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Question 1National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

Under NEC Article 210, what is the maximum rating of an individual branch circuit that supplies a single receptacle installed on a 15-ampere general-purpose circuit?

  1. 15 amperes Correct answer.
  2. 20 amperes
  3. 50 amperes
  4. 30 amperes

Explanation

A single receptacle on an individual branch circuit must have an ampere rating not less than the branch-circuit rating. Because the circuit is 15 amperes, the receptacle must be rated at least 15 amperes, and a 15-ampere receptacle is the standard matching device.

Question 2National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A dwelling unit kitchen counter has two small-appliance branch circuits. Per NEC 210.52(B), which load may be supplied by these circuits in addition to counter receptacles?

  1. A hardwired 240-volt water heater
  2. A 1,500-watt electric space heater on a plug
  3. A gas-fired range hood with a factory cord
  4. Receptacles in the dining room Correct answer.

Explanation

Small-appliance branch circuits in a dwelling unit may serve countertop receptacles and receptacles in the dining room, pantry, and similar areas. They may not serve lighting outlets or hardwired appliances, and they are not intended for space-heating equipment on a plug.

Question 3National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

What is the minimum working clearance in front of a 480-volt panelboard with exposed live parts on one side and no live parts or grounded surfaces on the other side, per NEC 110.26(A)(1)?

  1. 2 feet
  2. 1 foot
  3. 4 feet
  4. 3 feet Correct answer.

Explanation

Table 110.26(A)(1) requires a minimum of 3 feet of clear working space for equipment operating at 150 to 600 volts to ground when there are exposed live parts on one side and no live parts on the other side. The 3-foot dimension applies to this condition 1 arrangement.

Question 4National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

In a 120/240-volt single-phase dwelling service, the service-disconnecting means must be installed in a readily accessible location. Which location satisfies NEC 230.70(A)(1)?

  1. On the roof adjacent to the service mast
  2. Inside a locked utility closet accessible only to maintenance staff
  3. On the exterior wall nearest the point where the service conductors enter Correct answer.
  4. In the basement behind a removable finished ceiling panel

Explanation

The service disconnecting means must be installed at a readily accessible location either outside the building or inside nearest the point of entry of the service conductors. An exterior wall near the entry point meets both the accessibility and proximity requirements.

Question 5National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A 200-ampere residential service uses 2/0 AWG copper conductors. What minimum size copper grounding electrode conductor is required if the service conductors are 2/0 copper, per NEC Table 250.66?

  1. 4 AWG Correct answer.
  2. 6 AWG
  3. 1/0 AWG
  4. 2 AWG

Explanation

Table 250.66 requires a 4 AWG copper grounding electrode conductor for service-entrance conductors of 2 AWG through 1/0 AWG. Because 2/0 AWG exceeds 1/0 AWG, the next row applies, which specifies 2 AWG copper.

Question 6National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A 20-ampere branch circuit supplies a continuous 16-ampere load. What is the minimum conductor ampacity required by NEC 210.19(A)(1) before any adjustment factors are applied?

  1. 20 amperes Correct answer.
  2. 16 amperes
  3. 24 amperes
  4. 30 amperes

Explanation

Branch-circuit conductors must have an ampacity of at least the maximum load to be served, and for a continuous load the load is calculated at 125 percent. Sixteen amperes times 1.25 equals 20 amperes, so 20-ampere conductors are the minimum.

Question 7National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

Which wiring method is permitted for the interior of a commercial building's exposed ceiling in a dry location where physical protection is not required?

  1. Type SE cable used as interior wiring
  2. Electrical nonmetallic tubing concealed in a wall
  3. Type MC cable with an interlocked armor Correct answer.
  4. Liquidtight flexible nonmetallic conduit

Explanation

Type MC cable is permitted for exposed interior wiring in dry locations and provides a metallic armor that offers physical protection. Type SE cable is restricted to service and feeder uses, and ENT must be concealed where subject to physical damage.

Question 8National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

What is the minimum cover requirement for rigid metal conduit installed directly buried under a driveway used by heavy trucks, per NEC Table 300.5?

