Voltage Drop Calculator (wire run) mechanism

Model scope

The arithmetic methods are conditionally standard, but the specification needs explicit definitions for one-way length, source-voltage reference, conductor temperature, material/table convention, AC power factor/reactance treatment, and the meaning of the 3%/5% checks. The honest estimate label is appropriate and should remain prominent.

• The stated formulas are standard only for balanced circuits with conductor resistance treated as purely resistive: Vdrop = 2 × one-way length × current × resistance per length for DC/single-phase, and Vdrop = √3 × one-way length × current × resistance per length for balanced three-phase line-to-line voltage.
• The formula omits AC conductor reactance and power factor. For nontrivial AC runs, voltage drop should use impedance and load power factor, not resistance alone.
• The specification does not define whether length is one-way or total loop length. The formulas require one-way length because the DC/single-phase expression supplies the factor of 2.
• The specification does not define conductor operating temperature. Resistance tables may be at 20 °C, 75 °C, or another temperature, and voltage drop can differ materially.
• The 3%/5% pass/fail guideline is not universally a code maximum; the calculator must label it as a recommendation and identify whether it applies to a branch circuit, feeder, or total circuit.

Units and conventions

• Length is one-way conductor-run length. For DC/single-phase, the factor 2 accounts for outgoing and returning conductors.
• R_per_ft is the resistance of one conductor in ohms per foot at the stated reference temperature; all vectors use 20 °C copper resistance derived from rho = 1.68e-8 ohm·m.
• Current is RMS current for AC and ordinary load current for DC.
• For three-phase vectors, source voltage is line-to-line voltage, the load is balanced, and the √3 formula calculates line-to-line voltage drop.
• Voltage-drop percentage is Vdrop divided by source voltage multiplied by 100.
• The 3% and 5% checks use pass when percentage is less than or equal to the threshold; these are guideline checks, not universal code determinations.

Inspectable vector

One of 4 source-bound review vectors:

{
  "inputs": {
    "length": 100,
    "length_unit": "ft",
    "current": 15,
    "current_unit": "A",
    "conductor": "copper",
    "gauge": "12 AWG",
    "area_mm2": 3.31,
    "resistivity_ohm_m": 1.68e-8,
    "phase_config": "DC",
    "source_voltage": 120,
    "source_voltage_unit": "V"
  },
  "expected_outputs": {
    "voltage_drop_V": 4.6411,
    "voltage_drop_percent": 3.8676,
    "pass_3_percent": false,
    "pass_5_percent": true
  },
  "reference_data": {
    "copper_resistivity_ohm_m_20C": 1.68e-8,
    "copper_resistivity_source_convention": "widely tabulated standard value; CRC/NIST textbook value at approximately 20 °C",
    "awg_12_copper_area_mm2": 3.31,
    "awg_area_source_convention": "widely tabulated standard AWG cross-sectional-area value",
    "feet_to_metres": 0.3048,
    "feet_to_metres_source_convention": "exact SI/international definition"
  },
  "working": "R_per_m = rho / area = 1.68e-8 ohm·m / (3.31e-6 m²) = 0.00507553 ohm/m. R_per_ft = 0.00507553 × 0.3048 = 0.00154702 ohm/ft. DC voltage drop = 2 × L × I × R_per_ft = 2 × 100 ft × 15 A × 0.00154702 ohm/ft = 4.64106 V, rounded to 4.6411 V. Drop percentage = 4.64106 / 120 × 100 = 3.86755%, rounded to 3.8676%. Since 3.8676% > 3%, the 3% check fails; since 3.8676% ≤ 5%, the 5% check passes."
}

Failure boundary

BREAK_CLAIMED · SELF_FLAGGED

A zero source voltage produces a finite voltage-drop result but makes the required percentage and guideline pass/fail result undefined. The instrument also has a material one-way-versus-loop-length ambiguity unless the length convention is explicitly captured.

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