Tap rules on the Texas exam, and the four questions that name the subdivision for you

What the exam asks here

Three of the 500 questions in our bank use the word tap, all of them in wiring methods and installations. That is a small count attached to an outsized cost, because the tap family is among the densest material in the book.

The neighbours matter more than the count. The small conductor cap at 240.4(D) is named in seven of the 500 and it opens by excepting taps, and the rounding permission at 240.4(B) is named in ten and is withdrawn from every tap rule. 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. Our page on small conductors and 240.4 covers the other side of that flip.

The bank item that carries the topic gives the shape. A smaller set of conductors is connected to a feeder with no overcurrent device at the point of connection, and the working answer is a tap rule conditioning how far the run goes, where it lands and what it terminates in. The trap lines name three standard failures: calling the installation unlawful because every conductor must be protected where it receives its supply, matching the tap ampacity to the feeder, and sizing the feeder device down to the tap.

What a tap actually is

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 and it says nothing about the joint, so a splice or a mechanical connection to a bigger wire is a separate subject.

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

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, and 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. One option imports the ampacity condition from a neighbouring 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.

Two eliminations that hold across the family

One sentence at the top of 240.21(B) throws out a class of answers, and it is true of every subdivision underneath it. The parent subsection shuts the door on 240.4(B) for tap conductors, so whatever that rounding permission allows elsewhere, it is unavailable on a tap. An option that sizes a tap conductor and then rounds the device up to the next standard size is wrong under every one of 240.21(B)(1) through (B)(5), and you can strike it before working out which subdivision the stem describes.

A second one reaches just as far. A tap conductor may supply another conductor only through an overcurrent device meeting 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 and apply to all of the children by construction. They also cost nothing to apply on a paper where the passing percentage is seventy and the clock is the thing you are watching.

The subdivision with no length limit

Outside taps have no length limit. 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 most likely to turn up here, because it reads like an invented answer. The subdivisions around it are lengths, so an option saying there is no limit looks made up, and it is the correct answer.

What it charges is location and termination in place of distance. The conductors are protected from physical damage, they end at a single circuit breaker or a single set of fuses holding 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. Count the conditions off the subdivision in your own copy, because a summary will not survive a careful question.

The same idea exists on the other side of a secondary. 240.21(C) carries an outside secondary conductor rule that also runs to any length, so the word outside in a stem leaves you with two candidates and no answer yet.

Length and ampacity move apart

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 needs a fatter conductor, so any option pairing the longest run with the smallest share of the feeder device can be struck on sight. Two of the indoor subdivisions behave that way, and the rest part company with it.

The subdivision permitting the longest measured run states the same fraction of the feeder device as the shorter indoor one. It buys its extra distance with conditions on the building it runs in, on the minimum conductor size, on splices and on how high above the floor the tap is made, and none of that is copper. The subdivision with no length limit at all states no fraction of the feeder device, because its ampacity comes from the single device the conductors terminate in. Longest possible run, no share of the upstream rating, and it is the correct answer, so a heuristic built on the pattern strikes the one option most likely to be right.

Read the ampacity condition out of the subdivision the stem puts you in, and let the length name the rule while the clause comes off the page. Name the rule first, then read its clause, which is slower by a few seconds and right every time. The fractions sit together in one section of your book, and reading them in the copy you carry into the room is worth more than reading them anywhere else.

When a secondary is in the middle

Conductors leaving a secondary and running to the first overcurrent device downstream are feeder conductors, because the Article 100 definition of a feeder runs from the service equipment, the source of a separately derived system, or another power supply source, up to the final branch circuit device. How they are protected is a separate question, answered by 240.21(C).

The general section says why. 240.4(F) declines to credit the primary device with protecting those secondary conductors, except on two configurations: a single phase unit with a two wire secondary, and a three phase delta-delta unit with a three wire secondary. Read that sentence for what it carves out. Every other secondary needs protection of its own or a subdivision of 240.21(C) permitting something else, and reaching for a feeder tap subdivision is the error the question was written to collect.

The 2026 edition added a definition of secondary conductors of that kind to Article 100, which is worth reading once, because the whole difficulty in this family is knowing where the feeder rules stop and the secondary rules start.