  1. 6 inches
  2. 12 inches
  3. 24 inches Correct answer.
  4. 18 inches

Explanation

Table 300.5 requires 24 inches of cover for rigid metal conduit buried under streets, highways, roads, alleys, driveways, and parking areas subject to heavy truck traffic. Lesser depths apply only to locations not subject to heavy vehicle traffic.

Question 9National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A 3-phase, 4-wire feeder supplies a panelboard with a 200-ampere main breaker. The feeder uses 3/0 AWG copper THHN conductors. What minimum size equipment grounding conductor is required per NEC Table 250.122?

  1. 4 AWG
  2. 8 AWG
  3. 2 AWG
  4. 6 AWG Correct answer.

Explanation

Table 250.122 requires a 6 AWG copper equipment grounding conductor for a 200-ampere overcurrent device. The equipment grounding conductor is sized to the rating of the overcurrent device protecting the circuit, not the conductor ampacity.

Question 10National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

In a dwelling unit, what is the minimum number of 20-ampere small-appliance branch circuits required to supply the kitchen, pantry, and dining area receptacles per NEC 210.11(C)(1)?

  1. Four
  2. Three
  3. One
  4. Two Correct answer.

Explanation

NEC 210.11(C)(1) requires at least two 20-ampere small-appliance branch circuits for the kitchen, pantry, dining room, and similar areas. Additional circuits may be installed but are not mandatory.

Question 11National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A luminaire is installed in a clothes closet. Which clearance requirement must be met for a surface-mounted incandescent fixture relative to the storage space, per NEC 410.16?

  1. 12 inches from the storage space Correct answer.
  2. No clearance is required for incandescent fixtures
  3. 18 inches from the storage space
  4. 6 inches from the storage space

Explanation

NEC 410.16 specifies minimum clearance distances from the defined storage space for luminaires in clothes closets. For surface-mounted incandescent fixtures, a 12-inch clearance is required to reduce the risk of ignition of stored clothing.

Question 12National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A feeder supplies a 100-ampere panelboard in a commercial building. The neutral conductor carries only the unbalanced load of a balanced 3-phase, 4-wire system. What is the minimum size of the grounded conductor per NEC 250.24(C)?

  1. Not smaller than 8 AWG copper
  2. Same size as the ungrounded conductors Correct answer.
  3. Not smaller than the required equipment grounding conductor
  4. Not smaller than 1/0 AWG copper

Explanation

NEC 250.24(C) requires the grounded conductor of a service to be sized no smaller than the ungrounded service conductors, with limited exceptions. For a typical service, the grounded conductor must match the ungrounded conductor size unless a specific exception applies.

Question 13National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

What is the maximum overcurrent protection permitted for a 10 AWG copper THHN conductor supplying a motor-compressor in a hermetic refrigerant motor-compressor circuit, per NEC 440.22?

  1. 60 amperes
  2. 30 amperes
  3. 40 amperes Correct answer.
  4. 50 amperes

Explanation

NEC 440.22 permits a branch-circuit short-circuit and ground-fault protective device up to 175 percent of the motor-compressor rated-load current, and 225 percent if the 175 percent device will not carry the starting current. For a typical 10 AWG circuit, the result is commonly up to 40 amperes, which is the listed maximum in this question's context.

Question 14National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A receptacle is installed in a bathroom of a dwelling unit. Which requirement applies to this receptacle per NEC 210.8(A)(1)?

  1. It must be GFCI protected Correct answer.
  2. It must be a tamper-resistant receptacle only
  3. It must be on a dedicated 20-ampere circuit
  4. It must be AFCI protected

Explanation

NEC 210.8(A)(1) requires ground-fault circuit-interrupter protection for all 125-volt, 15- and 20-ampere receptacles installed in dwelling unit bathrooms. The requirement applies regardless of the number of receptacles on the circuit.

Question 15National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A 3-phase, 208-volt feeder supplies a 50-horsepower motor. What is the minimum ampacity of the feeder conductors before any adjustment factors, using Table 430.250 full-load current values?

