EstatePass

Wiring Methods & Materials — Electrician Practice Questions

89 questions · 18% of the Electrician exam

Worked questions

1. A raceway run is classified as a wet location. Which conductor insulation type carries a 90 degree C rating in both wet and dry locations?

  • ATHHN

    THHN is a heat-resistant thermoplastic listed for dry and damp locations only. It has no wet-location rating at all, so it cannot be used where water is expected inside the raceway.

  • THWN-2
  • CXHHW

    XHHW is rated 90 degree C only in dry and damp locations. In a wet location its rating drops to 75 degree C, which is why the -2 version exists.

  • DRHH

    RHH is a thermoset insulation carrying a 90 degree C dry rating. It is not a wet-location insulation; the wet-rated companion designation is RHW or RHW-2.

Why B is correct

Insulation trade names encode both a temperature and an environment. The W means the thermoplastic passed long-term water-immersion testing, and the -2 suffix means it was listed to hold 90 degrees C while wet rather than only while dry. Table 310.4(A) is where that pairing lives, and it is why a single dual-marked building wire can start at the 90 degree C column indoors or in a flooded rooftop run.

What this question is testing

This item tests whether you can read the conductor insulation table and connect an insulation designation to its permitted operating environment and temperature rating, rather than assuming all 90 degree C wire behaves identically.

On the job

Every rooftop conduit, every underground run, and every raceway on the outside of a building is a wet location. Inspectors routinely reject pulls where plain THHN was used because the reel on the truck was single-marked. Before you pull, read the surface print on the conductor: if it says THHN/THWN-2 you are covered in both conditions, and if it only says THHN you cannot use it outdoors or underground. Conductor marking disputes are one of the most common correction notices on commercial jobs.

Memory technique

W is for water, and dash-two doubles down: 90 degree C wet and dry.

Exam tip

The letter W means wet-rated, and the suffix -2 means 90 degree C in wet locations too. No W in the designation means dry and damp only.

Where to look it up

Turn to the conductor applications and insulations table in Article 310 and read across the Maximum Operating Temperature and Application Provisions columns.

2. A run of trade size 1 rigid PVC conduit is installed exposed and horizontally across a basement ceiling. What is the maximum spacing permitted between supports for this conduit?

  • 3 feet
  • B5 feet

    Five feet is the support spacing for trade sizes 1-1/4 through 2, one row down in the table. It is too far apart for trade size 1.

  • C10 feet

    Ten feet is the support interval for metal raceways such as EMT. Plastic conduit will visibly sag long before 10 feet.

  • D6 feet

    Six feet applies to trade sizes 2-1/2 through 3 in the PVC support table, not to trade size 1.

Why A is correct

Thermoplastic conduit has almost no beam strength and creeps under its own weight once a building warms up, so the Code ties support spacing to stiffness, which rises with trade size. Table 352.30(B) starts at 3 feet for everything through trade size 1 and widens from there. A trade size 1 run sits in that first row, so straps go on 3-foot centers no matter how the metal pipe beside it is hung.

What this question is testing

This item tests whether you can use a size-dependent support table rather than applying a single memorized number to every raceway type.

On the job

PVC droops badly in a warm building, and a sagging run looks unprofessional and traps water at every low point. On outdoor and rooftop runs the sag also fights against the expansion fittings you installed. Small PVC in particular surprises people: at trade size 3/4 you need a strap every 3 feet, which is a lot more hardware than the 10-foot spacing you use on EMT of the same size. Price the straps into the bid.

Memory technique

Small plastic pipe is floppy: 3 feet for anything an inch or under.

Exam tip

PVC support spacing is the one that changes with trade size. Small pipe, tight straps.

Where to look it up

Open the PVC conduit article and go to the support table in the .30 section; the left column is trade size and the right column is maximum spacing.

3. Type NM cable is stapled to wood studs during a dwelling remodel. What is the maximum support interval, and what is the maximum distance from an outlet box at which the cable must be secured?

  • Supported every 4-1/2 feet and secured within 12 inches of the box
  • BSupported every 6 feet and secured within 12 inches of the box

    Six feet is the support interval for MC cable, not for nonmetallic sheathed cable.

  • CSupported every 3 feet and secured within 8 inches of the box

    The 8-inch figure belongs to the special case of a single-gang nonmetallic box without internal clamps, and 3 feet is not the general support interval for this cable.

  • DSupported every 10 feet and secured within 3 feet of the box

    Ten feet and 3 feet are the numbers for rigid metal raceways such as EMT. Cable requires far tighter support.

Why A is correct

Nonmetallic sheathed cable carries no mechanical load of its own, so the support intervals exist to keep the jacket from being stretched and to keep pulling strain off the box connection. NEC 334.30 sets 4-1/2 feet along the run and 12 inches from each box for exactly that reason: the last staple is what absorbs a tug on the cable instead of the clamp or the terminal screws.

What this question is testing

This item tests recall of the general securing and supporting numbers for nonmetallic sheathed cable and awareness that a different distance applies at nonmetallic boxes without clamps.

On the job

Rough-in inspections in residential work turn on this rule more than any other. Inspectors count staples across a wall and check the first staple above every box. Drooping cable between joists also gets flagged, and cables running across the bottom of floor joists must be protected or run through bored holes. Keeping a staple within a foot of every box and roughly every 4 feet along the run makes the walkthrough painless.

