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by quickthrowman
1 day ago
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> Usually the exposed metallic parts will be “grounded” (bonded to the ground / protective earth / equipment grounding conductor / whatever your jurisdiction calls it at the inverter). It’s not usually, all of the panels and also the metal racking must be bonded and grounded. Supplementary grounds are allowed by the NEC, article 250.54 There are zero requirements for supplemental grounds, you could use a single 24AWG conductor bonded to a brad nail or a #6 bare copper conductor bonded to (3) 5/8” dia’ 10’ ground rods. The fact that there are no requirements should tell you something about the necessity of supplemental grounds. > 250.54 Auxiliary Grounding Electrodes.
One or more grounding electrodes shall be permitted to be connected to the equipment grounding conductors specified in 250.118 and shall not be required to comply with the electrode bonding requirements of 250.50 or 250.53(C) or the resistance requirements of 250.53(A)(2) Exception, but the earth shall not be used as an effective ground-fault current path as specified in 250.4(A)(5) and 250.4(B)(4). |
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And just because the NEC doesn’t say you need to mitigate touch potentials for a specific installation doesn’t mean that you shouldn’t. The NEC is just a bunch of requirements, not a complete guide to building safe, high quality electrical installations. And there appears to be plenty of guidance from IEEE about this if you feel like paying for a copy of the standard:
https://store.accuristech.com/ecia/products/preview/2085911
The NEC does have plenty to say about grounding for purposes of reducing potential differences in other (non-solar) installations, though. Swimming pools are a notable example (with no specific requirement IIRC to connect the fancy bonding to the Earth at the pool, but a typical concrete pool with NEC-mandated bonding is likely an excellent connection to the local soil).
Amusingly, an inspector could plausibly require an “equipotential plane” per NEC 547.44 if the solar array is accessible to livestock.
Alternatively, from first principles: suppose you are standing with bare feet on wet soil 100 meters from a building. That building has a very nice ground rod array, giving an impedance of 50 ohms from the building’s ground to your feet. Now take a long wire that is insulated except at the ends, connect one end to the building ground, and firmly hold the other end in your hand. How do you feel about this situation? You have a nice wire loop, potentially with area on the order of 100m^2, containing your heart. It can inductively couple to time-varying magnetic fields (e.g. the fields around nearby transmission lines) and it can capacitively couple to other conductors. It can resistively couple to power lines with multiply grounded neutral or to electrified railways or to nearby buildings with old-style (earlier NEC revisions) shared neutral/ground feeds And lightning can strike the array. I think it would be wise to ground the array to earth to reduce the potential difference between the frame and earth.