Voltage Drop Calculator (wire run)

Inspectable records

Ledger state

The current ledger marks this instrument verified clean within the source-bound verification corpus.

Area

Electrical & Electronics Engineering — Circuits, Power Systems, Electronics Lab

Tranche

tranche-7

Evidence ID

t7-076

Ledger rows

1

No ledger note is attached.

Review findings

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.

Formula and scope findings

• 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.

Unit assumptions

• 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.

Boundary hardening

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.

Errata and corrections

No applied erratum is attached to this unique-name record.

Inspectable example

4 review vectors are recorded. One source-bound sample is shown below.

{
  "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."
}

Related workflows

No source-defined multi-instrument workflow membership is recorded.

Sources and evidence

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

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