Memory technique

A foot off the box, and four and a half between staples.

Exam tip

Twelve inches from the box and 4-1/2 feet along the run covers NM, AC, FMC, and LFMC alike.

Where to look it up

Look at the .30 section of the nonmetallic sheathed cable article, and read the subsection that addresses nonmetallic single-gang boxes.

4. Type MC cable containing three 12 AWG circuit conductors and an equipment grounding conductor is run through a commercial ceiling space. At what maximum interval must this cable be supported and secured along the run?

  • A4-1/2 feet

    4-1/2 feet is the interval for armored cable and nonmetallic sheathed cable. MC cable is allowed the longer 6-foot interval.

  • B10 feet

    Ten feet is the support spacing for EMT and other rigid metal raceways, not for a cable assembly.

  • 6 feet
  • D3 feet

    Three feet is the securing distance from a box for rigid metal raceways and the support interval for small PVC, not the MC cable interval.

Why C is correct

Interlocked armor gives MC enough stiffness to bridge a longer span without deforming, so NEC 330.30(B) allows 6 feet where the softer cable assemblies are held to 4-1/2. The interval is still short enough that the armor never carries a pulling load into the connector. Support must also come from the building structure itself, which is why draping the cable over grid wires or ductwork does not satisfy the rule.

What this question is testing

This item tests whether you can distinguish the support interval for MC cable from the intervals used by other cable assemblies and by rigid raceways.

On the job

In commercial ceilings MC is often laid across the grid wires or draped over ductwork, which is not support. It must be independently supported from the building structure, and it may not be attached to the ceiling grid support wires unless those wires are additional wires identified for the purpose. Inspectors pop ceiling tiles at random and look for cable resting on tile. Bridle rings or J-hooks on 6-foot centers solve it.

Memory technique

MC has muscle: it stretches to 6 feet while AC and NM stop at 4-1/2.

Exam tip

MC is the odd one out among cables at 6 feet; AC and NM are both 4-1/2 feet.

Where to look it up

Go to the .30 section of the metal-clad cable article and read the securing subsection separately from the supporting subsection.

5. A long exposed run of rigid PVC conduit is installed outdoors where the temperature swings widely between summer and winter. At what amount of calculated length change must an expansion fitting be provided in a straight run?

  • A1/8 inch or more

    One eighth of an inch is below the threshold stated in the Code and would require expansion fittings on runs that do not need them.

  • 1/4 inch or more
  • C1/2 inch or more

    Waiting for a half inch of movement allows visible bowing and puts real stress on couplings and box entries before any relief is provided.

  • D1 inch or more

    A full inch of unrelieved movement will pull terminations loose or crack fittings long before the fitting would be installed.

Why B is correct

PVC moves several times as much as steel for the same temperature change, and a straight run fixed at both ends has nowhere to put that movement except into couplings and box entries. NEC 352.44 sets the relief threshold at a quarter inch of calculated change because that is roughly where the strain stops being absorbed harmlessly by the run and starts loading terminations. The calculation uses the full seasonal swing, not the daily one.

What this question is testing

This item tests whether you know the trigger threshold for providing thermal expansion relief in a nonmetallic raceway, a requirement driven by the material's high coefficient of expansion.

On the job

PVC moves roughly 4 inches per 100 feet for a 100 degree F swing, so exposed exterior runs of any length trip the threshold quickly. Set the piston of the expansion fitting according to the temperature at the time of installation, not centered by default, or you will run out of travel in one direction. Vertical risers on the outside of a building are the classic case, and a bowed run there is an immediate visual flag to an inspector.

Memory technique

A quarter inch of creep is where PVC needs a slip joint.

Exam tip

The trigger is 1/4 inch of calculated movement; use the expansion characteristics table to get the number for your run length and temperature swing.

Where to look it up

Go to the expansion fittings section of the PVC conduit article and use the expansion characteristics table printed with it.

6. Flexible metal conduit is used as a fixture whip in an accessible suspended ceiling, running from a junction box to a luminaire. Measured from the last point where the raceway is securely fastened, what length is permitted before further support is required?

  • A18 inches

    Eighteen inches is not one of the flexible-raceway allowances. It is close to the 12 inch securing distance at boxes and fittings, which is a different measurement entirely.

  • B3 feet

    Three feet is the allowance for a length where flexibility is necessary at a termination, such as the final connection to a vibrating motor, and it is the wrong allowance for a luminaire whip in an accessible ceiling.

  • C4-1/2 feet

    Four and one-half feet is the ordinary securing interval for this raceway along a run. It is not the unsupported length permitted for a tap to a luminaire.

  • 6 feet

Why D is correct

Fixture whips exist because luminaires get moved when ceiling grid changes. The Code allows 6 feet of unsupported flexible raceway from the last securing point when that raceway is a tap to a luminaire in an accessible ceiling, which is enough to reach a fixture two or three grid squares away without adding a strap in the middle of the plenum.

What this question is testing

This item tests whether you can keep three different numbers straight in one article: the distance to a box, the general securing interval, and the special allowances for flexibility and for luminaire taps.

