Journeyman Electrician (NEC) — All Questions

On a feeder supplying several motors, 125 percent is applied to which motor's full-load current?

• a.The highest-rated motor, meaning the one with the largest full-load current✓
• b.The smallest motor
• c.Every motor on the feeder
• d.The motor with the highest horsepower nameplate regardless of current

Feeder conductors are sized at 125 percent of the largest motor full-load current plus the sum of the full-load currents of the other motors, and the largest motor is the one with the highest rated full-load current per 430.17. Applying 125 percent to every motor over-sizes the feeder.2023 NEC §430.24

An outlet box used as the sole support of a ceiling-suspended paddle fan must meet what requirement?

• a.Any 4-inch box rated for 50 pounds is acceptable
• b.It must be listed and marked for the purpose of supporting a fan, and fans over 70 pounds require additional independent support✓
• c.It must be a nonmetallic box only
• d.No special outlet box is required as long as two long wood screws are driven through the box and directly into the structural framing member above

Outlet boxes are not permitted as the sole support of a ceiling fan unless they are listed and marked for that purpose, and a fan exceeding 70 pounds must be supported independently of the box. A standard lighting outlet box is not rated for the dynamic load of a rotating fan.2023 NEC §314.27(C)

Within what zone measured from the rim of a bathtub or the threshold of a shower stall are hanging luminaires and ceiling-suspended paddle fans generally prohibited?

• a.2 feet horizontally and 6 feet vertically
• b.5 feet horizontally and 10 feet vertically
• c.3 feet horizontally and 8 feet vertically✓
• d.6 feet horizontally and 8 feet vertically

Cord-connected luminaires, hanging luminaires, track lighting, pendants and ceiling fans are not permitted within a zone of 3 feet horizontally and 8 feet vertically from the top of the bathtub rim or shower threshold, keeping them out of reach of a wet person. Fixed luminaires outside that zone are acceptable.2023 NEC §410.10(D)

A cord-and-plug-connected room air conditioner is the only load on its branch circuit. Its total rating must not exceed what percentage of the branch-circuit rating?

• a.100 percent
• b.80 percent✓
• c.50 percent
• d.125 percent

Where the room air conditioner is the only load on the circuit, its marked rating may not exceed 80 percent of the branch-circuit rating. If lighting units or other appliances are also supplied by the circuit, that ceiling drops to 50 percent.2023 NEC §440.62(B)

An indoor dry-type transformer rated more than 112.5 kVA must generally be installed in what manner?

• a.Installed no less than six inches away from any combustible material, or otherwise provided with a listed thermal barrier, with no requirement for a fire-resistant transformer room no matter how large the unit is
• b.On a raised concrete pad only
• c.Within sight of the main service
• d.In a transformer room of fire-resistant construction, unless it has Class 155 or higher insulation and is separated from combustibles by a barrier or by adequate distance✓

Dry-type transformers over 112.5 kVA installed indoors must be in a transformer room of fire-resistant construction, with exceptions for units having Class 155 or higher insulation that are either completely enclosed or separated from combustible material by a fire-resistant barrier or by clearance. Units of 112.5 kVA or less instead follow the 12-inch clearance rule.2023 NEC §450.21(B)

As defined in Article 100, ampacity is best described as which of the following?

• a.The maximum current a conductor can carry continuously under the conditions of use without exceeding its temperature rating✓
• b.The current that will instantly melt the conductor
• c.The rated current of the overcurrent device protecting the conductor, taken directly from the marking on the breaker or fuse without regard to installation conditions
• d.The current at which voltage drop reaches 3 percent

Article 100 defines ampacity as the maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. It is a property of the conductor and its environment, not the rating of the protective device ahead of it.2023 NEC Art. 100

Under the Article 100 definitions, what does it mean for metal parts to be bonded?

• a.Connected to the earth through a ground rod
• b.Insulated from all other metal parts
• c.Connected together to establish electrical continuity and conductivity✓
• d.Painted to prevent corrosion

Bonding means connecting parts together to establish electrical continuity and conductivity, which is what allows fault current to return to the source and open the overcurrent device. Connecting a part to the earth is grounding, a related but distinct concept.2023 NEC Art. 100

Three 30-ohm resistors are connected in parallel. What is the total resistance?

• a.90 ohms
• b.10 ohms✓
• c.30 ohms
• d.15 ohms

For equal resistors in parallel, total resistance equals the value of one resistor divided by the number of resistors: 30 / 3 = 10 ohms. The 90-ohm answer adds them as if in series, and total parallel resistance is always less than the smallest branch.

