What's actually on the Calculations test
The calculations part draws from the same NEC you use open-book, but it's applied math. The recurring categories:
Conductor sizing & ampacity
Pick the right conductor for a load, then apply temperature and conduit-fill derating. Free ampacity calculator →
NEC 310Voltage drop
Size up a conductor so voltage drop stays within recommended limits over a run. Free voltage drop calculator →
NEC Ch. 9Conduit fill
How many conductors fit in a raceway by area percentage. Free conduit fill calculator →
NEC Ch. 9, T1/T4/T5Box fill
Count conductors, devices, clamps, and grounds to size an outlet box. Free box fill calculator →
NEC 314.16Load calculations
Dwelling and commercial service/feeder loads with demand factors.
NEC 220 → 120 in 2026Motors
FLC from tables, conductor sizing at 125%, and overload/branch protection.
NEC 430Transformers
Primary/secondary current and overcurrent protection sizing.
NEC 450OCPD sizing
Match overcurrent devices to conductor ampacity and the next-standard-size rule.
NEC 240The formulas worth memorizing cold
On 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).
Why people who "know the math" still fail
- Multi-step error cascade. A load calc might be eight steps. One wrong demand factor and the final answer is off — partial credit doesn't exist.
- The clock. ~26 questions in ~110 minutes means a little over four minutes each. Hunting for a table burns that fast.
- Table navigation. Half the battle is knowing which NEC table to open. That's a lookup-speed skill, not a math skill.
- Mixed units and conditions. Temperature rating, number of current-carrying conductors, and continuous-load factors all stack — miss one and the ampacity is wrong.
How to study the calculations half
- Drill it separately from the NEC half. It's scored on its own and it's the lower pass rate. Give it dedicated reps.
- Build a tabbed table index. You should be able to flip to 310.16, 314.16, Chapter 9 tables, and 430 motor tables in seconds.
- Practice the full problem, timed. Don't stop at "I know how." Do it in under four minutes, start to finish, including the lookup.
- Memorize the workhorses above so the formula recall is instant and your time goes to the code lookup.
The NEC 2026 wrinkle for calculations
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 →
Practice the calculations free
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FAQ
How hard is the Texas Journeyman calculations exam?
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.
What topics are on the calculations part?
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.
Can I use a calculator and the code book?
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.
What's the fastest way to improve on calculations?
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.
Does NEC 2026 change the calculations?
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.