Texas publishes its electrician exam results every year, broken out by paper. In fiscal year 2025, the journeyman calculations exam was passed by 1,301 candidates out of 6,328 — 20.56 percent. The master calculations paper came in at 19.08 percent, 753 of 3,946. Four out of five people sitting down to do load calculations for a license walk back out without one.
That is not a mathematics problem. The arithmetic in a service calculation is addition, multiplication and one division at the end. What people fail is the structure: knowing which method they are in, which loads belong in it, and which demand factor applies to what.
Why demand factors exist at all
Start with the honest question an apprentice asks and gets waved off. If a house has a 12 kW range, two 4.5 kW water heaters, a dryer, an air handler and forty receptacle outlets, why is the service not sized to run all of that at once?
Because nothing built for people ever runs all of it at once. The range is at full output for minutes a day. The water heater cycles. Nobody dries laundry while running the oven while the strip heat is at maximum while every receptacle in the house has a load on it. Sizing for the arithmetic sum of nameplate ratings would mean 600-amp services on ordinary houses, conductors nobody can afford, and transformers that spend their lives at four percent load.
Demand factors are the code's way of encoding observed diversity. They are not a safety margin being spent, they are an admission that connected load and actual load are different quantities. Article 220 is, read properly, a document about statistics written as a set of tables.
The place this bites people is that diversity is an assumption, and assumptions can be wrong. A house with one EV charger has less diversity than the same house without one, because that load runs for hours at a fixed current. That is why 625 treats charging equipment as continuous and why the calculated result on a modern remodel so often lands above what the same house needed in 1995.
Standard method versus optional method
For a one-family dwelling you have two legitimate routes to an answer, and they will not give you the same number.
The standard method lives in Part III of Article 220. You build the load up in categories: general lighting and receptacle load from square footage, small-appliance and laundry branch circuits, then apply the demand factor from Table 220.42 to that general lighting total. Fixed appliances get their own treatment, the range comes from Table 220.55, the dryer from Table 220.54, and heating and air conditioning go in under 220.60 where you take the larger and drop the smaller. Then you add the whole thing up.
The optional method is 220.82, and it is available only for a one-family dwelling or an individual unit served at 120/240 volts or 208Y/120 volts, three wire, with a service or feeder of at least 100 amperes. You total effectively everything connected, apply 100 percent to the first 10 kVA and 40 percent to the remainder, then handle heating and cooling separately under 220.82(C) by taking the largest of a short list of possibilities.
Two things about the optional method. It is usually the smaller number, which is why contractors like it. And it is optional — you may use it, you are never required to, and a jurisdiction may have opinions. Existing dwellings have their own path under 220.83, which matters for service upgrades and is the one that decides whether a panel change requires a service change.
Where candidates and working electricians go wrong
The mistakes cluster, and they are the same in an exam room and in a truck.
- Mixing methods. Starting in the standard method, reaching for 220.82's 10 kVA at 100 percent because it is remembered, and producing a number that belongs to neither. Pick a method on the first line and write it at the top of the page.
- VA against amperes. Working in volt-amperes through the whole calculation and then dividing by 120 instead of 240, or the reverse. A single-phase service divides by 240. Three-phase divides by the voltage times the square root of three.
- The range table. Table 220.55 has columns and notes, and the notes are where the exam lives. A single range over 12 kW, ranges of unequal rating, counter-mounted units and wall ovens on the same circuit — each has its own handling.
- Continuous loads. The 125 percent multiplier applies to continuous load for the overcurrent device and conductor sizing. It is not a general-purpose fudge factor to be applied everywhere, and it is not applied twice.
- Neutral load. 220.61 allows a reduction on the feeder or service neutral for certain loads, and specifically does not for others. This shows up on master papers constantly and is a common reason an otherwise correct calculation is marked wrong.
- Reading past the question. The exam asks for the minimum service conductor size, and the candidate computes the calculated load and stops, or computes the load and then sizes without going to 310.12 for dwelling service conductors.
The last one is worth dwelling on because Texas splits its journeyman exam into a calculations paper and an NEC paper, and the pass rates differ: 24.46 percent on the NEC paper against 20.56 percent on calculations. The gap is not extra mathematics. It is that a calculation question requires you to navigate the book and do arithmetic under the same clock.
Most people who fail the calculations paper can do the arithmetic. They run out of time finding the table.
How to actually get good at it
Work complete calculations, not fragments. A worked problem that ends at "the general lighting load is 4,500 VA" teaches you nothing about the part that fails people. Do the whole thing, both methods, on the same house, and reconcile why the answers differ.
Then do it with a timer. The exam content outline in TDLR's Candidate Information Bulletin tells you how many questions and how long you get; divide it out and practice at that pace. Tab the tables you will need before you sit down — 220.42, 220.54, 220.55, 310.12 — because minutes spent flipping are the actual failure mode.
Our 2026 Journeyman Electrician Exam Prep Study Guide works the calculations end to end rather than in fragments, and the code text is available through NFPA's free access portal with a free account.