Current thru green wire ground

Discussion in 'General Electronics Chat' started by marcf, Mar 25, 2015.

  1. marcf

    Thread Starter Member

    Dec 29, 2014
    136
    19
    I realize causing current to flow thru the green wire ground in 120vac systems is a big no no, but....

    I recently saw a schematic diagram that may lead someone who does not know better to do this by connecting the project up to a 3 wire wall outlet.

    What are some of the consequences of doing this. I am not an electrician. Just wondering.
     
  2. #12

    Expert

    Nov 30, 2010
    16,248
    6,745
    In American homes, the green wire is connected to the white wire at the circuit breaker box. Amateurs will never realize they violated the safety scheme until they get hurt. This is why electricians were invented.

    That being said, no matter what schematic you saw, it can not be fool proof. There is no limit to the ingenuity of fools.

    More specifically, the current going through the green wire will cause a voltage to be developed on it. That voltage will be present on the metal case of anything plugged into that circuit. It usually only causes a tickle, and only if bare feet on concrete. The problem is: At the moment the circuit breaker should be blowing, the barefoot boy is getting killed.
     
  3. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    In my country we have 240 V 50 Hz single phase distribution to outlets around our homes. Active, Neutral and Earth are available at any outlet. The MEN (Multiple Earthed Neutral) system is widely adopted.
    If I build any apparatus inside a metal enclosure & which is mains powered from such an outlet, I always bond the exposed metallic parts to Earth and ensure an intentional contiguous Earth connection is made between all exposed metal surfaces irrespective of whether they are mechanically fixed together or not.
    I'm not violating any code - rather I'm adhering to it.
     
  4. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
    2,778
    1,211
    The EMF gradient set-up along the 'ground' line during high/over current events will result in potentially dangerous G to (environmental) 'earth' offsets --- Hence the convention of N to G connection solely at the load center... Of course this scheme (IMO, shortsightedly) addresses drops owed to resistive impedance only.

    Best regards
    HP
     
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    the American wiring system also has the white wire isolated from the green ground wire in some applications. hospital wiring, for instance.. and wiring using GFCI ( ground fault circuit interrupters). hospital wiring requires isolated grounds, and gfci sees the current difference between white and green wires to detect ground faults.
     
  6. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    One purpose of the earth is to deliberately carry sufficient fault current to activate the disconnection devices (fuses, breakers, whatever).

    All earths should be sized to accomodate this current.

    You should look up the terms
    Prospective Fault Current
    Prospective Short Circuit Current

    http://en.wikipedia.org/wiki/Prospective_short_circuit_current
     
  7. marcf

    Thread Starter Member

    Dec 29, 2014
    136
    19
    Thanks for the input.

    I assume if the wiring was properly done in the first place and if the green wire ground were the same gage as the white wire neutral and if everything was properly bonded in junction boxes, etc., this fault could exist without being discovered and GFIC devices would operate. (they are color blind and can't tell green from white).

    However.. if an open circuit occurred somewhere in the return path of the green wire, someone or something could compete the path to the neutral buss of the load center by coming in contact with a metal junction box or outlet cover and very bad things could happen.

    I have heard that more electricians are electrocuted because of grounding faults than are killed coming in contact with 'live' wires.
     
  8. Stuntman

    Active Member

    Mar 28, 2011
    181
    47
    I think you have the wrong idea if I am interpreting this statement properly. Yes, you could run AC devices between hot and ground (green wire, not white neutral wire), but this is reckless and could cause injury. I have seen this erroneously done more than once.

    A GFCI protected outlet, breaker, device, etc. triggers when it sees a discrepancy between the current in the black wire (hot) and the white wire (neutral). So no, if you had a device powered between hot and ground, a GFCI would trip the moment you turned the device on.

    Yes, but I would say more accurately, a body could touch the metal junction box and complete a circuit to ground, not to the neutral buss (which is also tethered to ground). And you won't necessarily need an open circuit to do so. As long as you provide an "easier" path to ground that the length of wire and grounding rod, why wouldn't the electrons use your body to drain current instead of the properly wired equipment ground circuit?


    I almost worry where these kinds of conversations go. AC wiring is not trivial, and there are a plethora of codes and methods to keep people safe. Don't get a false sense of knowing what is okay and not okay. I've seen WAY too many botched wiring jobs in my lifetime, please be cautious.
     
  9. Mike33

    AAC Fanatic!

    Feb 4, 2005
    349
    25
    I saw this post, and what I'd really like to know is...do you have the schematic that led you to believe that current would flow thru the ground? Love to see it, mostly to either be able to dispel that fear, or to be able to yell "WOAH!!!!!"

    Like Stuntman said...utmost respect for line current should always be used, and it's good you're questioning what you saw.
     
Loading...