Ground v. Neutral Question (Again)

Discussion in 'General Electronics Chat' started by DeanFran, Feb 25, 2013.

  1. DeanFran

    Thread Starter New Member

    Feb 25, 2013
    My boss and I, (neither of us electricians or EEs) have been arguing about neutral and ground. Specifically how to correctly install a sub-panel. I know that the NEC code states that the ground and neutral are only bonded at the main panel and in sub-panels they must be isolated. He argues that you can isolate all you want, if they are bonded at the main panel, they are in essence bonded throughout the system. I understand that the neutral is a return path from all loads to the power source, and that chassis ground is just that, but I can't seem to win this argument with him, though I know they are two different things. Can anybody take the time to help me better understand this concept, so I can finally win one argument with this guy?
  2. #12


    Nov 30, 2010
    Neutral is a current carrying ground. Bond never carries current except during a fault condition. That still doesn't mean you can win.
  3. crutschow


    Mar 14, 2008
    You boss doesn't understand the big picture. The ground is for fault protection. The neutral is to carry load current. You don't ever want the ground to carry load current and that's why they can only be connected together at one point. If you bond the ground to neutral at a sub-panel then some of the load current at that point will likely travel on the ground wire (depending upon the relative resistance of the two wires) and that's a no-no. Also connecting them together at the sub-panel means that effectively you only have one common neutral/ground connection between the sub-panel and the main panel, not two separate connections as required.

    So you win the argument (unless he's one of those that can never admit they are wrong). ;)
  4. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    Star Grounding

    That article is related to audio circuits, but if you boost the voltage and current to mains level, and replace "noise" and "ground loop" with "fault", you should get an idea of how to explain it to the boss.
    #12 likes this.
  5. #12


    Nov 30, 2010
    Thanks. Good reference material. I marked it so I can call it when another noobie needs it.
  6. Neosec


    Feb 25, 2013
    I had this same argument with my Father. I was right :D
    I couldn't explain it to him either but one night I was hanging up a drop-light in the basement that was on a circuit in a sub panel. There were small blue sparks coming from the hook on the drop-light as I hung it on a grounded BX cable. It was the difference in voltage between the sub-panel's ground and the true ground because of the resistance in the feeder and the loads on the panel. Sub-panels must have an isolated ground. Wire does not have ZERO ohms resistance.
    It's the Ohms, man.
  7. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    You bond in one and only one place to prevent the ground from carrying current that should be in the neutral wire.

    If they are connected in more then one place then neutral current can flow thru the ground wiring.

    I don't have any problem with what you say your boss said.

    I do not understand what you mean by the "two different things."
  8. DenzilPenberthy

    New Member

    May 28, 2012
    As has been said above, your boss does not seem to have considered that wires are not zero ohms which means that your earth wire would have a volt drop on it if it was carrying neutral current.

    Also, if you connect N&E at your sub-panel then the N and E conductors feeding it from the main panel are broken then all of your appliance chassis etc upstream will become live.
  9. dsk

    New Member

    Feb 24, 2013
    In Norway we have 2 supply systems, with and without Neutral. (Without Neutral is quite similar to your 240V 3 pin grounded outlets) This has caused lots of confusions, and some real practice with the differences.

    All new systems has Neutral, and separate grounding, but in the start 60 years ago,they tried out bonding in each outlet, just using a common Neutral and ground wire. Sometimes 2 grounded units supplied from different circuits got so different voltage drop tat touching them was uncomfortable. Probably not dangerous, but ...

    To feel a voltage differens you need a sudden voltage (to be electrocuted?).
    This practice was quickly abandoned. The neutral may actually have a voltage to real ground due to voltage drop in the conductor.

    Today's Norwegian rules (NEK =~NEC) demands a separate ground conductor, a max total voltage drop of 4% (after the meter) and multi-pole breakers even protecting the Neutral. The neutral should be treated as a live conductor. Even when electrical heating and high loads are common here, we have far less problems than in the older days.

  10. DeanFran

    Thread Starter New Member

    Feb 25, 2013
    Thanks for all the replies. I am beginning to get it now. I drew him a quick sketch on his white board, showing a typical household setup with a sub-panel in a separate building. I had him trace the flow of current if there was a break in the neutral wire twice. Once with a bonded G-N at the sub-panel, and once with them isolated. I asked him if he wanted to be the ground rod on the first one by touching the sub-panel.