Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Connecting ground to return wire?

  1. Jan 17, 2012 #1
    Several years ago I got in a big argument with the folks that wired a new control room (a project I had nothing to do with, but jumped in as a concerned employeed).

    These guys provided 3-terminal power outlets, but on each terminal they connected the ground to the return, based on the practice in my home country of providing just two wire cables between the distribution box and the wall outlets.

    They argued that if they had carried 3-wire cables to the distribution boxes, they would ground the neutral bar anyway, so they could just as well do that in the outlet and save on the cables.

    I argued that if the return wire broke or had a bad connection before the distribution panel, the supposedly grounded chassis of the electric equipment would get the line voltage and they would eletrocute someone - to what I was called alarmist.

    As the contract didn't specify one way or another (it just said 3-terminal outlets), and the building code in my home country is (or was at the time) suspiciously silent about that, the contract manager couldn't get the contractors to rewire the building.

    So, was that really a danger as I stated? In that case, if rewiring the building is not an option, what would be the best palliative for that situation?
  2. jcsd
  3. Jan 17, 2012 #2
    Yes if the return wire breaks the chassis will not be grounded anymore.

    EDIT: Also proper grounding may not be achieved in the outlet.
  4. Jan 17, 2012 #3


    User Avatar
    Science Advisor
    Gold Member

    You could create a earth ground and connect each outlets ground terminal to it.

  5. Jan 17, 2012 #4

    jim hardy

    User Avatar
    Science Advisor
    Gold Member
    2018 Award

    in this country (US) it's a rule that the "ground" conductor must not be asked to carry normal load current. there are specific exceptions, for example ranges and dryers in some circumstances..

    ""what would be the best palliative for that situation?""

    Parkinson's "Buckmastership".

    if it's a real concern and if you can find a suitable paragraph in your code,
    your design department might be able to force them to take out the three prong [strike]plugs[/strike] receptacles and install old fashioned two prong ones with no ground . that should force the issue when they find people cutting off ground prongs.

    nobody in a bureaucracy wants to be responsible for a hazardous or illegal design.
    Last edited: Jan 17, 2012
  6. Jan 17, 2012 #5

    Yeah, and that was the problem in my country of origin... everybody uses (or used) 2-prong receptacles (where the prongs can be connected either way, by the way), and all wiring is (or was) done with 2 wires, so there's no culture of grounding the chassis. I grew up with a refrigerator that I was scared of, because it always gave me an electric shock when I opened its door. Only high-power, tri-phase applications, like a big electric motor, would have a proper grounding.

    I was anyway amazed that the said electric technicians would just keep doing what they did out of habit, even when faced with rather clear arguments against that...
  7. Jan 17, 2012 #6

    This situation was some 20 years ago, but I remember I struggled with a similar option, which was to connect the ground at the outlet to the metal tubes that carried the cables to the outlets, and have these metal tubes grounded.

    I didn't propose that, though, because I couldn't estimate the effect of rust on the joints of the tubes; and I was scared what effect a lightning could have, if it leaked through those tubes - might end up in those chassis...
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook