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Just sorta interested in whether or not any type of lightning protection was installed?
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Is lightning protection required by NEC-2008?Comment
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NFPA 780 deals with lightning protection. NFPA 70 or better known as the NEC has the "grounding" requirements for structures. The NEC does not directly address lightning protection. But again check with your AHJ for actual requirements, especially if you are in a lightning prone area.
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I would be very surprised if the inspector mentions anything about lightning protection. There are probably in the neighborhood of a dozen systems in my entire county, so I'm not expecting them to be overly critical of some of the fine details.
I'm not saying that I don't want to install lightning protection, but I don't want to "have to do anything". I'd rather have the ability to decide if and how I'd like to do it.Comment
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There is a lot of good information on this site about lightning protection and grounding of arrays if you care to search.
Many different thoughts on the subject of lightning protection and even the experts will disagree on some of the finer points. IMO a direct strike cannot be mitigated without fairly large investment in equipment but for side strikes or nearby strikes then the voltage step potential created can be mitigated with proper design. Primarily through the use of SPD's in strategic locations in the array and at the service entrance.Comment
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As mentioned no equipment will survive direct strike. The point of protection is slightly different- to reduce damage, to prevent loss of life, to mitigate damage from nearby strikes. There's common misconception about grounding rod being able to 'ground' the lightning strike. If you search the site there was recent thread on the topic with links to other sources showing what actually happens. Those should provide you enough guidance for your case. Your EGC green wire definitely won't be a good idea for lightning protection and might even make things worse if you are not careful.Comment
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After reading through the NFPA 780/LPI 175 thread created by tyab, with great discussion from Sunking, I think I'll minimally disconnect my equipment ground from the ground coming from my subpanel (I get confused between the terminologies between EGC & GEC). I'll instead tie it to a couple grounding rods near the array. Generally speaking, I think my risks for a strike are low (knock on wood), considering I have plenty of taller trees and structures in the area. That said, there's no sense inviting a potential source from a nearby strike into my house, when I could very easily dissipate it 100' away.Comment
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Whatever you do just make sure it is code compliant. I can not tell from this comment....."I think I'll minimally disconnect my equipment ground from the ground coming from my subpanel".....whether you will have a code compliant installation.
The EGC is for your safety and it should not be compromised no matter what you think about lightning protection.Comment
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I would still have a panel sourced ground connected to my multigates and micros. See the picture below. Do I need to also have the panel frames and micros tied to this ground? or can that be tied directly to local ground rods?
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Grounding - let me make a stab at this and hopefully I don't get flamed too bad
Lets break this up into two sections - NEC and then anything you do for LPS.
NEC:
First we need to clarify that if you have a AC subpanel at your solar site, then AC circuit from your service panel to your subpanel is a feeder. And your subpanel being on a separate structure requires a GEC/GE. This would be a four wire setup but some AHJ's may let you use a three wire but current code does require a 4 wire. If you don't have a subpanel on the solar (just a combiner box - no AC circuit breakers) then you don't have a feeder and thus no subpanel. This is important - I don't know if you do or don't. (It's handy to have one since you can add an outlet, router, etc). We will bring this up in the next paragraph.
The two grounds are easily confused. EGC is the equipment ground conductor - this is a fault path that is there to protect a person from getting a lethal shock in the case of some fault. In your home you have this (hopefully) on all wall sockets - the ground plug.On your system you should have one going back to your service panel (aka you did a 4 wire install) and convention for insulated wire is the color green or green/yellow or it can be taped green. To this circuit on your solar system bond any metal that is likely to be energized by any sort of fault. For example a green or bare wire bonding the case and the DIN bars. Note that this is NOT designed to trip a circuit breaker (Mike Holt has a great video on this). It just provides (hopefully) a significantly lower resistance path than your body to keep you alive in the case of a fault and you have body contact with something energized that should not be. This has nothing to do with lightning protecting - it is only for personal protection (and to some degree fire protection) from a fault.
