, Question 1
A 480V, 3-phase, 4-wire service supplies a 200A continuous load and a 100A
noncontinuous load. The service conductors are parallel 4/0 AWG THWN-2
copper in two raceways. What is the minimum allowable ampacity of each
parallel set after applying continuous-load adjustment?
A. 150A
B. 175A
C. 200A
D. 250A
Correct Answer: B - 175A
RATIONALE
Continuous load is multiplied by 125%: 200A × 1.25 = 250A, plus
100A noncontinuous = 350A total. For parallel sets, each must carry
350A ÷ 2 = 175A. NEC 215.2(A)(1)(a) and 310.16 require the
conductor ampacity to be at least 175A per set, making B correct; A,
C, and D fail to apply the 125% continuous-load factor or parallel
division correctly.
Question 2
A 25 kVA, 480V-120/208V, 3-phase transformer supplies a 60A continuous
load and a 40A noncontinuous load. The transformer is protected by a primary
breaker. What is the maximum standard size primary-only overcurrent device
permitted by NEC 450.3(B)?
A. 40A
B. 50A
C. 60A
D. 70A
Correct Answer: C - 60A
Page 2
, RATIONALE
Primary current = 25,000 ÷ (480 × 1.732) = 30.1A. NEC Table
450.3(B) allows primary-only protection at up to 125% of primary
current for transformers >9A: 30.1 × 1.25 = 37.6A, next standard size
40A. However, if secondary protection is omitted, the next higher
standard device is permitted up to 250% for primary-only, but the
question specifies primary-only with maximum standard size; 60A is
the next standard size after 40A that does not exceed 250% (30.1 × 2.5
= 75.25A). The correct maximum standard size is 60A per NEC 240.6
and 450.3(B).
Question 3
In a Class I, Division 1 location, a rigid metal conduit run must transition to a
flexible connection at a motor terminal. Which wiring method is permitted for
the flexible connection?
A. Liquidtight flexible metal conduit with listed termination fittings
B. Liquidtight flexible nonmetallic conduit with integral conductor
C. Type MC cable with a gas/vapor-tight continuous sheath
D. Flexible metal conduit with a listed sealing fitting within 18 in. of the
enclosure
Correct Answer: A - Liquidtight flexible metal conduit with listed
termination fittings
RATIONALE
NEC 501.10(A)(1)(c) permits liquidtight flexible metal conduit with
listed termination fittings in Class I, Division 1 for flexible
connections. LFNC is limited to Division 2 or unclassified, MC cable
is not permitted in Division 1 unless specifically listed, and FMC
requires an approved sealing fitting but is not the preferred method;
the sealing fitting is required at the boundary, not within 18 in. of the
enclosure for the flexible connection itself.
Page 3
, Question 4
A Vermont electrical contractor is installing a 100A feeder to a detached
garage. The feeder is 120/240V, 1-phase, with a 3-wire plus equipment ground.
The garage has a concrete floor and a metal water pipe. Which grounding
electrode system is required at the detached structure?
A. Only the equipment grounding conductor from the main service
B. A grounding electrode system using the metal water pipe and a ground
rod
C. A grounding electrode system using the concrete-encased electrode
and a ground rod
D. No grounding electrode system is required if the feeder includes an
equipment ground
Correct Answer: C - A grounding electrode system using the
concrete-encased electrode and a ground rod
RATIONALE
NEC 250.32(A) requires a grounding electrode system at a separate
building or structure. The concrete-encased electrode (Ufer) is present
in the concrete floor and must be used per 250.52(A)(3), supplemented
by a ground rod per 250.53. The metal water pipe may also be an
electrode, but the concrete-encased electrode is mandatory if available.
Option D is incorrect because an equipment ground does not eliminate
the need for a grounding electrode system.
Question 5
A 50 hp, 460V, 3-phase motor has a nameplate FLA of 65A. The motor is
started with a reduced-voltage autotransformer starter. The branch-circuit
short-circuit and ground-fault protective device is a dual-element time-delay
fuse. What is the maximum standard size fuse permitted by NEC 430.52?
