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Thread: High Voltage Fence Heights

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    High Voltage Fence Heights

    NEC 110.31 specifies that fences around high voltage equipment need to be 7' high, or 6' + 1' of barbed wire. Unlike pool fencing, it's not very specific about maximum gaps, particularly at the bottom. I'm inclined to say a 6' chain link fence with a 1' gap at the bottom would be permissible- anyone else have strong opinions?

    As we dedicate large areas of land across the country to these solar farms, I'd really like to see the NEC consider the fact that these fences are now being applied to much larger areas than your typical substation. I don't see why we shouldn't allow for small gaps at the bottom to promote the movement of small animals... no need to take away their habitats entirely, right?

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    Quote Originally Posted by jcrawford View Post
    NEC 110.31 specifies that fences around high voltage equipment need to be 7' high, or 6' + 1' of barbed wire. Unlike pool fencing, it's not very specific about maximum gaps, particularly at the bottom. I'm inclined to say a 6' chain link fence with a 1' gap at the bottom would be permissible- anyone else have strong opinions?

    As we dedicate large areas of land across the country to these solar farms, I'd really like to see the NEC consider the fact that these fences are now being applied to much larger areas than your typical substation. I don't see why we shouldn't allow for small gaps at the bottom to promote the movement of small animals... no need to take away their habitats entirely, right?
    Unfortunately, this is a blind spot in the NEC & NESC. Our conservation commission actually required that we trench the fence 6 inches below finished grade, to keep small animals out.

    This fence height issue is a consistent problem. Few (if any) manufacturers actually make a 7 ft fence fabric, so it is a practical choice between a 6 ft fence with barb wire and an 8 ft fence.

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    A one foot gap at the bottom, unless restricted by a run of barbed wire, seems to me to be a very attractive nuisance for small kids as well as small animals. Not a great idea.
    A lot would depend, IMHO, on whether the actual high voltage danger areas inside the large area outer fence had their own local protection too.

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    Quote Originally Posted by GoldDigger View Post
    A one foot gap at the bottom, unless restricted by a run of barbed wire, seems to me to be a very attractive nuisance for small kids as well as small animals. Not a great idea.
    A lot would depend, IMHO, on whether the actual high voltage danger areas inside the large area outer fence had their own local protection too.
    I agree. I'd rather see a 5 foot fence then have a 1 foot gap at the bottom if the main intent is keeping people and animals away from exposed high voltage components.

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    This is an interesting topic. I have reviewed several projects that have a 1' gap, or more, at the bottom of the fence to allow for the movement of animals through the site. Obviously a small person or child could easily get under the fence. The question is then, does the fence count as a means of isolating the energized conductors in the array from unqualified persons or do we need to install some type of protection on the back of the arrays to contain the conductors? Most AHJs seem to feel that the fence, even with a huge gap at the bottom, will prevent unqualified persons from accessing the array. I am personally not sold on this idea.

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    Quote Originally Posted by pv_n00b View Post
    This is an interesting topic. I have reviewed several projects that have a 1' gap, or more, at the bottom of the fence to allow for the movement of animals through the site. Obviously a small person or child could easily get under the fence. The question is then, does the fence count as a means of isolating the energized conductors in the array from unqualified persons or do we need to install some type of protection on the back of the arrays to contain the conductors? Most AHJs seem to feel that the fence, even with a huge gap at the bottom, will prevent unqualified persons from accessing the array. I am personally not sold on this idea.
    I am a bit confused. Is a fence even required for a typical commercial or utility scale PV system? I breezed through 110 and 225 and dont think so. I havent seen any exposed energized parts on the ones I have worked on. Why would these require more protection than a system on a residential property?
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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    Yeah, I've worked on quite a few solar and wind projects where you could walk right up to all the apparatus. I really don't see how the intent of 110.31 was that everything using electricity should have a fence around it: The vast majority of that equipment would fall under the exception for section (D) anyway.

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    The problem for solar is the second paragraph of 690.31. The fence has been considered a means to make the conductors no longer 'readily accessible'.

    There's also a new requirement in the 2017 code for 5MW and up. 691.4 (2).

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    Quote Originally Posted by jaggedben View Post
    The problem for solar is the second paragraph of 690.31. The fence has been considered a means to make the conductors no longer 'readily accessible'.

    There's also a new requirement in the 2017 code for 5MW and up. 691.4 (2).
    There is also a change in "readily accessible" in 2017, a keyed lock on the gate will now make those conductors "readily accessible".

    Don't know if they changed things like you mentioned in 690.31, if not they may be left with some sections whose intent is contradicted.

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    Quote Originally Posted by kwired View Post
    There is also a change in "readily accessible" in 2017, a keyed lock on the gate will now make those conductors "readily accessible".

    Don't know if they changed things like you mentioned in 690.31, if not they may be left with some sections whose intent is contradicted.
    Yes, good points. Something was bothering me about what I said about readily accessible. I had read that definition revision the other day but couldn't put my finger on it. I do think a change to 690.31 would be in order.

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