Grounding wire same trench as solar (NEC question)

I have approximately a 100' run from my proposed PV mounting location to the grounding rod for my pole barn. I plan on installing a grounding rod at the PV structure location, tieing the structure to it, then running a #6 bare solid copper run between the two copper grounding rods. Can the wires coming off the PV (#0AWG) be buried in the same trench as the bonding ground wire? If so, how deep and how much separation?

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  • vtmapsvtmaps Solar Expert Posts: 3,739 ✭✭✭✭
    Re: Grounding wire same trench as solar (NEC question)
    Brewgonia wrote: »
    I have approximately a 100' run from my proposed PV mounting location to the grounding rod for my pole barn. I plan on installing a grounding rod at the PV structure location, tieing the structure to it, then running a #6 bare solid copper run between the two copper grounding rods. Can the wires coming off the PV (#0AWG) be buried in the same trench as the bonding ground wire? If so, how deep and how much separation?

    My (limited) understanding of code is that there must be an insulated green ground wire in the conduit with your #0 PV wires. Personally, I think it is better to have bare copper in the trench. I guess the code is paranoid that the bare wire could be interrupted, but the green wire in conduit is better protected.

    Yes, the ground and power wires can share a trench, they can even share a conduit (but ground needs green insulation if in conduit).

    I don't know how deep the trench must be... that may depend on your local geology, local frost conditions, and which schedule conduit you use. Is the trench running under a driveway? My local phone company required my trench to be 2 ft deep (with 6 inches of sand) with 2 inch PVC conduit. The conduit was schedule 40, except where it crossed the driveway where it is schedule 80. I'm off grid, but I believe the local power company requires 4 ft deep trenches with more sand.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: Grounding wire same trench as solar (NEC question)
    Brewgonia wrote: »
    I have approximately a 100' run from my proposed PV mounting location to the grounding rod for my pole barn. I plan on installing a grounding rod at the PV structure location, tieing the structure to it, then running a #6 bare solid copper run between the two copper grounding rods. Can the wires coming off the PV (#0AWG) be buried in the same trench as the bonding ground wire? If so, how deep and how much separation?


    Do yo have drawings or pics. I don't get it.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grounding wire same trench as solar (NEC question)

    A ground wire doesn't actually do anything until something goes wrong.

    Were it me I would ground the array at the site with its own rod and not make a run back to the house.

    As vtMaps said, when you do this you use an insulated #6 minimum wire in the conduit. There does not need to be any separation because the ground wire doesn't do anything, is insulated (as are the other wires), and protected by conduit. No different than ordinary AC cable through conduit in that respect.

    Use of uninsulated copper ground wire in a trench is for connecting two grounding points together so they act as one.

    What an inspector will approve may be something altogether different.
  • BrewgoniaBrewgonia Solar Expert Posts: 31
    Re: Grounding wire same trench as solar (NEC question)

    So I guess my next question is "are the two grounding points REQUIRED to be bonded together?" And if so, why. I imagine if there's a potential to use a grid tie inverter that would be one reason?
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: Grounding wire same trench as solar (NEC question)
    Brewgonia wrote: »
    So I guess my next question is "are the two grounding points REQUIRED to be bonded together?" And if so, why. I imagine if there's a potential to use a grid tie inverter that would be one reason?
    If it's a "complete" mechanical system all points of that system should be ground bonded.
    Not only because possible defective labor, because also PV is prone to lightning.
    If an event occurs at point a destination and it isn't bonded to point B there could be a point of failure between the 2 points, which can then cause a fire. Refer to NFPA investigation of the sunpower bakers field fire that didn't have ground fault protection between 2 points of conduit interconnection.
    personally I exceed code. I don't use 6AWG I use 4AWG for GEC. I do this because many manufacturers now call out for lightning supression (I.E) enphase, powerone, if following the bare minimum code requirements.
    For my installations it's cheaper to just spend the extra .10 per foot on bare solid 4AWG rather than 6AWG. That way I can disregard the install time for lightening suppressor.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grounding wire same trench as solar (NEC question)

    In case anyone is confused about this the use of 4 AWG in place of 6 AWG for connecting the ground points is in no way a substitute for having a lightning arrestor on the PV lines.
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: Grounding wire same trench as solar (NEC question)
    In case anyone is confused about this the use of 4 AWG in place of 6 AWG for connecting the ground points is in no way a substitute for having a lightning arrestor on the PV lines.
    So are you telling me it has to be used?
    In all the instruction manuals it says "recommended". Or we "recommend"for warranty.
    i've had 2 disputes over warranty claims not using the arrestor/suppressors. Since I've built beyond the minimum, I have sufficed warranty and been covered on equipment, beyond not using arrestors, what exactly does the arrestor do that an improved GEC can't do?
    Just want to get down to the nitty gritty behind this.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grounding wire same trench as solar (NEC question)

