WireWicket / Methodology

Accuracy & Methodology

Each tool is limited to the reference rows and calculation paths listed here. The dated examples below are individual regression cases whose automated tests passed; they do not establish universal accuracy, code compliance, or coverage beyond their stated inputs and source data.

An expected value may be a published table value or arithmetic derived from cited source data and the stated formula. When a source supplies inputs rather than a final answer, the derived calculation is identified as such.

Reference coverage

Scope and exclusions

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Raceway fill

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Covers

Uses the checked-in NEC 2026 Chapter 9 Tables 1, 4, and 5 data for THHN / THWN-2 conductor areas and EMT, RMC, PVC Schedule 40, and PVC Schedule 80 raceway areas. Listed conductor sizes are 14, 12, 10, 8, 6, 4, 3, 2, 1, 1/0, 2/0, 3/0, and 4/0 AWG, then 250, 300, 350, 400, 500, 600, 700, 750, 800, 900, and 1000 kcmil; sizes between listed rows are not implied. Each raceway table includes trade sizes 1/2, 3/4, 1, 1-1/4, 1-1/2, 2, 2-1/2, 3, 3-1/2, 4, 5, and 6. It applies the one-, two-, and three-or-more-conductor permitted-fill bands and can total mixed conductor groups.

Excludes and limits

A size or conductor/raceway combination absent from the checked-in tables is unsupported. The calculation does not switch code editions, include local amendments, or model installation, pulling, derating, or project conditions. Verify the adopted edition and installation with the AHJ.

References

NFPA 70 (NEC) 2026 in NFPA LiNK

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Box fill and pull-box sizing

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Box fill uses the checked-in NEC 314.16 standard box-volume and conductor-volume rows for 18, 16, 14, 12, 10, 8, and 6 AWG, with custom measured interior depth and modeled allowances for conductors, qualifying loops, clamps, luminaire fittings, device yokes, grounding/bonding conductors, and terminal blocks. It reports over-capacity visibly. Pull sizing covers straight, angle, and U pulls under 314.28, including repeated-entry spacing; the tested applicability boundary is insulated conductors of 4 AWG or larger.

Excludes and limits

Unsupported conductor, box, or raceway inputs do not receive a calculated result. Pull sizing below 4 AWG is not applicable. Box listing, field dimensions beyond entered measurements, local amendments, adopted-edition differences, and other project or installation conditions require separate review.

References

NFPA 70 (NEC) 2026 in NFPA LiNK

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Ampacity derating

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Applies the loaded identity factors to an entered ampacity using the NEC 2026 90°C starting-column basis: ambient is supported only at exactly 86°F, and current-carrying conductor count only from one through three. The checked-in ambient and conductor-count factors are both 1.00 for those supported conditions.

Excludes and limits

Other ambient temperatures and counts above three return unavailable factors; no non-identity correction rows are loaded. The entered starting ampacity is not independently established by this calculator. The result does not replace 75°C terminal limits, the adopted code edition, amendments, installation conditions, or project review.

References

NFPA 70 (NEC) 2026 in NFPA LiNK

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Voltage drop

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The newer calculation supports single- and three-phase circuits using the checked-in Southwire SIMpull THHN/THWN-2 AC resistance/reactance rows for PVC Schedule 40 or 80. Copper rows are 8, 6, 4, 3, 2, 1, 1/0, 2/0, 3/0, 4/0 AWG and 250, 300, 350, 400, 500, 600, 750, 1000 kcmil; aluminum rows are 6, 4, 2, 1, 1/0, 2/0, 3/0, 4/0 AWG and 250, 300, 350, 400, 500, 600, 700, 750, 900, 1000 kcmil. The Southwire reactance row assumes non-ferrous conduit and one conductor diameter center-to-center spacing. These AC rows use resistance at 75°C and reactance at 60 Hz, with no ambient or temperature correction applied. AC voltage drop is 2 × I × (L / 1000) × (R × PF + X × √(1 − PF²)) single-phase, or √3 × I × (L / 1000) × (R × PF + X × √(1 − PF²)) three-phase; entered PF is treated as a lagging-load assumption. The retained legacy resistance-only K-factor formulas are 2 × K × I × L ÷ CM single-phase and 1.732 × K × I × L ÷ CM three-phase, with K = 12.9 for copper and 21.2 for aluminum. I is current in amperes, L is one-way length in feet, R and X are in Ω/1000 ft, and CM is conductor area in circular mils.

