Commercial Electrical Contractor License
Exam Practice Questions And Correct
Answers (Verified Answers) Plus Rationales
2025|2026 Q&A | Instant Download Pdf
1. Which type of wiring is typically used for commercial branch circuits?
a) Non-metallic sheathed cable
b) Metal-clad (MC) cable
c) Romex cable
d) Knob-and-tube wiring
Rationale: MC cable is commonly used in commercial settings due to
its durability and code compliance.
2. The purpose of a ground fault circuit interrupter (GFCI) is to:
a) Protect against overcurrent
b) Reduce voltage fluctuations
c) Prevent electrical shock by detecting ground faults
d) Increase current flow
Rationale: GFCIs protect people by detecting leakage current to
ground and shutting off power quickly.
,3. What is the minimum working space required in front of electrical
panels?
a) 18 inches
b) 24 inches
c) 36 inches
d) 48 inches
Rationale: NEC 110.26 requires 36 inches of clear working space in
front of panels.
4. In commercial wiring, the typical voltage for branch circuits is:
a) 120/208V or 277/480V
b) 120V only
c) 120/208V or 277/480V
d) 240V only
Rationale: Commercial buildings commonly use three-phase systems
at 208Y/120V or 480Y/277V.
5. Which conduit type is non-metallic and used for underground
installations?
a) EMT
b) PVC
c) IMC
d) RMC
Rationale: PVC is resistant to corrosion and suitable for direct burial
applications.
,6. The main purpose of a bonding conductor is to:
a) Carry normal load current
b) Ensure electrical continuity and safety
c) Increase voltage
d) Reduce resistance of conductors
Rationale: Bonding connects metal parts to the grounding system to
prevent shock hazards.
7. What is the maximum allowable voltage drop for feeder circuits?
a) 1%
b) 2%
c) 3%
d) 5%
Rationale: NEC recommends a maximum total voltage drop of 5%
(combined feeder and branch circuits) for efficiency.
8. Which type of overcurrent protection is suitable for motors?
a) Standard fuses
b) Motor circuit breakers or overload relays
c) GFCI breakers
d) AFCI breakers
Rationale: Motors require protection against overloads, typically
with dedicated breakers or relays.
9. In commercial lighting, high-intensity discharge (HID) lamps are often
used for:
, a) Residential kitchens
b) Warehouses and large areas
c) Bathrooms
d) Bedrooms
Rationale: HID lamps provide high lumen output suitable for large
commercial spaces.
10. The ampacity of a conductor is determined by:
a) Voltage
b) Conduit type only
c) Conductor size, insulation type, and temperature rating
d) Circuit length only
Rationale: Ampacity depends on wire gauge, insulation, and
installation conditions.
11. Which NEC article covers commercial panelboards?
a) Article 210
b) Article 408
c) Article 250
d) Article 310
Rationale: Article 408 specifies panelboard construction, installation,
and overcurrent protection.
12. The primary function of a transformer in commercial wiring is to:
a) Increase current
b) Change voltage levels
Exam Practice Questions And Correct
Answers (Verified Answers) Plus Rationales
2025|2026 Q&A | Instant Download Pdf
1. Which type of wiring is typically used for commercial branch circuits?
a) Non-metallic sheathed cable
b) Metal-clad (MC) cable
c) Romex cable
d) Knob-and-tube wiring
Rationale: MC cable is commonly used in commercial settings due to
its durability and code compliance.
2. The purpose of a ground fault circuit interrupter (GFCI) is to:
a) Protect against overcurrent
b) Reduce voltage fluctuations
c) Prevent electrical shock by detecting ground faults
d) Increase current flow
Rationale: GFCIs protect people by detecting leakage current to
ground and shutting off power quickly.
,3. What is the minimum working space required in front of electrical
panels?
a) 18 inches
b) 24 inches
c) 36 inches
d) 48 inches
Rationale: NEC 110.26 requires 36 inches of clear working space in
front of panels.
4. In commercial wiring, the typical voltage for branch circuits is:
a) 120/208V or 277/480V
b) 120V only
c) 120/208V or 277/480V
d) 240V only
Rationale: Commercial buildings commonly use three-phase systems
at 208Y/120V or 480Y/277V.
5. Which conduit type is non-metallic and used for underground
installations?
a) EMT
b) PVC
c) IMC
d) RMC
Rationale: PVC is resistant to corrosion and suitable for direct burial
applications.
,6. The main purpose of a bonding conductor is to:
a) Carry normal load current
b) Ensure electrical continuity and safety
c) Increase voltage
d) Reduce resistance of conductors
Rationale: Bonding connects metal parts to the grounding system to
prevent shock hazards.
7. What is the maximum allowable voltage drop for feeder circuits?
a) 1%
b) 2%
c) 3%
d) 5%
Rationale: NEC recommends a maximum total voltage drop of 5%
(combined feeder and branch circuits) for efficiency.
8. Which type of overcurrent protection is suitable for motors?
a) Standard fuses
b) Motor circuit breakers or overload relays
c) GFCI breakers
d) AFCI breakers
Rationale: Motors require protection against overloads, typically
with dedicated breakers or relays.
9. In commercial lighting, high-intensity discharge (HID) lamps are often
used for:
, a) Residential kitchens
b) Warehouses and large areas
c) Bathrooms
d) Bedrooms
Rationale: HID lamps provide high lumen output suitable for large
commercial spaces.
10. The ampacity of a conductor is determined by:
a) Voltage
b) Conduit type only
c) Conductor size, insulation type, and temperature rating
d) Circuit length only
Rationale: Ampacity depends on wire gauge, insulation, and
installation conditions.
11. Which NEC article covers commercial panelboards?
a) Article 210
b) Article 408
c) Article 250
d) Article 310
Rationale: Article 408 specifies panelboard construction, installation,
and overcurrent protection.
12. The primary function of a transformer in commercial wiring is to:
a) Increase current
b) Change voltage levels