    Nope. Surge/lightning arrestors are not mandatory. In areas not subject to lightning strikes and even those that are there is no certainty that the PV wiring will ever become energized in this manner.
    But you can just bet it's an easy-out for manufacturers to say "no surge suppressor, that's what caused the damage" rather than honour a warranty claim.

    I'm just pointing out that a ground wire alone will not do anything towards stopping the damage that can result because the PV wiring itself can become energized in a strike situation. This is what the arrestors do; provide a path for the high Voltage, high frequency energy on the positive and negative wires to the ground wire.
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Re: Grounding wire same trench as solar (NEC question)

    So is it a Myth that electricity will flow at the least path of resistance, or am I not understanding the magnitude of lightning voltage?
    In theory if everything is bonded and exceeds ohm tests one would think that a surge of electricity would travel directly to ground electrode, rather than point of energized conductors.
    Isnt that the main point of bonding racking and weebing to GEC? Or why a lightening suppressor makes bonding with GEC? It just seems like another redundant failsafe to me.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grounding wire same trench as solar (NEC question)
    So is it a Myth that electricity will flow at the least path of resistance, or am I not understanding the magnitude of lightning voltage?
    In theory if everything is bonded and exceeds ohm tests one would think that a surge of electricity would travel directly to ground electrode, rather than point of energized conductors.
    Isnt that the main point of bonding racking and weebing to GEC? Or why a lightening suppressor makes bonding with GEC? It just seems like another redundant failsafe to me.

    Electricity will flow along any path it finds. The lower the resistance, the more flows through it.

    Lightning and its relate stray Voltage is extremely high Voltage compared to what we normally deal with. It can jump the high resistance gap of miles of air, so anything that even remotely resembles a conductor is no challenge for it. Fortunately it tends to be fairly low current.

    The supressors provide a 'gap' (not precisely) the high Voltage can 'jump' to ground from the positive and/or negative wires.

    Don't confuse lightning protection with electrical safety ground regulations.
  • BrewgoniaBrewgonia Solar Expert Posts: 31
    Re: Grounding wire same trench as solar (NEC question)

    My house has whole-house surge protection and surge protection on most electronic devices. However, that did little to stop damage done to several devices plugged in during two lightning strike events. The strikes took out the first device it found on each circuit.

    Sure wish I has lightning protection. The energy unleashed by a strike is of such magnitude and speed that only a full-blown and well designed system can help.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grounding wire same trench as solar (NEC question)
    Brewgonia wrote: »
    My house has whole-house surge protection and surge protection on most electronic devices. However, that did little to stop damage done to several devices plugged in during two lightning strike events. The strikes took out the first device it found on each circuit.

    Sure wish I has lightning protection. The energy unleashed by a strike is of such magnitude and speed that only a full-blown and well designed system can help.

    Yep: MOV surge suppressors aren't the same as lightning arrestors, and even arrestors need to be tailored for the circuit they protect. You may notice MidNite offers ones for nominal Voltages of 115, 300, and 600.
  • BrewgoniaBrewgonia Solar Expert Posts: 31
    Re: Grounding wire same trench as solar (NEC question)

    Interesting product. Mine is definitely old and is due for an upgrade. The MidNite product seems like a step up.
  • BB.BB. Super Moderators, Administrators Posts: 32,004 admin
    Re: Grounding wire same trench as solar (NEC question)

    And Lighting is an "RF" event (radio frequency around 7.5kHz maximum)... So it is no longer 'pure resistance' but complex impedance (inductance and capacitance affects the flow of lightning).

    Lightning events are not always "obvious" and there (appears) to be still a lot that we do not understand.

    As the others have said, you are almost designing two separate grounding systems. Once that is the traditional "green wire" to divert short circuits (DC/60 Hz) current back to the source (to pop the fuse/breaker and prevent people from getting shocked/starting fires).

    The second is a grounding system that follows the laws that lightning follows.

    And sometimes, the two sets of rules/practices are in conflict (follow some NEC requirements/recommendation and bring lightning inside the home from the solar array if struck by lightning).

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