Source: https://guthlabs.ai/docs/instruments/inrush-current-fuse-breaker-sizing-estimator/
instrument / verified-clean
# Inrush Current / Fuse & Breaker Sizing Estimator
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**: t7-099
**Ledger rows**: 1
No ledger note is attached.
## Review findings
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.
### Formula and scope findings
- 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.
### Unit assumptions
- 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.
## Boundary hardening
**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.
## 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": {
"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."
}
````
## 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`