Try a full lesson: Branch circuits: continuous loads and the 125% rule

What this lesson covers

The 125% rule for continuous loads shows up in both portions of the Texas journeyman exam: as a rule to find in NEC Knowledge, and as a sizing step in Calculations. Branch circuits and conductors is the largest subject area on the PSI outline, 14 of the 80 scored questions. This lesson gives you a four-step habit that works on every continuous-load question: is it continuous, which rule, apply 125%, check the conductor.

We cite the 2026 NEC by section number in our own words. Keep your own copy open beside this page.

Step 1: is the load continuous?

Article 100 defines a continuous load as one whose maximum current is expected to last 3 hours or more. Questions signal it in plain words: "store lighting", "runs all night", "dusk to dawn", "operates 8 hours a shift". If the question does not say how long the load runs, do not assume it is continuous.

Some articles decide for you. A fixed storage water heater of 120 gallons or less is treated as continuous (422.13). Fixed electric space heating is sized at 125% under Article 424; find the section in your 2026 index. When the equipment article says so, apply the 125% whatever the run time.

Step 2: find the rule for the conductor you are sizing

The same idea appears in several places. Turn to the one that matches the conductor in the question:

The three conductor rules work the same way: 125% of the continuous load plus 100% of the noncontinuous load. The branch-circuit and feeder device rules use the same 125%.

Step 3: apply 125% to the continuous part only

Split the load. Multiply the continuous part by 1.25. Add the noncontinuous part at 100%. That total is the minimum for both the conductor ampacity and the overcurrent device rating.

Then round the device up to a standard rating from 240.6(A). You may not round down.

Step 4: check the conductor

The conductor has two separate tests under 210.19(A)(1):

1. The 125% figure from Step 3, checked against the conductor's ampacity without correction or adjustment, in the column the terminations allow (110.14(C)).
2. The actual load, at 100%, checked against the ampacity after correction for ambient temperature and adjustment for the number of current-carrying conductors.

The conductor must pass both. Do not multiply the 125% and the adjustment factor together; that oversizes the wire and leads you to a wrong answer choice that is often on the list.

Last, check the small-conductor limits in 240.4(D). For example, 12 AWG copper is limited to 20 A protection.

Worked examples

Example 1: mixed load on a feeder. A feeder serves 24 A of store lighting that runs all day and 8 A of noncontinuous receptacle load. Under 215.2(A)(1) and 215.3, 24 × 1.25 = 30 A, plus 8 A = 38 A. The smallest standard device at or above 38 A is 40 A. The conductor needs at least 38 A; on 60°C terminations, 8 AWG copper (40 A) passes.

Example 2: the two tests are separate. A 16 A continuous load is on 12 AWG THHN copper in a raceway with nine current-carrying conductors at a normal ambient.

• Test 1: 16 × 1.25 = 20 A against the 60°C column, where 12 AWG carries 20 A. Pass.
• Test 2: 16 A against the 90°C value of 30 A × 70% for nine conductors = 21 A. Pass.
• The device is 20 A, which 240.4(D) allows on 12 AWG. 12 AWG works.

If you had multiplied instead, 16 × 1.25 ÷ 0.70 = 28.6 A, you would wrongly move up a size.

Example 3: equipment that is continuous by rule. A 5,500 W, 240 V, 40-gallon storage water heater. 5,500 ÷ 240 = 22.9 A. 422.13 makes it continuous, so 22.9 × 1.25 = 28.6 A. Use a 30 A device and 10 AWG copper.

Common traps

• 125% belongs to sizing, not to the load total. You apply it when you size conductors and overcurrent devices. Do not add an extra 125% to a load calculation unless the question tells you to.
• Only the continuous part gets 125%. Multiplying the whole load by 1.25 overshoots when part of it is noncontinuous.
• Exceptions only when asked. Some sections let a device listed for 100% operation skip the 125%. PSI tells candidates to ignore exceptions unless the question directs you to them, so use that only if the question says the assembly is listed for it.
• Equipment articles can override. Air-conditioning circuits are sized at 125% of the compressor current under 440.32 whatever the run time, and their breakers follow the nameplate, not 240.4(D).
• Copper unless stated. PSI's rule. Read the aluminum column only when the question names aluminum.

Check yourself

Try the five questions in the free practice set for this lesson. The same four-step habit works on each one.

Where to look in the NEC

• Article 100: continuous load
• 210.19(A)(1) and 210.20(A) for branch circuits
• 215.2(A)(1) and 215.3 for feeders; 230.42(A) for service-entrance conductors
• 240.4(D) and 240.6(A); 110.14(C); Table 310.16 and Table 310.15(C)(1)
• 422.13 and Article 424 for equipment treated as continuous