Professional-Use Disclosure — Screening Tools, Code Governs

Screening outputs, not approvals

Calculator results, reference values, guides, and Workspace reports are provided for informational screening. They are not engineering advice, not a code compliance determination, not a permit, not a contractor quote, and not a promise of savings or performance. Treat every number as the start of verification, not the end of it.

Code and authority having jurisdiction come first

Where this site discusses sizing, protection, or installation practice, the National Electrical Code (NFPA 70) as adopted and amended locally, the authority having jurisdiction (AHJ), and the equipment manufacturer instructions always govern. If a calculator result and a code rule disagree, the code rule wins. Electrical installation and service work should be performed or supervised by qualified, licensed persons in accordance with local law.

The articles behind the tools

• Continuous loads at 125%: NEC 210.19(A), 215.2(A), 230.42(A) — a load expected to continue 3 hours or more sizes conductors and overcurrent devices at 125% of the load current.
• Motors: NEC Article 430 — conductor sizing (430.22/430.24), branch short-circuit and ground-fault protection (430.52, inverse-time default 175% of FLA), overload protection (430.32, 115/125% by service factor). Table FLA (430.247/430.250) governs over nameplate for sizing.
• Overcurrent protection: NEC Article 240 — standard ampere ratings (240.6), next-size-up rules (240.4(B)), and the conductor-protection relationship.
• Raceway and boxes: NEC Chapter 9 Tables 1/4/5 for conduit fill, Table 8 for conductor properties; Article 314.16 for box fill; Article 310 (310.15/310.16) for ampacity with temperature and bundling adjustments.
• Transformers: NEC Article 450 for overcurrent protection of transformer windings.

What the tools deliberately do not model

• Ambient-temperature and multi-conductor derating beyond the stated bundling factors — verify against NEC Table 310.15(B)(1) and 310.15(C)(1).
• Short-circuit coordination, selective coordination studies, and arc-flash analysis.
• Motor starting inrush beyond the branch-protection multiplier, and drive harmonic heating of neutrals.
• Local AHJ amendments, utility service rules, hazardous-location rules, and fire-alarm / life-safety circuits.
• Enclosure ratings (NEMA/IP), seismic, and thermal behavior beyond the steady-state heat balance.

Verify before you buy or build

• Confirm the governing code: the locally adopted NEC edition plus AHJ amendments, and the article behind each sizing rule.
• Confirm installation facts: conductor material and temperature ratings, raceway routing, ambient temperature, available fault current.
• Confirm equipment facts: nameplate FLA and kVA, transformer impedance (%Z), PSU efficiency curves, enclosure ratings.
• Recompute one result by hand: if your numbers match the calculator within rounding, the inputs are ready for every tool on this site.

Corrections

If a page contains an unclear definition, a broken result, a stale reference, or missing source context, send the URL and the specific issue through Contact. Verified corrections are applied and noted. Contact the site.