Excludes and limits

The 75°C resistance source basis is fixed reference data, not a user-selected ambient correction. The legacy K-factor method also does not model temperature changes, reactance, or power factor. AC rows are not supplied for EMT/RMC or conductor combinations absent from the listed tables. The 3% and 5% thresholds are advisory only; they are not a code-compliance result.

References

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Motor branch-circuit sizing

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Uses supported NEC 2026 full-load-current rows from Tables 430.247–430.250, then calculates branch-conductor ampacity, supported branch short-circuit/ground-fault protection, overload limits from entered nameplate current/service factor/temperature rise, and copper EGC size. Corrections are available only at 86°F and one to three current-carrying conductors. Calculated conductor outputs use the 75°C terminal limit.

Excludes and limits

A missing horsepower/voltage/table row, unsupported motor design or protective-device combination, or unavailable conductor/protection/EGC row is reported unavailable; the calculator does not interpolate or extrapolate. It is not general motor-design coverage and does not replace adopted-edition, amendment, listing, controller, installation, or project review.

References

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Transformer sizing

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For ordinary two-winding transformers with primary and secondary rated at 1000 V nominal or less, it calculates winding full-load currents for single- or three-phase inputs. Supported protection choices are primary-only and primary-and-secondary, using the loaded NEC 450.5(B) rules and standard ratings. Where source rows exist it also selects copper conductors from the 75°C ampacity table, copper EGCs from Table 250.122, and exposes phase/EGC handoffs.

Excludes and limits

Protection, conductor, EGC, or handoff results remain unavailable when the corresponding table row or standard rating is absent. Above-1000-V inputs can show winding current but do not receive protection, conductor sizing, or handoff; Table 450.5(A) installation rules are not modeled. Secondary-conductor methods under 240.21(C), transformer installation, adopted-edition differences, amendments, and project conditions require separate review.

References

NFPA 70 (NEC) 2026 in NFPA LiNK

integrated workflow

Homepage electrical submittal sandbox

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Covers

This is an illustrative integrated workflow, not a seventh independent standard calculator. Its fixed demo starts at 480Y/277 V, 175 A, a 200 A illustrative OCPD, a 200 ft one-way run, copper THHN/THWN-2, EMT, three 2/0 AWG phase conductors, no neutral, 86°F, and 1-1/2 in EMT. It models Chapter 9 raceway fill, a 90°C copper ampacity starting row with only the loaded identity factors, a resistance-only three-phase voltage-drop screen, and a copper EGC based on Table 250.122 with a proportional adjustment when the selected phase conductor requires it. The PF input defaults to 0.90 for the optional verified PVC R/X calculation; the default EMT screening estimate is unity-PF and ignores that input. In PVC Schedule 40/80, a verified Southwire R/X path can be selected.

Excludes and limits

The base ampacity, imported project data, OCPD choice, and all project conditions require verification. EMT/RMC voltage drop is explicitly a unity-power-factor, resistance-only NCCER K-factor screening estimate; it omits reactance and raceway impedance. PVC R/X is limited to the source-backed non-ferrous conduit, one-conductor-diameter spacing rows at 75°C and 60 Hz, with no temperature correction. Unsupported factor combinations, conductor rows, and impedance paths remain unavailable; outputs are not a final design or compliance determination.

References

Regression evidence

Passing verification cases

Each entry names the maintained test and last date that its run passed. A passing case verifies only its asserted inputs and outputs. The list contains no planned or unexecuted examples.

Raceway fill

Passing test · 2026-09-30

tests/unit/emt-raceway-fill.test.ts :: calculates the selected PVC Schedule 40 area and NEC references

Source: NFPA 70 (NEC) 2026 in NFPA LiNK
Expected: For three 12 AWG THHN/THWN-2 conductors in 3/4 in PVC Schedule 40, the source rows give 0.0133 in² per conductor and 0.508 in² raceway area; the 40% allowance is 0.2032 in².
WireWicket result: 0.0399 in² total conductor area, 7.9% actual fill, and no fill-limit overflow.

