Panel grounding in conduit...

HairfarmHairfarm Solar Expert Posts: 225 ✭✭✭
Greetings,

When I run the bare ground wire from my panels to the ground rod, can I run it in conduit too (along with the other + & - wires from the three strings) or does the it have to be run by itself down the side of the cabin away from the other wires going into the combiner box?

Comments

  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: Panel grounding in conduit...

    You can do it either way.
    If outside, just continue the bare wire (#8 min) down to your ground rod (if far from the main ground rod) or to the inverter ground if close. The advantage of this method is it keeps any lightning strikes separate from the PV conductors and minimizes induced surges.
    If inside, you should transition to stranded, insulated green wire (same size as conductors) and need to use bond bushings on both ends of the conduit to minimize the inductance of the conduit in event of a lightning strike. The advantage of this method it it has a cleaner, better looking appearance.
    I'm not clear on whether this "bond wire" is correctly called a EGC (equipment grounding conductor) or a GEC grounding electrode conductor) or is serving as both.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Panel grounding in conduit...

    Some of us prefer to keep the panel frame/mount ground away from other conductors as it is the one most likely to become energized from lightning. Best not to give a potential path to introduce thousands of Volts to the rest of the system.
  • HairfarmHairfarm Solar Expert Posts: 225 ✭✭✭
    Re: Panel grounding in conduit...
    Some of us prefer to keep the panel frame/mount ground away from other conductors as it is the one most likely to become energized from lightning. Best not to give a potential path to introduce thousands of Volts to the rest of the system.


    OK. I'm using s WEEB system for grounding panels to frame. I just wasn't sure If I should keep the bare ground wire outside of the main conduit run. I'll just keep the ground wire run separate to be safe.
  • BB.BB. Super Moderators, Administrators Posts: 32,005 admin
    Re: Panel grounding in conduit...

    I think somebody mentioned there was an NEC requirement about conduit, insulation, and wire gauge requierment... Somebody?

    -bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Panel grounding in conduit...

    i don't know of the nec ruling on it, but in the case of metalic conduit i would prefer it be insulated going through conduit being they are dissimilar metals.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Panel grounding in conduit...
    niel wrote: »
    i don't know of the nec ruling on it, but in the case of metalic conduit i would prefer it be insulated going through conduit being they are dissimilar metals.

    A very broad summary of the most relevant NEC rules:
    1. It depends on whether this will be a lightning protective ground or a Equipment Grounding Conductor (EGC) (or both)
    2. For an EGC, if the conduit you are using and the various fittings along the way are rated for use as an EGC and installed following the instructions, then it automatically meets the size requirement and there is no need for an additional wire.
    3. For galvanized interior surface of the conduit (not Electrical Metallic Tubing, EMT, which is what we typically think of incorrectly at conduit), contact with bare copper should not be a problem.
    4. If you are required to or choose to run an EGC inside the conduit, there are a variety of complicated rules about the wire size required, but no requirement that it be insulated. If it is insulated, it must be green or some listed variation on that.
    Beyond that, you should consult an electrician, because roaming through the NEC looking for everything that applies to your situation is not an easy task.
    SMA SB 3000, old BP panels.
  • jaggedbenjaggedben Solar Expert Posts: 230 ✭✭
    Re: Panel grounding in conduit...

    Standard practice in the industry is to transition to stranded insulated conductor at the junction box at the roof.

    As far as the NEC...

    -Putting a solid conductor larger than 8awg inside conduit is not allowed. (310.106(C)).
    -Not protecting a conductor smaller than 6awg inside something is not allowed. (690.46).
    inetdog wrote: »
    2. For an EGC, if the conduit you are using and the various fittings along the way are rated for use as an EGC and installed following the instructions, then it automatically meets the size requirement and there is no need for an additional wire.

    Over 250 volts the requirements are a bit more stringent. See 250.97.
  • BB.BB. Super Moderators, Administrators Posts: 32,005 admin
    Re: Panel grounding in conduit...

    Thank you jaggedben,

    I think the insulation question about grounding/conduit (EMT) was a mistake on my part--It was probably the solid vs stranded that I was miss-remembering.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • HairfarmHairfarm Solar Expert Posts: 225 ✭✭✭
    Re: Panel grounding in conduit...
    solarix wrote: »
    You can do it either way.
    If outside, just continue the bare wire (#8 min) down to your ground rod (if far from the main ground rod) or to the inverter ground if close. The advantage of this method is it keeps any lightning strikes separate from the PV conductors and minimizes induced surges.
    If inside, you should transition to stranded, insulated green wire (same size as conductors) and need to use bond bushings on both ends of the conduit to minimize the inductance of the conduit in event of a lightning strike. The advantage of this method it it has a cleaner, better looking appearance.
    I'm not clear on whether this "bond wire" is correctly called a EGC (equipment grounding conductor) or a GEC grounding electrode conductor) or is serving as both.

    I need to use bond bushings only if connected to a metal box with metal conduit, right? Not for PVC electrical conduit, right?
  • ARTsolarARTsolar Registered Users Posts: 14 ✭✭
    Re: Panel grounding in conduit...

