Inspector tips for wiring solar PV

Solar PV inspections fail for the same reasons every time. Labels missing, working space ignored, conductor sizing off by one calc step. The code is clear but the field is messy. Here is what inspectors actually check on residential and small commercial PV jobs, and how to land your AHJ sign-off on the first trip.

Conductor sizing and the 125% rule stack

Per NEC 690.8(A) and 690.8(B), PV source and output circuit conductors get sized at 125% of Isc, then again at 125% for continuous duty. That is the 156% factor people argue about at plan review. Skip it and your wire gauge fails the first walkthrough.

For a string with Isc of 11A, you are sizing for 17.2A minimum before terminal temperature corrections per 110.14(C). Most 75C terminals on inverters and combiners push you to 12 AWG minimum, often 10 AWG once rooftop temperature adders from 690.31(A) and Table 310.15(B)(2)(a) hit you.

Run the rooftop temp adder before you pull wire. A black conduit on a Phoenix roof in July adds 33C to ambient. That bumps a 90C conductor ampacity calc hard, and inspectors will ask you to show the math.

Rapid shutdown labeling and function

NEC 690.12 rapid shutdown is the number one callback on inspections post-2017. The requirement is 80V or less within 30 seconds inside the array boundary, and 30V or less outside. Module-level electronics or a string-level RSD device both qualify, but the labeling at the initiator must match what is actually installed.

Inspectors will flip the switch and time it. They will also look for the 690.56(C) directory at the service equipment showing the location of all PV disconnects and the rapid shutdown initiator. Missing or wrong labels are an automatic correction.

• RSD initiator labeled per 690.56(C)(1) with the prescribed graphic and wording
• Solar PV system disconnect labeled per 690.13(B)
• DC conductor labels every 10 feet and at every transition per 690.31(D)(2)
• Bi-directional warning at the backfed breaker if applicable
• Plaque at service showing all power sources per 705.10

Working space and disconnect placement

110.26 working space is treated as if PV equipment is exempt by half the installers out there. It is not. Inverters, combiners, and disconnects all need 30 inches wide, 36 inches deep, and 6.5 feet headroom of clear working space when energized parts could be exposed during service.

705.12 service connections matter here too. If you backfeed a 200A panel with a 40A solar breaker, the 120% rule lets you do it only if the solar breaker is at the opposite end of the busbar from the main. Some panels physically cannot accommodate this. Check the panel listing before you promise the homeowner an interconnection.

Take a photo of the busbar and breaker layout before you leave the site for the design phase. Half the redesigns I have seen come from someone assuming the main is at the top when it is actually center-fed.

Grounding, bonding, and the EGC question

NEC 690.43 requires equipment grounding for all exposed non-current-carrying metal parts. Module frames, racking rails, combiner boxes, conduit, all of it. Use listed WEEB clips or equivalent bonding hardware, and document it. The inspector will ask which UL 2703 system you used.

The EGC sizing in 690.45 references 250.122, but for PV you size based on the OCPD protecting the circuit, not the conductor ampacity. A 20A string fuse means 12 AWG copper EGC minimum. Pull the larger gauge if you are running it any distance to keep voltage drop and fault clearing in check.

1. Verify racking system is UL 2703 listed for bonding
2. Use manufacturer-specified WEEB clips at every module-to-rail connection
3. Bond rails together with listed splice kits or jumpers
4. Land EGC on lay-in lug or listed grounding terminal at array
5. Run EGC continuous from array to inverter to service equipment

Conduit fill, expansion, and rooftop runs

Chapter 9 Table 4 and Table 5 fill calcs apply normally, but PV conduit on rooftops also needs expansion fittings per 352.44 for PVC. A 100 foot run on a roof that swings 60F seasonally needs roughly 3 inches of expansion accommodation. Without an expansion coupling, you will see broken conduit at the first cold snap.

EMT and metallic conduit get a pass on expansion in most cases but still need proper support per 358.30. Rooftop standoffs every 3 feet for EMT, 10 feet for rigid. Strut and clamp combinations need to be listed for outdoor use, not the indoor strut someone had in the truck.

Documentation the inspector wants in hand

Show up with a permit set, the equipment cut sheets, the wire and conduit schedule, and a one-line diagram. The inspector should not have to ask for any of it. If you do not have the listing label visible on a combiner, have the cut sheet ready.

For commercial jobs over 100kW or any system with energy storage, expect the inspector to ask about 690.4(B) qualified personnel requirements and 706 ESS code compliance. Have your installer certifications and the ESS commissioning report on the truck. A clean documentation package gets you signed off in 20 minutes. A messy one turns into a second trip.