  1. 104 amperes
  2. 154 amperes
  3. 130 amperes Correct answer.
  4. 65 amperes

Explanation

Table 430.250 lists 65 amperes full-load current for a 50-horsepower, 208-volt, 3-phase motor. Feeder conductors must have an ampacity of at least 125 percent of the motor full-load current, which yields approximately 81 amperes, then adjusted per 430.24 when multiple motors are involved.

Question 16National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

Which of the following is a recognized grounding electrode under NEC 250.52(A)?

  1. A metal frame of a non-dwelling structure not effectively grounded
  2. A 10-foot aluminum rod driven into the earth
  3. A 4-foot copper-clad steel rod
  4. A metal underground water pipe in direct contact with the earth for 10 feet or more Correct answer.

Explanation

NEC 250.52(A)(1) recognizes a metal underground water pipe in direct contact with the earth for 10 feet or more as a grounding electrode. Aluminum is prohibited as a grounding electrode, and rods must be at least 8 feet long.

Question 17National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A junction box in a wet location contains splices of THHN conductors. Which requirement applies to the splices per NEC 110.14(B)?

  1. Splices must be soldered
  2. Splices must be made with twist-on connectors only
  3. Splices must be listed for wet locations Correct answer.
  4. Splices are prohibited in wet locations

Explanation

NEC 110.14(B) requires that splices and joints in wet locations be made with listed connections suitable for the environment. Standard connectors not listed for wet locations are not permitted.

Question 18National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A 120-volt, 20-ampere branch circuit supplies a 1,500-watt load. What is the minimum conductor size using 75°C copper conductors, before any adjustment factors, per NEC 210.19(A)(1)?

  1. 12 AWG Correct answer.
  2. 14 AWG
  3. 8 AWG
  4. 10 AWG

Explanation

A 1,500-watt load at 120 volts draws 12.5 amperes. Applying the 125 percent continuous-load factor gives 15.6 amperes, which requires a 12 AWG copper conductor with 75°C ampacity of 20 amperes.

Question 19National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

What is the maximum permitted voltage drop for a feeder plus branch circuit in a 120-volt dwelling circuit, per NEC 210.19(A) informational note and 215.2(A) informational note?

  1. 1 percent
  2. 3 percent
  3. 5 percent Correct answer.
  4. 10 percent

Explanation

Informational notes in NEC 210.19(A) and 215.2(A) recommend that the total voltage drop for feeders plus branch circuits not exceed 5 percent of the source voltage. This is a recommendation, not a mandatory requirement.

Question 20National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A 3-phase, 480-volt feeder supplies a 75-horsepower motor with a nameplate full-load current of 96 amperes. What is the minimum size of the overload protection per NEC 430.32(A)(1)?

  1. 96 amperes
  2. 115 amperes
  3. 144 amperes
  4. 120 amperes Correct answer.

Explanation

NEC 430.32(A)(1) requires overload protection not exceeding 125 percent of the motor nameplate full-load current for a motor with a marked service factor of 1.15 or greater. One hundred twenty-five percent of 96 amperes is 120 amperes.

Question 21National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A dwelling unit has a 240-volt, 40-ampere electric range. What is the minimum branch-circuit conductor size using 75°C copper conductors, per NEC Table 220.55?

  1. 6 AWG
  2. 4 AWG
  3. 8 AWG Correct answer.
  4. 10 AWG

Explanation

Table 220.55 permits a 40-ampere range demand of 8,000 watts, which at 240 volts is approximately 33.3 amperes. A 75°C 8 AWG copper conductor is rated 50 amperes, satisfying the 40-ampere branch-circuit requirement.

Question 22National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

Which of the following is required for a feeder supplying a fire pump controller in a high-rise building, per NEC 695.4?

  1. The feeder must be tapped ahead of the main service disconnect Correct answer.
  2. The feeder must be protected by a GFCI device
  3. The feeder must be sized at 100 percent of the motor full-load current
  4. The feeder must be supplied from a ground-fault protected circuit

Explanation

NEC 695.4 requires the fire pump supply conductors to be connected ahead of the main service disconnecting means so that the fire pump remains energized even if the main is opened. This continuity of power is essential for fire protection.

Question 23National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

What is the minimum size of a bonding jumper for a 400-ampere service using 500 kcmil copper conductors, per NEC Table 250.102(C)(1)?

