ground rod

rplarry
rplarry Solar Expert Posts: 203 ✭✭
in PV Installers Forum - NEC, Wiring, Installation #1
I am trying to drive a ground rod into the earth but I keep hitting rock at about 3' down. Is it feasible to dig a trench and lay the ground rod into it?
Larry
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
    Re: ground rod

    yes, it is possible. often times in cases like this ground screens are utilized too because you couldn't gain the depth a rod would normally penetrate to. the ground screen tries to optimize the contact area with the ground to make up for the lack of depth. what you might do is use 2 ground rods in a trench that would now be 16-20ft long. it doesn't have to be in a perfectly straight line either, but don't lay them parallel to each other. the ground wire will attach to both rods well into the ground. trench it at least 1ft down, but 2ft may be better as the soil is more apt to stay moist further down.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,639 admin
    #3
    Re: ground rod

    You can get copper ground plates and bury that... I am not sure the proper size for your application--But they should work well (lots of surface area).

    If you have dry/rocky ground, I am not sure what the "proper" method is.

    Here is an interesting article.

    A Windy Dankoff ground article.

    As always, I ask what is it your are trying ground and protect against (lightning, 120/240 VAC grounded neutral, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • silvertop
    silvertop Solar Expert Posts: 155 ✭✭✭✭✭
    #4
    Re: ground rod

    In Colorado when I was working as an electrican the first inspector was OK with laying the ground rod in a trench because of the rocky land. Whan we changed inspectors the new one told us he didn't care if we had to dig a hole It had to be straight down, not much fun with a post hole pounder. Several times we had to cut off the ground rod, it would have been MUCH smarter to lay it in a trench:grr
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #5
    Re: ground rod

    We used to use dual rods,, and we often drove them on an angle.

    Tony
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #6
    Re: ground rod

    well he can't drive them, but he can bury them. i only mentioned 2 ground rods so as to increase the contact area with the soil. in fact, larry, you may even opt to bury some copper pipe and just attach the proper clamps to connect the ground wire to them. something like this is good,
    http://www.homedepot.com/h_d1/N-5yc1v/R-100198848/h_d2/ProductDisplay?catalogId=10053&langId=-1&keyword=ground+clamp&storeId=10051#.UEQ9iCK06Iw
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #7
    Re: ground rod
    niel wrote: »
    well he can't drive them, but he can bury them. i only mentioned 2 ground rods so as to increase the contact area with the soil. in fact, larry, you may even opt to bury some copper pipe and just attach the proper clamps to connect the ground wire to them. something like this is good,
    http://www.homedepot.com/h_d1/N-5yc1v/R-100198848/h_d2/ProductDisplay?catalogId=10053&langId=-1&keyword=ground+clamp&storeId=10051#.UEQ9iCK06Iw

    If you cannot drive rods to the specified length (per the NEC), you can use a buried rather than a driven ground electrode, but the requirements for it involve more than just putting that same ground rod into a trench.
    And an electrode placed full length downward in a dug hole will not initially have as low a resistance as a driven electrode. The second inspector was apparently ignoring that, since the code does not take it into account except to require a second electrode if the resistance of the first is above a certain value.

    You may want to do a concrete encased electrode instead, or a larger, longer, ground electrode assuming that you can reach damp soil in the first place.

    But for some purposes, grounding is not all that critical in a PV system.
    SMA SB 3000, old BP panels.
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  • SolaRevolution
    SolaRevolution Solar Expert Posts: 410 ✭✭
    #8
    Re: ground rod

    Will the Mexican inspector accept the rules of the NEC? (National Electrical Code, USA)

    NEC 250.53G "...where rock bottom is encountered, the electrode shall be driven at an oblique angle not to exceed 45 degrees from the verticle or, where rock bottom is encountered at an angle up to 45 degrees, the electrode shall be permitted to be burried in a trench that is at least 750mm (30 in.) deep. The upper end of the electrode shall be flush with or below ground level unless the above end of the grounding electrode conductor attachment are protected against physical damage as specified in 250.10."

    -Alex
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