A. 150A
B. 175A
Page 4
A 480V, 3-phase, 4-wire service supplies a 200A continuous load and a 100A
noncontinuous load. The service conductors are parallel 4/0 AWG THWN-2
copper in two raceways. What is the minimum allowable ampacity of each
parallel set after applying continuous-load adjustment?
A. 150A
B. 175A
C. 200A
D. 250A
Correct Answer: B - 175A
RATIONALE
Continuous load is multiplied by 125%: 200A × 1.25 = 250A, plus
100A noncontinuous = 350A total. For parallel sets, each must carry
350A ÷ 2 = 175A. NEC 215.2(A)(1)(a) and 310.16 require the
conductor ampacity to be at least 175A per set, making B correct; A,
C, and D fail to apply the 125% continuous-load factor or parallel
division correctly.
Question 2
A 25 kVA, 480V-120/208V, 3-phase transformer supplies a 60A continuous
load and a 40A noncontinuous load. The transformer is protected by a primary
breaker. What is the maximum standard size primary-only overcurrent device
permitted by NEC 450.3(B)?
A. 40A
B. 50A
C. 60A
D. 70A
Correct Answer: C - 60A
Page 2
, RATIONALE
Primary current = 25,000 ÷ (480 × 1.732) = 30.1A. NEC Table
450.3(B) allows primary-only protection at up to 125% of primary
current for transformers >9A: 30.1 × 1.25 = 37.6A, next standard size
40A. However, if secondary protection is omitted, the next higher
standard device is permitted up to 250% for primary-only, but the
question specifies primary-only with maximum standard size; 60A is
the next standard size after 40A that does not exceed 250% (30.1 × 2.5
= 75.25A). The correct maximum standard size is 60A per NEC 240.6
and 450.3(B).
Question 3
In a Class I, Division 1 location, a rigid metal conduit run must transition to a
flexible connection at a motor terminal. Which wiring method is permitted for
the flexible connection?
A. Liquidtight flexible metal conduit with listed termination fittings
B. Liquidtight flexible nonmetallic conduit with integral conductor
C. Type MC cable with a gas/vapor-tight continuous sheath
D. Flexible metal conduit with a listed sealing fitting within 18 in. of the
enclosure
Correct Answer: A - Liquidtight flexible metal conduit with listed
termination fittings
RATIONALE
NEC 501.10(A)(1)(c) permits liquidtight flexible metal conduit with
listed termination fittings in Class I, Division 1 for flexible
connections. LFNC is limited to Division 2 or unclassified, MC cable
is not permitted in Division 1 unless specifically listed, and FMC
requires an approved sealing fitting but is not the preferred method;
the sealing fitting is required at the boundary, not within 18 in. of the
enclosure for the flexible connection itself.
Page 3
, Question 4
A Vermont electrical contractor is installing a 100A feeder to a detached
garage. The feeder is 120/240V, 1-phase, with a 3-wire plus equipment ground.
The garage has a concrete floor and a metal water pipe. Which grounding
electrode system is required at the detached structure?
A. Only the equipment grounding conductor from the main service
B. A grounding electrode system using the metal water pipe and a ground
rod
C. A grounding electrode system using the concrete-encased electrode
and a ground rod
D. No grounding electrode system is required if the feeder includes an
equipment ground
Correct Answer: C - A grounding electrode system using the
concrete-encased electrode and a ground rod
RATIONALE
NEC 250.32(A) requires a grounding electrode system at a separate
building or structure. The concrete-encased electrode (Ufer) is present
in the concrete floor and must be used per 250.52(A)(3), supplemented
by a ground rod per 250.53. The metal water pipe may also be an
electrode, but the concrete-encased electrode is mandatory if available.
Option D is incorrect because an equipment ground does not eliminate
the need for a grounding electrode system.
Question 5
A 50 hp, 460V, 3-phase motor has a nameplate FLA of 65A. The motor is
started with a reduced-voltage autotransformer starter. The branch-circuit
short-circuit and ground-fault protective device is a dual-element time-delay
fuse. What is the maximum standard size fuse permitted by NEC 430.52?
A. 150A
B. 175A
Page 4
