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Thread: Grounding & Lightning (diagram for review...)

  1. #1

    Default Grounding & Lightning (diagram for review...)

    Attached is a diagram of an off-grid system I've been working on in rural Mexico and which I've had previous help with on another Wind&Sun forum. I am in an area of intense lightning activity and want to have the maximum protection possible. Please review the attached and let me know of any suggestions you might have. I also have a coupe fo specific questions relating to the system. They are:

    1) What gauge wire would be best for the bond between battery bank negative, and the equipment grounding conductor? (I used #6 bare stranded, same as that used throughout the rest of the system grounding )
    2) What gauge wire would be best for the bonding between the equipment grounding electrode, and the lightning protection grounding electrode? (I used #4, same that used throughout the lightning protection system)
    3) Does the AC Load Center ground bus need to have a ground connection to the main system equipment grounding conductor as illustrated? Or is the ground run from the AC Load Center GRND bus to the Inverter GRND sufficient? Does having it both ways as illustrated create a ground loop that should be avoided?
    4) Should the equipment ground lead coming off the combiner box go directly to the grounding electrode with the other equipment grounding starred to it, rather than having it pass via the DC load center first as pictured?

    Thanks!!!

    note: a copy of the diagram is also at: http://www.maytomex.com/MaytoMex.com...Protection.pdf

  2. #2

    Default Re: Grounding & Lightning (diagram for review...)

    I am in the very same process myself now for our place here in Baja so I am very interested to hear what the folks here much smarter than I am at this have to say. One thing that did jump out at me was the fact that you show it grounding your battery bank negative to the system ground.

    I was told that is a big no-no???

  3. #3

    Default Re: Grounding & Lightning (diagram for review...)

    I am no expert in lightning diversion, but few things I don't like in your diagram. Why no lightning rods for solar panel frames? You can get a strike right to your panels. The way you tie your triangle ground rods to ground wire going to the roof does not look good. Your ground rods will not share the current evenly.

  4. #4

    Default Re: Grounding & Lightning (diagram for review...)

    Thanks Guys,

    Re: the negative battery terminal to ground bond, I believe it is correct to do so, at least in some fashion. Here's an example I pulled from a Xantrex TR1524 install manual:

    DC Grounding

    The negative battery conductor should be bonded to the grounding system at only one point in the system. See “DC Circuit Grounding” on page 2–5. Consult your local electrical codes for additional information and requirements.

    To ground the DC circuits:
    1. Connect the negative (-) terminal of the battery bank to an appropriately sized conductor and connect it to the ground bus in the DC Disconnect.
    2. Connect an appropriately sized conductor to the Ground bus in the DC Disconnect and connect it to the primary system ground.


    And as far as the grounding triangle, I have seen lightening protection separate from the equipment grounding conductors set up similar to this in several books and the 3meter-per-leg triangle of electrodes is the way electricians in Mexico commonly set up their lightening protection. I've never heard of air terminals attached to the panels themselves, I'd be very interested to hear more specific feedback on all of this however!

  5. #5

    Default Re: Grounding & Lightning (diagram for review...)

    What is the purpose of the air ground. I am unfamiliar with this.
    " Help save earth, it's the only planet with chocolate" http://www.pbase.com/solorguy

  6. #6
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    Default Re: Grounding & Lightning (diagram for review...)

    The Air Terminals... Rods spaced along the roof line of the building tied to heavy braided cables that run to earth ground (in rounded curves--sharp right angles can cause lightning to not flow to ground properly--causes higher impedance to current flow).

    The idea being it is better to attract lightning to properly grounded conductors than have the lightning strike a chimney or your solar array or electrical wiring/roof/flashing around your home.

    A couple of discussions about genset grounding and lightning protection:

    Detailed discussion of AC Genset Grounding for Off-Grid Home
    Off Grid Grounding Technique?
    Another Question, this time about Lightning

    -Bill
    Last edited by BB.; August 21st, 2010 at 9:28 PDT.
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  7. #7

    Default Re: Grounding & Lightning (diagram for review...)

    One clarification/correction to my diagram:

    The DC-to-Inverter GRND and AC-to-Inverter GRND conductors are not connected or otherwise tied to the same GRND at the inverter. The Outback FX series inverter used has separate GRND connections for the DC and AC sides.

    In other words, there is only one common GRND point between the AC and DC sides of the system where the AC equipment GRND conductor ties into the DC equipment GRND conductor, and no connection between the two at the inverter as pictured in the diagram.

    Apologies for any confusion this may have caused...

  8. #8
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    Default Re: Grounding & Lightning (diagram for review...)

    Quote Originally Posted by solorone View Post
    What is the purpose of the air ground. I am unfamiliar with this.
    Air Terminals are the old reliable Franklin Rods. Just a new name, without the fancy glass balls.

    The more of a stroke the air terminals snag, the less goes into your battery shed.

    (But you don't want to ATTRACT a bolt, that would otherwise go to your neighbors house and battery shed.)

  9. #9
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    Default Re: Grounding & Lightning (diagram for review...)

    Quote Originally Posted by MexDog View Post
    One clarification/correction to my diagram:

    The DC-to-Inverter GRND and AC-to-Inverter GRND conductors are not connected or otherwise tied to the same GRND at the inverter. The Outback FX series inverter used has separate GRND connections for the DC and AC sides.

    In other words, there is only one common GRND point between the AC and DC sides of the system where the AC equipment GRND conductor ties into the DC equipment GRND conductor, and no connection between the two at the inverter as pictured in the diagram.

    Apologies for any confusion this may have caused...
    I know how crazy this sounds the first time and I spend tons of time with my new installs on this. There are strategies depending on how bad the storms are in your area. What ever you decide you want one thing to be apparent to the static storm or lightning bolt waiting to discharge. Everything must be at the same potential and therefore everything needs to be bonded # 6 or better! It must be your bible! Being nice to little old ladies is a helpful also!
    http://members.sti.net/offgridsolar/
    "we go where the power lines don't"

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