Bare Ground vs. Shielded Ground

I am in the final phase of a DIY ground mount PV system, utilizing SMA 5000 and SMA 7000 inverters. I was fortunate enough to be able to route all my wiring from the inverters to my service panel inside the wall for a clean look, so I have had to use romex for that portion of the wiring. Here is the electrical path: conductors from each inverter to a 100 amp combiner subpanel, then to the AC disconnect, and finally to the service panel. My romex from the combiner subpanel to the AC disconnect to the service panel is 4-3 with ground (okay, perhaps a little overkill). Here is my question: someone told me the ground I run from the subpanel to the AC disconnect and then to the service panel has to be either THHN or THWN, that I cannot use the bare ground wire provided in the 4-3 WG. Yet other subpanels that I have with similar wiring that licensed electrical contractors have installed utilize the included bare ground for the grounding to the lugs. Can anyone tell me if this alleged requirement to have the ground be THHN for real and if so, is it some kind of special solar requirement? Many thanks in advance.

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Bare Ground vs. Shielded Ground

    You have to find out what version of the NEC your local building inspector uses -- then find the chapter an verse that allows, or forbids, exactly what you want to do...

    Decades ago, the portion of the code on grounding for a home allowed either a 8 awg insulated wire or a 6 awg bare wire. (not saying that is true today).

    You may also need to look at conduit fill sections to ensure that you meet those requirements too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • newenergy
    newenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    Re: Bare Ground vs. Shielded Ground

    I haven't heard of anything like this. I'm about 90% sure this isn't required and 99.99% sure it doesn't have anything to do with solar. I participate in a couple other forums for electrical contractors, one at contractortalk.com and another at mikeholt.com. You might go post the questions there.

    The closest thing I can think of off hand (and I'm no expert) are:

    250.120(C) - paraphrasing - EG < 6awg must be protected by raceway or cable armor except where run in hollow spaces of walls or partitions

    Could also be some confusion about running in conduit with stranded wire - needing a jacket.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Bare Ground vs. Shielded Ground

    this does appear like an interpretation type situation. my first thought was no it doesn't need it, but as was pointed out an inspector may view otherwise no matter who says what on any forum.
    maybe newenergy would be kind enough to pose the question for you on some of the other sites to save you the trouble of signing up just for this question as more opinions would be good even if your inspector says otherwise.
  • newenergy
    newenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    Re: Bare Ground vs. Shielded Ground

    Sure, I'll post it and get back to you.

    Inspectors can't just require whatever they feel like. The AHJ (generally the city) will generally adopt a version of the NEC and may or may not have extra requirements, but they will be official requirements and not just left to the inspector.

    If it's not too big a thing, I'll do pretty much whatever an inspector wants. If what the inspector wants should not be required and would be difficult or expensive I'll try to figure out why they think it's required and explain why this isn't the same thing. If I can't figure it out, I just have to ask them for a code reference. I haven't yet failed to resolve it at that point, but if you have to you can ask for their supervisor.

    But, that's getting ahead of ourselves here. OP said "someone" told him, not the inspector.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Bare Ground vs. Shielded Ground

    And make sure you agree with the inspector's interpretations... He/she should be able to show you the requirement(s) in their code book.

    In many US locations, the inspector is not responsible for "inspection" failures.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Bare Ground vs. Shielded Ground

    it can be a local electrician's point of view too, but they charge $ and won't usually make you change another violation they may see so this is an alternative. as to the nec it is not law unless the local city or town adopts it as so and they can change it to suit themselves in their own city/town as long as that change becomes law or uniform for all. most towns, if they even have an inspector, have only one so it is whatever he wants. if you don't want to pay or chance the inspector then advice here may help, but could go against what your locality would allow and yes, we have to voice this almost to the point of being a disclaimer.
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Bare Ground vs. Shielded Ground

    Okay, first of all, there are a couple of different things covered under the label "grounding". There is "system ground" and "equipment ground" and "grounding electrode". There are also conductors, such as "grounding electrode conductor" and "equipment grounding conductor".

    What you are specifically talking about is an "equipment grounding conductor". And - what you're asking about is the type of conductor, not the size.

    Well...the thing is, equipment grounding conductors don't even have to be *wire* - much less THHN or THWN or whatever specific type of wire.

    So whoever told you what they told you isn't paying attention.

    The code requires that your equipment grounding conductor provide a suitable "effective fault current path to ground".

    Properly installed RMC or EMT conduit can serve as the equipment grounding conductor - and it's obviously not THHN or THWN. AC cable (similar to romex but armored with a metal outer layer AND has a metal bonding strip alongside the wires) is allowed to serve as an equipment grounding conductor, but MC cable (same thing, but without the little metal strip down the inside) is not.

