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ELECTRICAL WIRING RESIDENTIAL, 21ST EDITION (MULLIN, SIMMONS
& VIGSTOL) EXAM 2026 QUESTIONS LATEST EDITION 2026 – 2027
VERSION SOLVED QUESTIONS & ANSWERS
Electrical Wiring Residential, 21st Edition (Mullin, Simmons & Vigstol) — Questions
with Rationales
SECTION 1: GENERAL INFORMATION & ELECTRICAL THEORY (Questions 1–25)
1. What is the primary purpose of the National Electrical Code (NEC)?
A. To regulate the rates charged by electrical utilities
B. To provide minimum standards for the safe installation of electrical wiring and
equipment
C. To establish maximum standards for electrical efficiency
D. To govern the sale of electrical equipment
Answer: B
Rationale: The primary purpose of the National Electrical Code (NEC), published by the
National Fire Protection Association (NFPA), is to provide minimum standards for the
safe installation of electrical wiring and equipment. It is not a design specification or a
manual for maximum efficiency. Local and state codes must also be considered in
addition to the NEC.
2. According to Ohm's Law, what is the relationship between voltage, current, and
resistance?
A. Voltage equals current divided by resistance (E = I ÷ R)
B. Voltage equals current multiplied by resistance (E = I × R)
C. Current equals voltage multiplied by resistance (I = E × R)
D. Resistance equals voltage multiplied by current (R = E × I)
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Answer: B
Rationale: Ohm's Law states that voltage (E) equals current (I) multiplied by resistance
(R): E = I × R. This fundamental relationship is used extensively in electrical calculations.
The other forms are I = E ÷ R and R = E ÷ I.
3. What is the unit of electrical resistance?
A. Volt
B. Ampere
C. Ohm
D. Watt
Answer: C
Rationale: The ohm (Ω) is the unit of electrical resistance. The volt (V) is the unit of
electrical potential difference, the ampere (A) is the unit of electrical current, and the
watt (W) is the unit of electrical power.
4. Which instrument is used to measure voltage?
A. Ammeter
B. Voltmeter
C. Ohmmeter
D. Wattmeter
Answer: B
Rationale: A voltmeter measures electrical potential difference (voltage) between two
points in a circuit. An ammeter measures current, an ohmmeter measures resistance,
and a wattmeter measures power.
5. What is the power formula that relates watts, volts, and amperes?
A. P = E ÷ I
B. P = E × I
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C. P = I ÷ E
D. P = E × I²
Answer: B
Rationale: The power formula for DC circuits (and purely resistive AC circuits) is P = E ×
I, where P is power in watts, E is voltage in volts, and I is current in amperes. For AC
circuits with reactive loads, power factor must also be considered.
6. In a typical residential electrical system in the United States, what is the
standard voltage between the two "hots"?
A. 120 volts
B. 208 volts
C. 240 volts
D. 277 volts
Answer: C
Rationale: The standard residential electrical system provides 120 volts between one
hot and ground and 240 volts between the two hots. This 120/240-volt system is
standard for single-family dwellings in the United States.
7. What do the letters "UL" signify on an electrical product?
A. It has been tested by the Utility Laboratory
B. It has been listed by Underwriters Laboratories for safety
C. It is available for use in the United States
D. It meets minimum efficiency standards
Answer: B
Rationale: The UL mark signifies that the product has been tested and listed by
Underwriters Laboratories (or a similar recognized testing laboratory) for safety.
Products without a listing from a recognized testing laboratory should not be installed.
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8. What is the unit of electrical power?
A. Volt
B. Ampere
C. Ohm
D. Watt
Answer: D
Rationale: The watt (W) is the unit of electrical power. One watt equals one volt times
one ampere. The volt is the unit of potential difference, the ampere is the unit of current,
and the ohm is the unit of resistance.
9. Which of the following is a fundamental safety rule for electrical work?
A. Always work on live circuits to save time
B. Always de-energize circuits before working on them
C. Never use lockout/tagout procedures
D. Only wear safety glasses when working with high voltage
Answer: B
Rationale: The most fundamental safety rule is to always de-energize circuits before
working on them. Lockout/tagout procedures should be used to ensure circuits remain
de-energized. Live work should be avoided unless absolutely necessary and only by
qualified personnel.
10. What is the purpose of the grounded conductor in a residential electrical
system?