On the job

On tenant improvement work the ceiling grid is full of whips, and the inspector counts them. The two mistakes that show up are a whip longer than the allowance, usually because the electrician tried to feed two fixtures off one drop, and a whip in a ceiling that is not actually accessible, such as a hard-lid gypsum ceiling. In a hard ceiling the allowance does not apply and the raceway has to be secured on the normal interval, which is why hard-lid areas take so much longer to rough in.

Memory technique

Six feet to a fixture, three feet for flexibility, one foot to a box.

Exam tip

Read the securing section of a flexible raceway article all the way through the exceptions before answering. The exceptions carry the numbers the exam wants.

Where to look it up

Securing and supporting is the .30 section of every Chapter 3 raceway article. The luminaire tap allowance is one of the exceptions listed under it.

7. An electrician plans to hang a small luminaire directly from a run of rigid nonmetallic conduit in a covered outdoor walkway. How does the Code treat that plan?

  • AIt is acceptable wherever the conduit is trade size 1 or larger and is securely strapped on both sides

    Trade size and strapping are not a permission. A larger plastic raceway still creeps under sustained load and still softens at elevated temperature, whatever the support spacing.

  • BIt is acceptable wherever the luminaire and its lamp together weigh less than 6 pounds

    There is no weight threshold in this rule. Even a light fixture applies a continuous load and a lever arm at the fitting, and the conduit is not listed to take it.

  • It is prohibited unless the conduit is listed for the support of luminaires or other equipment
  • DIt is acceptable in any outdoor location as long as the conduit is schedule 80 PVC

    Schedule 80 has a thicker wall for physical damage, which is a separate topic. Wall thickness does not turn the conduit into a listed support for luminaires or other equipment.

Why C is correct

The prohibition is written against the material, not against a weight. Thermoplastic conduit deflects under a steady load and softens in heat, and a luminaire is a steady load hanging in the sun. The Code closes the question by requiring that the conduit itself be listed for supporting equipment before it can carry any.

What this question is testing

This item tests whether you can find a prohibition in the uses-not-permitted section of a raceway article and resist distractors that invent thresholds based on size, weight, or wall schedule.

On the job

Canopies, parking structures, and outdoor equipment yards are where crews are tempted to strap a fixture, a small box, or a photocell to the plastic run that is already there. Over a couple of summers that run bows visibly between supports, and in the worst cases the fitting separates and the conductors take the weight. The correct fix is a strut or a bracket back to the structure, which also gives the fixture a rigid mounting for aiming.

Memory technique

Plastic carries wire, not weight.

Exam tip

For plastic conduit, remember what it cannot do: support equipment, live in hazardous locations, or exceed its listed temperature.

Where to look it up

The rigid nonmetallic conduit article follows the standard layout, with uses not permitted in the .12 section.

8. Liquidtight flexible metal conduit is installed as a fixed run to a piece of rooftop equipment. Under the general rule, how must that run be secured and supported?

  • Fastened within 12 inches of each box or fitting and supported at intervals not over 4-1/2 feet
  • BFastened within 3 feet of each box or fitting and supported at intervals not over 10 feet

    Three feet from a box and ten feet between supports are the figures used for threaded rigid raceways. Applied to a flexible product they would let the run sag and would put pulling strain on the liquidtight connectors.

  • CFastened within 12 inches of each box or fitting and supported at intervals not over 6 feet

    Six feet between supports is the interval used for metal-clad cable, not for liquidtight flexible metal conduit, which is a heavier and far more flexible product that needs closer support.

  • DFastened within 8 inches of each box or fitting and supported at intervals not over 3 feet

    Eight inches and three feet are not the values used anywhere in this article. Over-supporting is not a violation in itself, but this answer shows the candidate is guessing rather than reading the support section.

Why A is correct

The article covering liquidtight flexible metal conduit sets two separate numbers: a fastening within 12 inches of every termination, and support along the run at no more than 4-1/2 feet. Both must be met. Because the product is flexible, the close fastening at terminations is what keeps strain off the connector and keeps the liquidtight seal intact.

What this question is testing

The item tests whether the candidate keeps separate support intervals straight for different wiring methods rather than remembering one generic number. It also tests reading a support section as two rules at once: the distance from terminations and the distance between supports along the run.

On the job

Rooftop work is where this gets caught. A liquidtight run from a disconnect to a condenser is easy to strap once at each end and call it done, and then the middle of the run pools water, sags into the roof membrane, and the connector at the equipment works loose from vibration. Inspectors on commercial jobs routinely fail rooftop liquidtight for missing intermediate supports. Getting the two numbers right also matters at pumps, motors, and any place a flexible whip crosses open space.

Memory technique

Flexible products get short leashes: twelve inches at the ends, four and a half feet between.

Exam tip

Support intervals differ by wiring method. Learn them as pairs: distance from the box, then distance along the run.

Where to look it up

Turn to the support section near the beginning of the installation part of the liquidtight flexible metal conduit article, roughly two-thirds of the way into Chapter 3.

9. Type NM cable is being bent where it turns a corner in a wall cavity. Measured at the inner edge of the bend, what is the smallest radius the Code permits?

