
Solar Wire Sizer
NEC 690.8 Wire Sizer
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Solar Wire Sizer helps solar energy professionals select the correct wire size for PV systems based on NEC standards.
FEATURES:
- Wire sizing per NEC Table 310.16 ampacity ratings
- Max circuit current per NEC 690.8(A)(1): Isc x 1.25, then both printed 690.8(B) checks: base ampacity vs 156%, corrected ampacity vs 125%
- Voltage drop calculation with configurable thresholds (2-3%)
- Temperature derating per NEC Table 310.15(B)(1)
- Copper and aluminum conductor support
- DC, AC single-phase, and AC three-phase circuits
- 60C, 75C, and 90C insulation temperature ratings
- Wire sizes from 14 AWG to 500 kcmil
NEC COMPLIANCE:
- NEC 690.8(A),(B)(1),(B)(2) - PV circuit current and two-step conductor ampacity
- NEC 690.31 - Methods permitted for PV wiring
- NEC Table 310.16 - Allowable ampacities of insulated conductors
- NEC Table 310.15(B)(1) - Ambient temperature correction factors
- NEC Chapter 9 Table 8 - DC resistance values
OPTIONAL PRO UPGRADE - $2.99 ONE-TIME IN-APP PURCHASE
The following features require a separate one-time in-app purchase. They are not required to use the calculator:
- Unlimited saved calculation history
- PDF export of results
- Dark theme
- Ad-free experience
UPGRADE TO PRO:
- Remove banner ads
- Unlimited calculations
- Dark theme support
Designed for solar installers, electricians, and PV system designers working in the United States.
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What's New in Solar Wire Sizer
1.0.2
June 12, 2026
Conductor sizing now follows the printed two-step NEC 690.8(B) check: - (B)(1) base ampacity vs 156% of Isc, (B)(2) corrected ampacity vs 125% - no more over-derating on hot or bundled runs - Voltage drop now computed at 125% max circuit current (was 156%) - Aluminum 300 kcmil corrected to printed 310.16 values (195/260 A)
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