Equipment grounding connects the metal parts that normally carry no current to ground. In a PV system these include module frames, racks, enclosures, junction boxes and conduit. Bonding these parts together keeps them at the same voltage, which reduces shock risk. Grounding also limits lightning and surge effects and lets the inverter's fault detection work. Every PV system needs equipment grounding, including systems whose inverter runs an ungrounded array. Only some systems also need system grounding, which connects a current-carrying conductor to earth. The equipment grounding conductor (EGC) can be a wire, busbar, metallic raceway or structural component. Once the PV circuit conductors leave the array area, the EGC must run with them. The EGC is sized from the overcurrent device rating using NEC Table 250.122 and must be at least 14 AWG. It does not need to be upsized for voltage drop. Modules can be bonded with listed bonding washers, clips, lay-in lugs or identified bonding jumpers. On anodized or oxidized aluminum, simply bolting parts together may not make a good bond, and copper should not touch aluminum directly. Inverters have a marked equipment grounding terminal for the EGC. Use the conductor sizes and materials given in the product manual. Related concepts include equipotential bonding, the grounding electrode system and DC ground-fault protection. Equipment grounding conductors and system grounding conductors are bonded together only at the source of supply.
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related_toc1 drafted · lead Equipotential bonding
Equipment grounding relies on bonding module frames, racks, enclosures, junction boxes and conduit together so they stay at the same voltage.
sec=4.4 h=cb6192e3e9e2sec=h151 h=4b8c8bf3de00c2 drafted · lead Electric shock
Grounding exposed metal parts lowers the risk of shock to personnel.
sec=4.4 h=cb6192e3e9e2sec=h151 h=4b8c8bf3de00c3 drafted · lead Grounding electrode system
The grounding electrode conductor connects the EGC or the grounded system conductor to the grounding electrode system.
sec=h151 h=4b8c8bf3de00c4 drafted · lead DC ground-fault protection
Inverter fault monitoring and detection depend on grounding. In PV systems that are not solidly grounded, the output EGC may serve as the ground connection for ground-fault protection.
sec=4.4 h=cb6192e3e9e2sec=h111 h=0e2ddb8366bbc5 drafted · lead Ungrounded PV array
Equipment grounding is still required when the inverter runs with an ungrounded PV array.
sec=h52 h=8c1e89a98c24sec=h51 h=e37d55903117sec=4.4 h=cb6192e3e9e2c6 drafted · lead NEC 2017 690.47 Grounding electrode system proposed
Scope: standard NFPA 70 (NEC) 2017 proposed
For PV systems that are not solidly grounded, the output EGC to distribution equipment may be the array's connection to ground.
sec=h111 h=0e2ddb8366bbc7 drafted · lead Overcurrent protection
The minimum EGC size follows from the rating of the upstream overcurrent device.
tbl=3 h=3dda0f83f298sec=h22 h=8cdfca5162dcsec=h24 h=0a63fd9f8895c8 drafted · lead Voltage drop
The code does not require the EGC to be upsized to address voltage drop.
sec=h22 h=8cdfca5162dcsec=h24 h=0a63fd9f8895c9 drafted · lead Dissimilar metal insulation
Copper grounding conductors should not touch aluminum frames directly. Special washers or lugs make the joint.
sec=h151 h=4b8c8bf3de00c10 drafted · lead UL 1703 proposed
Module manufacturers must state their approved grounding methods in the listed installation instructions.
sec=h151 h=4b8c8bf3de00c11 drafted · lead UL 2703 proposed
UL 2703 is the standard for module racking systems, which covers generic grounding and bonding.
sec=h151 h=4b8c8bf3de00review note: support check: partial - Passage mentions UL2703 as a standard for module racking systems being revised to accommodate generic grounding, but does not clearly say it covers generic grounding and bonding.
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