Verification
Worked examples published by engineers, manufacturers and a building department, re-run through the same code that powers each calculator. The “This site” column is computed when the page is built, and the build fails if any result drifts from the published answer — so this table can’t go stale.
12 AWG branch circuit at 0.85 PF
120 V 1Ø, 12 A, 12 AWG Cu, 100 ft one-way, PF 0.85 (Table 9 effective Z 1.7 Ω/kft)
Source: D. A. Snyder, PE — PDH Online course E426, Example 1 (2014)
- Voltage dropPublished 4.08 VThis site 4.08 Vexact
- Voltage dropPublished 3.4 %This site 3.4 %exact
250 hp motor feeder, 500 kcmil at 0.9 PF
480 V 3Ø, 302 A, 500 kcmil Cu, steel conduit, 200 ft one-way, PF 0.9 (R 0.029, X 0.048 Ω/kft)
Source: D. A. Snyder, PE — PDH Online course E426, "250 Hp Motor at 480V/3Φ" (2014)
- Voltage dropPublished 4.92 VThis site 4.92 V+0.10 %
- Voltage dropPublished 1.02 %This site 1.03 %+0.59 %
This case found a bug. Until 2026-10-26 the calculator interpolated linearly between the Table 9 1.0-PF and 0.85-PF columns and gave 4.50 V here (8.6 % low). It now uses R cosθ + X sinθ (Table 9 Note 2).
100 kW load from 0.80 to 0.97 PF
100 kW, existing PF 0.80, target 0.97, 480 V 3Ø
Source: Eaton — Power Factor Correction Solutions and Applications, "Example: Improving PF" (2012)
- Existing reactive powerPublished 75 kvarThis site 75 kvarexact
- Capacitor bankPublished 50 kvarThis site 50 kvarexact
- Apparent power afterPublished 103 kVAThis site 103 kVA+0.08 %
- Line current afterPublished 124 AThis site 124 Aexact
Secondary fault current, 300 kVA at 2 %Z
300 kVA, 208 V 3Ø secondary, 2 %Z with −10 % tolerance (1.8 %), infinite primary
Source: Cooper Bussmann — Point-to-Point Method of Short-Circuit Calculation, Electrical Plan Review
- Secondary full-load currentPublished 833 AThis site 833 Aexact
- Available fault currentPublished 46,273 AThis site 46,262 Aexact
The source rounds the full-load current to 833 A before multiplying (833 × 55.55); we carry 832.7 A, hence 46,262 A.
2,800 ft² home with EV charger, 220.82 optional method
2,800 ft², 2 small-appliance + 1 laundry circuit, range 12 kVA, water heater 3 kVA, dryer 5 kVA, dishwasher 1.5 kVA, EV charger 7 kVA, A/C 6.96 kVA
Source: Town of Truckee, CA — Residential Electrical Load Worksheet, step-by-step example (CEC 220.82)
- General loadPublished 41,400 VAThis site 41,400 VAexact
- Total service loadPublished 29,520 VAThis site 29,520 VAexact
- Calculated loadPublished 123 AThis site 123 Aexact
Entered as an appliance, the 7 kVA charger matches the worksheet exactly. Entered in the EVSE field, the calculator applies the NEC 2023 220.57 minimum of 7,200 VA and gives 29,600 VA (123.3 A).
Nine 12 AWG THHN in one raceway
12 AWG Cu THHN (90 °C column 30 A), 9 current-carrying conductors, 30 °C ambient
Source: Mike Holt — EC&M Code Quandaries (August 2008)
- Adjusted ampacityPublished 21.0 AThis site 21.0 Aexact
Six 12 AWG THHN at 40 °C ambient
12 AWG Cu THHN (90 °C column 30 A), 6 current-carrying conductors, 40 °C ambient, 60 °C terminals
Source: Open Exam Prep — Temperature Correction & Adjustment Factors (NEC 2020)
- Corrected and adjusted ampacityPublished 21.84 AThis site 21.91 A+0.32 %
- Allowable after 60 °C terminal limitPublished 20 AThis site 20 Aexact
The calculator uses the 310.15(B) equation (factor 0.913) instead of the table value rounded to 0.91, so the intermediate value differs by 0.3 %. The allowable ampacity is the same.
Know a published example we should add?
Send the source and the calculator link through the error report form. Only inputs and numeric answers are reproduced here, with a link to the original. See Methodology for the tables and formulas behind each result.