The 240.4(D) small conductor cap, and how Texas exam items get built around it

What the exam asks here

Conductor sizing and ampacity is the second largest area in our 500 question bank, with 68 items in it. The small conductor cap is named in seven of those 500. Six sit in conductor sizing and one sits in motor circuits, where it serves as a wrong answer.

Seven out of 500 sounds thin until you look at what sits beside it. The rounding permission in 240.4(B) is named in ten more, and those ten are usually decided by a limit sitting elsewhere in the same section, which puts the Article 240 protection family closer to seventeen items.

The items take three recognisable forms. One hands you a derated ampacity and asks for the largest device permitted. One asks what the rule limits, with the conductor ampacity and the termination rating offered beside the device rating. One names a motor, an air conditioner or a tap in the stem and then puts the small conductor figure on the answer list, where it reads as the safe choice because it is correct in every other setting. The bank's trap lines say where people land: using the derated value as though the derating had dealt with the cap, and believing the cap lowers the conductor ampacity.

The cap lands on the device

One distinction decides most of these items. The rule limits the rating of the overcurrent device and it leaves everything else alone. The conductor keeps whatever ampacity correction and adjustment gave it, the termination temperature limit in 110.14(C) is a separate ceiling arrived at separately, and the load is bounded by the device rating and by the sizing rules that produced it.

Hold that and the definitional item answers itself in about four seconds. An option saying the rule caps the ampacity is describing derating, which happened earlier, and an option saying it caps the termination temperature is describing 110.14(C), which our page on termination temperature covers in its own right.

Where the cap sits in the order

Six steps, in this order, and the last two are the ones that disappear when the clock is the thing you're watching.

1. Read the base ampacity out of the column that matches the conductor insulation rating.
2. Apply the ambient correction factor.
3. Apply the adjustment factor for the number of current carrying conductors.
4. Ask what kind of circuit this is, because a tap and several named applications leave Article 240 at this point.
5. If the conductor is one of the eight entries in the subdivision, cut the derated figure to the capped value.
6. Select the device, checking whether you're permitted to round up and which side of 800 amperes you're on.

Steps two and three commute, and the bank has an item built to prove it: a base of 200 amperes with factors of 0.76 and 0.70 gives 106 amperes whichever multiplication you do first. What carries consequences is the sequence on either side of them, since the termination comparison comes after both factors and the cap comes after the ampacity is settled. Our page on ampacity derating works the factor side in full.

Two cases show the cap doing both of its jobs. A 10 AWG copper conductor based at 40 amperes in the 90 degree column and bundled at 0.70 derates to 28 amperes, the device lands at 30 amperes through the rounding permission, and the cap for that size sits above 30. A 14 AWG copper conductor corrected and adjusted to 19 amperes ends differently, because the cap for that size sits below 20 and a 20 ampere device fails on it whatever 240.4(B) would otherwise allow.

Two ways a conductor leaves the cap

The subdivision opens by excepting two others, and a candidate who learned the figure without them will eliminate the right answer on any item that lands in either one.

The first exit is 240.4(E), which sends tap conductors to their own family of rules, where the conditions in those rules do the protecting. Our page on tap rules walks through what each permission charges in exchange.

The second exit is 240.4(G), which covers the applications listed in its table and points each one at the article that governs it: motors, motor control circuits, air conditioning and refrigeration equipment, control and instrumentation circuits, fire alarm circuits, welders and phase converters. A 14 AWG conductor in a motor control circuit can sit under a device rated well above the small conductor figure and remain compliant.

The bank puts this in its motor set, with conductors sized at 100 amperes behind a short circuit and ground fault device rated 200 amperes. Reaching for 240.4(B) treats a permission worth one step as though it could double a device rating, and reaching for 240.4(D) answers a motor circuit with a rule written for small conductors. The working answer is 240.4(G) handing the job to Article 430, where the overload device protects those conductors. Our motor circuits hub carries the rest of that family.

The rounding permission and its conditions

Most candidates remember that a device may sometimes sit at the next standard rating above the conductor ampacity. Fewer remember that the permission carries three conditions and depends on all of them holding.

• The conductors are no part of a branch circuit supplying more than one receptacle for cord and plug connected portable loads.
• The conductor ampacity fails to correspond already to a standard rating of a fuse or of a circuit breaker without overload trip adjustments above its rating.
• The next standard rating selected stays at or below 800 amperes.

The bank tests all three. A feeder at 244 amperes with every condition satisfied takes a 250 ampere device, since the standard ratings step through 225 and then 250. The same arithmetic on a branch circuit supplying several receptacles for cord and plug connected portable loads goes the other way, and a conductor at 42 amperes takes 40 amperes because the permission has been shut off. A run at 88 amperes on a circuit the permission misses takes 80 amperes, and the 90 ampere option sits there for the candidate who never checked which kind of circuit it was.

Above 800 amperes the direction reverses under 240.4(C), which requires the conductor ampacity to be equal to or greater than the device rating. A paralleled set good for 1150 amperes takes a 1000 ampere device, since 1200 is the next standard rating and the conductors fall short of it. Treat 800 as a boundary: it sits inside the rounding permission, and 240.4(C) governs above it.