  • Five times the diameter of the cable
  • BThree times the diameter of the cable

    Three times the diameter is tighter than the article allows and will visibly flatten the jacket on common cable sizes.

  • CTen times the diameter of the cable

    Ten times the diameter is a conservative practice figure used for some large cables and for fiber, but it is not what the nonmetallic-sheathed cable article requires.

  • DTwice the diameter of the cable

    Twice the diameter is a sharp bend that compresses the inner edge of the jacket severely and is well outside anything the article permits.

Why A is correct

The cable article states one bending limit: the inner edge radius must not be less than five times the cable diameter. That is a small radius for common two-conductor cable, but it is easy to violate when cable is forced around a corner post or into a shallow box. The intent is to preserve the jacket and the conductor insulation from mechanical damage that would never be seen again.

What this question is testing

The item tests recall of a simple, frequently cited numeric limit and whether the candidate knows the radius is measured at the inner edge of the bend rather than the centerline.

On the job

The sharp bend usually appears where cable enters a shallow old-work box or turns down a corner post in a remodel. The jacket splits at the inside of the bend, and by the time the drywall is up nobody will see it. Rough-in inspectors look at cable bends near boxes for exactly this reason. On larger cables the number matters more: a big feeder cable forced around a corner can crush its conductor insulation and fail years later under load.

Memory technique

Five times the diameter, measured on the inside of the turn.

Exam tip

Several wiring methods state bend radius as a multiple of diameter. Learn the cable figure separately from raceway bend rules.

Where to look it up

Look for the bends section near the installation requirements of the nonmetallic-sheathed cable article.

10. Several Type NM cables enter a flush-mounted panelboard cabinet through knockouts in its side. What does the Code require of those cables at the cabinet?

  • ACables may enter through open knockouts provided each one is stapled within 12 inches of the cabinet

    Stapling the cable nearby does not satisfy a rule that requires the cable to be secured to the enclosure. An open knockout also leaves an unclosed opening in the cabinet.

  • BOne connector may serve as many cables as the knockout will physically allow to pass through it

    Connectors are listed for a stated number and size of cables. Forcing extra cables through one fitting voids the listing and crushes the cable jackets.

  • Each cable must be secured to the cabinet with a fitting identified for use with that cable type
  • DCables need to be secured only where the cabinet is surface mounted rather than flush mounted

    The general rule applies to flush and surface enclosures alike. The narrow exception that mentions surface mounting has several further conditions and is not a blanket relief.

Why C is correct

The rule ties the cable to the enclosure itself, not merely to nearby framing. Securing the cable at the cabinet keeps mechanical strain off the terminations inside and keeps the cable from moving through a sharp-edged knockout. Connectors are listed by cable type and by the number of cables they accept, so a fitting rated for one cable holds one cable.

What this question is testing

The item tests whether the candidate knows that the securing obligation runs to the enclosure itself, and whether a commonly quoted exception is being over-applied.

On the job

Old panels routinely have three or four cables jammed into one connector, or cables run through bare knockouts with no fitting at all. Both are cited on service change inspections. The practical fix is either one listed connector per cable or a fitting listed for multiple cables, and there are plenty of the latter. The rule also matters for cable movement: a cable that can slide in and out of the cabinet eventually wears through its jacket on the knockout edge.

Memory technique

Every cable gets a fitting, and the fitting grabs the cabinet.

Exam tip

When an exception mentions surface mounting, check every other condition attached to it before relying on it.

Where to look it up

Look at the cabinets and cutout boxes article, in the section on cables entering enclosures.

11. Raceways and cables are being installed in the space directly beneath a metal-corrugated sheet roof deck. What minimum clearance must be maintained, measured from the lowest surface of the roof decking?

  • A1 inch

    One inch is less than the required clearance and leaves the raceway inside the range that a roofing screw reaches.

  • 1-1/2 inches
  • C1-1/4 inches

    Three inches exceeds the requirement. Candidates choose it by confusing this rule with the clearance rules for recessed luminaires and insulation.

  • D3 inches

    Six inches is not a figure used anywhere in this section and would make routing in a shallow ceiling space nearly impossible.

Why B is correct

Roofing fasteners are the hazard. Screws driven through the deck penetrate a predictable distance below it, and the 1-1/2 inch clearance keeps electrical work out of that zone. Because the measurement starts at the lowest surface of the decking, hanging a raceway tight to the underside of a flute does not comply even though it looks clear from below.

What this question is testing

The item tests a specific numeric clearance and whether the candidate knows the reference surface from which it is measured, a detail that changes the answer on a corrugated deck.

On the job

Any building with an exposed steel deck, which means most retail, warehouse, and light industrial construction, has this condition. It bites when a re-roof crew arrives years later and drives new fasteners through the deck into conduit that was strapped tight to the underside. The result is a dead circuit and a search that starts in the panel and ends on the roof. Keeping the run 1-1/2 inches down, or routing along the joists instead, avoids all of it.

Memory technique

Stay an inch and a half below the deck so the roofer's screw finds nothing.

Exam tip

Read what the measurement is taken from. On corrugated deck, that is the lowest surface, not the flute.

Where to look it up

Look in the protection against physical damage section of the general wiring requirements article, in the subsection on cables and raceways installed under roof decking.

