The assumed 400 V fault-duty case passes a 25 kA symmetrical rating with one transformer but fails with two tied behind one common source.
400 V; 630 kVA / 6%; 500 MVA; ≈15 kA open / ≈29 kA tied; 25 kA ratingderived
| Value kind | derived — Derived values are guide calculations; their result is only as fixed as the stated inputs, scope, and method. |
|---|---|
| Scope | Assumed screening case; use the full-precision equations for comparisons, not rounded display limits. Actual equipment qualification remains separate. |
| As of | Illustrative guide derivation, September 8, 2026 |
| Source | Guide derivation, September 8, 2026; Chapter 4.2 stated-assumption case. · Chapter 4.2 — Illustrative — stated assumptions |
| Derivation | Zs=400²/(500e6); Zt=400²/(630e3)×.06; Iopen=400/(sqrt(3)×(Zs+Zt))=14.843726 kA; Itied=400/(sqrt(3)×(Zs+Zt/2))=29.089145 kA. Common source impedance is not halved. Making/withstand/selectivity/arc remain separate. |
| Review | checking…cadence-derived review 2027-01-06 · standard cadence |
| Recorded changes | none recorded |
| Claim id | part4-open-tie-fault-screen |
Where the guide uses it
Not quoted in a chapter yet; it is kept in the curated register.
← Full numbers register — every date-stamped figure in the guide, with revision history.