How to Memorize the Code Tables You Need for the C-10 Exam

Nobody passes the C-10 trade exam by memorizing the code book. The 2025 California Electrical Code, which adopts the 2023 NEC, contains thousands of numbers, and the trade exam is closed book. What you walk in with is what is in your head.

The winning approach is narrow: memorize a short list of high-frequency values until they are automatic, and learn to derive everything else from a handful of formulas and rules. Below is the list I would drill, in order of return on effort.

Tier 1: memorize these cold

The 75 degrees C copper column of Table 310.16

This is the single highest-value block of numbers on the exam. Because of the termination temperature limits in 110.14(C), most real terminations are limited to 60 or 75 degrees C, and exam writers know it.

Learn the 75 degrees C column first as an anchor-and-step chain: 20, 25, 35, 50, 65, 85, 100, 115, 130. Then the 0-size run is easy because it is nearly the round numbers you already know: 150, 175, 200, 230. The 60 degrees C column is roughly one size down from the 75, and the 90 degrees C column is roughly one size up. That relationship is not exact, but it catches your own errors.

Two rules travel with this table and are worth memorizing in the same breath. First, 110.14(C): terminations on equipment rated 100 amps or less, or supplied by 14 through 1 AWG, are treated as 60 degrees C unless the equipment is marked otherwise, and larger equipment is treated as 75 degrees C. Second, 240.4(D), the small conductor rule: 14 AWG copper is limited to 15 amps, 12 AWG copper to 20 amps, 10 AWG copper to 30 amps, with 12 AWG aluminum at 15 amps and 10 AWG aluminum at 25 amps. That rule overrides the ampacity table for those sizes, and it is a favorite trap. More detail lives in our conductor ampacity and sizing guide.

Standard overcurrent device sizes

From 240.6(A): 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600.

The pattern is three runs. Fives up to 50, tens up to 100, then a mixed run that steps 25 at a time from 100 to 250 (with 110 tucked in) and 50 at a time from 250 to 600. If you can rattle that off, you can answer any "next standard size up" question instantly. Pair it with the rounding rule in 240.4(B), which lets you go up to the next standard size when the calculated ampacity does not correspond to one, for devices 800 amps or less. See our overcurrent protection breakdown for the exceptions.

Box fill volume allowances

From Table 314.16(B): 18 AWG is 1.50 cubic inches, 16 AWG is 1.75, 14 AWG is 2.00, 12 AWG is 2.25, 10 AWG is 2.50, 8 AWG is 3.00, and 6 AWG is 5.00.

Memory hook: start at 2.00 for 14 AWG and add a quarter for each size up through 10 AWG, then 8 AWG jumps to a flat 3.00 and 6 AWG jumps again to 5.00. The counting rules matter as much as the volumes: each current-carrying conductor entering and terminating counts one, all equipment grounding conductors together count one based on the largest, all cable clamps together count one based on the largest conductor in the box, each yoke or strap counts two, and conductors passing through unbroken count one. Practice these in the conduit and box fill guide rather than as a list.

Conduit fill percentages

Chapter 9, Table 1: one conductor 53 percent, two conductors 31 percent, over two conductors 40 percent. A nipple 24 inches or shorter gets 60 percent.

Say "fifty-three, thirty-one, forty" out loud until it sounds like a phone number. The counterintuitive one is two conductors at 31 percent, because two circles pack badly inside a round raceway. Knowing that reason keeps you from swapping it with 40.

Adjustment factors for more than three current-carrying conductors

From 310.15(C)(1): 4 to 6 conductors 80 percent, 7 to 9 conductors 70 percent, 10 to 20 conductors 50 percent, 21 to 30 conductors 45 percent, 31 to 40 conductors 40 percent, 41 and above 35 percent.

Hook: 80, 70, then a cliff to 50, then down by fives.

The demand factors that repeat

You do not need every demand table, but these show up constantly. Dwelling general lighting: first 3,000 VA at 100 percent, the next portion up to 120,000 VA at 35 percent, remainder at 25 percent. Four or more fastened-in-place appliances get 75 percent. Clothes dryers are calculated at 5,000 VA minimum each, with no reduction for four or fewer. A single 12 kW household range comes off the range table at 8 kW. The optional dwelling method takes the first 10 kVA at 100 percent and the remainder at 40 percent. Our load calculation walkthrough shows how these chain together.

Tier 2: derive, do not memorize

Voltage drop is a good example of what not to memorize. The 3 percent branch circuit and 5 percent combined figures are recommendations in informational notes, not enforceable requirements, and every question is solvable from the formula. Our voltage drop guide covers the setup.

For motors, memorize that full-load current comes from the code tables and not the nameplate, then bank a few anchors if you have room: at 460 volts three phase, 5 hp is 7.6 amps, 10 hp is 14 amps, and 20 hp is 27 amps. Those three let you sanity-check any motor problem.

Memory techniques that actually work

Recall, not review. Rereading a table feels productive and builds almost no recall. Close the book and write the 75 degrees C column from memory on blank paper. Check it, mark what you missed, repeat tomorrow.

Space it out. Same day, next day, three days, one week. Five short sessions beat one long one by a wide margin.

Chain, do not list. Values learned as a sequence with a starting anchor stick better than isolated facts. "Fourteen is twenty, and step up: twenty-five, thirty-five, fifty, sixty-five" is one item to remember, not five.

Brain dump on arrival. As soon as the exam starts and scratch paper is allowed, write out your core tables before you read a single question. You dump them while they are fresh, and you stop paying to hold them in working memory for the rest of the exam.

Drill in question form. Memorizing "8 AWG copper is 50 amps" is not the same skill as answering "what is the smallest copper conductor for a 45 amp continuous load." Practice the second form.

What to skip

Do not try to memorize Chapter 9 conductor and raceway area tables, conductor resistance values, or the full motor full-load current tables. Learn where each lives and how it feeds a calculation. Exam questions that require those numbers generally hand them to you, and the ones that do not are testing the method.

Also skip anything you have never seen in practice questions. Coverage on the trade exam follows the published blueprint, so let that steer you rather than your own sense of what feels important. Our overview of what is on the C-10 exam maps it out, and exam content outlines and rules are published by the CSLB at cslb.ca.gov, which is the only place to confirm current details.

A simple drill schedule

Week one, Table 310.16 and standard device sizes. Week two, add box fill and conduit fill. Week three, add adjustment and demand factors. Every session: blank paper first, book second, then ten questions that force you to use what you just wrote.

The values are the easy part. What separates candidates who pass from candidates who nearly pass is applying them under time pressure, on questions written to look like more than one rule applies. Working timed sets of practice questions is what turns memorized numbers into exam readiness, and it also tells you honestly which tables are still shaky.