007
This grounding electrode must be used if present in a building and in contact with earth for at least 10 feet.
What is a metal underground water pipe electrode?
NEC Location: 250.52(A)(1)
A 4″ square metal box (1½″ deep) contains:
(3) 12 AWG current-carrying conductors
(1) 12 AWG equipment grounding conductor
(1) internal clamp
(1) device yoke with a single receptacle
Is the box large enough?
Answer: B – No
Calculation:
Conductors: 3 × 2.25 = 6.75 in³
Grounds: 1 × 2.25 = 2.25 in³
Clamp: 1 × 2.25 = 2.25 in³
Device yoke: 2 × 2.25 = 4.50 in³
Total required = 15.75 in³
Box volume (Table 314.16(A)) = 15.5 in³
👉 Not sufficient.
A 3 HP, 230V, single-phase motor has a full-load current of 12 A. What is the minimum size overcurrent protection device (OCPD) allowed?
18 A
Calculation / Notes:
NEC Table 430.248: 3 HP, 230V, 1Ø → FLC = 12 A
OCPD max = 250% for short-circuit protection not allowed, normally 125% for overload → 12 × 125% = 15 A
Use next standard breaker size → 18 A
A new residential swimming pool requires bonding of all metal parts. Which of the following must be bonded?
A. Only the pool structure
B. Pool structure, metal piping, and pool lights
C. Pool deck only
D. Only underwater lights
B – Pool structure, metal piping, and pool lights
NEC References: 680.26(A), 680.26(B)
Which of the following defines a Class I, Division 1 location?
A. Location where flammable gases or vapors are not normally present
B. Location where flammable gases or vapors may exist under normal operating conditions
C. Location with combustible dusts
D. Location with ignitable fibers
B – Location where flammable gases or vapors may exist under normal operating conditions
NEC Reference: 500.5(A)
This is the minimum spacing required between two ground rods used as electrodes.
What is 6 feet?
NEC Location: 250.53(A)(3)
A box contains:
(6) 14 AWG conductors
(1) 14 AWG equipment grounding conductor
No devices, no clamps
Minimum box volume required?
A. 12 in³
B. 14 in³
C. 16 in³
D. 18 in³
Answer: B – 14 in³
Calculation:
Conductors: 6 × 2.0 = 12.0 in³
Grounds: 1 × 2.0 = 2.0 in³
Total = 14 in³
A 5 HP, 460V, 3-phase motor is connected to a branch circuit. What is the minimum conductor size (AWG) for THHN copper, 75°C insulation?
#8
Calculation / Notes:
Table 430.248: FLC ≈ 6.9 A for 5 HP, 460V, 3Ø
Branch-circuit conductors must be ≥ FLC × 125% → 6.9 × 1.25 ≈ 8.6 A
#8 Cu → 55A (75°C) → OK
A 20-foot by 40-foot pool is installed in a backyard. What is the minimum distance for receptacles from the pool edge?
A. 3 ft
B. 6 ft
C. 10 ft
D. 12 ft
B – 6 ft
NEC References: 680.22(A)(1), 680.22(A)(2)
A facility handles finely divided grain dust that may ignite. Which classification applies?
A. Class I, Division 2
B. Class II, Division 1
C. Class III, Division 1
D. Class I, Zone 0
B – Class II, Division 1
NEC Reference: 502.10(A)
This conductor connects the grounded service conductor to the equipment grounding conductors and enclosure at the service.
What is the main bonding jumper?
NEC Location: 250.28
A single-gang plastic box is marked 18 in³ and contains:
(2) 12 AWG cables entering (4 conductors total)
(1) switch on a yoke
Grounds present
Is the box compliant?
Answer: A – Yes
Calculation:
Conductors: 4 × 2.25 = 9.0 in³
Grounds: 1 × 2.25 = 2.25 in³
Switch yoke: 2 × 2.25 = 4.50 in³
Total = 15.75 in³
Box volume = 18 in³
A motor requires 25 A at full load. What is the maximum size of the overload protection (continuous) in amperes?
