. davenn

    davenn 3,975
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    neutral and earth are usually connected at the house entry buss board anyway

    Dave
     
  4. OldEngr63

    OldEngr63 718
    Gold Member

    The answer is nothing, provided that everything was properly wired and that the power source generator was grounded. This covers most cases, but certainly not all of them.

    With a Y-connected generator, it is easy to ground the center of the generator, and it is common practice to do so. With a delta-connected generator, there is no center point, and consequently such systems often have not grounded neutral (the happens in the US Navy in places).

    If in doubt, measure the potential between the two wires before you short them.
     
  5. nsaspook

    nsaspook 1,214
    Science Advisor

    With a ground to neutral connection at more than one place (at the main power panel) on a normal house AC system the risk of the ground connection becoming a current carrying connection increases. The voltage difference between ground and neutral might be several volts at a distant power plug on a circuit that draws significant current (due to voltage drops from line resistance). If the connection is made at the distant device a GFCI device will trip due the unsafe condition if you are lucky. High currents passing in grounding circuits can be dangerous because they are designed to handle fault currents that only last a short time and are not normally current carrying conductors.

    http://en.wikipedia.org/wiki/Residual-current_device
     
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  6. NascentOxygen

    Staff: Mentor

    Sometimes neutral and active get swapped around, accidently, as can happen when someone makes up their own extension cord, or replaces a broken plug, etc., and in the process gets the wiring reversed through carelessness. Many appliances [seem to] operate satisfactorily despite this, though they can be an electrical hazard to the user.

    You can picture the scene were you to unknowingly connect the lead marked "neutral" to ground in the event of it being one of those botched wiring jobs. :eek:
     
  7. there is a concern it that if there is a bad connection (Break) in the Neutral somewhere the Neutral would become live creating a short circuit (hopefully blowing the fuse )
     
  8. How do you figure? Where did you come up with this misinformation?
     
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  9. SteamKing

    SteamKing 9,899
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    It's like grounding a ground wire.
     
  10. Baluncore

    Baluncore 3,017
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    A “Multiply Earthed Neutral” MEN system is often used to distribute three phase power. The local transformer has a star (or Y) wound secondary. The centre connection is called neutral and is earthed at the transformer, and usually at every second pole. So it takes 4 wires to supply customers in one street. Single phase power is provided to a customer as a two wire line. One is neutral, the other is active. When they enter the customers meter/fuse box they meet the customers buried earth line which gives the three wires available at outlet sockets. There is only one connection (it is in the fusebox) where the earth is joined to the neutral. At no other point should they connect.

    Earth leakage detection, AKA residual current detection, compares the current flowing in the neutral and active wires. It does that by winding them together on a magnetic core. Their currents should be equal and opposite so there should be no magnetic field in the core. If a magnetic field is detected then the circuit is quickly broken automatically.

    Any current that returns through the earth rather than the neutral will trip the system because the neutral and active currents are no longer equal and opposite. That will happen if you connect an earth to a neutral on a circuit that is drawing current since part of that current will flow through the earth wire. If no current is being drawn while the earth to neutral connection is made it will not trip.

    For a street with several single phase customers, each will have their own grounded earth and a common neutral for the street. But their active will be taken alternately from the three phases available. That will tend to balance the load on the phases in the street. So your two neighbours will have a different active phase. Your neighbours neutral, active and earth are all different to yours so they cannot be paralleled.
     
  11. Where I live we have a multiple earth neutral electricity system. With that if you short the neutral to earth some of the current will return to the Neutral through the earth ( through the earth wire attached to the appliance and then through the link between the neutral and earth bus bars in the switch board ) so that if there is a RCD on the circuit it will trip as the current in the Neutral and phrase will not be balanced. If there is no RCD and no other faults it will keep operating with some of the current returning through the Neutral and some through the earth wire. There are differing electricity supply systems , I don't know about where you live.
     
    Last edited: Aug 14, 2013
  12. Yeah you are right I'm wrong , for the case of the appliance to become live there would have to be both a bad earth and Neutral and it wouldn't blow any fuse.
     
