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g/solar • Posted by u/roof_mount_ray •

Grounding and bonding on a residential rooftop solar system — AC and DC side

Working through NEC Article 690 for the first time on a new install. The DC side grounding requirements are the part that's confusing me. Specifically:

  1. Do I need equipment grounding conductors (EGC) on both positive and negative conductors?
  2. How does the grounding electrode system for the solar array relate to the existing building GES?
  3. What's the purpose of the AC grounding electrode at the inverter location when the inverter is already connected to the existing building GES?
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u/battery_backup_brad •

The 2023 NEC (Article 690) has some meaningful changes from 2020. If you're working from an older reference, make sure you're reading the code edition that your AHJ has adopted.

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u/solar_steve •

For a transformerless inverter (most modern string inverters): (1) NEC 690.41 requires the PV output circuit to be ungrounded — so no intentional grounding of positive or negative. EGCs are required for the metallic conduit and racking, but not the conductors. (2) The array GES is bonded to the building GES per 250.52 — they must be the same or interconnected. (3) The AC grounding electrode at the inverter is for the AC output equipment, same as any HVAC unit or subpanel at that location.

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u/nec_nerd •

Key distinction: Equipment grounding conductors (EGC) ground the metallic racking and hardware. Functional grounded systems (transformerless inverters) do not intentionally ground either conductor of the PV output circuit, but do require Ground Fault Detection and Interruption (GFDI). The old two-wire system with grounded conductor is mostly gone with modern equipment.

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