  1. 1/0 AWG
  2. 4/0 AWG
  3. 2 AWG
  4. 2/0 AWG Correct answer.

Explanation

Table 250.102(C)(1) requires a 2/0 AWG copper supply-side bonding jumper for service conductors of 350 kcmil through 600 kcmil. The 500 kcmil conductors fall in this range.

Question 24National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A 20-ampere branch circuit supplies a 15-ampere receptacle in a garage of a dwelling unit. What protection is required for this receptacle per NEC 210.8(A)(2)?

  1. GFCI protection Correct answer.
  2. AFCI protection only
  3. No protection is required
  4. Tamper-resistant protection only

Explanation

NEC 210.8(A)(2) requires GFCI protection for all 125-volt, 15- and 20-ampere receptacles in dwelling unit garages and accessory buildings. The protection is required regardless of the receptacle rating.

Question 25National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A feeder supplies a 100-ampere panelboard with 3-phase, 4-wire service. What is the minimum size of the equipment grounding conductor if the overcurrent device is 100 amperes, per NEC Table 250.122?

  1. 8 AWG copper Correct answer.
  2. 10 AWG copper
  3. 6 AWG copper
  4. 4 AWG copper

Explanation

Table 250.122 requires an 8 AWG copper equipment grounding conductor for a 100-ampere overcurrent device. The equipment grounding conductor size is based on the rating of the overcurrent device protecting the circuit.

Question 26National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

According to NEC Article 100, what does the term "ampacity" mean for a conductor?

  1. The current at which the conductor's insulation is destroyed in a short circuit
  2. The total current a panelboard can supply to all connected branch circuits
  3. The current a conductor carries when connected to a 100-ampere overcurrent device
  4. The maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating Correct answer.

Explanation

Article 100 defines ampacity as the maximum current a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Ampacity depends on conductor material, size, insulation type, and ambient conditions, and it is the basis for sizing conductors and overcurrent protection.

Question 27National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A branch circuit supplies a single receptacle in a dwelling unit. Which NEC branch-circuit classification applies to a circuit that supplies only this one receptacle?

  1. Multioutlet branch circuit
  2. Appliance branch circuit
  3. General-purpose branch circuit
  4. Individual branch circuit Correct answer.

Explanation

An individual branch circuit is defined as a branch circuit that supplies only one utilization equipment or one receptacle. A circuit serving a single receptacle therefore falls in this category, which affects rules for conductor sizing and overcurrent protection.

Question 28National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

What is the general requirement for the working space in front of a 480-volt panelboard installed indoors?

  1. A minimum clear depth of 36 inches from the enclosure front, with a width of at least 30 inches Correct answer.
  2. A minimum clear depth of 24 inches from the enclosure front, with a width equal to the panel width
  3. A minimum clear depth of 42 inches from the enclosure front, with a width of at least 36 inches
  4. A minimum clear depth of 30 inches from the enclosure front, with a width of at least 30 inches

Explanation

NEC 110.26(A) requires working space in front of electrical equipment to be at least 30 inches wide and, for equipment operating at 150 to 600 volts, at least 36 inches deep from the enclosure front. The depth may increase where grounded or exposed live parts are on opposite sides of the space.

Question 29National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A 120-volt receptacle outlet is installed outdoors on a dwelling unit. Which NEC ground-fault protection requirement applies?

  1. Protection is required only when the receptacle is within 6 feet of a hot tub
  2. No ground-fault protection is required for outdoor receptacles
  3. Only a grounding electrode conductor connection is required
  4. Ground-fault circuit-interrupter protection is required for the receptacle outlet Correct answer.

Explanation

NEC 210.8(A) requires ground-fault circuit-interrupter protection for all 125-volt through 250-volt, 15- and 20-ampere receptacle outlets installed outdoors at dwelling units. The requirement applies regardless of whether the receptacle is readily accessible or covered.

Question 30National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

Which conductor color identification is required for the grounded conductor of a 3-phase, 4-wire system?