    The "grounding electrode conductor" (from panel ground/neutral bus to ground rod) is a special case - it has to be unbroken. But an equipment grounding conductor doesn't even have that requirement.


    Anyway, NEC Section 250.118 covers the different types of whatzitz, gizmos and doohickeys allowed to serve as equipment grounding conductors, and I don't have a code book handy, so I'll leave it to someone else to look it up.


    Here's a link to something appropriate...has a couple of handy tables too:

    http://www.steelconduit.org/pdf/TechTalk_EquipmentGrounding.pdf
  • newenergy
    newenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    Re: Bare Ground vs. Shielded Ground

    On the electrical contractor's forum they are making fun of whoever this "someone" is. They are a tough crowd. I'm lucky no one has told me to burn up my license for even relaying the question.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Bare Ground vs. Shielded Ground

    i'll thank you for doing it for him seeing as how i asked you to. so besides making fun of that someone what else did they say just for the op? i know my first thought was that the covering was not required, but hey i don't know it all.;)
  • newenergy
    newenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    Re: Bare Ground vs. Shielded Ground

    "Someone was? An electrician? An anonymous person? An idiot?"

    "I would really like to meet Someone. It seems this Someone person needs educated."

    "i have not heard of this"


    I told you it was a tough crowd.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Bare Ground vs. Shielded Ground

    so i guess going there and saying watts up wouldn't fly.:roll::p
  • Jimsolar
    Jimsolar Registered Users Posts: 10
    Re: Bare Ground vs. Shielded Ground

    Wow, thank you all so much for your great advice (and for the humiliation involved in relaying my question to your other forum). For the record, the "someone" was the project manager for the solar company I am buying my equipment from. He never told me why I can't use bare, just twice said the ground had to be THHN or THWN. So, instead of contacting the County of San Diego Dept. of Building & Safety to try and clarify, I am going to simply leave my bare ground alone. If the inspector balks at it, I'll follow his direction and run the THHN ground. This ground is indeed different from the others: I also have direct grounds at my house to the grounding rod from: 1) my service panel, 2) each inverter; then at my solar ground mount field 150 feet away I have each DC disconnect as well as the grounds from all the modules and racks directly grounded to another ground rod. So, I think I am pretty well grounded here. Again, many thanks for your comments!
  • sub3marathonman
    sub3marathonman Solar Expert Posts: 300 ✭✭✭
    Re: Bare Ground vs. Shielded Ground
    dwh wrote: »
    Well...the thing is, equipment grounding conductors don't even have to be *wire* - much less THHN or THWN or whatever specific type of wire.

    So whoever told you what they told you isn't paying attention.

    The code requires that your equipment grounding conductor provide a suitable "effective fault current path to ground".

    Properly installed RMC or EMT conduit can serve as the equipment grounding conductor - and it's obviously not THHN or THWN. AC cable (similar to romex but armored with a metal outer layer AND has a metal bonding strip alongside the wires) is allowed to serve as an equipment grounding conductor, but MC cable (same thing, but without the little metal strip down the inside) is not.

    The "grounding electrode conductor" (from panel ground/neutral bus to ground rod) is a special case - it has to be unbroken. But an equipment grounding conductor doesn't even have that requirement.


    Anyway, NEC Section 250.118 covers the different types of whatzitz, gizmos and doohickeys allowed to serve as equipment grounding conductors, and I don't have a code book handy, so I'll leave it to someone else to look it up.


    Here's a link to something appropriate...has a couple of handy tables too:

    http://www.steelconduit.org/pdf/TechTalk_EquipmentGrounding.pdf

    That's what I thought too. The NEC said it was OK, but the local inspectors here didn't like the idea of conduit being the equipment grounding conductor at all. What I've found is that different areas of the country have different opinions about this, so you really must check with the local people.

    This resulted in me having to run another set of conduit, because I had calculated the wire fill without another wire for grounding (like the NEC says is OK). But, on the plus side, I was then able to greatly upsize the wire that I was using to reduce the losses. (On a side note, if you upsize the wire, the requirements for the grounding wire guage could change too.)
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Bare Ground vs. Shielded Ground
    Jimsolar wrote: »
    This ground is indeed different from the others: I also have direct grounds at my house to the grounding rod from: 1) my service panel, 2) each inverter; then at my solar ground mount field 150 feet away I have each DC disconnect as well as the grounds from all the modules and racks directly grounded to another ground rod. So, I think I am pretty well grounded here. Again, many thanks for your comments!

    Yea. See, in my mind the ground rods and the conductors leading to the ground rods are "grounding" and all the whatzitz (wire/conduit/raceway/whatever) that connects to it is what I consider "bonding".

    The "ground" conductor from one electrical box to another is actually just a "bond" that "leads to" the ground.

