Texas Electrician ExamTexas journeyman & master

Checked against primary sources 2026-08-24

Every tap rule buys the same thing, and each one charges differently

A tap is where the code lets a conductor sit behind a device far larger than its ampacity. Read each subdivision for what it charges in exchange and the family stops being a memory problem.

On this page
  1. What a tap actually is
  2. Why the code allows it
  3. Four questions, and the blanks are answers
  4. The subdivision with no length limit
  5. The elimination that actually holds
  6. Length and ampacity do not move together
  7. A transformer in the middle
  8. Reading the question
  9. What to tab before test day
  10. What this page cites

What a tap actually is

Not a splice, and not a mechanical connection to a bigger wire. A tap conductor is one whose overcurrent protection sits ahead of it at a rating higher than the conductor's own ampacity. The word describes the protection, not the joint.

Everywhere else the code works the other way around. Conductors are protected in accordance with their ampacities (NEC 240.4), and the device goes at the point where the conductor receives its supply (NEC 240.21). Taps appear in that first section as one of the situations where something else is allowed, and the pointer sends you into Part II of the article (NEC 240.4(E)).

So when an item hands you a small conductor behind a large breaker and asks whether the installation is acceptable, it is not trying to catch you out with a mistake. It is a tap question, and it is asking whether you know a permission exists and what that particular permission costs.

Why the code allows it

The device ahead of a tap cannot protect it against overload, and no amount of reading will change that. A large feeder breaker will sit there quite happily while a conductor good for a fraction of its rating heats up past its insulation.

What the code does instead is take away the conditions that turn an unprotected conductor into a building fire. A short run has little of itself to burn. A run kept in a raceway and out of reach is unlikely to be damaged into a fault at all. A run that lands in one device is protected from the far end, which is late but not useless. A run kept outdoors takes its chances where there is no building around it.

The subdivisions of NEC 240.21(B) mix those conditions in different proportions, and that is the part worth learning. What they do not do is charge for the same permission twice. A condition that carries one subdivision can be entirely absent from the next one, which is why the family has to be read subdivision by subdivision rather than averaged into a rule of thumb.

Four questions, and the blanks are answers

Ask these in the same order every time, and expect some of them to come back empty.

Each answer is one clause, except where a subdivision states no answer on purpose. That absence is the rule speaking, not a clause you skipped, and it is where the exam lives. A candidate who expects every tap rule to state a length will supply one from memory for the rule that states none.

The wrong answers are built out of the same four questions. An option imports the ampacity condition from a neighboring subdivision. Another gets the length and the ampacity both right and says nothing about what the conductors land in, which is the clause candidates stop reading before they reach.

The subdivision with no length limit

Outside taps have no length limit. NEC 240.21(B)(5) is titled for exactly that, and a tap run outside a building can be as long as the job needs it to be.

It is the item in this family most likely to turn up, because it reads like an invented answer. The subdivisions around it are lengths, so an option saying there is no limit looks like the one somebody made up to fill a slot. It is the correct answer, and it is correct for a reason worth holding onto.

What it charges is location and termination instead of distance. The conductors are protected from physical damage, they end at a single circuit breaker or a single set of fuses that holds the load to their ampacity, that device is part of the disconnecting means or sits immediately next to it, and the disconnect is at a readily accessible location outside the building or inside at the nearest point of entrance. Read the subdivision in your own copy and count the conditions off it yourself, because a summary will not survive a carefully written question.

The logic is the same trade as the short rules, priced differently. An unprotected conductor in open air outside a structure is not the hazard this part of the code exists to manage. The permission ends where the conductors come in, which is why the disconnect location is the clause the rule turns on.

The same idea exists on the other side of a transformer. NEC 240.21(C) carries an outside secondary conductor rule that also runs to any length, so the word outside in a stem does not on its own tell you which subdivision you are in.

The elimination that actually holds

One sentence at the top of NEC 240.21(B) throws out a class of answers, and it is true of every subdivision underneath it.