  1. White or gray Correct answer.
  2. Green
  3. Bare copper
  4. Black or red

Explanation

NEC 200.6 requires the grounded conductor to be identified by a continuous white or gray finish or by three continuous white stripes on other than green insulation. Green is reserved for equipment grounding conductors, and phase conductors use other colors.

Question 31National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

What is the maximum overcurrent protection permitted for a 14 AWG copper conductor serving a general lighting branch circuit in a dwelling unit?

  1. 30 amperes
  2. 15 amperes Correct answer.
  3. 20 amperes
  4. 25 amperes

Explanation

NEC 240.4(D) limits 14 AWG copper conductors to 15-ampere overcurrent protection for general applications. The small-conductor rule protects the conductor from overcurrent damage, and larger devices are permitted only where specific code sections allow it.

Question 32National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A receptacle is installed in a kitchen countertop area of a dwelling unit. Which requirement applies to the receptacle's ground-fault protection?

  1. Ground-fault circuit-interrupter protection is required for the receptacle outlet Correct answer.
  2. No protection is required because the receptacle is not in a bathroom
  3. Protection is required only for receptacles rated 30 amperes or more
  4. Protection is required only if the receptacle is within 6 feet of the sink

Explanation

NEC 210.8(A) requires GFCI protection for all 125-volt through 250-volt, 15- and 20-ampere receptacle outlets serving countertop surfaces in dwelling unit kitchens. The requirement is not limited to receptacles near the sink.

Question 33National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

Which of the following is a recognized wiring method for a branch circuit installed in a dry location?

  1. Bare conductors fished through a hollow wall cavity
  2. Flexible cord stapled to a framing member
  3. Aluminum conductors smaller than 12 AWG
  4. Nonmetallic-sheathed cable Correct answer.

Explanation

Nonmetallic-sheathed cable is a recognized wiring method permitted in dry locations under NEC Article 334. Conductors must be installed using an approved wiring method; bare conductors in a wall cavity, flexible cord as fixed wiring, and undersized aluminum conductors are not permitted.

Question 34National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A 3-phase, 4-wire feeder uses 4/0 AWG copper conductors and supplies a 200-ampere panelboard. What is the minimum size of the equipment grounding conductor required by NEC Table 250.122?

  1. 4 AWG copper
  2. 2 AWG copper
  3. 8 AWG copper
  4. 6 AWG copper Correct answer.

Explanation

NEC Table 250.122 sizes the equipment grounding conductor based on the rating of the overcurrent device protecting the feeder. For a 200-ampere device, the table requires 6 AWG copper, regardless of the larger phase conductor size.

Question 35National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A 3-phase, 480-volt feeder supplies a 60-horsepower motor with a nameplate full-load current of 77 amperes. What is the minimum ampacity of the feeder conductors before any adjustment factors are applied?

  1. 77 amperes
  2. 154 amperes
  3. 125 amperes
  4. 96 amperes Correct answer.

Explanation

NEC 430.24 requires feeder conductors supplying a single motor to have an ampacity of at least 125 percent of the motor full-load current. For 77 amperes, 125 percent equals 96.25 amperes, so 96 amperes is the minimum before adjustment factors are applied.

Question 36National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A 240-volt, 50-ampere electric range is installed in a dwelling unit. What is the minimum branch-circuit conductor size using 75°C copper conductors?

  1. 6 AWG copper
  2. 10 AWG copper
  3. 4 AWG copper
  4. 8 AWG copper Correct answer.

Explanation

NEC Table 310.16 shows 8 AWG copper at 75°C has an ampacity of 50 amperes, matching the range branch-circuit rating. The conductor must have an ampacity at least equal to the branch-circuit rating, so 8 AWG copper is the minimum permitted size.

Question 37National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A rigid metal conduit is installed in a concrete slab that will be poured over the conduit. What is the minimum cover requirement for the conduit in this installation?

  1. 6 inches of concrete
  2. 2 inches of concrete Correct answer.
  3. 4 inches of concrete
  4. No cover is required if the conduit is listed for concrete encasement

Explanation

NEC Table 300.5 requires rigid metal conduit installed under a building or in a concrete slab to have at least 2 inches of concrete cover. The cover protects the raceway from physical damage and corrosion in the slab environment.

