Free NEC Code Basic Questions and Answers 1 — Questions and Answers

Question 1: Every box, cabinet, or temperature fitting, such as a conduit body, must have electrical nonmetallic tubing secured within:

3 ft (Correct answer)
4 ft
5 ft
6 ft

Correct answer: 3 ft

NEC Article 362.30(A) requires Electrical Nonmetallic Tubing (ENT) to be securely fastened in place at intervals not exceeding 3 feet (900 mm). Furthermore, it must be secured within 12 inches (300 mm) of every box, cabinet, or fitting. These requirements ensure the tubing is properly supported, preventing sagging and protecting it from damage.

Question 2: Motor feeder tap conductors that are not more than ___ length must have an ampacity that is at least ten times the feeder protection device's rating.

10 ft (Correct answer)
15 ft
20 ft
25 ft

Correct answer: 10 ft

The 10-foot tap rule, found in NEC 240.21(B)(2) and referenced for motor feeder taps in 430.28, permits tap conductors not exceeding 10 feet in length under specific conditions. This rule allows for short, unprotected taps from a feeder, provided they meet specific ampacity requirements and do not extend beyond the control device they supply. The 10-foot length is a recognized short tap rule in the NEC for providing flexibility in connecting loads.

Question 3: For the purpose of sizing branch circuits, an electric heater with a capacity of __ gallons or less is regarded as a continuous load:

100
120 (Correct answer)
150
180

Correct answer: 120

According to NEC 422.13, a storage-type water heater with a capacity of 120 gallons (450 liters) or less is considered a continuous load. This classification requires the branch circuit conductors and overcurrent protection to be sized at 125% of the water heater's nameplate rating. This ensures the circuit can safely handle the sustained current draw typical of water heaters, preventing overheating and ensuring long-term reliability.

Question 4: With more than three levels. Behind floors, walls, or ceilings with a ____ minute finish rating, ENT must be hidden:

12
15 (Correct answer)
30
25

Correct answer: 15

NEC 362.10(2) permits Electrical Nonmetallic Tubing (ENT) to be installed in buildings exceeding three floors above grade, provided it is concealed within walls, floors, or ceilings. A critical condition for this use is that these structural elements must provide a thermal barrier with a minimum 15-minute finish rating. This requirement enhances fire safety by limiting the spread of fire and smoke in taller buildings.

Question 5: For connecting equipment or taps to luminaires, FMC Trade size 3/8 can be used in lengths no longer than :

3 ft
4 ft
6 ft (Correct answer)
7 ft

Correct answer: 6 ft

NEC 348.20(A)(2) provides an exception that allows 3/8 inch trade size Flexible Metal Conduit (FMC) to be used for tap conductors to luminaires or other equipment. However, this exception strictly limits the length of such applications to no more than 1.8 meters (6 feet). This ensures that while flexibility is provided for connections, the overall protection and integrity of the wiring system are maintained for these short runs.

Question 6: For a mast termination above the floor, RMC need not be firmly attached within __ of the service head:

2.5 ft
3 ft (Correct answer)
4 ft
6 ft

Correct answer: 3 ft

NEC 344.30(A) generally requires Rigid Metal Conduit (RMC) to be firmly supported within 3 feet (900 mm) of each box, cabinet, or conduit termination, including service heads. This rule ensures the conduit is securely held in place at critical points, preventing strain on connections and maintaining the integrity of the electrical system. While 230.28 addresses service masts, it refers back to 344.30 for support requirements.

Question 7: Ground fault protection for the overcurrent device for the primary feeder wires in marinas must not be greater than:

5mA
50mA
100mA (Correct answer)
500mA

Correct answer: 100mA

NEC 555.3 mandates ground-fault protection of equipment (GFPE) for feeder and branch-circuit overcurrent devices supplying marinas, boatyards, and docking facilities. This protection must not be greater than 100 mA. The 100 mA trip level is crucial for quickly detecting and interrupting ground faults in these wet environments, significantly reducing the risk of electric shock to persons in or near the water.

Question 8: The cord must contain a copper equipment grounding conductor that is not less than ____ and must end at a grounding type attachment plug for fixed or stationary equipment other than an underwater luminaire for permanently installed pools:

8 AWG
10 AWG
12 AWG (Correct answer)
14 AWG

Correct answer: 12 AWG

For fixed or stationary equipment, other than underwater luminaires, used with permanently installed pools, NEC 680.21(A)(1) requires the cord to contain a copper equipment grounding conductor not smaller than 12 AWG. This robust grounding conductor, terminating in a grounding-type attachment plug, provides a low-impedance path for fault current. This is essential for safety in the potentially hazardous pool environment, minimizing the risk of electric shock.