GEC is the ground electrode conductor. NEC wants one of these on a service panel, subpanels on a separate structure, and it also wants one from 690.47(D). This is to provide a path for the EGC to get to ground and for 690.47(D) what they were trying to do was provide a path for nearby higher voltage events. You have one on your home and code requires one on your system via 690.47(D). If you have a subpanel we talked about above, then code does require one for that subpanel. 250.52/53 and related sections cover the requirements for GEC which are different than all the bonds you have for your EGC's.
In a perfect world - you have a single GEC. But with ground solar systems (2014 code) you may have one from 690.47(D) and may have another one for your subpanel. 690.47(D) has allowances so if you have one from your subpanel you can share them if they would be close enough. Also 690.47(D) has TIA in place removing it but only from roof installations - not ground mounts - but not all jurisdictions are honoring that.
Lets take the case where you followed the code to the letter and you have a subpanel. Then you have three GEC's - one at your home, a GEC at your solar subpanel, and a GEC for 690.47(D). This is the NEC code and the AHJ is happy.
LPS.(Lightning Protection System)
First for residential - NFPA 780 is not code unless specifically in place by the jurisdiction. Thus consider it a guideline of peer reviewed ways based on current knowledge to reduce the effects of a nearby lightning strike. Sunking is an expert on this subject.
From NEC you may have multiple ground reference points and in the case of a lightning event (nearby) you have multiple ground reference points. This can be dangerous - side flashing. If your solar is on your roof then you can have multiple ground reference points for equipment and conductors inside of your home and this is freaking dangerous. But with a ground mount your home only has a single GEC so that dangerous part of 690.47(D) does not really apply. But at the solar system, you may have multiple GE's at the site and the GE from the home connected by a smallish EGC. Multiple grounds and this could lead to damage to equipment at the site. NFPA 780 gives ways to mitigate that multiple ground problem.
First 780 states that your LPS is separate from and cannot replace NEC required grounding. Then it gives ways to bond all nearby ground electrodes into a ground electrode system. The lowest cost way to do this is with #2 bare solid copper wire and run it in a loop around your system at least 18" underground and make sure it bonds to every GE using listed UL 96 clamps (these are not the clamps you find at Home Depot) and all bends are smooth with 8" radius at a minimum. Better would be class 1 copper conductor since it has lower impedance at the frequencies that a lightning event induces into the ground. This would be a 780 compliant ground ring that helps ensure that all ground electrodes at the site have the same potential. Section 12 of 780 specifically calls for ground rings around ground solar mounts. For extra credit and piece of mind, run a class 1 bond from that ground ring all the way back to the ground electrode at your house - but it is far enough away to not be required by 780.
In addition, 780 recommends a type 2 surge protector at your service panel and if you have a subpanel, one at your subpanel to at least try and provide a level of protection on your AC circuits from a nearby event. Lots of companies sell these and if they go bad, you toss them and put a new one in.
Anything more and then are you getting into all the above ground stuff in section 4 and 12 of the 780 spec and only you can decide if it is worth it.
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why not both?The ground around strike will be at tens of kV potential during strike. EGC is a wire like any other and no insulation will sustain those tens of kV at the panel's site during strike so you can consider all wires coming from the panels as 'shorted' between themselves and readily bringing those tens of kV into the house. Take a look at this video and pic at around 7:50 to get an idea of voltages involved and the profile of the 'ground' potential: https://www.youtube.com/watch?v=YuDqXFvRv94 It also illustrates what happens when the strike happens nearby, not necessarily directly hitting the array.
One option was to have separate thick copper conductor which would tie up the ground rod /GES of the panel's site to the house ground (directly at the rod, not through MSP etc) so when the strike happens both sites would 'jump' together keeping voltages inside them at safe levels. Grounding rods/systems are not capable of keeping potential low during the strike so the next best option is to leave potentials where they want to be but keep difference at the safe level.Last edited by max2k; 09-23-2017, 01:37 PM.Comment
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