Texas Electrician ExamTexas journeyman & master

Checked against primary sources 2026-08-24

The step people forget after doing the derating correctly

You derate the conductor, get a good number, and then a two-line rule in Article 240 caps it anyway. Skipping that step is how a correct calculation produces a wrong answer.

On this page
  1. The rule and the timing
  2. The two ways a small conductor escapes the cap
  3. The entries that carry conditions the others do not
  4. The next-higher rule, and the three conditions on it
  5. Over 800 amperes the permission reverses
  6. What counts as a standard rating
  7. Adjustable-trip breakers you can reach over a network
  8. The sequence, so nothing gets skipped
  9. What this page cites

The rule and the timing

For the small conductor sizes the overcurrent protection shall not exceed the figures listed in NEC 240.4(D), and the limit is applied after any correction for ambient temperature and any adjustment for the number of conductors.

The timing is the whole point. You do the derating first. Then this caps the result.

That direction matters because it only ever cuts. A derated ampacity that lands above the limit does not raise the limit. It gets cut down to it.

Look up the figures in your own code book. The subdivision is a list of eight numbered entries, 240.4(D)(1) through 240.4(D)(8), and they are the most cited limits in the trade.

The two ways a small conductor escapes the cap

240.4(D) does not open with the limit. It opens by excepting two other subdivisions, and a candidate who learned the cap without them will eliminate the right answer on any item that lands in either one.

That is why a 14 AWG conductor in a motor control circuit can sit under a device rated well above the small conductor figure and still be code compliant. The cap never reached it. Article 430 did.

The exam version of this is a stem that names a motor, an air conditioner or a tap and then offers you the small conductor figure as an answer. It is the most attractive distractor in the topic because it is right in every other context.

The entries that carry conditions the others do not

Three of the eight come with strings attached: 18 AWG copper, 16 AWG copper and 14 AWG copper-clad aluminum. The five larger ones do not.

Those conditions cover how much of the load may be continuous and what kind of overcurrent device or fuse class is protecting the conductor. Both parts have to hold.

Quoting a figure from one of those three entries without the conditions attached is a wrong answer, and it is a wrong answer that sounds authoritative. If a question involves 18 or 16 AWG, read the conditions before you answer.

The next-higher rule, and the three conditions on it

Separately, you are sometimes allowed to round the protective device up to the next standard rating above the conductor ampacity (NEC 240.4(B)). Most people remember that. Fewer remember it carries three conditions, and the permission depends on all three (NEC 240.4(B)).

Fail any one of them and you round down, not up.

Over 800 amperes the permission reverses

Where the device is rated over 800 amperes, the conductor ampacity must be equal to or greater than the rating of the device (NEC 240.4(C)). No rounding up.

Watch the boundary rather than the number. 240.4(B) allows the round-up as long as the rating you select does not exceed 800 amperes, so 800 itself is still inside the permission. 240.4(C) takes over above it.

Two rules, opposite directions, and that line is the entire question. An item that hands you a 1000 ampere scenario is checking whether you noticed you crossed it.

What counts as a standard rating

The standard ampere ratings for fuses and inverse time circuit breakers live at 240.6(A), with a few additional standard ratings that belong to fuses alone. You cannot answer a rounding question without that section, and it is worth a tab.

One thing about it gets misread constantly. The use of fuses and circuit breakers with nonstandard ampere ratings shall be permitted (NEC 240.6(A)). The list defines what counts as standard for the purpose of the next-higher rule. It does not forbid other sizes from existing.

So a question asking what devices are available and a question asking what the next standard size is are different questions with different answers.

Adjustable-trip breakers you can reach over a network

A breaker whose trip setting can be changed from somewhere else is a code question, not just an IT question, and 240.6(D) is where that lands. It arrived with the 2023 edition rather than this one, so a 2023 book has it too, and any source calling it new in 2026 is wrong.

Circuit breakers that can be adjusted remotely to modify the current setting shall be permitted to have an ampere rating equal to the adjusted current setting only where local restricted access is achieved by one of the methods in 240.6(C) and remote access is achieved by one of two routes (NEC 240.6(D)).

The first route is a local nonnetworked interface. The second is a networked interface, and it comes with a condition: either the breaker and its adjustment software have been identified as evaluated for cybersecurity, or a cybersecurity risk assessment of the network has been completed with documentation available to the people authorized to inspect, operate and maintain the system.

The section points at recognized cybersecurity standards from ANSI/ISA, UL, NIST and NEMA. You are not expected to know their contents. You are expected to know that the code sends you to them.

The sequence, so nothing gets skipped

  1. Find the base ampacity for the conductor from the ampacity table at the correct temperature column.
  2. Apply the ambient correction factor.
  3. Apply the adjustment factor for more than three current-carrying conductors.
  4. Ask what kind of circuit this is. A tap goes to 240.4(E), and an application named in Table 240.4(G) goes to its own article, and in both cases the small conductor limit is behind you.
  5. Otherwise, if the conductor is one of the eight entries, cut the derated result to the 240.4(D) figure. The cap never raises anything.
  6. Select the protective device, checking whether you are permitted to round up and which side of 800 amperes you are on.

Steps four and five are the ones that disappear under time pressure, because by then the calculation feels finished.

What this page cites

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Every rule here is cited to the section it comes from, and corrections are logged in public with the date. This is study material rather than electrical advice, and it does not replace your own code book or your inspector.