Question 9: Separately generated systems with a rating of __ or less are exempt from grounding requirements:

0.5 kVA
2 kVA
2.5 kVA
1 kVA (Correct answer)

Correct answer: 1 kVA

NEC 250.30(A)(1) Exception No. 1 exempts very small separately derived systems from the requirement of a grounding electrode conductor. Specifically, a system derived from a transformer or converter with a maximum current rating of 1000 amperes or less, and a system rating of 1 kVA or less, does not require a grounding electrode conductor. This simplifies installation for low-power systems that pose minimal risk.

Question 10: The permissible ampacity for copper conductor of 10 AWG at 60° C is .

30 A (Correct answer)
20 A
35 A
40 A

Correct answer: 30 A

According to NEC Table 310.16, the allowable ampacity for a 10 AWG copper conductor with 60°C insulation is 30 amperes. This value represents the maximum continuous current the conductor can safely carry without exceeding its temperature rating. Adhering to these ampacity limits is crucial to prevent conductor overheating, insulation degradation, and potential fire hazards in electrical installations.

Question 11: The overload device shall not be larger than ______ of the motor nameplate current ratings for motors with an indicated service factor (SF) of 1.15 or higher on the nameplate:

100%
115%
125% (Correct answer)
150%

Correct answer: 125%

NEC 430.32(A)(1) specifies that for continuous-duty motors with a nameplate service factor (SF) of 1.15 or higher, the overload device setting shall not exceed 125% of the motor's nameplate full-load current rating. A higher service factor indicates the motor can safely handle temporary overloads. This allowance provides adequate protection against sustained overloads while preventing nuisance tripping during normal, slightly elevated operating conditions.

Question 12: The cold water input must be _____ away from the underside of any mobile or constructed house pipe heat tape receptacle outlets:

1.5 ft
2 ft (Correct answer)
3 ft
5 ft

Correct answer: 2 ft

NEC 550.15(E) requires pipe heat tape receptacle outlets in mobile or manufactured homes to be located on the underside of the home and not more than 600 mm (2 ft) from the cold water inlet. This specific placement ensures convenient and accessible connection points for heat tape. It facilitates proper installation to prevent pipes from freezing, while also ensuring the outlet is readily available for its intended purpose.

Question 13: A device box or plaster ring fastened to a device box can hold a vertically mounted luminaire weighing no more than :

6 lb (Correct answer)
10 lb
12 lb
9 lb

Correct answer: 6 lb

NEC 314.27(A)(1) specifies that a device box or a plaster ring fastened to a device box is permitted to support a vertically mounted luminaire weighing no more than 2.7 kg (6 lb). This weight limit ensures that the box and its mounting method can safely bear the luminaire's weight without risking structural failure or detachment. For heavier luminaires, a dedicated outlet box or other approved support method is required.

Question 14: Equipment with cords and plugs cannot be rated at more than ______ of the branch circuit rating if it is not fixed in place.

75%
80% (Correct answer)
100%
125%

Correct answer: 80%

NEC 210.23(A)(1) states that the total rating of cord-and-plug-connected utilization equipment not fastened in place shall not exceed 80% of the branch-circuit ampere rating. This rule provides a safety margin, preventing continuous overloading of the circuit, which could lead to overheating of conductors and overcurrent devices. It accounts for the intermittent nature of such loads and the potential for multiple devices to be plugged in.

Question 15: Information technology equipment branch circuit conductors must have an ampacity that is at least ____ of the total load connected:

100%
125% (Correct answer)
150%
175%

Correct answer: 125%

NEC 645.5(A) requires that branch-circuit conductors supplying information technology equipment (ITE) shall have an ampacity not less than 125% of the total connected load. ITE typically operates continuously for extended periods, making it a continuous load. Sizing conductors at 125% provides a safety factor to prevent overheating and ensure reliable, long-term operation, accommodating the sustained current draw characteristic of such equipment.

Question 16: The maximum overcurrent protection for a transformer with primary windings not exceeding 600 V and primary current ratings under 2 A is as:

100%
125%
150%
300% (Correct answer)

Correct answer: 300%

According to NEC 450.3(B) and Table 450.3(B), for transformers with primary windings not exceeding 600 V and a primary current rating under 2 A, the maximum overcurrent protection is 300% of the primary current. This higher percentage is allowed to accommodate the significant inrush current that occurs when a transformer is first energized. It prevents nuisance tripping while still providing essential protection against sustained overloads or short circuits.

Free NEC Code Basic Questions and Answers 1

Every box, cabinet, or temperature fitting, such as a conduit body, must have electrical nonmetallic tubing secured within: