309A Wiring Methods and Materials 6 — Questions and Answers
Question 1: What type of conduit is required for a concrete-encased underground duct bank?
- EMT only
- Flexible conduit
- PVC Schedule 40 or rigid metal conduit (Correct answer)
- Liquid-tight flexible conduit
Correct answer: PVC Schedule 40 or rigid metal conduit
Concrete-encased duct banks typically use PVC Schedule 40 conduit for its corrosion resistance and smooth interior, or rigid metal conduit where additional mechanical protection is needed.
Question 2: What is the CEC requirement for identifying conductors that have been re-identified from their original colour?
- Paint the entire length a new colour
- Apply tape or markers at each end and at every accessible point (Correct answer)
- No re-identification is permitted
- Only label at the panel end
Correct answer: Apply tape or markers at each end and at every accessible point
When re-identifying conductors (such as marking a white conductor as a switch leg), the CEC requires identification at each end and at every point where the conductor is accessible.
Question 3: What is the minimum bending radius for NMD90 cable?
- 3 times the cable diameter
- 5 times the cable diameter (Correct answer)
- 7 times the cable diameter
- 10 times the cable diameter
Correct answer: 5 times the cable diameter
The CEC requires a minimum bending radius of 5 times the overall diameter of NMD90 cable to prevent damage to the conductors and insulation during installation.
Question 4: According to the CEC, what is the maximum height above finished floor for a receptacle outlet in a dwelling unit without being considered out of reach?
- 1200 mm
- 1500 mm
- 1700 mm (Correct answer)
- 2000 mm
Correct answer: 1700 mm
Receptacles mounted above 1700 mm are generally considered out of reach for standard accessibility. The CEC and building codes set this as a practical limit for general-purpose outlets.
Question 5: What material is the armour of AC90 cable typically made from?
- Steel
- Aluminium (Correct answer)
- Copper
- Stainless steel
Correct answer: Aluminium
AC90 cable armour is typically made from interlocking aluminium strips, which provide mechanical protection while being lighter and more corrosion-resistant than steel armour.
Question 6: What is the CEC requirement for supporting horizontal runs of rigid PVC conduit?
- Every 0.9 m for all sizes
- Every 1.5 m for all sizes
- According to Table 12-22 based on conduit size (Correct answer)
- Every 3.0 m for all sizes
Correct answer: According to Table 12-22 based on conduit size
CEC Table 12-22 specifies support spacing for PVC conduit based on trade size, with smaller sizes requiring more frequent support. The spacing ranges from 1.2 m to 2.4 m depending on size.
309A Wiring Methods and Materials 6
What type of conduit is required for a concrete-encased underground duct bank?