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The Calculations half of the Texas Journeyman exam has the lowest first-try pass rate of the two parts — about 20%. It's not because the math is advanced. It's because it's timed, multi-step, and one wrong code lookup wrecks the whole problem. Here's exactly what's on it and how to prepare.
The calculations part draws from the same NEC you use open-book, but it's applied math. The recurring categories:
Pick the right conductor for a load, then apply temperature and conduit-fill derating.
NEC 310Size up a conductor so voltage drop stays within recommended limits over a run.
NEC Ch. 9How many conductors fit in a raceway by area percentage.
NEC Ch. 9, T1/T4/T5Count conductors, devices, clamps, and grounds to size an outlet box.
NEC 314.16Dwelling and commercial service/feeder loads with demand factors.
NEC 220 → 120 in 2026FLC from tables, conductor sizing at 125%, and overload/branch protection.
NEC 430Primary/secondary current and overcurrent protection sizing.
NEC 450Match overcurrent devices to conductor ampacity and the next-standard-size rule.
NEC 240On a timed open-book test, the formulas you have memorized are the ones you won't waste minutes looking up. These are the workhorses:
Voltage drop (1φ): VD = (2 × K × I × L) / CM
K ≈ 12.9 for copper, 21.2 for aluminum · I = load amps · L = one-way length (ft) · CM = conductor circular mils
Voltage drop (3φ): VD = (1.732 × K × I × L) / CM
Same variables; the 2 becomes √3 (1.732) for three-phase.
Power (3φ): P = 1.732 × E × I × PF
E = line voltage · I = line current · PF = power factor
Single-phase current: I = VA / E | Three-phase: I = VA / (1.732 × E)
The starting point for most service and feeder problems.
Always confirm table values and the exact code method against your current NEC edition — the exam tests the code's method, and section locations change between editions (see NEC 2026 below).
If you test on or after September 1, 2026, load calculations move from Article 220 to Article 120 in the 2026 NEC. The method is similar but the location — and your muscle memory for finding it — changes. See the full NEC 2026 breakdown →
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It has the lowest first-try pass rate of the two parts — about 20.56% in FY2025. The difficulty is the multi-step, timed format more than advanced math: one wrong table or factor early makes the whole answer wrong.
Conductor sizing and ampacity, voltage drop, conduit fill, box fill, dwelling and commercial load calculations, motors, transformers, and overcurrent device sizing — all applied from the NEC.
It's an open-book exam, so you work from the NEC. Confirm the approved calculator and materials list in your PSI Candidate Information Bulletin when you schedule.
Timed, full-problem practice plus a tabbed table index. Most failures come from running out of time on table lookups, not from the arithmetic, so practice the whole problem under four minutes including finding the code.
The biggest change is location: load calculations move from Article 220 to Article 120 in the 2026 NEC, effective for Texas exams on or after September 1, 2026. Re-learn where to find them.