NEC guides
Worked explanations of the calculations that come up on the job, each one citing the article it comes from. Written to be useful on their own — you do not need the app to get the answer.
What size wire do I need? The whole run, in order
Sizing a conductor is six checks, not one lookup — continuous load, ampacity, termination temperature, the small-conductor cap, the equipment ground, and voltage drop. Do them in this order and the answer only moves one direction.
ReadAmpacity derating: two factors, two different tables
Ambient temperature and conductor count are separate adjustments that multiply together — and both apply to the 90°C column, not the one your terminations are rated for. The factors, the order of operations, and the two places this goes wrong.
ReadWhat actually changed in the NEC 2026
A working electrician's list of the NEC 2026 changes that move numbers on the job: Table 310.16 gained rows, 250.122 letters shifted, and one renumbered article now points somewhere else entirely.
ReadHow to calculate box fill, item by item
Box fill is six separate counts added together, not one. The volume table, what counts as a conductor, why device yokes are doubled, and the three different meanings of 'largest conductor' that make this easy to get wrong.
ReadWhere the 40% conduit fill rule comes from, and when it is not 40%
The 40% fill limit only applies to more than two conductors. One conductor gets 53%, two conductors get 31%, and a short nipple gets 60%. Plus the jam ratio, which the percentages will not warn you about.
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