12. Type NM cable is proposed for the branch circuits of a multifamily dwelling. What determines whether that use is permitted?

  • AThe number of stories, because the cable is limited to buildings of three floors or fewer above grade

    Story count is a building code concept that influences the construction type but is not the Code test. A three-story building of noncombustible construction is still outside the permitted uses.

  • The construction type of the building, since the cable is limited to Types III, IV, and V construction
  • CThe ampere rating of the circuits, because the cable is limited to branch circuits of 20 amperes or less

    Circuit rating has nothing to do with where this cable may be used. The cable is commonly used on circuits well above 20 amperes within its permitted occupancies.

  • DWhether the building is fully sprinklered, because a sprinkler system permits the cable in any construction type

    Sprinklers may affect the building code construction classification, but there is no Code provision that lets a sprinkler system extend this cable into any construction type.

Why B is correct

The uses permitted section ties this cable to construction type as classified by the building code. That makes the architect's construction type on the cover sheet the controlling fact, not the story count or the occupancy label. It is also why the same cable is routine in wood-framed garden apartments and prohibited in a concrete and steel high-rise.

What this question is testing

The item tests whether the candidate knows that a wiring method allowance can depend on a building code classification rather than on an electrical characteristic, and can identify which fact controls.

On the job

This is a bid-stage question. Estimators who price cable on a building that turns out to be Type I or II construction lose the difference to conduit and wire, and the discovery usually comes at submittal review. Reading the construction type off the architectural cover sheet before pricing is the habit that avoids it. On mixed projects it can vary between the podium and the wood-framed floors above, so the answer may differ within one building.

Memory technique

Wood frame yes, steel and concrete no. Construction type decides.

Exam tip

When a cable article references construction types, go find the architect's construction type before you assume anything.

Where to look it up

Look at the uses permitted and uses not permitted sections at the front of the nonmetallic-sheathed cable article.

13. Four multiconductor power cables, all 4/0 AWG and larger, are to be installed in a single layer in a ladder cable tray. Their outside diameters are 1.55 inches, 1.55 inches, 1.85 inches and 2.05 inches. For multiconductor cables of 4/0 AWG and larger in this type of tray, the sum of the cable diameters may not exceed the width of the tray. Standard tray widths available are 6, 9, 12 and 18 inches. What is the narrowest tray that may be used?

  • A6 inches

    This rounds the 7.00-inch sum down to the nearest available width. The sum is a minimum the tray width has to meet or exceed, so a narrower tray is not permitted.

  • B12 inches

    This adds roughly half again to the sum for spacing between cables. Cables of this size in a single layer are permitted to touch, so no spacing allowance belongs in the calculation.

  • 9 inches
  • D18 inches

    This doubles the sum on the assumption that each cable needs a diameter of clear space beside it. That spacing requirement belongs to other installations, not to this single-layer rule.

Why C is correct

Add the diameters: 1.55 + 1.55 + 1.85 + 2.05 = 7.00 inches. The tray width must be at least that sum, so a 6-inch tray is too narrow and the next standard width, 9 inches, is the smallest that works. The cables also have to lie in one layer, which is what makes a simple sum of diameters the right measure.

What this question is testing

Tests whether you apply the single-layer sum-of-diameters rule that governs large multiconductor cables in a tray rather than reaching for the percentage fill thinking that applies to raceways, and whether you round up to the next available tray width.

On the job

Tray sizing is normally settled at the design stage, but electricians are the ones who discover during installation that a change order added a cable the tray cannot take in a single layer. Stacking large cables to make them fit is a real field temptation and it defeats the whole basis of the tray ampacity tables, since the middle cable can no longer shed heat. The fix is a wider tray or a second run.

Memory technique

Side by side, one layer, add the diameters.

Exam tip

Large multiconductor cables in a tray: add the diameters, and the tray has to be at least that wide.

Where to look it up

Article 392 covers cable trays; the number-of-cables provisions separate multiconductor cables by size and by whether the tray is ladder, ventilated or solid bottom.

14. A device box has internal cable clamps and is fed by three 14-2 cables with ground, so six circuit conductors and three 14 AWG equipment grounding conductors enter it. It holds one single-pole switch on a strap, and two 14 AWG pigtails that begin and end inside the box. The volume allowance for 14 AWG is 2.00 cubic inches, one or more clamps count as a single allowance, and a device strap counts as double the largest connected conductor. What minimum box volume is required?

  • A24.00 cubic inches

    This counts the two pigtails as conductors. A conductor that neither enters nor leaves the box has no volume counted against it, because it displaces space the entering conductors were already credited for.

  • 20.00 cubic inches
  • C18.00 cubic inches

    This leaves out the allowance for the internal cable clamps. Clamps inside the box take one allowance based on the largest conductor present, however many clamps there are.

  • D22.50 cubic inches

    This uses the 2.25 cubic inch allowance that belongs to 12 AWG throughout. Every conductor here is 14 AWG, which carries the 2.00 cubic inch allowance.

Why B is correct

Six conductors entering the box take 6 x 2.00 = 12.00 cubic inches. The three grounding conductors count once, adding 2.00. The clamps add one allowance of 2.00. The switch strap adds 2 x 2.00 = 4.00. Conductors that begin and end inside the box are not counted at all, so the pigtails add nothing. The total is 20.00 cubic inches.

