Source: https://guthlabs.ai/docs/instruments/nec-iec-conduit-fill-calculator/implementation/

instrument implementation / implementation-contract

# NEC/IEC Conduit Fill Calculator implementation

A source-bound implementation contract for NEC/IEC Conduit Fill Calculator; deployment and executable qualification remain separate.

Status: **VERIFIED_CLEAN**Lifecycle: **implementation-contract**

## Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

**Record owner**: Guth Instruments

**Lifecycle**: verified-clean

**Evidence ID**: t7-106

**Effect**: Computation or source lookup only

## Input and validation requirements

A zero-area or invalid conduit lookup can cause an undefined division instead of a required rejection, and the grounding-conductor counting convention is not specified, producing different max-additional results.

## Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

## Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

````
{
  "inputs": {
    "jurisdiction": "NEC",
    "conduit_type": "EMT",
    "trade_size": "3/4 in",
    "conductors": [
      {
        "material": "copper",
        "size": "12 AWG",
        "insulation": "THHN/THWN-2",
        "count": 3
      }
    ]
  },
  "expected_outputs": {
    "conduit_internal_area_in2": 0.533,
    "allowed_fill_percent": 40,
    "allowed_area_in2": 0.2132,
    "total_conductor_area_in2": 0.0399,
    "fill_percent": 7.4859,
    "passes": true,
    "max_additional_matching_conductors": 13
  },
  "reference_data": {
    "conduit_row": {
      "trade_size": "3/4 in",
      "internal_area_in2": 0.533,
      "source_convention": "NEC Chapter 9 Table 4, EMT; widely tabulated standard NEC value"
    },
    "conductor_row": {
      "material": "copper",
      "size": "12 AWG",
      "insulation": "THHN/THWN-2",
      "outside_area_in2": 0.0133,
      "source_convention": "NEC Chapter 9 Table 5, insulated copper conductor; widely tabulated standard NEC value"
    },
    "fill_rule": {
      "conductor_count": "3 or more",
      "allowed_fill_percent": 40,
      "source_convention": "NEC Chapter 9 Table 1; widely tabulated standard NEC value"
    }
  },
  "working": "1. Conduit internal area = 0.533 in².\\n2. Three conductors use the 40% limit. Allowed area = 0.40 × 0.533 = 0.2132 in².\\n3. Existing conductor area = 3 × 0.0133 = 0.0399 in².\\n4. Fill = (0.0399 ÷ 0.533) × 100 = 7.4859%.\\n5. Remaining allowed area = 0.2132 − 0.0399 = 0.1733 in².\\n6. Additional conductors = floor(0.1733 ÷ 0.0133) = floor(13.0301) = 13.\\n7. Check: 16 × 0.0133 = 0.2128 in² ≤ 0.2132 in²; 17 × 0.0133 = 0.2261 in² > 0.2132 in²."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/nec-iec-conduit-fill-calculator/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/nec-iec-conduit-fill-calculator/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/nec-iec-conduit-fill-calculator/qualification/>)

## 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`