309A Wiring Methods and Materials 2 — Questions and Answers
Question 1: What is the primary advantage of using MC (metal-clad) cable over NMD90 in commercial applications?
- Lower cost per metre
- Higher ampacity ratings
- Mechanical protection from the metal armour (Correct answer)
- Easier to install in residential settings
Correct answer: Mechanical protection from the metal armour
MC cable's interlocking metal armour provides superior mechanical protection compared to NMD90's non-metallic sheath, making it suitable for exposed commercial and industrial installations.
Question 2: What is the CEC requirement for supporting NMD90 cable within a distance of an electrical box?
- Within 150 mm
- Within 300 mm (Correct answer)
- Within 450 mm
- Within 600 mm
Correct answer: Within 300 mm
CEC Rule 12-510 requires NMD90 cable to be supported within 300 mm of every box, cabinet, or fitting to prevent strain on the connections.
Question 3: What type of raceway is most suitable for a corrosive chemical processing environment?
- EMT (Electrical Metallic Tubing)
- Rigid metal conduit (galvanized)
- PVC conduit (Schedule 40) (Correct answer)
- Flexible metal conduit
Correct answer: PVC conduit (Schedule 40)
PVC conduit is highly resistant to chemical corrosion and is the preferred raceway material in corrosive environments such as chemical processing plants.
Question 4: What is the maximum percentage fill for a wireway (auxiliary gutter) according to the CEC?
- 20%
- 40%
- 50%
- 75% (Correct answer)
Correct answer: 75%
CEC rules permit wireways to be filled to a maximum of 75% of their cross-sectional area at any point, providing more space than conduit but still allowing for adequate wiring access.
Question 5: When is it acceptable to use flexible metal conduit (FMC) as the sole equipment grounding conductor?
- When the conduit is 25 mm trade size or smaller and the circuit is 20 A or less (Correct answer)
- In all applications up to 60 A
- Only in dry locations regardless of size
- It is never acceptable as a grounding conductor
Correct answer: When the conduit is 25 mm trade size or smaller and the circuit is 20 A or less
The CEC permits FMC to serve as the equipment grounding conductor only when the trade size is 25 mm or smaller and the circuit overcurrent device rating does not exceed 20 A.
Question 6: What colour identification is required for a high-leg (wild leg) conductor in a 4-wire delta system?
- Red
- Blue
- Orange (Correct answer)
- Yellow
Correct answer: Orange
The CEC requires the high-leg conductor in a 4-wire delta system to be identified by an orange colour marking to warn electricians of its higher-than-expected voltage to neutral.
309A Wiring Methods and Materials 2
What is the primary advantage of using MC (metal-clad) cable over NMD90 in commercial applications?