Then the exception that catches candidates going the other way. Where the primary side is itself fed by a tap off a feeder, 240.21(B) has a subdivision measuring the primary and secondary conductors together as one run. The question that sorts it is about the supply end: a feeder puts you in 240.21(B), and a secondary puts you in 240.21(C) unless that unit is sitting on a tap.

What to tab before test day

The Texas examination is open book and you carry your own current copy, which Texas adopted as the 2026 edition effective 1 September 2026 under 16 TAC 73.100. The PSI candidate information bulletin updated 9 July 2026 says the examinations are referenced to that edition, so confirm the subdivision numbering in the book you bring.

• Tab 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 240.21(C). Moving between the feeder taps and the secondary conductor rules is the flip you will make most often, and they sit far enough apart to cost seconds.
• Put a third on 240.4, because a tap question and a small conductor question look identical for the first ten seconds.
• Write the four questions in the margin at 240.21(B), with a note that a blank is an answer.
• Write the two eliminations at the top of the same page, since they apply to every subdivision and cost nothing to use.

Build the habit of naming the subdivision before doing any arithmetic. A tap question answered from the general protection rule produces a conductor far too large and an answer missing from the list, while one answered from the wrong subdivision produces a number that is on it. the question set carries the code side of this topic at the question set, which is where the worked detail lives. Our page on ampacity derating covers the ampacity a tap rule is measured against.

Questions people ask

What makes a conductor a tap conductor?

Its overcurrent protection sits ahead of it at a rating higher than the conductor's own ampacity. The word describes the protection and says nothing about the joint, so a splice or a mechanical connection to a bigger wire is a separate subject. Everywhere else the code protects conductors in accordance with their ampacities under 240.4 and puts the device where the conductor receives its supply under 240.21. Taps appear in that first section as one of the departures, and 240.4(E) points into Part II of the article where the permissions live.

Which tap rule has no length limit?

Outside taps, at 240.21(B)(5), and the subdivision is titled for exactly that. It is the item most likely to turn up, because an option saying there is no limit reads like one somebody invented to fill a slot. What it charges is location and termination in place of distance: the conductors are protected from physical damage, they end at a single circuit breaker or single set of fuses limiting the load to their ampacity, that device is part of the disconnecting means or immediately adjacent to it, and the disconnect is readily accessible outside the building or inside at the nearest point of entrance.

Can I round the overcurrent device up on a tap?

No. The opening sentence of 240.21(B) withdraws the rounding permission in 240.4(B) from tap conductors, and it does so for every subdivision underneath it. An option that sizes a tap conductor and then rounds the device up to the next standard size is wrong under all of 240.21(B)(1) through (B)(5), so you can strike it before working out which subdivision the stem describes. A second elimination reaches as far: a tap conductor may supply another conductor only through an overcurrent device meeting 240.4.

Does a longer tap always need a larger conductor?

No, and the rule of thumb costs you the item it looks most useful on. Two of the indoor subdivisions behave that way. The subdivision permitting the longest measured run states the same fraction of the feeder device as the shorter indoor one, buying its distance with conditions on the building, the minimum conductor size, splices and the height of the tap above the floor. The subdivision with no length limit states no fraction at all, taking its ampacity from the single device the conductors terminate in. Read the clause out of the subdivision the stem names.

How do I tell a feeder tap from a secondary conductor?

Ask what the conductor you are being asked about is connected to where it starts. A feeder puts you in 240.21(B). A secondary puts you in 240.21(C), unless the unit supplying that secondary is itself sitting on a tap, because 240.21(B) has a subdivision measuring the primary and secondary conductors together as one run. Conductors leaving a secondary are feeder conductors by the Article 100 definition, since a feeder starts at any source, and the protection question is answered separately from the naming question.

How many exam questions reach the tap rules?

Three of the 500 questions in our bank use the word tap, all of them in wiring methods and installations. The count understates the reading, because 240.4(D) opens by excepting taps and is named in seven more items, while 240.4(B) is withdrawn from every tap rule and is named in ten. A tap question and a small conductor question look identical for the first ten seconds, so study the two sections as one block and tab them separately, since one flip of the page decides which rule you are working in.