Build 4.0.0-rc1 provides independent device screening from entered evidence. It does not solve a network fault study or calculate successive current reduction through devices in series.
Quantities and units
- Prospective current: kA RMS symmetrical, supplied by the user from an applicable fault study.
- Peak let-through / cut-off: kA peak, read from a separate device source curve. This is distinct from prospective peak current.
- Total-clearing I²t: A²s, read from its own source. It is not calculated by squaring the peak, and must not be replaced with pre-arcing I²t.
Curve reading
For source points (x₁,y₁), (x₂,y₂) bracketing x, log–log interpolation computes ln(y) = ln(y₁) + ln(x/x₁) / ln(x₂/x₁) × ln(y₂/y₁). Interpolation is indicative and cannot produce a positive withstand criterion result. Upper-adjacent reading uses max(y₁,y₂); this is conservative only if the underlying published envelope is nondecreasing throughout that interval. The user must verify the envelope and transcription, including graph resolution and tolerances. An exact stored x returns its stored y. One-point records are supported only at that exact x. No extrapolation is performed.
Numerical criteria
- Interrupting ratio = applicable interrupting rating / prospective RMS current.
- Peak ratio = equipment peak withstand / device peak let-through.
- Thermal ratio = equipment I²t withstand / device total-clearing I²t.
- Cable thermal limit = k²S², with S in mm² and k in A√s/mm². The source must support k, temperatures, material and the adiabatic method. A documented maximum clearing duration ≤ 5 seconds across the entered range is required. This does not determine ampacity, voltage drop or overload protection.
A ratio ≥ 1 meets only the entered numerical inequality. An optional target above 1 is a user preference, not a universal standards requirement. Displayed numbers are rounded; comparisons use full numerical precision.
Evidence controls
Exact voltage, frequency and rating-basis matches are required by this simplified implementation; it may reject otherwise valid applications at lower voltages. Poles, fault type, X:R/test power factor, installation and all remaining source conditions require explicit user confirmation. Icu, Icn and UL interrupting ratings are kept distinct; Ics is not evaluated. Source review is a user declaration, not independent approval.
Peak and energy criteria require reviewed maximum envelopes, upper-adjacent reading, adequate device interrupting capacity and confirmed equipment evidence. Typical curves, missing data, unconfirmed sources and log interpolation stay indicative or unevaluated. Synthetic examples never generate a design approval. Missing checks prevent an overall positive conclusion.
Excluded conclusions
No automatic cascading, selectivity, series ratings, complete panel SCCR, Type 2 coordination, arc-flash study or certification. Upstream peak current is never passed into another device as its prospective RMS current. IEC and UL/NEC screening do not replace the applicable standard edition or manufacturer-approved combinations.
Background: Schneider Electric cable short-circuit guidance; UL machinery SCCR guidance.