Box fill and pull-box sizing

Passing test · 2026-09-30

tests/unit/nec-314.test.ts :: sizes a straight pull at eight times the largest raceway trade size

Source: NFPA 70 (NEC) 2026 in NFPA LiNK
Expected: For the tested 4 AWG straight pull with a largest raceway trade size of 2.5 in, 314.28(A)(1) requires 8 × 2.5 = 20 in on the controlling width.
WireWicket result: Required width 20 in; the entered 20 in width complies. The result is limited to this tested input.

Ampacity derating

Passing test · 2026-09-30

tests/unit/ampacity-derating.test.ts :: retains the unrounded result and rounds only the displayed value

Source: NFPA 70 (NEC) 2026 in NFPA LiNK
Expected: For a 100.125 A base at 86°F and one current-carrying conductor, the loaded identity factors are 1.00 × 1.00, so the adjusted value is 100.125 A.
WireWicket result: 100.125 A internally; displayed as 100.13 A.

Voltage drop

Passing test · 2026-09-30

tests/unit/single-phase-voltage-drop.test.ts :: calculates single copper 8 AWG from its verified row

Source: Southwire SIMpull THHN/THWN-2 Copper, SPEC 10000, Table 2 Southwire Power Cable Installation Guide, AC single-phase equation 6-26
Expected: The source row is R = 0.786 Ω/1000 ft at 75°C and X = 0.052 Ω/1000 ft at 60 Hz. Applying the cited single-phase equation to 20 A, 100 ft, 120 V, and lagging PF 0.90 gives 2.92 V / 2.43% (derived arithmetic, not a value printed by the source).
WireWicket result: 2.92 V / 2.43%; no ambient or temperature correction is applied.

Motor branch-circuit sizing

Passing test · 2026-09-30

tests/unit/motor-branch-circuit.test.ts :: uses table FLC for conductors and branch protection, and nameplate current for overloads

Source: NFPA 70 (NEC) 2026 in NFPA LiNK NFPA 70 (2026 code-cycle) P11 public-input response cross-check
Expected: Table 430.250 lists 14 A for a 10 hp, 460 V, three-phase motor. The tested inputs use 14 A nameplate current, 75°C terminals, 86°F, three current-carrying conductors, service factor 1.15, and 75°C rise.
WireWicket result: 17.5 A minimum conductor ampacity and 14 AWG; 35 A inverse-time breaker; 17.5 A maximum overload setting; 10 AWG copper EGC.

Transformer sizing

Passing test · 2026-09-30

tests/unit/transformer-sizing.test.ts :: sizes both protection arrangements and applies Note 1 only to the 125% cells

Source: NFPA 70 (NEC) 2026 in NFPA LiNK
Expected: For the tested 45 kVA, 480 V to 208 V, three-phase, primary-and-secondary case, the current equations give about 54.13 A primary and 124.91 A secondary. Table 450.5(B) produces a 135.32 A primary maximum (125 A standard rating not above it) and a 156.13 A secondary maximum with Note 1 permitting the next 175 A standard rating.
WireWicket result: Primary protection: 125 A, not above the table maximum. Secondary protection: 175 A, next-higher treatment under Note 1.

Homepage electrical submittal sandbox

Passing test · 2026-09-30

tests/unit/submittal-sandbox.test.ts :: calculates the default mixed-conductor fill, resistance-only drop, ampacity, and references

Source: NFPA 70 (NEC) 2026 in NFPA LiNK NCCER Electrical Formula Sheet Southwire SIMpull THHN/THWN-2 Copper, SPEC 10000, Table 2
Expected: At the fixed 175 A / 200 A OCPD / 200 ft demo inputs, the checked-in source rows and formulas imply 0.7176 in² conductor area, 35.25% EMT fill, a 5.88 V / 1.22% resistance-only estimate, 195 A adjusted ampacity under identity factors, and a 6 AWG base copper EGC.
WireWicket result: 0.7176 in² area and 35.25% fill; 5.88 V / 1.22% screening drop; 195 A adjusted ampacity; 6 AWG base EGC. This passing fixture does not validate arbitrary project or imported data.