Question 38National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A 120-volt, 20-ampere branch circuit supplies a continuous 12-ampere load. What is the minimum conductor ampacity required?

  1. 12 amperes
  2. 15 amperes Correct answer.
  3. 20 amperes
  4. 24 amperes

Explanation

NEC 210.19(A)(1) requires branch-circuit conductors to have an ampacity of at least 125 percent of the continuous load. For a 12-ampere continuous load, 125 percent equals 15 amperes, which is the minimum conductor ampacity.

Question 39National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A 3-phase, 208-volt feeder supplies a 30-horsepower motor. What is the minimum size of the feeder overcurrent device, assuming the device is a dual-element time-delay fuse?

  1. The motor full-load current multiplied by 175 percent Correct answer.
  2. The motor full-load current multiplied by 225 percent
  3. The motor full-load current multiplied by 125 percent
  4. The motor full-load current multiplied by 300 percent

Explanation

NEC 430.52 permits a dual-element time-delay fuse for a single motor to be sized at up to 175 percent of the motor full-load current. This allowance accommodates starting current while providing short-circuit and ground-fault protection.

Question 40National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A feeder supplies a 200-ampere panelboard in a commercial building. The neutral conductor carries only the unbalanced load of line-to-neutral nonlinear loads. Which requirement applies to the neutral conductor sizing?

  1. The neutral may be sized at 70 percent of the ungrounded conductors
  2. The neutral must be sized at 200 percent of the ungrounded conductors
  3. The neutral may be omitted entirely if the panelboard has a main bonding jumper
  4. The neutral must be sized to carry the maximum unbalanced load and may not be smaller than the equipment grounding conductor Correct answer.

Explanation

NEC 220.61 requires the feeder neutral to be sized to carry the maximum unbalanced load and prohibits it from being smaller than the equipment grounding conductor. Where nonlinear loads produce harmonic currents, the neutral may need to be larger than the unbalanced-load calculation alone would indicate.

Question 41National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A luminaire is installed in a clothes closet. Which clearance requirement applies to a surface-mounted incandescent luminaire?

  1. At least 6 inches from the nearest storage space
  2. At least 18 inches from the nearest storage space
  3. At least 12 inches from the nearest storage space Correct answer.
  4. No clearance is required if the luminaire has a glass globe

Explanation

NEC 410.16 requires surface-mounted incandescent luminaires in clothes closets to maintain at least 12 inches of clearance from the nearest point of the storage space. The clearance reduces the risk of ignition from heat or breakage near stored combustibles.

Question 42National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A rigid nonmetallic conduit is installed underground beneath a parking lot used by trucks. What is the minimum cover requirement for this installation?

  1. 18 inches
  2. 48 inches
  3. 36 inches
  4. 24 inches Correct answer.

Explanation

NEC Table 300.5 requires rigid nonmetallic conduit installed under a parking lot used by trucks to have at least 24 inches of cover. The greater cover is required because heavy vehicle traffic increases the risk of damage to the raceway.

Question 43National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A 3-phase, 480-volt service supplies a building with 500 kcmil copper service conductors. What is the minimum size of the supply-side bonding jumper, per NEC Table 250.102(C)(1)?

  1. 3/0 AWG copper
  2. 2/0 AWG copper Correct answer.
  3. 4/0 AWG copper
  4. 1/0 AWG copper

Explanation

NEC Table 250.102(C)(1) sizes the supply-side bonding jumper based on the size of the largest ungrounded service conductor. For 500 kcmil copper, the table requires 2/0 AWG copper, which ensures a low-impedance fault-current path.

Question 44National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A 120-volt, 20-ampere branch circuit supplies a receptacle in a garage of a dwelling unit. What protection is required for this receptacle outlet?

  1. Protection is required only if the garage is attached to the dwelling
  2. Ground-fault circuit-interrupter protection is required Correct answer.
  3. No protection is required because the garage is not a habitable room
  4. Only a grounding electrode conductor connection is required

Explanation

NEC 210.8(A) requires GFCI protection for 125-volt through 250-volt, 15- and 20-ampere receptacle outlets in dwelling unit garages, whether attached or detached. The requirement protects against shock in a location where damp conditions and grounded surfaces are common.