What this question is testing

Tests whether you can assemble a box fill total from several different kinds of allowance at once and whether you correctly exclude conductors that both originate and terminate inside the enclosure while still counting clamps, the device strap and the grounding conductors.

On the job

Pigtails are everywhere in modern work, since a device is not permitted to be the splice point for a circuit that continues on, and grounding pigtails to metal boxes are routine. Crews who count them condemn perfectly good boxes and cut in larger ones for no reason. The rule is easy to remember once you see the logic: volume allowances follow conductors that come from somewhere else, not ones born and buried in the same box.

Memory technique

Born in the box, buried in the box, counted nowhere.

Exam tip

If a conductor never leaves the box, it takes no volume allowance. Everything else does.

Where to look it up

The box fill provisions of Article 314 list the allowances one at a time: conductors, clamps, support fittings, devices and grounding conductors.

75 more in the bank

Answers and explanations for these are in the app.

  • Type XHHW conductors are installed in an underground raceway that is subject to water. What maximum operating temperature rating applies to those conductors under that condition?
  • A rigid PVC raceway is buried in the earth between a dwelling and a detached shop. How must the interior of that underground raceway be classified when selecting conductor insulation?
  • Electrical metallic tubing is installed exposed along a warehouse wall. What is the maximum interval between supports, and how close to each box must the tubing be secured?
  • Flexible metal conduit is installed to feed a vibrating machine in a shop. Setting aside the special allowances for luminaire whips and short terminal lengths, how must this flexible metal conduit be secured and supported?
  • Type NM cable is pulled through holes bored in wood studs in a wall that will be covered with drywall. How far from the nearest edge of the framing member must the hole be, or what protection must be added instead?
  • A 240-volt circuit is installed in direct-buried Type UF cable across an open yard with no vehicle traffic and no special conditions. What is the minimum cover required, measured to the top of the cable?
  • A panelboard 24 inches wide is installed in a mechanical room where examination and servicing will be performed while energized. What minimum width of clear working space must be maintained in front of the equipment?
  • An electrician wants to run Type NM cable through an unheated crawl space that floods seasonally and stays damp the rest of the year. What does the Code require regarding NM cable in that environment?
  • Two circuit conductors are joined inside a junction box on a commercial project. What does the Code require about how that splice is made?
  • Type SE cable is used as an interior branch circuit or feeder inside a dwelling rather than as a service conductor. Which installation requirements govern how that cable is run and supported?
  • A single-gang box contains one duplex receptacle mounted on a strap. How many conductor volume allowances must be counted for that device, and what conductor size are they based on?
  • A junction box receives four cables, and each of those cables brings in a 12 AWG equipment grounding conductor. How are those grounding conductors counted when the box fill is calculated?
  • A square box with internal cable clamps contains two 12-2 with ground nonmetallic sheathed cables and one duplex receptacle mounted on a strap. What minimum box volume is required for this installation?
  • A 4-inch square box 2-1/8 inches deep, rated 30.3 cubic inches, has internal clamps and contains three 12-2 with ground cables plus one duplex receptacle on a strap. How many more 12 AWG circuit conductors may be brought into that box?
  • A run of trade size 3/4 electrical metallic tubing is used for a group of 12 AWG THHN copper conductors, all of the same size and insulation. What is the maximum number of these conductors permitted in the tubing?
  • Four 6 AWG THHN copper conductors and one 10 AWG THHN copper conductor are to be installed together in a single run of electrical metallic tubing. What is the minimum trade size of tubing that will accept this combination?
  • A pull box is installed in a straight pull containing conductors of 4 AWG and larger, and the largest raceway entering the box is trade size 3. What minimum length must the box have measured in the direction of the pull?
  • Six current-carrying 12 AWG THHN copper conductors are installed in a single conduit at an ambient temperature of 30 degrees C, terminating on equipment rated for 75 degree C conductors. What is the adjusted ampacity of each conductor?
  • Eight current-carrying 10 AWG THWN-2 copper conductors are installed in one raceway in an ambient temperature of 40 degrees C. What is the resulting ampacity of each conductor after both the ambient correction and the conductor adjustment are applied?
  • Three current-carrying 3/0 AWG THHN copper conductors are installed in a raceway at a 30 degree C ambient, terminating on equipment whose terminations are rated 75 degrees C. What ampacity value governs these conductors?
  • A 3-wire circuit consisting of two ungrounded conductors and a neutral is supplied from a 4-wire, 3-phase wye system. How is that neutral treated when counting current-carrying conductors for ampacity adjustment?
  • Flexible metal conduit with listed fittings is being relied on as the equipment grounding path for a lighting circuit, with no separate wire-type grounding conductor installed. What conditions must be satisfied for the conduit itself to serve that role?
  • A 480-volt panelboard is likely to require examination while energized. Exposed live parts are on one side of the working space, and there are no live or grounded parts on the opposite side. What minimum depth of clear working space is required?
  • An electrician plans to splice three 12 AWG conductors inside a conduit body on an exposed raceway run. What does the Code require of a conduit body that is used to contain splices?
  • A raceway carrying 2 AWG insulated circuit conductors terminates at a metal cabinet. What must be provided to protect those conductors from abrasion where they emerge from the raceway into the enclosure?
  • Ferrous metal conduit is going to be installed in direct contact with the earth in an area where corrosive influences are known to be severe. What does the Code require of that raceway?
  • Electrical metallic tubing is proposed for an exposed run along a loading dock wall where forklift masts regularly strike the surface. How does the Code treat that installation?
  • Electrical nonmetallic tubing is proposed for branch circuits inside a five-story hotel. Under what condition does the Code permit this tubing in a building that exceeds three floors above grade?
  • In which environment does the Code permit Type AC armored cable to be installed?
  • Type MC cable is to be installed in a wet location. Which set of conditions makes that use acceptable under the Code?
  • Type USE conductors remain on the reel after a service lateral installation. What limitation does the Code place on where those conductors may be used?
  • Surface metal raceway is being considered for a run of receptacle circuits in an office. Which condition does the Code place on that wiring method?
  • A metal wireway is installed in a horizontal run across an equipment room wall. Under the general rule, at what interval must that wireway be supported?
  • Single insulated conductors are to be installed in a ladder-type cable tray in an industrial building. What is the smallest conductor size the Code recognizes for that use?
  • Conductors are spliced and tapped inside a metal wireway at one point along the run. What portion of the wireway cross-sectional area may the conductors, splices, and taps occupy at that point?
  • Nonmetallic-sheathed cable enters a nonmetallic single-gang box that measures no more than 2-1/4 inches by 4 inches and contains no internal clamps. Under what condition does the Code allow that cable to be left unclamped at the box?
  • An insulated grounded conductor larger than 6 AWG is pulled from a reel of black conductor. Which method of identification does the Code accept for that conductor?
  • A building is supplied by more than one nominal voltage system. Once a means of identifying the ungrounded conductors of each system has been chosen, what does the Code require?
  • A rigid nonmetallic conduit listed for direct burial without concrete encasement carries a 480-volt feeder underground across an open field with no vehicle traffic and no other special conditions. Using the Code's minimum cover table, what is the least cover permitted?
  • A 120-volt, 20-ampere residential branch circuit protected by a ground-fault circuit interrupter is buried in nonmetallic raceway out to a yard light. Using the Code's minimum cover table, what reduced cover is permitted for that circuit?
  • Underground conductors are routed beneath a building as part of a feeder to an addition. What does the Code require of the portion of that run that passes under the building?
  • An installer fastens a second conduit and a small junction box directly to a raceway that is already secured to the structure. How does the Code treat using a raceway as a support in that way?
  • A 12 AWG two-conductor nonmetallic-sheathed cable is run across the bottom of the floor joists in an unfinished basement. How does the Code require that cable to be installed?
  • A direct-buried cable is damaged below grade and must be repaired in place. What does the Code permit for that splice?
  • Three ungrounded conductors, the grounded conductor, and the equipment grounding conductor all belong to the same feeder and are being installed in metal raceway. What does the Code require about how those conductors are routed?
  • A two-conductor cable with one white and one black conductor is used to supply a 240-volt water heater, so the white conductor will serve as an ungrounded conductor. What does the Code require?
  • Lengths of conduit have been cut with a saw and will be assembled into couplings and connectors before conductors are pulled. What does the Code require be done to the cut ends?
  • A device box has internal cable clamps. It contains two 12 AWG circuit conductors that land on a duplex receptacle, three 14 AWG conductors belonging to a switch leg, one 12 AWG equipment grounding conductor, and one 14 AWG equipment grounding conductor. The volume allowance table gives 2.25 cubic inches for 12 AWG and 2.00 cubic inches for 14 AWG. What minimum box volume is required?
  • A ceiling outlet box has internal cable clamps, one luminaire stud, and one hickey. It is fed by two 14 AWG two-conductor cables, each carrying an equipment grounding conductor. The volume allowance table gives 2.00 cubic inches for 14 AWG. Counting only the items described, what minimum box volume is required?
  • Two 6 AWG THWN copper conductors, and nothing else, are to be installed in a run of electrical metallic tubing that is longer than 24 inches. The tables give the approximate area of one 6 AWG THWN conductor as 0.0507 square inch, and the total interior area as 0.304 square inch for 1/2 inch tubing and 0.533 square inch for 3/4 inch tubing. What is the smallest trade size that may be used?
  • A pull box is used for an angle pull with conductors of 4 AWG and larger. The same conductors enter through a trade size 3 raceway and leave through a trade size 3 raceway in an adjacent wall of the box. What is the minimum distance required between those two raceway entries?
  • Eleven current-carrying 8 AWG THWN-2 copper conductors share one raceway that is longer than 24 inches, at an ambient of 30 degrees Celsius. The ampacity table gives 8 AWG copper as 40 amperes at 60 degrees Celsius, 50 amperes at 75 degrees Celsius, and 55 amperes at 90 degrees Celsius. Equipment at both ends is rated for 75 degree Celsius terminations. What allowable ampacity does each conductor have after adjustment?
  • Six current-carrying 6 AWG THWN-2 copper conductors pass through an 18-inch conduit nipple between two enclosures, at an ambient of 30 degrees Celsius. The ampacity table gives this conductor 55, 65, and 75 amperes in the 60, 75, and 90 degree Celsius columns respectively. Terminations at both ends are rated 75 degrees Celsius. What ampacity applies to these conductors?
  • Five current-carrying 10 AWG THHN copper conductors run in one raceway longer than 24 inches where the ambient is 40 degrees Celsius. The ampacity table gives this conductor 30, 35, and 40 amperes in the 60, 75, and 90 degree Celsius columns respectively. The correction factor for this ambient in the 90 degree Celsius column is 0.91 and the adjustment factor for five current-carrying conductors is 0.80. Terminations are rated 75 degrees Celsius and the circuit supplies no receptacles. What is the largest standard overcurrent device permitted?
  • A busway is installed horizontally along the ceiling of an industrial building. Unless the busway is designed and marked otherwise, what is the maximum spacing permitted between its supports?
  • A metal outlet box with a volume of about 30 cubic inches will be supported only by the rigid metal conduits entering it, with no other means of support. What does the Code require of that arrangement?
  • Direct-buried conductors and cables come up out of the earth and run up the outside of a support to reach equipment above. Over what portion of that riser does the Code require enclosure or raceway protection?
  • Type NM cable is run parallel to and alongside a wood stud in a wall that will later be covered with a finished surface. What does the Code require about the position of that cable?
  • Type UF cable is being considered for several parts of a residential project. Which of these installations does the Code specifically prohibit for Type UF cable?
  • A conduit passes through a fire-rated wall, and the core hole is noticeably larger than the raceway. What does the Code require at that penetration?
  • A metal wireway with inside dimensions of 6 inches by 6 inches runs across an equipment room and will carry only 500 kcmil THWN copper conductors. Conductors in a wireway may occupy no more than 20 percent of the interior cross-sectional area at any cross section, and each 500 kcmil THWN conductor has an approximate area of 0.7073 square inch. What is the greatest number of these conductors the wireway may contain?
  • A run of trade size 3/4 electrical metallic tubing longer than 24 inches already contains four 10 AWG THHN copper conductors. The total interior area of the tubing is 0.533 square inch, the permitted fill is 40 percent, a 10 AWG THHN conductor has an area of 0.0211 square inch, and a 12 AWG THHN conductor has an area of 0.0133 square inch. How many additional 12 AWG conductors may be pulled into that run?
  • An installer plans to tie a run of electrical metallic tubing to the wires that support a suspended ceiling grid. How does the Code treat that method of support?
  • Individual ungrounded conductors of a large alternating-current feeder must pass through the sheet metal wall of a ferrous metal enclosure, with a separate opening punched for each conductor. What does the Code require?
  • Splices and taps are being made inside the wiring gutter space of a cabinet whose gutter has a cross-sectional area of 24 square inches. What is the greatest combined area that the conductors, splices, and taps may occupy at that cross section?
  • In an industrial establishment, a designer proposes relying on the metal cable tray system itself as the equipment grounding conductor for the circuits it carries. Under what conditions does the Code permit that?
  • Insulated conductors will be installed where they are exposed to the direct rays of the sun for most of the day. What does the Code require of those conductors?
  • A power-limited control circuit and a 120-volt branch circuit are proposed to share a single raceway between two enclosures. How does the Code treat that arrangement?
  • Current-carrying conductors are being installed in a metal wireway. Above what number of current-carrying conductors at any cross section must the ampacity adjustment factors be applied?
  • Two circuit conductors must be spliced at a point along an exposed raceway run where no enclosure currently exists. What does the Code require at that point?
  • Setting aside the special allowance for listed assemblies and utilization equipment, what range of trade sizes does the Code permit for electrical metallic tubing?
  • Splices will be made inside a conduit body on a raceway run. The conduit body will contain four 10 AWG circuit conductors that are spliced there, plus one 10 AWG equipment grounding conductor arriving from each of the two raceways. Conduit bodies containing splices must be durably and legibly marked with their volume, and the same volume allowances used for boxes apply, with 2.50 cubic inches for 10 AWG and 2.25 cubic inches for 12 AWG. What minimum marked volume does this conduit body need?
  • A run of trade size 1/2 electrical metallic tubing longer than 24 inches contains four 12 AWG THHN circuit conductors and one 12 AWG THHN equipment grounding conductor. Each of those conductors has a cross-sectional area of 0.0133 square inch. The tables give the total interior area of the tubing as 0.304 square inch and the area available at 40 percent fill as 0.122 square inch. What percentage of the tubing's interior area do these conductors occupy?
  • A device box marked 18.0 cubic inches is fitted with a raised plaster ring marked 3.6 cubic inches. The assembly will contain one duplex receptacle mounted on a strap, and there are no cable clamps because the box is fed by raceways. The volume allowance for a 12 AWG conductor is 2.25 cubic inches and a device on a strap counts as twice the allowance of the largest conductor connected to it. Counting individually, how many 12 AWG conductors may the assembly contain?
  • Twenty-four conductors are to be installed in a metal wireway, and each conductor has a cross-sectional area of 0.2679 square inch. Conductors in a wireway may not fill more than 20 percent of its interior cross-sectional area. What minimum interior cross-sectional area must the wireway have?

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