Draft, pending technical review
How the math works
NEC® citations on this site name the edition in use. The calculators show computed results and the specific values used in that run. They do not publish code tables.
3-phase current
I = kVA × 1000 / (√3 × V_LL). If you enter kW, kVA = kW / PF first.
Fault current
Point-to-point method. Transformer secondary current uses the effective impedance, then each conductor segment applies f = √3 × L × I / (C × n × V) and M = 1 / (1 + f). The C value shown is the one used for that segment. Cite: Point-to-point method and C values: Bussmann (Eaton) Selecting Protective Devices.
Generator step-load
dip = X·S / (1 + X·S), with S = step kVA / generator kVA. A linear X·S figure is shown beside it. Code-letter kVA uses the top of NEC Table 430.7(B). ISO 8528-5 is referenced by number only.
Feeders and voltage drop
Ampacity uses NEC Table 310.16 with ambient and conductor-count factors, termination temperature, and the 240.4 protection check for the edition you select. Voltage drop uses the Chapter 9 Table 9 effective impedance, Ze = R·PF + XL·sin(arccos PF). Where a 2026 section number is not verified, the page says so.
Transformers
Design kVA is the load times demand and growth. The selected rating is the smallest common ANSI/IEEE C57.12 size at or above the required kVA. Secondary fault current on this page assumes an infinite source.
Redundancy capacity
N is the count of units needed for the design load at the max loading you set. Installed units, stranded capacity, and loading after one failure follow the scheme. The count is not a certification.
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