    Your neutral has to be "bonded to ground" - but only at the main panel. All the other "green or bare stuff" is just a way to bond all the metal (boxes, chassis, metal straps on receptacles and switches (and the screws that hold the plates on) etc.) together to get any fault current back to the place where the ground is.


    (There is generally nothing wrong with extra connections from the equipment grounding system to ground rods as well as the rest of the equipment grounding system; i.e., directly connecting inverter chassis to ground rods. (Though there may be noise problems due to ground loops.)

    Readers should note however that multiple connections from the ground system to ground rods IS different than multiple connections between neutral and ground - which is normally not allowed.)
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Bare Ground vs. Shielded Ground
    That's what I thought too. The NEC said it was OK, but the local inspectors here didn't like the idea of conduit being the equipment grounding conductor at all. What I've found is that different areas of the country have different opinions about this, so you really must check with the local people.

    This resulted in me having to run another set of conduit, because I had calculated the wire fill without another wire for grounding (like the NEC says is OK). But, on the plus side, I was then able to greatly upsize the wire that I was using to reduce the losses. (On a side note, if you upsize the wire, the requirements for the grounding wire guage could change too.)


    No doubt.

    When I was a working journeyman probably 70% of my work was Beverly Hills estates. At that time (probably still the same) Beverly Hills had their own standards...for instance, no PVC or Romex allowed - everything had to be run in metallic conduit. AND every conduit had to have a ground wire pulled in it. Every box, every device, every fixture had to be pigtail bonded to the ground wire.

    Burbank was pretty much the same - I remember having to remove an armored #4 grounding electrode conductor and re-install it because the inspector decided (after the fact) that it would be better if it was run inside of RMC...armor *inside* of rigid.

    I asked several inspectors "why", but they didn't know. Finally one guy (an architect IIRC) did answer the question, though whether he was correct or not I can't say. Either way, his answer was, "Because neither Burbank nor Beverly Hills has ever had a HUD loan for public housing 'projects', and thus they've never had to lower their standards to comply with the NEC."
  • boB
    boB Solar Expert Posts: 1,030 ✭✭✭✭
    Re: Bare Ground vs. Shielded Ground

    One problem (I think), with using conduit as the gnd conductor is that the conduit usually has fittings that can add resistance and get loose or bad (between sections of spliced conduit)

    I prefer insulated gnd wire only because I might slip while holding a hot conductor and short it out to that bare ground wire.

    my 3 cents for today.

    boB
  • newenergy
    newenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    Re: Bare Ground vs. Shielded Ground

    It seems pretty clear that metal conduit inside the walls is to protect the conductors from nails and such. Lots of cities have some extra requirements though - I could be wrong, but don't think taking HUD money = you can't have any extra requirement over the NEC.

    In theory you can count the metal conduit as equipment grounding, but I don't think any of the cities here would let you get away with it if they noticed. If they did let you use the raceway as an equipment grounding conductor how would you know what it's ampacity is? You are required to size the EGC of a system with ground fault protection by table 250.122 (690.45 (A)). That table lists AWG sizes.
  • tallgirl
    tallgirl Solar Expert Posts: 413 ✭✭
    Re: Bare Ground vs. Shielded Ground
    newenergy wrote: »
    It seems pretty clear that metal conduit inside the walls is to protect the conductors from nails and such. Lots of cities have some extra requirements though - I could be wrong, but don't think taking HUD money = you can't have any extra requirement over the NEC.

    In theory you can count the metal conduit as equipment grounding, but I don't think any of the cities here would let you get away with it if they noticed. If they did let you use the raceway as an equipment grounding conductor how would you know what it's ampacity is? You are required to size the EGC of a system with ground fault protection by table 250.122 (690.45 (A)). That table lists AWG sizes.

    The cross-sectional area of EMT and Rigid is pretty much high enough to cover any fault current requirements.

    As I understand it, the restrictions against using pipe as the EGC is that too many electricians can't seem to make permanent and effective connections from one piece of pipe to the next. The NFSA folks should get rid of the option to use pipe that way, but that would mean admitting a boat load of electricians can't run pipe properly!
  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Bare Ground vs. Shielded Ground
    tallgirl wrote: »
    As I understand it, the restrictions against using pipe as the EGC is that too many electricians can't seem to make permanent and effective connections from one piece of pipe to the next.

    Hrmm..thought I had posted on this but I guess I somehow screwed it up...

    I don't think it's so much from one pipe to the next as it is from the pipe to the box. Cast-type lockrings have teeth which protrude out both sides, so it doesn't matter which way you install it - as long as it's tight it'll bite.

    But stamped-type lockrings generally only have teeth protruding on one side - so they have to be installed with the teeth toward the penetration.

    I cannot begin to count how many times I've seen stamped-type lockrings installed with the teeth pointing out and thus NOT biting into the box.