Source: https://guthlabs.ai/docs/instruments/voltage-drop-calculator-wire-run/
instrument / verified-clean
# Voltage Drop Calculator (wire run)
The current ledger marks this instrument verified clean within the source-bound verification corpus.
Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**
## Inspectable records
[01**Overview**Purpose and lifecycle]()[02**Mechanism**Method and assumptions]()[03**Implementation**Binding and validation]()[04**Qualification**Evidence and errata]()
## 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`