How much energy does a 1,500-watt electric heater consume when operated continuously for 4 hours?

• a.375 watt-hours
• b.1.5 kilowatt-hours
• c.600 watt-hours
• d.6 kilowatt-hours✓

Energy equals power multiplied by time: 1,500 watts x 4 hours = 6,000 watt-hours, or 6 kilowatt-hours. The 1.5-kilowatt-hour answer reports only the power rating, and 375 watt-hours divides instead of multiplying.

A 40-ohm resistor and a 20-ohm resistor are connected in series across a 120-volt source. What is the voltage drop across the 40-ohm resistor?

• a.80 volts✓
• b.40 volts
• c.60 volts
• d.48 volts

In series the total resistance is 40 + 20 = 60 ohms, so the current is 120 / 60 = 2 amperes. The drop across the 40-ohm resistor is 2 x 40 = 80 volts, and the remaining 40 volts appears across the 20-ohm resistor, confirming the two drops sum to the source voltage.

Article 100 defines a qualified person as one who has which of the following?

• a.A journeyman license issued in any state
• b.Skills and knowledge related to the construction and operation of the electrical equipment and installations, plus safety training to recognize and avoid the hazards involved✓
• c.At least eight thousand hours of documented field experience working under the direct supervision of a licensed master electrician, regardless of whether any formal safety or hazard-recognition training has been completed
• d.A current first-aid and CPR certification

A qualified person is defined by demonstrated skills and knowledge related to the construction and operation of the equipment and installations, together with safety training to recognize and avoid the hazards involved. The definition is competency-based and does not hinge on a specific license, hour count or certificate.2023 NEC Art. 100

A continuous load draws 16 amperes. What is the minimum standard overcurrent device rating permitted?

• a.15 amperes
• b.16 amperes
• c.25 amperes
• d.20 amperes✓

An overcurrent device supplying a continuous load must be rated at not less than 125 percent of the load: 16 A x 1.25 = 20 A, a standard rating in NEC 240.6(A). See NEC 210.20(A).

A service uses 4/0 AWG copper ungrounded service-entrance conductors. What is the minimum size copper grounding electrode conductor?

• a.4 AWG
• b.2 AWG✓
• c.1/0 AWG
• d.6 AWG

Table 250.66 places service conductors over 3/0 through 350 kcmil copper in the row requiring a 2 AWG copper grounding electrode conductor. The 4 AWG row is for 2/0 and 3/0, so reading one row low understates it. See NEC Table 250.66.

A box contains six 14 AWG conductors, one internal cable clamp and one duplex receptacle wired with 14 AWG. What minimum box volume is required?

• a.16.0 cubic inches
• b.12.0 cubic inches
• c.20.25 cubic inches
• d.18.0 cubic inches✓

Count six conductors, one allowance for all internal clamps, and two allowances for the device yoke = 9 allowances. Each 14 AWG allowance is 2.00 cubic inches: 9 x 2.00 = 18.0. See NEC 314.16(B).

A 20-horsepower, 460-volt, three-phase squirrel-cage motor has a table full-load current of 27 amperes. Using 75 degrees C copper terminations, what is the minimum branch-circuit conductor size?

• a.8 AWG
• b.12 AWG
• c.6 AWG
• d.10 AWG✓

Single-motor branch-circuit conductors must carry at least 125 percent of the table full-load current: 27 x 1.25 = 33.75 A. In the 75 degrees C column 12 AWG (25 A) fails and 10 AWG (35 A) qualifies. See NEC 430.22, Table 430.250 and Table 310.16.

A heating element of 10 ohms is connected across 120 volts. What current flows?

• a.1,200 amperes
• b.10 amperes
• c.12 amperes✓
• d.0.083 ampere

Ohm's law gives I = E / R = 120 / 10 = 12 amperes. Inverting the division gives the 0.083-ampere trap, and multiplying gives 1,200.

For a 16-ampere continuous load, what is the minimum copper branch-circuit conductor at 75 degrees C terminations using THWN?

• a.14 AWG
• b.10 AWG
• c.8 AWG
• d.12 AWG✓

The conductor must carry 125 percent of the continuous load = 20 A. In Table 310.16 (75 degrees C) 14 AWG copper is 20 A but the small-conductor rule NEC 240.4(D) limits 14 AWG to a 15 A device, so 12 AWG (25 A) is the minimum. See NEC 210.19(A).

A service is supplied by a single set of 400 kcmil copper ungrounded conductors. What is the minimum size copper grounding electrode conductor?