The provisions of 240.4(B) shall not be permitted for tap conductors.

NEC 240.21(B), 2026 edition

NEC 240.4(B) is the familiar permission to round up to the next standard device rating when a conductor ampacity falls between two of them. It is off the table here. An option that sizes a tap conductor and then rounds the device up to the next standard size is wrong under every one of NEC 240.21(B)(1) through (B)(5), and you can strike it before you have worked out which subdivision the stem is describing.

A second one reaches just as far. A tap conductor may not supply another conductor except through an overcurrent device that meets NEC 240.4, so a stem that runs one tap into a second unprotected run has already failed on structure, whatever the lengths in it are.

Both of those are worth more than any rule of thumb about lengths, because they come from the parent section rather than from a pattern across the children. A rule stated once at the top applies to all of them by construction.

Length and ampacity do not move together

There is a tempting rule of thumb in this family and it will cost you the item it looks most useful on. It says a longer permitted run always has to be a fatter conductor, so any option pairing the longest run with the smallest share of the feeder device can be eliminated on sight. Two of the indoor subdivisions do behave that way. The rest do not.

So read the ampacity condition out of the subdivision the stem puts you in, and never infer it from the length. Name the rule first, then read its clause. That is slower by a few seconds and it is right every time.

The fractions themselves sit together in one section of your book and this page is deliberately not printing them. Reading them once in the copy you carry into the room is worth more than reading them ten times here.

One further clause catches people. Some subdivisions restrict where the tap conductors may run relative to the enclosure they started in, and some restrict what the tap may terminate in. Those are separate conditions in separate sentences, and an item can turn on either one without mentioning the other.

A transformer in the middle

Conductors leaving a transformer secondary are governed by NEC 240.21(C), and the general section of Article 240 says why.

Single-phase other than 2-wire and multiphase other than delta-delta 3-wire transformer secondary conductors shall not be considered to be protected by the primary OCPD.

NEC 240.4(F), 2026 edition

Read that sentence for what it carves out rather than for what it forbids. A single-phase secondary that is 2-wire, and a multiphase secondary that is delta-delta 3-wire, are the two configurations where the device on the primary can still be credited with protecting the secondary conductors. Every other secondary needs protection of its own or a subdivision of NEC 240.21(C) that permits something else, and reaching for a feeder tap subdivision instead is the error the question was written to collect.

The 2026 edition added a definition of transformer secondary conductors to Article 100. It is worth reading once, because the whole difficulty in this family is knowing where the feeder rules stop and the secondary rules start, and that definition is what the change was written to settle.

Now the exception that catches candidates going the other way. Where the transformer is itself fed by a tap off a feeder, NEC 240.21(B) has a subdivision that measures the primary conductors and the secondary conductors together as one run. A transformer in the stem does not automatically move you into NEC 240.21(C). It moves you out of the plain feeder tap subdivisions, which is not the same thing.

The question that sorts it is about the supply end. Ask what the conductor you are being asked about is connected to where it starts. A feeder, and you are in NEC 240.21(B). A transformer secondary, and you are in NEC 240.21(C) unless that transformer is sitting on a tap.

Reading the question

The habit worth building is to name the subdivision before doing any arithmetic. A tap question answered from the general protection rule produces a conductor that is far too large and an answer that is not on the list, which at least tells you something. A tap question answered from the wrong subdivision produces a number that is on the list.

What to tab before test day

Tab NEC 240.21 on its own. The front of Article 240 holds the general protection rules and it will not get you into Part II fast enough under a clock.

Put a second tab at NEC 240.21(C). Moving between the feeder taps and the secondary conductor rules is the flip you will make most often in this subject area, and they are far enough apart in the section to cost you real seconds.

Put a third on NEC 240.4. A tap question and a small conductor question look identical for the first ten seconds, and the two sections sit close enough together that one flip decides which one you are in.

What this page cites

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