Engineering Tools — Stinger Pro™

Motor Calculator — NEC Article 430 (3-phase)

Full-load current from Table 430.250, with branch conductor, protection, and grounding.

Motor horsepower

Voltage

FLC per NEC Table 430.250 (3-phase induction). Branch conductor at 125% FLC (430.22) from the 75°C copper column; maximum inverse-time-breaker protection at 250% FLC (430.52); EGC per 250.122. Verify motor nameplate and design type.

Code Reference — plain language

Common NEC rules for takeoff and estimating. Scroll to find what you need.

Conduit fill

NEC	Rule
Ch.9 Table 1	Max conduit fill: 53% for 1 conductor, 31% for 2, 40% for 3 or more.
Ch.9 Note 4	A nipple (24 in or shorter) between enclosures may fill to 60%, and the 310.15(C)(1) derating does not apply to it.
Ch.9 Note 7	When all conductors are the same size, round the count up to the next whole number if the decimal is 0.8 or larger.

Ampacity & derating

NEC	Rule
310.15(C)(1)	More than 3 current-carrying conductors: 4–6 = 80%, 7–9 = 70%, 10–20 = 50%, 21–30 = 45%, 31–40 = 40%, 41+ = 35%.
Table 310.15(B)(1)	Ambient hotter than 86°F (30°C) lowers ampacity by a correction factor (e.g., 90°C wire at 113°F = 0.87).
110.14(C)	Start derating from the conductor’s rating column (often 90°C), but the final usable ampacity can’t exceed the 75°C column for typical terminations.
310.15(B)(2)	Raceway in direct sunlight, less than 3/4 in. above a roof: add 60°F (33°C) to the outdoor ambient before correcting.
310.14(A)(2)	When ampacity varies along a circuit, the lowest value governs — unless the derated section is ≤ the lesser of 10 ft or 10% of the run.

Overcurrent protection

NEC	Rule
240.4(D)	Small-conductor rule caps the breaker: 14 / 12 / 10 Cu = 15 / 20 / 30 A.

Motors

NEC	Rule
430.22	Motor branch-circuit conductor: size at 125% of the motor full-load current (FLC).
430.52	Motor branch protection maximums (% of FLC): inverse-time breaker 250%, dual-element/time-delay fuse 175%, non-time-delay fuse 300%, instantaneous-trip breaker 800%.
250.122	Size the equipment grounding conductor from the rating of the overcurrent device protecting the circuit.

For estimating and reference only. These calculators are provided as a convenience and demonstration. They do not replace engineering judgment. Always verify against the current adopted edition of the NEC (NFPA 70), manufacturer data, and your local authority having jurisdiction (AHJ) before designing or installing.

The motor calculator and code reference are a sample of the tools built into Stinger Pro. Conduit fill, voltage drop, pull box, wireway, duct bank, transformer and generator sizing, and fuse charts all run inside your estimate — tied to the takeoff, with save and print.

Inside the program

The same tools, with the full in-program view.

Live calculators above give you the idea — but inside Stinger Pro each tool shows its full work, reference tables, and code citations, on the same screen where you price the job. A look at the real thing:

NEC 430 motor calculator inside Stinger Pro — NEC 430 Motor Calculator

Conduit Fill & Ampacity calculator inside Stinger Pro — Conduit Fill & Ampacity

Pull & Junction Box calculator inside Stinger Pro — Pull & Junction Box

Wireway / Gutter Fill calculator inside Stinger Pro — Wireway / Gutter Fill

Transformer FLA & Sizing calculator inside Stinger Pro — Transformer FLA & Sizing

Generator Sizing calculator inside Stinger Pro — Generator Sizing

Duct bank concrete calculator inside Stinger Pro — Duct Bank Concrete

Voltage Drop
(screenshot)

Pull Box
(screenshot)

Wireway
(screenshot)

Duct Bank
(screenshot)

Transformer Sizing
(screenshot)

Generator Sizing
(screenshot)

Fuse Charts
(screenshot)

Field-tested electrical calculators.

The same tools, with the full in-program view.

Want all of it in one program?