High Voltage Fence Heights

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jcrawford

Member
Location
NY
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?
 

Carultch

Senior Member
Location
Massachusetts
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.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
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.
 

kwired

Electron manager
Location
NE Nebraska
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.
 

pv_n00b

Senior Member
Location
CA, USA
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.
 
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?
 

big john

Senior Member
Location
Portland, ME
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.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
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).
 

kwired

Electron manager
Location
NE Nebraska
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.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
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.
 

shortcircuit2

Senior Member
Location
South of Bawstin
NFPA-1 Rules

NFPA-1 Rules

There are some requirements in NFPA-1 related to Ground Mounted Photovoltaic System (GMPV) also.

Section 11.12.3 covers GMPV Systems

11.12.3.1 requires a 10' clear area around a GMPV system

11.12.3.2 states that a noncombustible base under a GMPV be installed acceptable to the AHJ (of note is that dirt with minor growth in not considered noncombustible by appendix A)

11.12.3.3 Fencing, skirting or other suitable security barriers shall be installed when required by the AHJ

These rules apply to all Ground Mounted PV Systems if adopted in your area. I would say the Fire Chief would be the AHJ on these rules.


Having a 1' space at the bottom of a GMPV seems to high to me. Curious kids would easily crawl under that space. We were required to a have 6 inch bottom clearance on a GMPV system for turtles to pass through.
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
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?

I am an animal lover, but realistically, I can't see providing easy access for curious kids in order to provide easy access for small animals to be very prudent. For one thing, most small animals, if not all, wanting access to the inside of the fence will just dig under it. To an adventurous 10 year old, a fence with a one foot gap at the bottom is pretty much no fence at all.
 

kwired

Electron manager
Location
NE Nebraska
If you are an animal lover, you probably don't want them inside and subject to the high voltage either.

Risk for a turtle may not be that high. A migrating turtle has other obstacles to go around as well, so this structure isn't really that big of a deal IMO, when they cross roads they are in higher danger.
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
If you are an animal lover, you probably don't want them inside and subject to the high voltage either.

Risk for a turtle may not be that high. A migrating turtle has other obstacles to go around as well, so this structure isn't really that big of a deal IMO, when they cross roads they are in higher danger.

We actually have a turtle fence that cost taxpayers $318,000. Here is a video of it. The power plant in the background is the B.C. Cobb plant. It was totally shut down a few months ago. The 660 foot stack is going to be demo'd sometime in the future. That has nothing to do with the fence, the fence was to keep the turtles off the highway.

 

kwired

Electron manager
Location
NE Nebraska
We actually have a turtle fence that cost taxpayers $318,000. Here is a video of it. The power plant in the background is the B.C. Cobb plant. It was totally shut down a few months ago. The 660 foot stack is going to be demo'd sometime in the future. That has nothing to do with the fence, the fence was to keep the turtles off the highway.

Did they give the turtles an alternate route? My understanding is many of them migrate to a certain place for breeding, and that is where they want to go to. The fence though it protects them from the road hazards doesn't change the fact they have a destination they are seeking.
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
Did they give the turtles an alternate route? My understanding is many of them migrate to a certain place for breeding, and that is where they want to go to. The fence though it protects them from the road hazards doesn't change the fact they have a destination they are seeking.

Mother Nature gave them an alternate route. Several branches of the Muskegon River that pass under the highway.

Michigan is big into nature and natural resources. The fence was very well thought out, but still is the butt of many jokes. One has to be careful driving in Michigan as we have to share the roads with all sorts of critters, big and small.

The pesky EPA and DNR made all the local factories stop puking chemicals into the air and water and now we have critters everywhere. Even bald eagles and pileated woodpeckers, that were non-existent here 30 years ago.
 

kwired

Electron manager
Location
NE Nebraska
Mother Nature gave them an alternate route. Several branches of the Muskegon River that pass under the highway.

Michigan is big into nature and natural resources. The fence was very well thought out, but still is the butt of many jokes. One has to be careful driving in Michigan as we have to share the roads with all sorts of critters, big and small.

The pesky EPA and DNR made all the local factories stop puking chemicals into the air and water and now we have critters everywhere. Even bald eagles and pileated woodpeckers, that were non-existent here 30 years ago.

What about this story I remember hearing about quite some time ago http://www.snopes.com/humor/letters/dammed.asp
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
What about this story I remember hearing about quite some time ago http://www.snopes.com/humor/letters/dammed.asp

Oh, the dam beavers!

Yeah, it's true and and that letter was read on the local radio stations more than once. I thought it was earlier than '97, but I remember watching people come to tears hearing the story for the first time, especially after being told it was not a joke. Pierson is about 35 miles from here.

The letter truly is a work of art and has earned it's place in Michigan history.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
There was an apparently true story a few years ago about a woman who went on the air on a call in radio show to complain that the deer crossing signs were being erected in unsafe locations for the deer to cross when there were much safer places nearby. :angel:
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min from the winged horses.
Occupation
Licensed Electrician
There was an apparently true story a few years ago about a woman who went on the air on a call in radio show to complain that the deer crossing signs were being erected in unsafe locations for the deer to cross when there were much safer places nearby. :angel:
Paul Harvey début that to a nation wide audience back in the 80's.
 
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