A. To carry current under normal conditions and provide a path to ground
B. To carry fault current only
C. To provide a return path for current under normal conditions
D. To act as the primary overcurrent protection
Answer: C
Rationale: The grounded conductor (neutral or white wire) provides a return path for
ELECTRICAL WIRING RESIDENTIAL, 21ST EDITION (MULLIN, SIMMONS
& VIGSTOL) EXAM 2026 QUESTIONS LATEST EDITION 2026 – 2027
VERSION SOLVED QUESTIONS & ANSWERS
Electrical Wiring Residential, 21st Edition (Mullin, Simmons & Vigstol) — Questions
with Rationales
SECTION 1: GENERAL INFORMATION & ELECTRICAL THEORY (Questions 1–25)
1. What is the primary purpose of the National Electrical Code (NEC)?
A. To regulate the rates charged by electrical utilities
B. To provide minimum standards for the safe installation of electrical wiring and
equipment
C. To establish maximum standards for electrical efficiency
D. To govern the sale of electrical equipment
Answer: B
Rationale: The primary purpose of the National Electrical Code (NEC), published by the
National Fire Protection Association (NFPA), is to provide minimum standards for the
safe installation of electrical wiring and equipment. It is not a design specification or a
manual for maximum efficiency. Local and state codes must also be considered in
addition to the NEC.
2. According to Ohm's Law, what is the relationship between voltage, current, and
resistance?
A. Voltage equals current divided by resistance (E = I ÷ R)
B. Voltage equals current multiplied by resistance (E = I × R)
C. Current equals voltage multiplied by resistance (I = E × R)
D. Resistance equals voltage multiplied by current (R = E × I)
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Answer: B
Rationale: Ohm's Law states that voltage (E) equals current (I) multiplied by resistance
(R): E = I × R. This fundamental relationship is used extensively in electrical calculations.
The other forms are I = E ÷ R and R = E ÷ I.
3. What is the unit of electrical resistance?
A. Volt
B. Ampere
C. Ohm
D. Watt
Answer: C
Rationale: The ohm (Ω) is the unit of electrical resistance. The volt (V) is the unit of
electrical potential difference, the ampere (A) is the unit of electrical current, and the
watt (W) is the unit of electrical power.
4. Which instrument is used to measure voltage?
A. Ammeter
B. Voltmeter
C. Ohmmeter
D. Wattmeter
Answer: B
Rationale: A voltmeter measures electrical potential difference (voltage) between two
points in a circuit. An ammeter measures current, an ohmmeter measures resistance,
and a wattmeter measures power.
5. What is the power formula that relates watts, volts, and amperes?
A. P = E ÷ I
B. P = E × I
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C. P = I ÷ E
D. P = E × I²
Answer: B
Rationale: The power formula for DC circuits (and purely resistive AC circuits) is P = E ×
I, where P is power in watts, E is voltage in volts, and I is current in amperes. For AC
circuits with reactive loads, power factor must also be considered.
6. In a typical residential electrical system in the United States, what is the
standard voltage between the two "hots"?
A. 120 volts
B. 208 volts
C. 240 volts
D. 277 volts
Answer: C
Rationale: The standard residential electrical system provides 120 volts between one
hot and ground and 240 volts between the two hots. This 120/240-volt system is
standard for single-family dwellings in the United States.
7. What do the letters "UL" signify on an electrical product?
A. It has been tested by the Utility Laboratory
B. It has been listed by Underwriters Laboratories for safety
C. It is available for use in the United States
D. It meets minimum efficiency standards
Answer: B
Rationale: The UL mark signifies that the product has been tested and listed by
Underwriters Laboratories (or a similar recognized testing laboratory) for safety.
Products without a listing from a recognized testing laboratory should not be installed.
, Page 4 of 71
8. What is the unit of electrical power?
A. Volt
B. Ampere
C. Ohm
D. Watt
Answer: D
Rationale: The watt (W) is the unit of electrical power. One watt equals one volt times
one ampere. The volt is the unit of potential difference, the ampere is the unit of current,
and the ohm is the unit of resistance.
9. Which of the following is a fundamental safety rule for electrical work?
A. Always work on live circuits to save time
B. Always de-energize circuits before working on them
C. Never use lockout/tagout procedures
D. Only wear safety glasses when working with high voltage
Answer: B
Rationale: The most fundamental safety rule is to always de-energize circuits before
working on them. Lockout/tagout procedures should be used to ensure circuits remain
de-energized. Live work should be avoided unless absolutely necessary and only by
qualified personnel.
10. What is the purpose of the grounded conductor in a residential electrical
system?
A. To carry current under normal conditions and provide a path to ground
B. To carry fault current only
C. To provide a return path for current under normal conditions
D. To act as the primary overcurrent protection
Answer: C
Rationale: The grounded conductor (neutral or white wire) provides a return path for