• a.2 AWG
• b.4 AWG
• c.1/0 AWG✓
• d.3/0 AWG

Service conductors over 350 through 600 kcmil copper require a 1/0 AWG copper grounding electrode conductor. The 2 AWG row applies to over 3/0 through 350 kcmil. See NEC Table 250.66.

A device box has two 12-2 nonmetallic-sheathed cables with equipment grounding conductors entering through internal clamps, and one single-pole switch (12 AWG). What minimum box volume is required?

• a.18.0 cubic inches✓
• b.16.0 cubic inches
• c.20.25 cubic inches
• d.15.75 cubic inches

Four insulated 12 AWG conductors, all grounding conductors as one, all clamps as one, and the switch yoke as two = 8 allowances. At 2.25 cubic inches each: 8 x 2.25 = 18.0. See NEC 314.16(B).

That 20-horsepower motor has a nameplate full-load current of 26 amperes and a marked service factor of 1.15. What is the maximum separate overload device rating?

• a.33.75 amperes
• b.29.9 amperes
• c.32.5 amperes✓
• d.26 amperes

Overload protection is based on nameplate current, and a service factor of 1.15 or greater permits 125 percent: 26 x 1.25 = 32.5 A. The 115 percent factor (29.9 A) applies only to lower-rated motors. See NEC 430.32(A)(1).

What power is consumed by a 240-volt resistive load drawing 15 amperes?

• a.16 watts
• b.3,000 watts
• c.255 watts
• d.3,600 watts✓

Power in a resistive single-phase circuit is P = E x I = 240 x 15 = 3,600 watts. Dividing gives 16 and adding gives 255.

Seven current-carrying 8 AWG THWN-2 copper conductors are installed in one raceway at a 30 degrees C ambient. What is the adjusted ampacity of each?

• a.44 amperes
• b.38.5 amperes✓
• c.33 amperes
• d.27.5 amperes

Begin at the 90 degrees C ampacity of 8 AWG copper, 55 A (Table 310.16), then apply the 70 percent adjustment for 7 through 9 current-carrying conductors: 55 x 0.70 = 38.5 A. See NEC 310.15(C)(1).

A service uses 1 AWG copper ungrounded service-entrance conductors. What is the minimum size copper grounding electrode conductor?

• a.2 AWG
• b.6 AWG✓
• c.4 AWG
• d.8 AWG

Table 250.66 groups 1 and 1/0 AWG copper service conductors together and requires a 6 AWG copper grounding electrode conductor. The 8 AWG row is for 2 AWG and smaller. See NEC Table 250.66.

How many 12 AWG conductors may be installed in a 22.5-cubic-inch box with no clamps, devices or fittings?

• a.9
• b.10✓
• c.12
• d.11

Each 12 AWG conductor requires 2.25 cubic inches: 22.5 / 2.25 = 10 conductors exactly. See NEC 314.16(A) and (B).

For that 27-ampere three-phase motor, what is the maximum inverse-time circuit breaker for branch-circuit short-circuit and ground-fault protection, using the next standard size allowance?

• a.90 amperes
• b.70 amperes✓
• c.60 amperes
• d.80 amperes

An inverse-time breaker is permitted at 250 percent of full-load current: 27 x 2.50 = 67.5 A, which is not standard, so the next standard size of 70 A may be used. See Table 430.52(C)(1) and 430.52(C)(1) Exception 1.

How much power is dissipated when 6 amperes flows through a 25-ohm resistor?

• a.150 watts
• b.6.25 watts
• c.3,600 watts
• d.900 watts✓

Using P = I squared x R = 6 x 6 x 25 = 900 watts. Multiplying current by resistance without squaring gives 150 watts.

Five current-carrying 6 AWG THHN copper conductors run in a raceway through a 40 degrees C ambient. What is the adjusted ampacity of each?

• a.65 amperes
• b.48 amperes
• c.60 amperes
• d.54.6 amperes✓

The 90 degrees C ampacity of 6 AWG copper is 75 A. Apply the 36 to 40 degrees C correction of 0.91 and the 4 to 6 conductor adjustment of 0.80: 75 x 0.91 x 0.80 = 54.6 A. See NEC 310.15 and Table 310.16.

What is the minimum size copper equipment grounding conductor for a circuit protected at 100 amperes?

• a.8 AWG✓
• b.10 AWG
• c.6 AWG
• d.4 AWG

Table 250.122 is entered by the overcurrent device rating, and the 100-ampere row calls for 8 AWG copper. The 10 AWG row is 60 amperes and 6 AWG is 200 amperes. See NEC Table 250.122.

