PV array grounding

[JoeR]

I have a question. I had a PV array installed, and noticed they ran a #6 solid bare copper around the array. No problem here since they used stainless steel clamps, but the installer ran the wire straight through the roof under a shingle. He sealed it well, but something doesn't seem right. The DC cables go through a junction box into armored cable through the attic, yet the ground wire is straight through the wood. I then started to wonder how hot the ground wire would get if lightning hit it, and if it could start the wood on fire since there is no insulation between the wire and the wood. I looked in the NEC 2002 book, but couldn't find any reference to ground wire penetrating wood or roofing.

The inspector is due to come out, but I have found that many inspectors are not up to date on PV installations.

Any references to how this should be done?

Thanks,

Joe

[jml755]

I would think it would be OK, considering that ground wires are fastened to bare wood in homes when running them to either a ground rod or a water pipe. Your inspector will tell you for sure if the entire installation is "up to snuff".

[Pat]

Code or not I would not be comfortable with a "lightning" ground running through wood and under shingles.

Ground wires in the stud cavities of house wiring come from the breaker box and not from an exposed roof top installation. They are much less likely to have a lightning bolt discharged through them by far than a roof mounted PV installation.

Again, code or not, I wouldn't be too comfortable with what is actually by default a lightning rod installation equivalent having the ground wire run through a roof, under shingles, and or into an interior space. I suggest the wire should be run in accordance with good practice as applicable to a lightning rod installation.

I don't care how long they have been taking these shortcuts and getting away with them, that won't help you if you take a lightning hit. It won't take much of a lightning discharge to melt/vaporize the undersized ground wire and potentially set any nearby combustible materials ablaze.

I hope for your sake that if there is a problem that the company is still in business and has good insurance. I'd be tempted to write them an official letter expressing my concerns and requesting their assurance that their procedure is in accordance with proper engineering practices.

You may get some BS back about how expensive it is to do it right, how they have done bunches of installations with no problems, and on and on. None of this is meaningful if you get hit by lightning.

Pat

[JoeR]

I agree Pat, and feel the same way. Something just doesn't sit well with me. You and I have both seen what lightning can really do to wire. They also did not connect the ground wire to the PV mounting rails. I checked NEC code, and it clearly states the mounting rails need to be grounded. I am just waiting on the County Inspector to catch it. If he/she doesn't, then I am going to have a nice long call with the County Inspector. I doubt the grounding will pass inspection, but some of the County inspectors may not be up to par on PV systems and the NEC code about PV arrays. The inspector should be here Monday or Tuesday, so I will let you know the outcome.

Thanks,

Joe

[jimbrown]

What the heck did they ground if it is not connected to the panel rails. It must be some sort of ground for the inverters and not a lighting ground. You probably need both. Although in reality a direct hit from some gazillion mega watt lighting bolt is gonna vaporise it all anyway.

[Pat]

Joe, Is there an advantage to hiding in the weeds and watching to see if the inspector misses it? Why not express your concerns in person, by phone, or hang a note with ref to NEC chapter and verse on the solar array. You don't really want to "slip" it past the inspectors do you. I would want the inspector's leverage to motivate the installing company to do it right.

The game, NIGYYSOB, as explained in "Games that People Play" can be fun but probably has no utility in this situation.

You have piqued my curiosity. How much PV did you put up and are you charging batts, using the DC directly like in water pumping to a storage tank, or what?

My current largest installation is on the roof of my camper which is a single aluminum sheet so the fasteners attaching the frames then ground the frames to the roof which is part of the all metal "skin" so I am as lightning protected as I can be (whatever good that is.)

Pat

[JoeR]

Hi Pat,

Actually, I am waiting on the inspector so I can share my thoughts and hopefully get his feedback. I know for a fact that the rails must be grounded, along with the PV panels. Although, I have no firm documentation on running a ground wire through the roof and under the shingles. Therefore, once I had some sort of confirmation, then I can call the installer back and have them correct the issues all at once. Rather than me calling them for one issue, and then the inspector calling them for something I didn't catch. I am just trying to be fair to the installer, and I am making sure I know what the rules are before I bring any issues to their attention.

They installed a 2KW array, using 12 Sharp 167W panels. The panels then feed a Fronius IG 2KW inverter which is a grid tie system. My local power company wants the green credits, so they give me 5 cents for every KWH the system generates even if I am the consumer of that green power. If I backfeed the grid, then I get 9 cents per KWH. Therefore, whatever excess energy I generate, I still get money for it. This way, I really don't need a battery system to store power since I am getting full credit for any excess power I generate. The State of FL also gives a 4 dollar per Watt rebate on PV arrays. So, I basically received an 8K discount on the installation which makes solar PV more economically feasible. Based on my calculation my return on investment will be about 7 years if power cost only increase 4% per year. Although, I am actually betting it will go up over 50% in the next 5 years due to the political climate change towards carbon emissions. Just recently our Governor killed all the new coal power plant projects for the state of FL, and mandated a carbon emission rollback to pre 1996 levels. Obviously, more demand, less supply, and increasing operation costs will be passed onto the consumer, so it is just a matter of time before the prices go up... Even if they started building a nuclear plant today, it will take 10 years before the plant goes on-line. Not to mention you need at least 7 acres of land to generate 1 MW of power using PV... So, there is not enough dry land for that either. Overall, I am betting power costs are going to climb pretty fast in the near future.

Enough rambling on my part... [img]/forums/images/icons/smile.gif[/img]

Joe

[Pat]

Joe, I am familiar with all the topics you mention. Your arrangement with the utility sounds pretty good. Yeah, Florida doesn't have enough empty land available for solar farms but there were schemes for say a 50% coverage with agriculture of plants that would be happy with 1/2 of the insolatioin available in Florida. That and using solar shingles on all the buildings would help. The economics aren't quite there yet but with $100/barrel oil and the prospect for higher prices we are getting closer.

I'm glad you got the subsidies and good arrangement because solar can't compete with the grid yet in a head to head competition with a level economic playing field. But that is OK as I believe it is the duty of Government and certain segments of private industry to distort the economic playing field for the long term good of the citizens.

About the ground wire. Make sure the inspector isn't holding a mental picture of that wire as a standard 120VAC "safety" ground like the green wire in a 3 wire appliance plug intended to prevent your electrocution if the washer's motor shorts out or similar. There is no 120 VAC on the roof and the most likely use of the wire is to conduct powerful static charges to ground as in lightning protection. Ultimately if the system is hit by lightning it is not appropriate to configure the installation so that it increases the likelihood of starting a fire. If you lose the battle, I think one of the first things you should do is remove the offending wire and run your own, external to the bld to the nearest ground point or drive your own copper plated ground rod.

Good luck with the inspector and contractor. Oh, and one last comment, do not accept "but that is the way we always do it" as a satisfactory resolution.

Pat

[turtlej3]

There are a variety of items which make it completely safe to have grounding rods touch wood or any other surface for that matter. One of those thats probably the most effective is a lightning arrestor. In case of a lightning strike it redirects the energy into the arrestor wheres its absorbed. Another thing you should always do is have a fuse to protect your circuits. For 2.4k watts and below use a 200 amp fuse. For 2.5k watts and above use a 300 amp fuse. Having an unprotected system is far more dangerous than a little lightning strike. We sell those items if you call us at (928)337-2600 we can help you out.

T. John

[jml755]

turtlej3,
can you read the rules? advertising is prohibited.