    Article 690.43(f) states that the EGC must be installed in the same raceway or cable, or or run with single conductor listed and identified PV wire when leaving the vicinity of the array.

    Also if the conductor is subject to physical damage you would need at least a 6AWG conductor.

    One more article to consider is 250.64(c) that talks about the EGC being continuous but does give options for splicing
  • jaggedbenjaggedben Solar Expert Posts: 230 ✭✭
    Re: Panel grounding in conduit...
    ARTsolar wrote: »
    Article 690.43(f) states that the EGC must be installed in the same raceway or cable, or or run with single conductor listed and identified PV wire when leaving the vicinity of the array.

    The red part is incorrect. Requirements for single conductors are in different sections and don't apply to conductors in raceways.
    One more article to consider is 250.64(c) that talks about the EGC being continuous but does give options for splicing

    This applies to Grounding Electrode conductors. Not exactly the same subject. Many installers use irreversible splicing on array EGCs to avoid questions and confusion, and also because they are suitable for outdoor connections, but technically it's not required.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Panel grounding in conduit...
    jaggedben wrote: »
    The red part is incorrect. Requirements for single conductors are in different sections and don't apply to conductors in raceways.

    The quote was indeed incorrect, in that it included the word "single". It also does not appear to require use of PV wire for the EGC, but rather that the EGC must be with the PV wires. It for sure means that although you can use the frames and racking as part of the EGC connection, the part of the EGC going back to the electrical panel cannot travel by a different route than the associated DC or AC conductors.
    Anyway, you can all interpret it as you will. And so will the AHJ. :-)
    (F) All Conductors Together. Equipment grounding conductors
    for the PV array and structure (where installed)
    shall be contained within the same raceway or cable or
    otherwise run with the PV array circuit conductors when
    those circuit conductors leave the vicinity of the PV array
    .

    PS: 2011 NEC.
    SMA SB 3000, old BP panels.
  • HairfarmHairfarm Solar Expert Posts: 225 ✭✭✭
    Re: Panel grounding in conduit...

    Ok. This sounds like I can run up to 8AWG in my metal conduit and that it can be bare. Is this correct?
  • vtmapsvtmaps Solar Expert Posts: 3,739 ✭✭✭✭
    Re: Panel grounding in conduit...
    Hairfarm wrote: »
    Ok. This sounds like I can run up to 8AWG in my metal conduit and that it can be bare. Is this correct?

    No. If its in conduit it must be insulated. You don't want bare copper touching your conduit because dissimilar metals will corrode. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • HairfarmHairfarm Solar Expert Posts: 225 ✭✭✭
    Re: Panel grounding in conduit...
    vtmaps wrote: »
    No. If its in conduit it must be insulated. You don't want bare copper touching your conduit because dissimilar metals will corrode. --vtMaps

    So I can run 8 awg bare from the array to the combiner (on the roof) then convert to 8awg green insulated down the conduit. I just don't want a bare wire hanging on the side of my cabin. I'd rather have a cleaner look.

    Is that acceptable then?
  • jaggedbenjaggedben Solar Expert Posts: 230 ✭✭
    Re: Panel grounding in conduit...

    I really don't think bare copper inside galvanized conduit presents a corrosion concern. I've worked on dozens of systems where it was done and never has an inspector objected to it. Steel is used to connect copper wires all the time, and copper is used to bond steel all the time.

    (What does cause galvanic corrosion is copper contacting aluminum. When running bare wire for array grounding, do not zip-tie it directly against the aluminum. Let grounding lugs or whatever attachment methods you are using keep it separated.)

    With that said, running green insulated wire from the roof to the inverter is the usual method. I've only ever used bare copper in chases between arrays that did not have junction boxes on the end.
  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: Panel grounding in conduit...

    Good luck trying to jam 8awg bare copper through a conduit. Just use same size THHN green stranded wire (probably 10awg) as the conductors in the conduit. The real GEC grounding confusion comes between the inverter and the Grounding Electrode which has to be continuous, minimum of 8awg, or 6awg if run separately.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Panel grounding in conduit...

    Chemistry.
    Galvanization is done with zinc. Put it next to copper wire. Add moisture (electrolyte) and what have you got?

    Thing is, galvanized conduit is usually only coated on the outside, so it should not be a problem. If it were, well we couldn't connect the ground wires to the boxes could we? It would corrode off in one year.
  • HairfarmHairfarm Solar Expert Posts: 225 ✭✭✭
    Re: Panel grounding in conduit...
    With that said, running green insulated wire from the roof to the inverter is the usual method. I've only ever used bare copper in chases between arrays that did not have junction boxes on the end.

    That's sort of what I was planning to do. Except that after running bare #8 along my panel array to my combiner box (which is mounted on the roof near my panels.) I would then switch to #8 green insulated from the combiner down to the grounding earth rod.

    Does this sound acceptable or does the bare ground wire from the panels have to be run as one continuous unbroken line to the ground rod, and not be transitioned to green insulated in the combiner box? That is my main question.

    Hope that makes sense.

    thanks!
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Panel grounding in conduit...

    I believe the rule is that the line should be continuous, but this includes splices of the type that can't be taken apart. So no junctions with lugs and screws or wire bugs but solid crimp connections are okay.
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