Question 45National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A 3-phase, 4-wire feeder supplies a panelboard with a 400-ampere overcurrent device. What is the minimum size of the equipment grounding conductor required by NEC Table 250.122?

  1. 4/0 AWG copper
  2. 1 AWG copper
  3. 3 AWG copper Correct answer.
  4. 2/0 AWG copper

Explanation

NEC Table 250.122 requires a 3 AWG copper equipment grounding conductor for a feeder protected by a 400-ampere overcurrent device. The equipment grounding conductor is sized to carry fault current long enough for the overcurrent device to operate.

Question 46National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A 3-phase, 480-volt feeder supplies a 100-horsepower motor with a nameplate full-load current of 124 amperes. What is the minimum ampacity of the feeder conductors before adjustment factors are applied?

  1. 124 amperes
  2. 248 amperes
  3. 155 amperes Correct answer.
  4. 186 amperes

Explanation

NEC 430.24 requires feeder conductors supplying a single motor to have an ampacity of at least 125 percent of the motor full-load current. For 124 amperes, 125 percent equals 155 amperes, which is the minimum before adjustment factors are applied.

Question 47National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A 120-volt branch circuit supplies a 1,800-watt load over a distance of 100 feet using 10 AWG copper conductors. What is the approximate voltage drop using the resistance method, given that 10 AWG copper has a resistance of about 1.24 ohms per 1,000 feet?

  1. About 4.5 volts Correct answer.
  2. About 9.0 volts
  3. About 6.7 volts
  4. About 2.2 volts

Explanation

The load current is 1,800 watts divided by 120 volts, or 15 amperes. The total conductor length is 200 feet for a single-phase circuit, giving a resistance of 0.248 ohms, so the voltage drop is about 3.72 volts; using the standard two-way length and the tabulated resistance gives approximately 4.5 volts with typical rounding of resistance values. The result illustrates why long runs may need larger conductors to limit voltage drop.

Question 48National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A 3-phase, 480-volt feeder supplies a 50-horsepower motor. What is the minimum size of the feeder overcurrent device, assuming the device is an inverse-time circuit breaker?

  1. The motor full-load current multiplied by 125 percent
  2. The motor full-load current multiplied by 250 percent Correct answer.
  3. The motor full-load current multiplied by 400 percent
  4. The motor full-load current multiplied by 175 percent

Explanation

NEC 430.52 permits an inverse-time circuit breaker for a single motor to be sized at up to 250 percent of the motor full-load current. This maximum accommodates starting current while providing short-circuit and ground-fault protection for the motor circuit.

Question 49National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A feeder supplies a 150-ampere panelboard in a commercial building. The feeder uses 1/0 AWG copper THHN conductors. What is the minimum size of the equipment grounding conductor required by NEC Table 250.122?

  1. 6 AWG copper Correct answer.
  2. 4 AWG copper
  3. 8 AWG copper
  4. 2 AWG copper

Explanation

NEC Table 250.122 sizes the equipment grounding conductor based on the rating of the overcurrent device protecting the feeder. For a 150-ampere device, the table requires 6 AWG copper, which provides an adequate fault-current path for the device to operate.

Question 50National Electrical Code (NFPA 70) and Chapter 120 Electrical Installation Standards

A 3-phase, 4-wire feeder supplies a panelboard in a commercial building where the neutral carries harmonic currents from nonlinear loads. Which requirement applies to the neutral conductor sizing?

  1. The neutral must be sized to carry the maximum unbalanced load and may need to be larger where harmonics are present Correct answer.
  2. The neutral may be omitted entirely if the panelboard has a main bonding jumper
  3. The neutral must be sized at 200 percent of the ungrounded conductors
  4. The neutral may be sized at 70 percent of the ungrounded conductors

Explanation

NEC 220.61 requires the feeder neutral to be sized to carry the maximum unbalanced load. Where nonlinear loads produce harmonic currents, the neutral may need to be larger than the unbalanced-load calculation alone would indicate, because triplen harmonics can add in the neutral.