How many 14 AWG conductors may be installed in an 18.0-cubic-inch box with no clamps, devices or fittings?

• a.12
• b.10
• c.8
• d.9✓

Each 14 AWG conductor requires 2.00 cubic inches: 18.0 / 2.00 = 9 conductors. See NEC 314.16(A) and (B).

For the same 27-ampere motor, what is the maximum dual-element time-delay fuse at the standard 175 percent, using the next standard size allowance?

• a.40 amperes
• b.50 amperes✓
• c.60 amperes
• d.45 amperes

Dual-element time-delay fuses are permitted at 175 percent: 27 x 1.75 = 47.25 A, and the next standard size is 50 A. See Table 430.52(C)(1).

Three resistors of 5, 10 and 20 ohms are connected in series across 105 volts. What is the circuit current?

• a.0.33 ampere
• b.6 amperes
• c.30 amperes
• d.3 amperes✓

Series resistances add: 5 + 10 + 20 = 35 ohms, so I = 105 / 35 = 3 amperes.

A 120-volt single-phase circuit carries 16 amperes 150 feet on 10 AWG copper (10,380 circular mils). Using K = 12.9, what is the approximate voltage drop?

• a.3.0 volts
• b.12.0 volts
• c.6.0 volts✓
• d.9.0 volts

Single-phase VD = (2 x K x I x L) / CM = (2 x 12.9 x 16 x 150) / 10,380 = 61,920 / 10,380, about 6.0 V. Omitting the factor of 2 gives the 3.0-V trap. See NEC Chapter 9, Table 8.

What is the minimum size copper equipment grounding conductor for a 300-ampere feeder?

• a.2 AWG
• b.6 AWG
• c.3 AWG
• d.4 AWG✓

The 300-ampere row of Table 250.122 specifies 4 AWG copper. 6 AWG is 200 amperes and 3 AWG is 400 amperes, so those are adjacent rows. See NEC Table 250.122.

What is the minimum trade size of EMT required for sixteen 12 AWG THHN conductors?

• a.One-half inch
• b.One inch
• c.Three-quarter inch✓
• d.One and one-quarter inch

Annex C, Table C1 shows one-half-inch EMT holds nine 12 AWG THHN and three-quarter-inch EMT holds sixteen, so three-quarter inch is the minimum. See NEC Annex C, Table C1.

For the same 27-ampere motor, what is the maximum non-time-delay fuse at the standard 300 percent, using the next standard size allowance?

• a.110 amperes
• b.80 amperes
• c.90 amperes✓
• d.100 amperes

Non-time-delay fuses are permitted at 300 percent: 27 x 3.00 = 81 A, and the next standard size is 90 A. See Table 430.52(C)(1).

A 10-ohm resistor and a 40-ohm resistor are connected in parallel. What is the total resistance?

• a.4 ohms
• b.8 ohms✓
• c.25 ohms
• d.50 ohms

For two resistors in parallel, R = (R1 x R2) / (R1 + R2) = (10 x 40) / 50 = 400 / 50 = 8 ohms. Total parallel resistance is always less than the smallest branch.

A 480-volt three-phase feeder carries 30 amperes 300 feet on 4 AWG copper (41,740 circular mils). Using K = 12.9, what is the approximate voltage drop?

• a.4.8 volts✓
• b.9.6 volts
• c.5.6 volts
• d.2.8 volts

Three-phase VD = (1.732 x K x I x L) / CM = (1.732 x 12.9 x 30 x 300) / 41,740, about 4.8 V. Using 2 instead of 1.732 gives the 5.6-V answer. See NEC Chapter 9, Table 8.

What is the minimum size copper equipment grounding conductor for a 20-ampere branch circuit?

• a.14 AWG
• b.10 AWG
• c.8 AWG
• d.12 AWG✓

Table 250.122 lists 12 AWG copper at 20 amperes. 14 AWG is the 15-ampere value and 10 AWG is the 60-ampere value. See NEC Table 250.122.

When exactly one conductor is installed in a conduit or tubing, what is the maximum permitted fill percentage?

• a.40 percent
• b.31 percent
• c.53 percent✓
• d.60 percent

Chapter 9, Table 1 permits 53 percent fill for a single conductor, 31 percent for two, and 40 percent for three or more. See NEC Chapter 9, Table 1.

A 25-horsepower, 208-volt, three-phase squirrel-cage motor has a table full-load current of 74.8 amperes. Using 75 degrees C copper terminations, what is the minimum branch-circuit conductor size?

