Field reference for utility scale solar technicians. 8 entries, taken from the FieldWatt app.
Reference notes from FieldWatt, the offline field toolkit for utility scale solar commissioning and O&M technicians. It works with no cell signal, because the sites do not have any.
Get FieldWatt on the App StoreArticle 690 carries the prescriptive PV rules: string voltage calculation, conductor sizing, overcurrent protection, disconnects. Article 691 covers large scale PV electric supply stations, generally 5 megawatts and larger, not open to the public, under qualified supervision: there the plant is designed under engineering supervision and documented practices can replace some prescriptive 690 requirements. Utility scale technicians live under 691 plants designed by a PE, which is why the stamped drawings and site engineering documents always govern over generic calculations. FieldWatt calculators follow 690 math and flag when 691 likely applies.
The authority having jurisdiction and the stamped drawings govern. Code cycles 2017, 2020, 2023, and 2026 differ in detail.
Multiply rated module Voc by the factor for the lowest expected ambient temperature. Applies to crystalline and multicrystalline silicon when the manufacturer temperature coefficient is not used. Ambient 24 to 20 C: 1.02 Ambient 19 to 15 C: 1.04 Ambient 14 to 10 C: 1.06 Ambient 9 to 5 C: 1.08 Ambient 4 to 0 C: 1.10 Ambient −1 to −5 C: 1.12 Ambient −6 to −10 C: 1.14 Ambient −11 to −15 C: 1.16 Ambient −16 to −20 C: 1.18 Ambient −21 to −25 C: 1.20 Ambient −26 to −30 C: 1.21 Ambient −31 to −35 C: 1.23 Ambient −36 to −40 C: 1.25 Using the module Voc temperature coefficient with the record low ambient gives a more exact answer and is what the Max String Size calculator supports as its second method.
Confirm the factor against the code year adopted at the site.
Multiply conductor ampacity by the factor for the design ambient. 10 C or less: 1.15 11 to 15 C: 1.12 16 to 20 C: 1.08 21 to 25 C: 1.04 26 to 30 C: 1.00 31 to 35 C: 0.96 36 to 40 C: 0.91 41 to 45 C: 0.87 46 to 50 C: 0.82 51 to 55 C: 0.76 56 to 60 C: 0.71 61 to 65 C: 0.65 66 to 70 C: 0.58 71 to 75 C: 0.50 76 to 80 C: 0.41 81 to 85 C: 0.29
From the NEC ambient correction table for 90 C insulation on a 30 C base; verify against the adopted code year.
When more than three current carrying conductors share a raceway or cable, multiply ampacity by: 4 to 6 conductors: 0.80 7 to 9 conductors: 0.70 10 to 20 conductors: 0.50 21 to 30 conductors: 0.45 31 to 40 conductors: 0.40 41 and more: 0.35 On DC source circuits both polarities count as current carrying. Stacking many strings in one conduit murders ampacity; this factor is why.
Verify against the adopted code year and any engineering supervision provisions under Article 691.
Base ampacities before correction and adjustment (90 C insulation such as PV wire, in raceway): Copper: 14 AWG 25 A, 12 AWG 30 A, 10 AWG 40 A, 8 AWG 55 A, 6 AWG 75 A, 4 AWG 95 A, 3 AWG 115 A, 2 AWG 130 A, 1 AWG 145 A, 1/0 170 A, 2/0 195 A, 3/0 225 A, 4/0 260 A, 250 kcmil 290 A, 300 kcmil 320 A, 350 kcmil 350 A, 400 kcmil 380 A, 500 kcmil 430 A, 600 kcmil 475 A, 750 kcmil 535 A, 1000 kcmil 615 A Aluminum: 6 AWG 60 A, 4 AWG 75 A, 3 AWG 85 A, 2 AWG 100 A, 1 AWG 115 A, 1/0 135 A, 2/0 150 A, 3/0 175 A, 4/0 205 A, 250 kcmil 230 A, 300 kcmil 260 A, 350 kcmil 280 A, 400 kcmil 305 A, 500 kcmil 350 A, 600 kcmil 385 A, 750 kcmil 435 A, 1000 kcmil 500 A
Small conductor overcurrent limits and terminal temperature ratings still apply; verify against the adopted code year.
Stranded conductors, for voltage drop estimates. Copper: 14 AWG 3.14, 12 AWG 1.98, 10 AWG 1.24, 8 AWG 0.778, 6 AWG 0.491, 4 AWG 0.308, 3 AWG 0.245, 2 AWG 0.194, 1 AWG 0.154, 1/0 0.122, 2/0 0.0967, 3/0 0.0766, 4/0 0.0608, 250 kcmil 0.0515, 300 kcmil 0.0429, 350 kcmil 0.0367, 400 kcmil 0.0321, 500 kcmil 0.0258, 600 kcmil 0.0214, 750 kcmil 0.0171, 1000 kcmil 0.0129 Aluminum: 12 AWG 3.25, 10 AWG 2.04, 8 AWG 1.28, 6 AWG 0.808, 4 AWG 0.508, 2 AWG 0.319, 1 AWG 0.253, 1/0 0.201, 2/0 0.159, 3/0 0.126, 4/0 0.100, 250 kcmil 0.0847, 300 kcmil 0.0707, 350 kcmil 0.0605, 400 kcmil 0.0529, 500 kcmil 0.0424, 600 kcmil 0.0353, 750 kcmil 0.0282, 1000 kcmil 0.0212
From NEC Chapter 9 Table 8 values; the Voltage Drop calculator uses these.
Minimum insulation resistance by system voltage, with the matching test voltage: System voltage under 120 V: test at 250 V, minimum 0.5 megohm System voltage 120 to 500 V: test at 500 V, minimum 1 megohm System voltage over 500 V (includes 1000 and 1500 V plants): test at 1000 V, minimum 1 megohm These are pass or fail floors, not health targets: dry healthy utility scale circuits usually read far higher. Disconnect surge protective devices before testing and follow manufacturer guidance on maximum test voltage.
From the IEC 62446 1 test method table; site O&M agreements may impose stricter targets.
The manufacturer label on the enclosure or lug is always the authority. When a label is unreadable and no documentation exists, the recognized defaults (from UL 486A style tables) for wire binding and lug screws: Slotted screw lugs, 10 AWG and smaller: 20 to 25 inch pounds Slotted screw lugs, 8 AWG: 25 to 30 inch pounds Hex or Allen drive lugs, 6 to 4 AWG: 45 inch pounds Hex or Allen drive lugs, 3 to 1 AWG: 50 inch pounds Hex or Allen drive lugs, 1/0 to 2/0: 120 inch pounds Hex or Allen drive lugs, 3/0 to 350 kcmil: 275 inch pounds Hex or Allen drive lugs, 400 to 500 kcmil: 375 inch pounds Use a calibrated torque tool, mark completed terminations, and recheck aluminum terminations within the first year.
Generic defaults only. The equipment label and manufacturer sheet govern.
Reference notes from FieldWatt, the offline field toolkit for utility scale solar commissioning and O&M technicians. It works with no cell signal, because the sites do not have any.
Get FieldWatt on the App StoreThese notes are a field aid, not a substitute for the governing codes, the stamped drawings, the authority having jurisdiction, or manufacturer manuals. Verify against the current documentation for your installed equipment.