35A
Calculation / Notes:
FLC = 25 A
OCPD sizing per 430.32(A) → 125% × FLC = 25 × 1.25 = 31.25 → next standard breaker size 35 A
NEC References: 430.32(A), 430.52
Which of the following requires GFCI protection in a pool area?
A. Outdoor lighting within 20 ft of the pool
B. Pool pump motor
C. Receptacles within 20 ft of pool
D. All of the above
D – All of the above
NEC References: 680.22, 680.21(A), 680.22(B)
Class III locations include which of the following?
A. Locations with flammable gases
B. Locations with combustible dusts
C. Locations with easily ignitable fibers or flyings not likely to be in suspension
D. Locations with conductive liquids
C – Locations with easily ignitable fibers or flyings not likely to be in suspension
NEC Reference: 503.2
This table is used to size the grounding electrode conductor based on the largest ungrounded service conductor.
What is Table 250.66?
NEC Location: 250.66
A box contains:
(5) 10 AWG conductors
(1) internal clamp
No devices
Required minimum volume?
Answer: D – 21 in³
Calculation:
10 AWG allowance = 2.50 in³ each
Conductors: 5 × 2.50 = 12.5 in³
Clamp: 1 × 2.50 = 2.5 in³
Total = 15.0 in³
👉 BUT PSI trap: box must be equal or greater than required.
Closest compliant standard size ≥15 in³ is typically 21 in³
Which of the following statements is correct about a motor branch circuit supplying a 7.5 HP, 230V, 3-phase motor?
A. OCPD must not exceed 100% of FLC
B. Motor conductor ampacity must be at least 125% of FLC
C. Motor overload protection is optional
D. Conductor ampacity can be less than FLC
B – Motor conductor ampacity must be at least 125% of FLC
NEC References: 430.22(A), 430.32(A), Table 430.248
An elevator is installed in a commercial building. The NEC requires that the power circuit supplying the elevator be:
A. Fed from a dedicated branch circuit
B. Fed from the nearest lighting panel
C. On a multi-purpose circuit
D. Only grounded at the elevator motor
: A – Fed from a dedicated branch circuit
NEC References: 620.11(A), 620.51
n a Class I, Division 2 location, which of the following is allowed without explosion-proof equipment?
A. Ordinary branch-circuit receptacles
B. Motors rated for Division 1
C. Equipment approved for Division 2 only
D. None of the above
C – Equipment approved for Division 2 only
NEC Reference: 504.5(C)
This rule requires normally non-current-carrying metal parts of equipment to be connected together and to the supply system grounded conductor.
What is equipment bonding?
NEC Location: 250.4(A)(3) & 250.110
A box contains:
(3) 12 AWG conductors
(2) 12 AWG conductors that pass through unbroken
(1) receptacle yoke
Grounds present
How many conductor equivalents must be counted?
Total = 8 conductor equivalents
A 10 HP, 460V, 3-phase motor operates with continuous duty. What percent of full-load current is the minimum rating for the branch-circuit OCPD?
A. 100%
B. 115%
C. 125%
D. 150%
Answer: C – 125%
Notes:
NEC requires branch-circuit conductors to handle 125% FLC for continuous motors
In a high-rise building, an elevator must be provided with emergency power. The source must:
A. Be a 120V receptacle in the machine room
B. Be capable of operating only the lowest car
C. Be supplied from the building emergency system
D. Be optional
C – Be supplied from the building emergency system
NEC References: 620.51(C), 700.10(A)
A storage facility is rated as Zone 1, 3-phase, 480V motors with flammable vapors present intermittently. According to the NEC, what type of overcurrent protection is required?
A. Standard OCPD with no special rating
B. OCPD rated for hazardous (explosion-proof) location
C. OCPD rated only for Class II, Division 1
D. OCPD rated for Class III
B – OCPD rated for hazardous (explosion-proof) location
NEC Reference: 505.15(B), 500.7(C), 430.52(B)