• a.6 AWG
• b.4 AWG
• c.2 AWG
• d.3 AWG✓

The conductor must carry 74.8 x 1.25 = 93.5 A. In the 75 degrees C column 4 AWG (85 A) fails and 3 AWG (100 A) qualifies. See NEC 430.22, Table 430.250 and Table 310.16.

Three 60-ohm resistors are connected in parallel. What is the total resistance?

• a.30 ohms
• b.180 ohms
• c.20 ohms✓
• d.60 ohms

For equal resistors in parallel, total resistance equals one value divided by the number of resistors: 60 / 3 = 20 ohms. Adding them gives the 180-ohm series answer.

A 240-volt circuit must carry 20 amperes 200 feet with voltage drop held to 3 percent. Using K = 12.9 for copper, what is the smallest conductor that meets the target?

• a.6 AWG
• b.10 AWG
• c.8 AWG✓
• d.12 AWG

Three percent of 240 V is 7.2 V, so required area = (2 x 12.9 x 20 x 200) / 7.2 = 103,200 / 7.2 = 14,333 circular mils. From Chapter 9, Table 8, 10 AWG (10,380 cmil) fails and 8 AWG (16,510 cmil) meets it. Voltage-drop sizing is advisory per the Informational Notes to NEC 210.19 and 215.2.

What is the minimum size copper equipment grounding conductor for a 500-ampere feeder?

• a.1 AWG
• b.4 AWG
• c.3 AWG
• d.2 AWG✓

The 500-ampere row of Table 250.122 requires 2 AWG copper. 3 AWG is 400 amperes and 1 AWG is 600 amperes. See NEC Table 250.122.

Four 250 kcmil THWN conductors, each 0.3970 square inch, are pulled into EMT. What is the minimum trade size?

• a.3 inch
• b.1 and 1/2 inch
• c.2 inch
• d.2 and 1/2 inch✓

Total area = 4 x 0.3970 = 1.588 square inches at 40 percent fill. Two-inch EMT allows about 1.342 square inches and fails; 2 and 1/2-inch EMT allows about 2.343 square inches and works. See NEC Chapter 9, Tables 1 and 4.

For that 74.8-ampere motor, what is the maximum inverse-time circuit breaker at 250 percent, using the next standard size allowance?

• a.150 amperes
• b.200 amperes✓
• c.225 amperes
• d.175 amperes

74.8 x 2.50 = 187 A, which is not standard, so the next standard size of 200 A may be used. See Table 430.52(C)(1).

A balanced three-phase load draws 30 amperes at 208 volts with a power factor of 0.90. What is the true power?

• a.Approximately 6.2 kilowatts
• b.Approximately 10.8 kilowatts
• c.Approximately 5.6 kilowatts
• d.Approximately 9.7 kilowatts✓

True power = 1.732 x E x I x PF = 1.732 x 208 x 30 x 0.90, about 9,730 watts. Omitting the power factor gives about 10.8 kVA of apparent power.

A feeder supplies 40 amperes of continuous load plus 60 amperes of noncontinuous load. What is the minimum standard overcurrent device rating?

• a.90 amperes
• b.125 amperes
• c.110 amperes✓
• d.100 amperes

The device is sized for the noncontinuous load plus 125 percent of the continuous load: 60 + (40 x 1.25) = 110 A, which is a standard rating. See NEC 215.3 and 240.6(A).

A ground ring encircling a building must be formed from at least 20 feet of bare copper conductor not smaller than what size?

• a.4 AWG
• b.6 AWG
• c.2 AWG✓
• d.1/0 AWG

A ground ring must encircle the building and consist of at least 20 feet of bare copper conductor not smaller than 2 AWG. See NEC 250.52(A)(4).

What is the maximum support spacing for a horizontal run of 1/2-inch trade size rigid metal conduit?

• a.10 feet✓
• b.6 feet
• c.5 feet
• d.12 feet

Rigid metal conduit of 1/2 and 3/4 inch is supported at intervals not exceeding 10 feet, and it must be secured within 3 feet of each termination. See NEC 344.30(B)(2).

A feeder supplies a 25-horsepower motor (34 amperes) and a 15-horsepower motor (21 amperes), both 460 volts three-phase. What minimum conductor ampacity is required?

• a.68.75 amperes
• b.48.75 amperes
• c.63.5 amperes✓
• d.55 amperes

Feeder conductors carry 125 percent of the largest motor plus the other full-load currents: (34 x 1.25) + 21 = 42.5 + 21 = 63.5 A. See NEC 430.24.