What moved for the 2026 edition

Texas adopted the 2026 National Electrical Code effective 1 September 2026 under 16 TAC 73.100, with one state amendment that keeps a ground fault exception for listed outdoor heating, ventilating and air conditioning equipment which the national text retires on that date. The PSI candidate information bulletin, updated 9 July 2026, states in capitals that the examinations are referenced to the 2026 edition from the same day, and Texas amends nothing in the 240.4 family.

One correction is worth carrying. The rule on circuit breakers whose trip setting can be changed over a network, at 240.6(D), arrived with the 2023 edition, and study material describing it as new for 2026 has that wrong.

What getting this wrong costs a Texas candidate

The journeyman examination fee is seventy-eight dollars, paid to the examination provider, and a retake costs seventy-eight dollars again with no discount attached. The department application fee is thirty dollars under 16 TAC 73.80(a), and every department fee is non-refundable under 16 TAC 73.80(e). The minimum passing percentage is seventy, so a handful of items in one family is enough to decide a close paper.

The clock costs more than the fee. From the date the department receives your application you have one year to satisfy every requirement, passing the examination included, under 16 TAC 73.20(b), and a retake eats weeks of that window while scheduling and the department queue run at their own pace. After a pass the position is comfortable, because results stay valid for the license term plus three years under 16 TAC 60.56, and an electrician license runs a year, which makes a journeyman pass good for four years from the examination date.

On the job the same error leaves a device rated above what the conductor's own subdivision allows, which becomes a correction notice and a device change as soon as somebody with a code book reads the panel schedule.

What to do about it before test day

The Texas examination is open book and you carry your own current copy of the code into the room, so the work here is making a section findable under a clock.

• Tab 240.4 as a whole. The subdivisions that decide these items sit within two pages of each other and the flip between them is what costs seconds.
• Tab 240.6(A) separately, because a rounding question is unanswerable without the list of standard ratings, and note beside it that the list defines what counts as standard for the permission.
• Write the six step sequence in the margin at 240.4, ending with the cap and the device selection.
• Look up the eight capped entries in your own book and read the conditions on the three smallest of them, which cover how much of the load may be continuous and what kind of device or fuse class is protecting the conductor. Our page on continuous loads handles that multiplier in full.
• Practise the arithmetic backward, from a required device rating to the base ampacity a conductor needs.

For the worked arithmetic on each of these, digit by digit, the question sets carries the code side of the same topic at the question set, where every line is set out with the section behind it.

Questions people ask

Does the small conductor rule lower the conductor's ampacity?

No. It caps the rating of the overcurrent device and leaves the ampacity where correction and adjustment put it. That matters because the cap is applied after those factors, so a conductor whose derated ampacity comes out above the cap still has its device held down, while a conductor whose derated ampacity comes out below the cap is governed by the ampacity itself. Whichever of the two figures is lower decides the device. The rule also stays clear of the termination temperature limit in 110.14(C) and puts no ceiling of its own on the load.

When does 240.4(D) stop applying to a small conductor?

Two exits. A tap conductor goes to 240.4(E), where the tap rules protect it through conditions on length, routing and what it terminates in, so the cap stays behind. An application listed in the table at 240.4(G) goes to its own article, which covers motors, motor control circuits, air conditioning and refrigeration equipment, control and instrumentation circuits, fire alarm circuits, welders and phase converters. A 14 AWG conductor in a motor control circuit can therefore sit under a device rated well above the capped figure and remain compliant, because Article 430 is doing the protecting.

Can 240.4(B) be used to round up past the cap?

No. They are separate rules and the cap is the one that finishes the problem. The bank has a worked case: a 14 AWG copper conductor corrected and adjusted to 19 amperes, with a candidate selecting a 20 ampere device on the strength of the rounding permission. That permission lets a device sit at the next standard rating above a conductor ampacity, and it cannot climb past a limit another subdivision has already set. Once the derated figure is in hand, compare it with the capped value for that size and let the lower one decide.

Where does the 800 ampere line sit?

The rounding permission allows the climb as long as the rating you select stays at or below 800 amperes, so 800 itself is inside the permission. Above that figure 240.4(C) takes over and requires the conductor ampacity to be equal to or greater than the device rating, which removes the climb entirely. The bank tests the boundary with a paralleled set good for 1150 amperes: the standard ratings step 1000 and then 1200, the conductors fall short of 1200, so the answer is a 1000 ampere device. An item handing you a four figure scenario is checking whether you noticed the crossing.

How many exam questions actually turn on this?

In our 500 question bank, conductor sizing and ampacity holds 68 items, and the small conductor cap is named in seven of the 500, six of them in that area and one in motor circuits. The rounding permission at 240.4(B) is named in ten more, and those ten are usually decided by a limit sitting elsewhere in the same section. Treat the Article 240 protection family as roughly seventeen items and study it as one block, because the sections sit within a few pages of each other in the book.

Which edition does the Texas exam use for this?

The 2026 National Electrical Code, from 1 September 2026. Texas adopted it under 16 TAC 73.100 with a single state amendment concerning a ground fault exception for listed outdoor heating, ventilating and air conditioning equipment, and no part of the 240.4 family is amended. The PSI candidate information bulletin updated 9 July 2026 states that the examinations are referenced to that edition from the same date. A job in your hand can still be held to an earlier edition, because that is the authority having jurisdiction's call and cities amend on top of the state adoption.