309A Wiring Methods and Materials 3 — Questions and Answers
Question 1: What is the main purpose of using armoured cable (AC90) in a commercial installation?
- To reduce electromagnetic interference
- To provide mechanical protection and grounding continuity (Correct answer)
- To increase the ampacity of the conductors
- To allow installation in hazardous locations
Correct answer: To provide mechanical protection and grounding continuity
AC90 armoured cable provides mechanical protection through its interlocking aluminium armour and also serves as an equipment grounding path, combining two functions in one cable assembly.
Question 2: According to the CEC, what is the minimum trade size of conduit that may contain a No. 6 AWG conductor?
- 16 mm (1/2")
- 21 mm (3/4") (Correct answer)
- 27 mm (1")
- 35 mm (1-1/4")
Correct answer: 21 mm (3/4")
Based on CEC conduit fill tables, a minimum 21 mm (3/4") trade size conduit is required for a No. 6 AWG conductor to comply with fill requirements.
Question 3: What is the purpose of an expansion fitting in a PVC conduit run?
- To change direction in the conduit run
- To provide a pull point for conductors
- To accommodate thermal expansion and contraction (Correct answer)
- To transition from PVC to metal conduit
Correct answer: To accommodate thermal expansion and contraction
PVC conduit expands and contracts significantly with temperature changes. Expansion fittings allow the conduit to move without stressing joints or distorting the raceway.
Question 4: What is the minimum depth of a device box for a receptacle installation?
- 19 mm (3/4")
- 25 mm (1")
- 38 mm (1-1/2") (Correct answer)
- 50 mm (2")
Correct answer: 38 mm (1-1/2")
The CEC requires a minimum box depth of 38 mm (1-1/2") for device boxes to provide adequate space for conductor splicing, device mounting, and heat dissipation.
Question 5: When installing conductors in a vertical raceway, at what height intervals must they be supported?
- Every 3 m for No. 14 to No. 1/0 AWG
- Every 5 m for all conductor sizes
- According to CEC Table 12-18 based on conductor size (Correct answer)
- No support is required in vertical raceways
Correct answer: According to CEC Table 12-18 based on conductor size
CEC Table 12-18 specifies support intervals for conductors in vertical raceways based on conductor size. Larger conductors require more frequent support due to their greater weight.
Question 6: What is the minimum size of copper bonding jumper required across a raceway expansion joint?
- Same size as the largest conductor in the raceway
- Same size as the equipment grounding conductor (Correct answer)
- No. 6 AWG minimum
- No. 8 AWG minimum
Correct answer: Same size as the equipment grounding conductor
The bonding jumper across an expansion joint must be at least the same size as the equipment grounding conductor required for the circuit to maintain grounding continuity.
309A Wiring Methods and Materials 3
What is the main purpose of using armoured cable (AC90) in a commercial installation?