Inrush Current / Fuse & Breaker Sizing Estimator mechanism

Model scope

The exact ambiguity requiring review is the undefined meaning and application of safety margin, plus the undefined relationship between estimated inrush and the recommended protection-device rating. The four outputs therefore use a clearly stated provisional interpretation for arithmetic verification only. The honest-label warning is necessary but insufficient to make this a code-compliant fuse or breaker selector; final selection must use the applicable electrical code, equipment documentation, conductor ratings, and protective-device time-current data.

• The specification does not define how the safety margin is applied. The test vectors provisionally interpret safety_margin as a multiplicative factor, so 1.10 means 10% extra; it could instead mean a percentage such as 10.
• The stated 1.25 × continuous-current rule is not a complete or universally applicable fuse/breaker-sizing method. Fuse and breaker selection depends on applicable code articles, conductor ampacity, equipment ratings, interrupting rating, coordination, ambient temperature, and time-current behavior.
• The inrush multiplier table is only a rough heuristic. Motor inrush varies with motor design and starting method; transformer inrush varies with energization phase angle, residual flux, transformer design, source impedance, and duration.
• The algorithm does not define how the estimated inrush current affects the recommended device rating. As provisionally interpreted, the output rating uses only 1.25 × continuous current × safety margin, while inrush is reported separately and does not influence device selection.
• No rule is given for rounding the calculated value to an available standard fuse or breaker rating.
• The input load type lists resistive, but the data needs specifically lists incandescent. Generic resistive loads do not necessarily have a 10× inrush multiplier; the supported load categories must be defined.

Units and conventions

• All current values are interpreted as RMS amperes unless explicitly labeled otherwise.
• In the fourth vector, 500 mA is converted to 0.500 A before calculation; mixing amperes and milliamperes without an explicit unit field is unsafe.
• The provisional rating formula is recommended_rating_A = 1.25 × steady_current_A × safety_margin_factor.
• The provisional inrush formula is inrush_current_A = steady_current_A × table_multiplier.
• A safety_margin_factor of 1.00 means no additional margin; 1.10 means 10% additional margin, not 10 percentage points.
• The 1.25 factor is treated as the specified NEC-style rule of thumb, not as a universal code-compliant device-selection rule.

Inspectable vector

One of 4 source-bound review vectors:

{
  "inputs": {
    "steady_current": 10,
    "steady_current_unit": "A",
    "load_type": "motor",
    "safety_margin": 1
  },
  "expected_outputs": {
    "recommended_rating_A": 12.5,
    "inrush_current_estimate_A": 60
  },
  "reference_data": {
    "continuous_current_factor": 1.25,
    "continuous_current_factor_source_convention": "NEC-style rule of thumb; widely tabulated 125% sizing heuristic, not a universal NEC device-rating table entry",
    "inrush_multiplier": 6,
    "inrush_multiplier_source_convention": "widely tabulated standard engineering rule-of-thumb value for a typical across-the-line induction motor"
  },
  "working": "1. Continuous-current basis = 1.25 × 10.0 A = 12.5 A.\n2. Apply safety margin = 12.5 A × 1.00 = 12.5 A.\n3. Estimated inrush = 6.0 × 10.0 A = 60.0 A.\n4. Provisional outputs: recommended rating = 12.5 A; inrush estimate = 60.0 A."
}

Failure boundary

BREAK_CLAIMED · SELF_FLAGGED

The estimator has hazardous boundary behavior unless it validates inputs: zero current produces a meaningless zero rating, negative current can produce invalid negative ratings under a literal signed interpretation, and a very large transformer current causes the inrush calculation to overflow to infinity. The transformer multiplier is also only specified as a 10–15x range, so the selected table endpoint must be documented.

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