1.38 KW Enphase D380 Grid Tie

FL SUN
FL SUN Solar Expert Posts: 94 ✭✭✭✭
Been a while since I have posted and wanted to do a small grid tie using the latest Enphase D380 dual inverters available on the market. System consists of 6 Ningbo 230 watt modules and 3 D380 inverters.

Layout, racking, rooftop electrical, and module installation took a day and 1/2 for me. My helpers all went to the Gator game today, so I had no choice but to do this by myself.:cry: Or wait for another weekend and that's not going to happen.

This roof is East facing on a 5/12 pitch. It fit 6 modules filling out most of the roof. My South facing exposure is great until this time of year when the sun sinks below some monstrous live oak trees in the front. Will eventually do something with them as they do block the winter sun on the roof, and I fear a hurricane will send one through the house one day when we get the 'big one'.

Tomorrow I hope to tie into the panel and be done with the electric. I do like how the system is configured except for the trunk cable. It is big and chunky. What to do with all that extra wire in between the factory take offs that you can't cut? I hate to see extra wire hanging below the array. Was able to secure it all, but it was a challenge.

Grounded all the rails, inverters, and panels with continuous #6 bare copper.

Question - The electrical will be penetrating the roof through a Soladeck combiner box, and run into the attic, punching through to the main panel below the meter. What should the ground wire be from the grounding block to the main panel ground be? #6 or #10 Bare or THHN? The concern is lightning being brought into the house by the ground wire ran in the attic. The branch feed circuit requires a 20 amp breaker.

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Comments

  • System2
    System2 Posts: 6,290 admin
    Re: 1.38 KW Enphase D380 Grid Tie

    I just did 6 sharp 235 watt on an old satalite pole and used #8 bare copper ground panal to inverter etc then to ground rod to my subpanel then 3 #6 wires with a ground back to my main. The ground from sub to main was a 10 or 12. I think if I would have put them on the roof I would have run a nice size ground to a ground rod and tied the two with the main. Just my 2 cents, no elect.
  • FL SUN
    FL SUN Solar Expert Posts: 94 ✭✭✭✭
    Re: 1.38 KW Enphase D380 Grid Tie

    Thanks for your response zank. Watch out for multiple ground rods that might create a ground loop (differing ground potential) if tied back to the main panel.

    I am still trying to get a handle on the grounding conductor from the array running through the attic to the main panel outside. What is the characteristic of lightning following a ground path through the attic of a house? Is there a chance that lightning could jump out of the wire and start a fire in the attic? I do know that lightning characteristics are very fickle. I used 10-3 Romex with ground from the grounding block in the Soladeck to the panel.

    So far on my array, got all the electric done, and verified output. Am having issues with the Envoy unit picking up signal from the inverters. I'll have to move it around today to get the signal to improve.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,422 admin
    Re: 1.38 KW Enphase D380 Grid Tie

    I hope Solar Guppy comes in with his experience...

    From a theoretical/engineering point of view---You want lightning ground conductors to be on the outside surface of the home, and if you have two or more down conductors, they should be on opposite sides of the home/building.

    Basically, lightning is a high frequency impulse current (around over 7-10 kHz or so). And RF energy wants to travel on the "skin" of the conductors--i.e., the self generated magnetic field forces the current "away from the center" of any conductors.

    So, for example, if you have some intentional or un-intentional lightning conductors (such as down spouts) on the outside of the building and you have DC ground going down the inside of the building--the lightning will try to leave the conductors inside the building for those on the outside edge (another thing to read about is Faraday Cages).

    So, you have the NEC normal safety requirements that use ground conductors to make exposed metal "safe" (if a power lead insulation fails, or a panel breaks) any energizing current to exposed/contacted metal framework will be safety sent to ground). Normally all AC conductors should travel in the same path/conduit--otherwise the AC flow from wires traveling different paths can act like a transformer and heat up metal enclosures, etc..

    Then you have the lightning ground requirements which require conductors to be outside the building at the extreme corners from other lightning conductors.

    Personally, I would not want the array grounding conductors to run through the middle of my home (if they are not in metal conduit).

    If they did run in the middle of my home, I would install a lightning grounding system with air conductors at the ridge line / near solar panels and run the heavy gauge/braided arrestor cable system down the outside of my home.

    I assume you saw the recent thread from "JESSICA" where the lightning jumped from a perfectly good long iron rod to the concrete building beside it and blew out some chunks of concrete.

    Weird thing 2

    Just because you have lightning current in some metal conductor--do not assume it will stay there.

    In the end--I do not live in lightning country, and I do not claim any special knowledge--I hope others here can add more experience to the conversation.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • FL SUN
    FL SUN Solar Expert Posts: 94 ✭✭✭✭
    Re: 1.38 KW Enphase D380 Grid Tie

    Bill, you hit the nail on the head regarding the dilemma with grounding conductors.
    So, you have the NEC normal safety requirements that use ground conductors to make exposed metal "safe" (if a power lead insulation fails, or a panel breaks) any energizing current to exposed/contacted metal framework will be safety sent to ground).
    Then you have the lightning ground requirements which require conductors to be outside the building at the extreme corners from other lightning conductors.

    NEC 690.31(E) requires all DC conductors to be in metal raceways or enclosures if run inside a building or structure. Typically that would also include the (chassis) grounding conductor. But with inverters on the roof, I only have AC conductors to bring down which doesn't require metal raceways or enclosures.

    My opinion is that the NEC does need to be re-written regarding rooftop micro-inverter use for solar systems and grounded conductors. It is confusing. :confused:
  • BB.
    BB. Super Moderators, Administrators Posts: 33,422 admin
    Re: 1.38 KW Enphase D380 Grid Tie

    I would also add, that placing copper grounding cables inside metal conduit/raceways is not, in my humble opinion, an answer either.

    The "ground current" will move to the outside conduit--and since it is a ferrous metal (iron/steel) conductor, it will have [I should say "may have"--there are lots of variables here that will affect common mode impedance] even higher inductance that a non-ferrous conductor (copper or aluminum).

    Again--leading to giving more reason for the lightning to leave the "ground path" and find other/lower impedance paths to ground (again, see "JESSICA's" Rebar Lightning Rod and damage at base).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset