NEC Practice Questions by Topic

54 topics, 25 original questions each, 1,350 in all. Every answer names the 2026 NEC section it comes from. Pick a topic, answer on the page, and read the explanation on every miss. Free, no account.

Installation rules

• Agricultural Buildings

  Article 547 is a scope article before it is a requirements article, and most items on it are decided by whether the described conditions exist at all. These questions lean on 547.1 and 547.5 for scope, on 547.20 through 547.31 for the wiring and equipment rules, and on 547.40 through 547.44 for the distribution point and the equipotential plane. Section numbers are the 2026 addresses, which are not the ones most published material still uses.

• Appliances and Water Heaters

  The circuit that feeds one appliance is sized in Article 422 from what is stamped on the appliance, and the service that supplies a building full of them is sized in Article 120 from something else. These questions work the branch circuit and overcurrent rules in 422.10 and 422.11, the storage water heater sentence at 422.13, the disconnect rules in Part III, and the two Article 120 sentences that keep the load calculation from double counting the same heater.

• Cable Types

  A cable question is answered on two axes. One is the location, which is a set of Article 100 definitions rather than a description of the weather, and the other is the building, which nonmetallic-sheathed cable cares about far more than it cares about moisture. These questions work the paired permitted and not permitted lists in Articles 320, 330, 334, 338 and 340, the ampacity ceilings those articles set, and the 2026 listing sentence that now covers the hardware holding the cable up.

• Disconnecting Means

  Every disconnect rule in the book is asking the same question, whether the person about to work on this equipment can kill the power and then see that it stayed dead. These questions work the two halves of the in sight from test and the section that now carries it, the lockable provision that stands in for line of sight, the disconnect rules in the motor, air conditioning and service articles, and the ratings and operating conditions the motor article sets for the device itself.

• Enclosure Types

  An enclosure-type number is a statement about the conditions the box was tested against, not a grade, and the numbering does not behave like a ladder. These questions work what NEC 110.28 requires to be marked and what it says the enclosures do not protect against, how Table 110.28 is entered by condition and read across, the pairs of types that differ by one row, and the rules in Articles 110, 300, 314, 404 and 409 that spoil a correctly chosen enclosure after the fact.

• Expansion Fittings and Deflection

  An expansion fitting question is one of four shapes, and the first job is telling them apart. A calculated PVC or RTRC run works off a temperature change and a length against a quarter inch threshold, a structural joint takes a listed fitting with no arithmetic, a buried run coming out of the ground is an arrangement problem, and a metal raceway with a fitting in it turns into a bonding question in Article 250. These 25 work all four, with the table values used exactly as the 2026 edition prints them.

• GFCI and AFCI Locations

  Ground fault requirements move nearly every code cycle, so an answer learned two editions ago will be wrong in several places and will not announce itself. These 25 items work the opening sentence of each subsection of 210.8 before its list, because the voltage and ampere limits are different from one subsection to the next and that is where most of the traps sit. Arc fault protection is a separate section with a different first question, and the receptacle replacement rule pulls both requirements forward.

• Hazardous Locations

  Class, then division, then group, asked in that order and never out of it. These 25 items work the classification rules at 500.5, the material groups at 500.6, the protection techniques at 500.7, the bonding section that is new for 2026 at 500.30, and the sealing rules at 501.15 where most of the numbers live. Class III and its division split get the attention the exam gives them.

• Health Care Facilities

  Two equipment grounding paths in one run is what makes a patient care space different, and 517.13 is where an item writer starts. These 25 questions work both halves of that section, the space categories and the patient care vicinity as Article 100 defines them, the receptacle counts at a patient bed location, wet procedure locations, and the rule at 90.3 that lets a Chapter 5 article ask for something the general chapters never did.

• Luminaires and Clothes Closets

  The closet item comes up on every form of this examination, and it is two lookups rather than one: the storage space volume first, then the clearance that pairs with the luminaire you have. These 25 questions work all four parts of 410.16, the bathtub and shower zone, luminaire support and grounding, recessed luminaire clearances and thermal insulation, and the conditions under which a luminaire may be used as a raceway.

• Marinas and Boatyards

  Article 555 exists because the current that kills a swimmer is measured in milliamperes and no breaker in the facility will ever see it. These 25 items work the three ground-fault levels in 555.35 and the point each one sits at, the leakage current measurement device and its qualifiers, the shore power receptacle and disconnect rules, the electrical datum plane distances, and the listing and testing material the 2026 edition added.

• Multiwire Branch Circuits

  Two circuits sharing one neutral is efficient wiring and a specific hazard, and the exam tests both halves. These 25 items work the Article 100 definition and the phase relationship it forces, the simultaneous disconnect at the origin and what a handle tie does about it, the grouping and identification rules that actually live in Article 200, what an open neutral does to the loads, and how the shared neutral is counted when conductors are bundled.

• Panelboards

  Article 408 is short, and most items built on it are really testing another article. These 25 items work the one device that protects the panel and the two exceptions that release it, the back-fed fastener and the one place Article 705 relaxes it, the terminal bar rules, the service disconnect count and what does not count toward it, the location bars that live in Article 240, and the two spaces around the panel that Article 110 reserves.

• Pools and Spas

  Article 680 is organized by the kind of water rather than by the kind of gear, with general sections at the front that reach all of it, so the first move on any item is deciding which part you are standing in. These 25 items work that split, then the two kinds of rule inside it: the location rules that turn on a distance from the inside wall, and the equipment rules that follow the motor or the heater wherever it sits. The equipotential bonding section gets the largest share, because it is the spine of the article.

• Protection From Physical Damage

  Protection against physical damage for Chapter 3 wiring methods sits at 300.6 in the 2026 edition, and the number it used to carry now holds a rule about damaged conductors that reads close enough to cost you a minute. These 25 items work the framing subsections inside that section, the fittings and roof decking paragraphs, the uses-not-permitted lists in the method articles that overrule it, and the separate damage rule the grounding electrode conductor carries in Article 250.

• PV and Rapid Shutdown

  One idea carries most of this article: a module makes power whenever light lands on it, so the code cannot be built around de-energizing the source. These 25 items work rapid shutdown and its two voltage limits on either side of the array boundary, the three permitted methods for maximum voltage and the one that is restricted by module technology, the two 125 percent multipliers in circuit sizing, and the two disconnects that do two different jobs.

• Receptacle Spacing

  Nobody measures 6 feet from a receptacle. The rule is about how far a point on the floor line can sit from one, and the 2026 edition changed which stretches of floor line you are allowed to skip. These 25 items work the general provisions and the wall space definition first, then the countertop provisions that answer a kitchen question, then the subdivisions that carry their own threshold for bathrooms, outdoors, laundry areas, garages, hallways and foyers.

• Receptacle Types

  Where a receptacle goes is a branch circuit question. What it is, and whether that one may be installed here, is a different article and a different kind of item. These 25 items work Article 406 as the 2026 edition reorganized it: the damp and wet location triggers with their definitions in Article 100, the tamper-resistant list that is wider than the reasoning behind it, the rating pairing that lives back in Article 210, and the replacement provisions that treat a swap as new work.

• Required Circuits

  Four branch circuits go into a dwelling because the code says so, and three of them carry a second sentence limiting what else they may feed. These questions work the Article 100 labels that decide which rule applies, the required circuit list in 210.11(C) with its restrictions and exceptions, the two navigation changes the 2026 edition made inside Article 210, and the point where those same circuits reappear as fixed volt-amperes in a load calculation.

• Services

  Article 230 is the one place on the premises with no overcurrent device upstream, and most of what looks arbitrary in it follows from that. These 25 items work the disconnect count and the arrangements that carry it, the outdoor location the 2026 edition writes into the dwelling rule, the clearances graded by what sits underneath, the conductor sizing rule with its 100 percent exception, and the short list of equipment allowed on the supply side. Several turn on section numbers that moved for this edition.

• Support and Securing

  Securing keeps the wiring method where you put it and supporting carries its weight, and a support item is usually asking which of the two went missing. These 25 items work the general obligation and the prohibitions in Article 300, the interval and the termination distance that every method article writes separately, the relaxations that suspend securing under stated conditions, the box that is itself a support question in Article 314, and the conductors hanging in a vertical raceway, which is a different section again.

• Switches After 2026

  Device-type switches left Article 404 for the 2026 edition and arrived in Article 406, which is now titled for wiring devices. These 25 items work the boundary the way the book draws it, through the Article 100 definition and the two halves of 404.1, then run the requirements on both sides of the line: the heights, the grouping and voltage limits, the grounded conductor at a switch location, the grounding of the device and its faceplate, and the load ratings that decide what a given snap switch may control.

• Temporary Installations

  Article 590 starts by saying that everything the code asks of permanent work still applies, and every paragraph after that is either a named departure or an addition. These 25 items work the three permitted uses and the one day count that belongs to only one of them, the wiring methods that actually get relaxed, the ground-fault paragraph that is the most tested part of the article, the written program that stands in for devices in one narrow case, and the removal sentence people walk past.

• Underground and Burial

  Minimum cover at 1000 volts and below is a table inside 300.7 in the 2026 book, and it was Table 300.5(A) in the 2023 one, so Article 300 sits two sections lower this cycle. These 25 items work the columns, the rows, the notes printed underneath, and the short paragraphs around the table that carry as many questions as the grid does. A few ask you to tell cover apart from trench depth, which is where the arithmetic lives.

• Wet, Damp and Dry Locations

  Dry, damp and wet are defined terms, and protection from weather is the condition that separates the middle one from the outer two. These 25 items work the three Article 100 definitions and then the sections that hang off them, the interior of a raceway above grade and underground, the conductor types permitted in a wet location, boxes and their drainage, receptacle enclosures and covers, and the luminaire markings that run in one direction only.

• Wiring Methods

  Chapter 3 is a set of articles built to one template, so the number after the decimal point carries meaning before you know which article you are in. These 25 items work that template, the split between Article 300 and the method article, and the sections inside Article 300 that moved down two places for the 2026 edition. Several ask for a distance, and the fastest way to those is knowing whether the question is about the run or about the termination.

• Working Space

  Depth, width and height are three separate requirements and an installation satisfies all three or it fails, and none of them is the zone above the gear, which is a different subsection with different logic. These 25 items work the depth table by condition and voltage, the two dimensions nobody looks up, the two ampere thresholds that govern entrances and doors, the illumination rule with no number in it, and the dedicated space that people go looking for and cannot find.

Conductor sizing and derating

• Ampacity Derating

  The arithmetic here is two multiplications, and the marks are lost on either side of them: picking the wrong correction table before, and running the termination check on the derated number after. These questions work the sequence in 310.15(B) and 310.15(C), the counting rules in 310.15(E) and 310.15(F), and the two limits that finish the problem at 110.14(C) and 240.4(D). Table values come from Table 310.16, Table 310.15(B)(1)(1) and Table 310.15(C)(1).

• Branch Circuit Ratings

  The rating of a branch circuit comes from the overcurrent device, not from the conductor and not from the load, and almost everything else in this subject follows from that one sentence. These questions work the rating rule at 210.18, the permitted loads and receptacle ratings in 210.19 through 210.23, the two conductor sizing paths in 240.4, and the pair of sentences in Article 120 that keep the maximum load question apart from the continuous load question.

• Continuous Loads

  Three hours of maximum current is the whole test for whether a load is continuous, and everything that costs points happens after that. These questions work the articles that declare their equipment continuous outright, the 125 percent as it lands on branch circuit, feeder and service conductors and on the device ahead of each of them, the listing that takes the multiplier back off, the termination temperature that caps the result, and the sentence in the load calculation article that reads as though the whole thing had been withdrawn.

• Counting the Neutral

  The rule that decides whether a neutral counts for the adjustment factors never asks how much current it carries. It asks what kind of circuit it is and, in one case, what kind of load is on it. These 25 items work the positive list in 310.15(E)(1) against the exclusion in 310.15(E)(2), the grounding conductor rule that sits outside both, the counting notes printed with the adjustment table, and the corrected and adjusted ampacity that comes out the other end.

• Parallel Conductors

  Two conductors joined at both ends divide current by impedance rather than by intention, so the code makes the paths identical and then makes each raceway carry its own complete set and its own grounding conductor. These 25 items work the 1/0 AWG floor and the two exceptions under it, the five matching conditions and what they are compared against, the grounding conductor sized on the whole device, and the adjustment factor that a parallel run in one raceway walks straight into.

• Small Conductors

  The two-line rule that caps the protective device on the smallest conductors, and the four rules standing around it that decide whether the cap applies at all. These 25 items work the eight numbered entries and the conditions on the three smallest, the two subdivisions that carry a conductor out of reach of the cap, the next higher standard rating permission and the three conditions on it, the reversal above 800 amperes, and the standard ratings list the rounding depends on.

• Tap Rules

  A tap conductor is one whose overcurrent protection sits ahead of it at a rating higher than its own ampacity, so the word describes the protection rather than the joint. These 25 items work the feeder tap subdivisions and the transformer secondary subdivisions one at a time, the two eliminations the parent sections hand you for free, and the arithmetic each rule asks for: a tenth of the feeder device, a third of it, and a voltage ratio times a third. Several are calculations you can finish with Table 310.16 and the standard device ratings.

• Termination Temperature

  The temperature limitation does not change what a conductor carries. It changes which column of Table 310.16 you are allowed to read the final answer out of, and it splits on one ampere figure and one conductor marking. These 25 items work the two subdivisions of 110.14(C)(1), the separate connector rule, and the arithmetic that follows when correction and adjustment run against a termination limit that gets no factors at all.

calc_conduit

• Box Fill

  Box fill is a counting exercise before it is an arithmetic one, and six categories count six different ways. These questions work the volume you have under 314.16(A) against the volume you need under 314.16(B), category by category, using the metal box volumes in Table 314.16(A) and the per conductor allowances in Table 314.16(B)(4). The miscounts cluster in the clamp, support fitting and grounding conductor categories, so those get the most attention.

• Boxes and Conduit Bodies

  One box on one drawing generates three separate items, and they are answered from three separate places: whether an enclosure is needed, whether this one is big enough, and whether it is supported, deep enough and reachable once it is in. These questions work 300.17 and 300.16 for where enclosures go, 314.16(C) and 314.28 for the two sizing methods that are not box fill, and 314.23 through 314.29 for support, depth, weight and access. The 2026 addresses are used throughout.

• Conduit Fill

  Conduit fill is one comparison, the total area of the conductors against a permitted percentage of the raceway area, and the notes under Chapter 9 Table 1 decide what goes on each side of it. These questions work the three percentage rows, the notes that count a cable as one conductor and a grounding conductor at its actual size, the 24 inch nipple allowance, the rounding rule and the condition attached to it, and the lookups in Table 4 and Table 5 that turn the method into a number.

Grounding and bonding

• Equipment Grounding Conductor Sizing

  These questions size the wire type equipment grounding conductor the way the code does it, from the rating of the overcurrent device ahead of the circuit and not from the conductor beside it. Table 250.122 gives the starting number, and the subdivisions under 250.122 then cap it, scale it, or replace the input entirely for motors, parallel runs and feeder taps. Watch for the two ceilings and for the one upsizing rule that ambient correction and conductor count adjustment do not trigger.

• Grounding Electrode Conductor

  Sizing straight off Table 250.66 gives the wrong answer on any rod only or footing only system, because three short subsections cap the result depending on what sits at the far end of the conductor. These 25 items work the table, the three ceilings and the condition attached to all of them, then move on to the installation rules in 250.64 where the continuous length requirement, the 6 AWG protection hinge and the ferrous raceway jumper live. Every conductor size comes out of the table as the 2026 edition prints it.

• Grounding Electrodes

  Three sections carry this whole topic, and telling them apart is most of the work. 250.50 asks what is present at the building and bonds all of it together, 250.52 says what a thing has to be before it counts, and 250.53 says what you have to do with it once it does. These 25 items lean on the qualifying conditions inside each electrode entry, the installation rules for rods and rings, and the 25 ohm sentence read the way it is actually written, as an exception to a requirement rather than a requirement of its own.

• Grounding vs Bonding

  Grounding heads for the earth and bonding heads back to the source, and Article 250 keeps the two jobs apart even where the field uses one word for both. These 25 items work the performance requirements at 250.4, the Article 100 definitions the exam builds distractors from, the objectionable current rules at 250.6, and the sorting question that decides whether a conductor sizes from 250.66 or from 250.122.

• Neutral to Ground Bond

  One bond, made once, inside the service disconnect enclosure, and separation everywhere after it. These 25 items work the main bonding jumper rule and the word unspliced that rides with it, the load side bar and the two named ways past it, the single point rule for a separately derived system, the second building on the same property, and the range and dryer allowance that survives only for existing work.

• Separately Derived Systems

  The identification question sits in front of everything else here. Get it wrong and you apply a correct set of rules to a system they do not govern, which produces a confident wrong answer rather than a blank. These 25 items start with the definition and the two cases it decides, the transformer winding and the transfer switch, then work 250.30 itself: where the system bonding jumper goes, where the grounding electrode conductor connects, when a supply-side bonding jumper is called for, and what an ungrounded system changes.

Load, motor and transformer calculations

• Feeders

  Article 215 is short, and most of a feeder question is answered somewhere else. What genuinely lives here is the minimum rating and size, the overcurrent device, ground fault protection of equipment, identification and a handful of small rules, and the two sections that carry the work both changed numbers for the 2026 edition. These 25 items work the 125 percent increase where it applies, the classification questions that need one sentence out of Article 100, and the motor sum in Article 430 that replaces the general approach.

• Transformer Calculations

  Volt-amperes in equal volt-amperes out, so the kVA is the same number on both sides and every current in the problem comes from dividing it by the voltage on the side you were asked about. These 25 items work that division with and without the square root of three, then the protection percentages in Table 450.5(B), which is 450.5 in the 2026 book and was 450.3 in the 2023 one. Several run the secondary conductor rules that live in Article 240 rather than Article 450.

calc_motor

• HVAC Circuits

  A sealed compressor has no horsepower on its plate, so Article 440 works from the currents the manufacturer measured and modifies Article 430 rather than replacing it. These 25 items work the rated-load and branch-circuit selection currents, the conductor and device percentages, the marked minimum circuit ampacity and maximum device rating, the disconnect rules, and the outdoor ground-fault subsection at 210.8(F) with all three of its exceptions.

• Motor Calculations

  Every motor problem hands you two currents, and the code is specific about which step each one belongs to. These 25 items work the table current against the nameplate current, the 125 percent conductor rule and its duty-cycle alternative, the branch-circuit device percentages with the next standard rating permission, the several-motors feeder sum, and the disconnect rating. Full-load currents come from Table 430.248 and Table 430.250, and conductor sizes from Table 310.16 in the 75 degree column.

• Motor Feeder Sizing

  A feeder to a group of motors is a sum with four parts, and only one motor in the group gets the 125 percent. These 25 items work that sum, the separate and differently shaped sum that sizes the feeder protective device, the rounding that runs the opposite way from the branch circuit, how the highest rated motor is picked, the four exceptions, and the packaged equipment section that stops the calculation before it starts. Full-load currents come from Table 430.248 and Table 430.250.

• Motor Overload Protection

  A motor circuit fails two ways that have almost nothing in common, so the code puts two devices on it and adds a third that protects nothing at all. These 25 items separate the overload device sized from the nameplate, the short-circuit and ground-fault device sized from the table, and the disconnecting means, then work the three overload percentages, the permitted increase and its ceiling, the thermal protector bands, and the control circuit rules alongside them.

Electrical theory and arithmetic

• Ohm's Law

  The relationship itself is arithmetic rather than a code rule, so these items cite the formula they turn on and reach for a section only where the book genuinely governs the numbers going in. That happens in three places: the nominal voltages a load calculation uses, the rounding permission on a fraction of an ampere, and the definitions that say what a voltage name means. The rest is the wheel, the three-phase factor and the series and parallel pair, worked with numbers you can check both ways.

• Power and Volt-Amperes

  The code calculates in volt-amperes and equipment is often rated in watts, so the items in this group are built in the gap between the two. These 25 work the single-phase and three-phase forms with the numbers given, power factor and efficiency, the unit loads and per-outlet figures in Article 120 that turn floor area and outlet counts into volt-amperes, and the one place the code refuses to let you calculate at all and sends you to a full-load current table instead.

• Series and Parallel

  Series shares current and parallel shares voltage, and everything else on this topic follows from those two sentences. These 25 items work the two configurations directly, the way voltage and current split inside each one, the two parallel shortcuts with the exact condition on each, and the check that catches an arithmetic slip in two seconds. The last few reach the places the code itself turns on this arithmetic: a paralleled set of conductors, protective devices joined at both ends, and the fused switch.

• Voltage Drop

  For an ordinary branch circuit or feeder the code sets no percentage, because the 3 and 5 percent figures everybody quotes sit in informational notes and the code says its own notes are not requirements. Two articles make a limit enforceable, and the paper tests the arithmetic in both cases. These 25 items run the formula forward and backward, in single phase and three phase, off Chapter 9 Table 8, and sort out where a real limit lives.