Ground wire size

Discussion in 'Electrical Forum discussion & Blog' started by Giles, Feb 7, 2011.

  1. Giles

    Giles Retired tool & Die and Mechanic

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    Aug 28, 2007
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    Retired
    Location:
    N.W. Alabama--Florence--
    Over the years, I have noticed that on some romex type wire and some extension cords have a ground wire that is smaller then the load wires.
    I always thought it was correct to have the same gauge wires.
    When is a smaller ground wire ok?
     
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Sep 2, 2004
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    Retired Systems engineer for defense industry.
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    New England
    The ground wire is there for safety...not for normal current flow. Current flow is designed to go from the hot to the neutral. If, for some reason, there is a fault, the ground provides a path that is sufficient to blow the fuse or trip the CB...therefore, any current in the ground is only there a very short time, so it shouldn't heat up like a larger wire could, and is sufficient. For this reason, you can save some money by using a smaller wire there, and most places do.
     
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  4. cacher_chick

    cacher_chick Test, Don't Guess!

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    An equipment grounding conductor is sized based on the over-current protection installed on the circuit. 15A circuit=14ga, 20A=12 ga, 30-60A=10ga, 70-100A= 8ga, 110-200A= 6ga. The grounding conductor may be larger than this minimum requirement, but should not be smaller.
     
  5. TWEAK

    TWEAK New Member

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    Bay Area CA
    NEC and most all local codes allow a smaller equipment ground for most general circuits. IIRC, there are some exceptions in the NEC where you can't do this. But for the most part it's allowed and perfectly safe. Most current Romex I get (southwire) has the same size ground as the conductors, though - but I've torn out a lot that had a smaller equipment ground. When running THHN/THWN I always take advantage of the code and run smaller ground... with the cost of copper it really saves money, and is perfectly safe. There's no reason I can see for ever running an equipment ground that's larger than the current carrying conductors.
     
  6. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

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    Jun 16, 2007
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    Licensed Electrical Contractor
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    NY State, USA
    The question was WHEN was the reduced ground NM cable used or allowed. I for one do not know for sure, but it was definitely popular in the 50's and 60's. I think once they realized that a #16 ground was not adequate for a 20A or 30A circuit that is when they went to full size grounds for #14 thru #10 cables.
    Most likely early 70's?
     
  7. jwelectric

    jwelectric Electrical Contractor/Instructor

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    Jun 14, 2007
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    Instructor
    Location:
    North Carolina
    The 1962 cycle in Section 250-95 a 20 amp circuit was the lowest listed with a number 16 as the equipment grounding conductor. By the 1968 cycle a 15 amp overcurrent device required a 14 for equipment grounding
     
  8. NanH

    NanH New Member

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    Oct 25, 2019
    Location:
    Colorado
    I have a specific question about this topic. If the house is older and already wired with the smaller ground wire, what is the situation if I replace the breaker box? Can I connect the old wires with the small grounds into the new box? If not, what are my options?
     
  9. Stuff

    Stuff Well-Known Member

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    Location:
    Pennsylvania
    Some places have a renovation code but most allow everything to remain as is when replacing a service entrance or other panel. Most of the time if the new panel is withing 6' of the old you don't have to change any branch circuits, but maybe the feeder to the panel. I've heard that some places require you to upgrade to AFCI circuit breakers as needed. This is where you check with your "authority having jurisdiction" for clarification.
     
  10. NanH

    NanH New Member

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    Oct 25, 2019
    Location:
    Colorado
    Stuff, many thanks for the information.
     
  11. Norcal01

    Norcal01 Member

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    Aug 16, 2008
    The reduced sized grounding conductors in 10,12,14, AWG NM cable went away with either the 1968, or 1971, NEC. I don't have a 1968, but do have a 1971 NEC, in looking at the 1971 NEC it requires full sized 10,12,14 AWG grounding conductors with the same sizes of ungrounded conductors so it must of changed in the 1968 edition.
     
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