Wire Ampacity Calculator mechanism

Model scope

The supplied honest label is appropriate but incomplete. Before implementation, require material, code edition and jurisdiction, current-carrying-conductor count, terminal temperature rating, conductor installation method, and an explicit distinction between NEC and IEC calculation engines. No interpolation is used in these vectors; every lookup lands exactly on a cited table row or factor.

• NEC Table 310.16 is not sufficient by itself: its ampacities assume no more than three current-carrying conductors in a raceway or cable, 30 °C ambient, and the applicable conductor material and insulation temperature column.
• The input schema omits conductor material. AWG/kcmil ampacity differs substantially between copper and aluminum, so the material must be an explicit input or a documented default.
• Conductor count is not necessarily current-carrying conductor count. Equipment grounding conductors, some neutrals, and certain control or balanced-circuit conductors may be excluded under NEC rules; the calculator must either request current-carrying conductor count or clearly state its counting convention.
• Ambient-temperature correction and conductor-count adjustment are multiplicative factors, but the result must also be limited by conductor terminal temperature ratings and other applicable code limits.
• Conduit fill is generally a separate physical-fill calculation, not an ampacity derating factor. It may affect how many conductors can be installed and therefore the current-carrying-conductor count, but it should not be applied as an independent ampacity multiplier.
• The formula must specify the insulation rating used for adjustment, normally the 90 °C column for THHN/THWN-2 adjustment, while final allowable ampacity is limited by the applicable 60 °C or 75 °C terminal rating.

Units and conventions

• All currents are in amperes, conductor sizes are AWG, and ambient temperature inputs are degrees Celsius.
• The test vectors assume copper conductors, because material is absent from the supplied input schema.
• THHN is treated as having a 90 °C insulation rating for adjustment calculations; final ampacity is limited to the 75 °C terminal column.
• The NEC convention used is NEC 2020: Table 310.16 values at 30 °C ambient and no more than three current-carrying conductors; ambient correction factors from Table 310.15(B)(1); conductor-count adjustment factors from Table 310.15(B)(3)(a); and small-conductor limits from 240.4(D).
• The reported code_max_allowable_ampacity_A is min(adjusted 90 °C ampacity, terminal-temperature ampacity, any applicable small-conductor limit).

Inspectable vector

One of 4 source-bound review vectors:

{
  "inputs": {
    "material": "copper",
    "size": "12 AWG",
    "insulation": "THHN",
    "ambient_C": 30,
    "current_carrying_conductors": 3,
    "terminal_rating_C": 75
  },
  "expected_outputs": {
    "base_ampacity_90C_A": 30,
    "adjusted_ampacity_90C_A": 30,
    "terminal_limited_ampacity_A": 25,
    "code_max_allowable_ampacity_A": 20
  },
  "reference_data": {
    "table_310_16_copper_12_AWG": {
      "60C_A": 20,
      "75C_A": 25,
      "90C_A": 30,
      "source_convention": "NEC 2020 Table 310.16"
    },
    "ambient_correction_90C_at_30C": {
      "factor": 1,
      "source_convention": "NEC 2020 Table 310.15(B)(1)"
    },
    "current_carrying_adjustment_for_3": {
      "factor": 1,
      "source_convention": "NEC 2020 Table 310.15(B)(3)(a)"
    },
    "small_conductor_limit_12_AWG": {
      "maximum_A": 20,
      "source_convention": "NEC 2020 240.4(D)"
    }
  },
  "working": "Base 90 °C ampacity = 30 A. Ambient factor at 30 °C = 1.00. Three current-carrying conductors require no adjustment, factor = 1.00. Adjusted ampacity = 30 × 1.00 × 1.00 = 30 A. The 75 °C terminal limit is 25 A, so terminal-limited ampacity = min(30, 25) = 25 A. NEC 240.4(D) limits 12 AWG copper to 20 A, so final code maximum = min(25, 20) = 20 A."
}

Failure boundary

BREAK_CLAIMED · SELF_FLAGGED

An ambient temperature such as 200 C lies outside the NEC correction-factor table and has no defined derating result. The calculator must reject it; extrapolating a factor or returning a numeric ampacity would be a hazard. The convention probe also shows that the conductor-count field needs an explicit current-carrying-versus-total definition.

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche7/tranche7-results.json
• BOUNDARY_HAZARD_CATALOG.json