Latest NEC rules with Unistrut

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davidwillis
davidwillis Solar Expert Posts: 104 ✭✭
in Advanced Solar Electric Technical Forum #1
I am trying to figure out the rules I need to follow to use unistrut for my panel racking on a metal roof (entire building is metal).

So from what I understand so far, I need to bond each piece of unistrut together, as well as each solar panel.  And from what I understand, just bolting the unistrut together is not up to code.

I am going to be doing a large system, so I need to make sure I get this right the first time.  I will be doing 16 rows of 12  panels each.  The will be stood up at a 45 deg angle, so I will run line of unistrut along the bottom, and one along the top, with braces every 5 feet to hold them up at an angle.  I can see the bonding and grounding to get expensive if I have to run a bond to each unistrut and to each brace.

I looked into using snap-rack or iron ridge (they have all the bonding done), but they cannon support over 40" span, and the roof I am going to mount on has 5' spans between beams.  So I am hoping there is an easy solution to this problem.

If it were up to me, I would just bolt the panels down to the unistrut with star washers, then ground the unistrut, but I don't think this will meet current code.

Also another issue is that the inverters will be mounted and connected into a different building (the building the panels are on has no electricity).  Will it be ok to run the ground wire from the panels to the other building, and to it's ground?

P.S.  I am planning on using 4 Fronius Primo inverters.

Thanks!
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  • mvas
    mvas Registered Users Posts: 395 ✭✭✭
    edited January 2017 #2
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    RE: Grounding the Panels
    The AHJ may prefer that you have a Ground Wire attached to each panel via an approved connector.
    This way, you can un-mount the panel from the rack, then pull the DC connectors and lastly disconnect the ground wire.
    If the mounting hardware is also the ground connection, then you lose the ground connection first - not a good thing.

    Yes, the equipment ground wire is typically run with the Pos / Neg PV power wires.
    Article 690.47(c) has three options for AC & DC Grounding.

    Is your AHJ following 2011 NEC or 2014 NEC?
    2017 NEC is around the corner.

    Do you need to implement Rapid Shutdown?

    Your AHJ may interpret the NEC differently than another AHJ within the same state.
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  • davidwillis
    davidwillis Solar Expert Posts: 104 ✭✭
    #3
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    So for grounding you would say run a ground to each panel, then also bond each unistrut together and ground them as well.  I am fine with grounding each panel, but I really don't want to have to bond each piece of unistrut...?  I don't really get it, where do I stop, do I need to bond each metal roof panel on the whole roof, and every metal beam in the shed? 

    I am not sure which code they use, I need to call and find out, but they have been out of the office for the last couple of weeks.  I will ask about Rapid Shutdown.  If they make me implement that, then I may just go with micro inverters...?
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,746 ✭✭✭✭✭✭
    edited January 2017 #4
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    You need to know which code or all of this is a waste of time. Go see the AHJ and ask what they want? I use Prosolar and so I would say you need to go to  Unistrut and get some help.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • mvas
    mvas Registered Users Posts: 395 ✭✭✭
    edited January 2017 #5
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    RE: Grounding PV Panels .
    You said, "... run a ground to each panel ..."
    Let me clarify...
    YES, I would run a single equipment ground wire from panel to panel to panel to panel to the grounding point = daisy chain.
    NO, I would not run a separate ground wire from the grounding point to each panel = star layout 

    Unistrut shows a "WEEB Bonding Jumper" to bond to all parts to gound
    Also, WEB makes lay-in connectors.
    http://www.unistrut.us/a_files/TechRef/Unistrut_Installation_Manual_104-0404-000085-000.pdf

    You have to find out what the AHJ allows vs requires.
    At least, submit a 1-wire diagram with all volts and amps clearly labelled.
    Clearly show the equipment ground, all wire sizes and all wire types.

    Has the Electric Company approved your Grid-Tie plans?
    Do you have a NET Electric Meter that will record the power you generate?
    Are you doing a Supply Side Connection or are you Backfeeding the Main Panel?

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  • davidwillis
    davidwillis Solar Expert Posts: 104 ✭✭
    #6
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    Thanks!

    I am still trying to get a hold of someone to find out what they will allow.  It seems they are taking an extra long break.

    I am still in the planning stages, I need to find out what will be required to find out the cost for the system.  So I have not submitted anything,  Also I don't have the net meter yet,  they will not connect the net meter until the entire project has finished, and passed inspection.

    I will be back feeding the Main panel.
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  • mvas
    mvas Registered Users Posts: 395 ✭✭✭
    #7
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    What is the maximum AMPS that you are allowed to Back-Feed into your Main Service Panel?
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  • davidwillis
    davidwillis Solar Expert Posts: 104 ✭✭
    #8
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    I just talked to the guy in charge of solar in Idaho (where I am). 

    We will need to comply with NEC 2014 code.
    I need to bond every part of the mounting with certified bonding straps
    The panels need to be bonded to the mounting.
    I also need to incorporate "Rapid Shutdown"

    I am not sure the amps right now, but the electrician said it adding the inverters is under the 120%
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,746 ✭✭✭✭✭✭
    #9
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    You will be taking out a permit as the owner in this project correct? If not get your bids and pick the one that makes sense and is from a reputable company with metal roof experience. My 2 cents are just how I always avoid putting solar on a nice metal roof but....
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • mvas
    mvas Registered Users Posts: 395 ✭✭✭
    edited January 2017 #10
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    davidwillis said:
    I just talked to the guy in charge of solar in Idaho (where I am). 

    We will need to comply with NEC 2014 code.
    I need to bond every part of the mounting with certified bonding straps
    The panels need to be bonded to the mounting.
    I also need to incorporate "Rapid Shutdown"

    I am not sure the amps right now, but the electrician said it adding the inverters is under the 120%
    Rough Estimate ...
    16 rows x 12 panels/row  x 200 watts/panel = 38,400 Watts
    38,400 Watts / 240 Volts = 160 Amps 
    A 200 Amp Main Service Panel typically allows 20% more, or 40 Amps, max back-feed.
    Are you sure you can back-feed 160 Amps into your existing Main Service Panel ?
    This seems more like a Supply Side Connection via a new sub-panel dedicated to the four GTI's.

    Also, make sure you over-size ($$$) your long wires between the two buildings to prevent power loss.

    Make sure the AHJ approves your new DC grounding & AC grounding method.
    1) Will you need to add another Ground Rod?
    2) How will the DC Ground and AC Ground be bonded together?
    3) Can the PV Panels, the Rack & the Inverters be grounded to the existing AC Grounding Electrode System?
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  • davidwillis
    davidwillis Solar Expert Posts: 104 ✭✭
    #11
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    Thanks

    I will have the electrician verify the 20% on the panel, I am not sure.

    The AHJ says I may be able to ground to the shed structure if it is grounded, or I will need to run a ground rod, and connect to the AC ground.  He sounded like I would just connect both the ground rod and the AC ground to the panels/frame ground.


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