  13. Evo

    Staff: Mentor

    Stop me if I am wrong here. But in English the term is GROUND not Earth. I remember years ago my Toyota car manual said to EARTH one end of a connection. They meant GROUND one end.

    I think we should be correcting these errors if they are born originally from translation errors.

    I look at this

    http://forum.allaboutcircuits.com/showthread.php?t=6050

    and http://wiki.answers.com/Q/What_is_the_difference_between_earth_and_ground

    http://ecmweb.com/nec/grounding-bonding-definitions

    My dad was an ee, and he never taught me to use earth instead of ground. (he's been dead for over thirty years, so I can't ask him) Is this just an acceptance of the misuse of the translation, or is this something that just wasn't in common use 45 years ago, that has a different meaning now, (earth doesn't mean ground)?

    I find it confusing. Please help me out here. Is it correctly grounding, or is earthing something different from grounding now? And if it is different, what is the difference?

    I'm beginning to think this stems first from bad translation then becomes literal... Any old folk out there that know what I am saying? I know my dad's old books never said earth, I read them all, he made me do all of the exercises.

    Thanks!

    well, lost all of what i just posted thasnks to chrome crashing again.

    Anyway.

    So it is the result of an old translation error.

    http://electricalnotes.wordpress.com/2012/09/07/difference-between-bonding-grounding-and-earthing/
     
    Last edited: Aug 15, 2013
  14. Baluncore

    Baluncore 3,017
    Science Advisor

    What Toyota really meant was “connect it to the chassis”.

    I have always interpreted the meaning of Ground and Earth as being synonyms.
    My guess is that the terms arose about 100 years ago when radio (or wireless) used long wavelengths (or Low Band). At those wavelengths a dipole was not possible, so the local Earth (or ground) had to be used with the aerial (or antenna).
     
  15. dlgoff

    dlgoff 3,149
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  16. russ_watters

    Staff: Mentor

    Yes, but I believe in Britishese, the term is "earth".
     
  17. Evo

    Staff: Mentor

    Yes, that was the case.


    Thanks!

    Yes, and they call cookies "biscuits" and french fries are "chips".

    Thanks all of you, I was wondering if terminology had changed or if it was just that 40 years ago I was only exposed to American books and with the internet, terminology became mixed, it seems the latter is responsible for a lot of the mixed terminology I see now. This is what happens when you stop learning and then pick up after 40 years.
     
    Last edited: Aug 15, 2013
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  18. Naspook said, "If the connection is made at the distant device a GFCI device will trip due the unsafe condition if you are lucky."
    As others explained, that could happen if part of the return current went through ground rather than neutral.

    But the opposite is scarier: If an unlucky person touched a life wire at the remote site, current would flow through them to ground (or earth if you like). But as ground and neutral are connected there, the harmful current may return through the extra earth-neutral connection and through the neutral wire. After all, a solid copper neutral wire likely offers a path of less resistance than traveling through the soil. And the remote grounding rod might have a better connection. That means that the GFCI will detect matching opposite currents on life vs. neutral, and fail to trip.

    Does this scenario make sense? If yes, then I'd be safer disconnecting the remote neutral-ground short.
     
  19. If someone disconnects the ground while working on the wiring they could end up getting a voltage fed from your incorrectly wired outlet. Generally the green wire is always at 0V potential. Making it easier for that to be untrue is always a bad thing.

    BoB
     
  20. Thanks rbelli1. I'd hope that the person working on the wiring would know what they're doing, and turn off power anyway. With the GFCI I'm primarily aiming to protect the normal user from damaged or worn appliances, maybe held in wet hands. BTW, there's no ground wire at the remote barn -- it's all old 2 conductor wiring & 2 prong outlets.
     
  21. In a normally grounded system there could be faults that cause multiple branches to have one ground segment. For example if your panel has a left and right hand ground bar and they are isolated types. Pulling the jumper between them could have one half of the installation with a floating ground. Any faults to ground on that side will cause a dangerous voltage on the ground. However I agree in that case the whole panel should be de-energized.

    This clearly is not the case you are talking about. You are starting a totally new ground domain. You should consult your local codes and a qualified electrician.

    BoB
     
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