Panel grounding question

Discussion in 'Electrical Forum discussion & Blog' started by wahoo33, Nov 1, 2013.

  1. wahoo33

    wahoo33 New Member

    Messages:
    2
    Location:
    Destin Fl
    We just finished having a log cabin built in North Carolina and we have 200 amp service with 3 lines coming in from the power compony to a Square D panel with a meter and master disconnect and a couple breakers feeding outside stuff, located on the outside of the basement. The main breaker panel is located on the inside basement wall almost directly in line with it. The electricians have it grounded to the outside panel which is in turn grounded to 2 ground rods. My home in Florida has this exact same setup except the inside panel is grounded to a re bar rod put into the foundation. I was curious if both are correct or if one is better than the other for grounding? Neither inside panel has the green bonding screw installed. Thanks for any answers,, Matt (Both homes were wired by licensed electrical contractors)
  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,047
    Location:
    Cave Creek, Arizona
    Normally the wire connected to the rebar in the foundation is the UFER, bonded to the rebar inside the footing and foundation, which is different from the ground rods into the earth. Modern construction has both, since they serve different purposes.
  3. guy48065

    guy48065 Member

    Messages:
    117
    Location:
    SE and north MI
    The earth ground should be attached to whatever panel has the first (Main) disconnect. Is your Florida home the "exact same setup" with a Main disconnect in the meter box? I suspect not--in which case it's correctly grounded.
    Your cabin panel should have 2 busbars--one for grounds, one for neutrals. The home panel can have just one with both grounds & neutrals sharing and the bonding screw (or a separate bonding strap) should be tightened to ground the busbar to the enclosure.
  4. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,445
    Location:
    Houston, TX
    Using your Concrete Slab as a UFER can result in damage from a lightning strike. But great for bomb storage.

    The Ground rods will help dissipate the energy, and is more better. You should have one at the pole also.

    By code I do believe they need to be bonded together, as they should be.


    Grounds can save lives, and Grounds can Kill bodies.


    Be careful playing with Electricity.
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,266
    Location:
    New England
    The inside panel in your layout is a subpanel, and needs four wires from the main panel: 2-hot, neutral, and ground. The neutral and ground busses on the inside subpanel need to be separated. Bonding and grounding are similar, but different. You ground only at the main panel.
  6. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,559
    Location:
    North Carolina
    It helps if one understands why we have grounding electrodes for in the first place.
    In the 2011 NEC we have eight grounding electrodes and are instructed to bond any and all that are present together to form the grounding electrode system. They are 1) 10 foot of metal water pipe, 2) Steel of a building that is effectively grounded (connected to earth) 3) rebar in the bottom of the footer, 4) ground ring that circles the building, 5) rod or pipe, 6) chemical electrode, 7) plate electrode, 8) oil drum buried in the back yard.

    If the electrode system is a metal water pipe, single rod, pipe, or plate electrode then it is required to be bonded to another electrode as outlined above.

    The electrode system serves four purposes and these four purposes only. They are installed to help dissipate lightning, line surges, unintentional contact with higher voltage lines, and to stabilize during normal operation.

    In most of Florida ground rods are not used due to the water table. Driving an 8 foot ground rod can cause water to ooze out to the earth. Orlando is only 8 feet above sea level so think about knocking a hole in the bottom of Florida should one drive a rod eight feet down and sinking Florida to the bottom of the sea.

    I live in the center of NC and am 689 feet above sea level so driving an eight foot rod into the earth will not knock a hole in the bottom of the most beautiful place God ever created and it will not sink to the bottom of the sea.

    To say one electrode is any better than any other electrode is nothing but a wives tale. Remember why we are installing an electrode for, it has nothing to do with how our system works but is there only to dissipate unwanted current to protect our systems from high voltages generated from an outside source.

    Should we drive a rod and connect it to a 15 amp breaker the breaker will not trip. 120 volts divided by 25 ohms will equate to 4.8 amps but should the primary of the transformer touch the service drop then it would be 7200 volts divided by 25 ohms that would equate to 288 amps and clear the fuse on the primary side of the transformer. Lightning is a very high voltage that is seeking a connection to earth therefore an electrode is needed. Lightning 30 miles down the road can cause a surge on our homes and again an electrode is needed. Look at your switch cover, see those two 6/32 by ½ inch screws? We connect to earth to keep those screws stable during normal operation.

    The grounding electrodes have no role in the normal operation of our electrical systems. We wouldn’t know if there was one or not in everyday use of our electrical systems. The equipment grounding conductors of our electrical systems are bonded to the grounded neutral conductor at our service equipment in order to establish a low impedance path for clearing fault currents in our systems. This fault clearing path will work without a grounding electrode system of any kind. The grounding electrode system plays no role in the fault clearing of our systems.

    The grounding electrode system is installed for the reasons outlined below as mentioned above;
    250.4 General Requirements for Grounding and Bonding.
    The following general requirements identify what grounding and bonding of electrical systems are required to accomplish. The prescriptive methods contained in Article 250 shall be followed to comply with the performance requirements of this section.
    (A) Grounded Systems.
    (1) Electrical System Grounding. Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by 1) lightning, 2) line surges, or 3) unintentional contact with higher-voltage lines and that will 4) stabilize the voltage to earth during normal operation. (numbering was added by me)
  7. wahoo33

    wahoo33 New Member

    Messages:
    2
    Location:
    Destin Fl
    Yes the Florida home does have a Main disconnect on the box where the meter is. Thanks for all the reply's but you guys are confusing me, LOL, you are talking over my head as what I know about electricity you could but in a thimble.
  8. DonL

    DonL Jack of all trades Master of one

    Messages:
    4,445
    Location:
    Houston, TX

    Both Boxes have to have a common Ground.

    Simple enough.

    How you achieve that needs to meet code.

    JW pretty much summed it up.


    Have Fun.
  9. Glennsparky

    Glennsparky New Member

    Messages:
    22
    Location:
    Oviedo, FL near Orlando
    Wahoo33, hello from Orlando. Both grounding system types are to code. Both structures are fine.

    The rebar ground attached to the inside panel is a bit wonky, but not dangerous to people. Do not remove it under any circumstances.

    We do get a potload of thunderstorms in the sunshine state. Many people complain of losing fridge, microwave, stove and electronics. All from one lightning surge. It fried my boss's central air three times this summer. The warranty is running out so he let me install whole house surge protectors in every panel box on his property. You should get at least one.

    With an electrician it's a one time install, until they wear out.

    Many utilities have them for a monthly fee. When installed it should include a check of your ground.

    It's a little unsettling that surges would have to come inside the house to dissipate. If it bothers you, too, a ground rod or two to the main outside disconnect wont hurt anything.
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