CPI Installation Techniques & Procedures 3 — Questions and Answers
Question 1: During cable tray installation, what minimum clearance above a cable tray is typically required for maintenance access?
- 3 inches
- 6 inches
- 12 inches (Correct answer)
- 18 inches
Correct answer: 12 inches
A minimum of 12 inches of clearance above cable trays is generally required by standards to allow for cable installation and future maintenance.
Question 2: A technician must install a wall-mounted bracket rated for 200 lbs. The stud finder shows studs 24 inches apart but the bracket only spans 18 inches. What is the best solution?
- Mount to drywall anchors only
- Use a backing board spanning two studs, then mount the bracket to the backing board (Correct answer)
- Reduce the load to 100 lbs
- Relocate the bracket until it aligns with studs
Correct answer: Use a backing board spanning two studs, then mount the bracket to the backing board
A backing board transfers load to two studs even when bracket spacing doesn't align with stud spacing, safely meeting the load rating.
Question 3: When installing flexible conduit (flex), what is the maximum unsupported length typically allowed between supports?
- 18 inches
- 3 feet (Correct answer)
- 6 feet
- 10 feet
Correct answer: 3 feet
The NEC generally requires flexible conduit to be supported at intervals not exceeding 4.5 feet (approximately every 3 feet in practice) and within 12 inches of each box.
Question 4: What technique should be used to prevent galvanic corrosion when fastening aluminum components to steel structure?
- Use stainless steel fasteners with no barrier
- Use an isolating washer or anti-corrosion coating between dissimilar metals (Correct answer)
- Apply standard machine oil
- Weld the connection instead
Correct answer: Use an isolating washer or anti-corrosion coating between dissimilar metals
Isolating washers or dielectric coatings prevent direct metal-to-metal contact, stopping the electrochemical reaction that causes galvanic corrosion.
Question 5: When mounting equipment on vibrating machinery, which mounting technique is essential to prevent fastener loosening?
- Over-torque the fasteners by 25%
- Use locking fasteners such as nylon insert nuts or thread-locking compound (Correct answer)
- Use standard hex nuts tightened by hand
- Apply tape over fastener heads
Correct answer: Use locking fasteners such as nylon insert nuts or thread-locking compound
Nylon insert nuts and thread-locking compounds resist vibration-induced rotation that causes standard fasteners to back out over time.
Question 6: What is the correct method for making a watertight conduit entry into an outdoor electrical enclosure?
- Insert conduit and seal with standard caulk
- Use a listed weatherproof conduit hub with gasket and seal all openings (Correct answer)
- Wrap conduit entry with electrical tape
- Leave a small gap for condensation drainage
Correct answer: Use a listed weatherproof conduit hub with gasket and seal all openings
Listed weatherproof hubs with gaskets and properly sealed openings maintain the enclosure's NEMA/IP rating and prevent moisture intrusion.
Question 7: When installing a ceiling fan rated at 35 lbs on an existing outlet box, what must the installer verify first?
- That the circuit breaker is 20 amps
- That the outlet box is rated for fan support (not just luminaire support) (Correct answer)
- That the room height is at least 8 feet
- That the fan blades are balanced
Correct answer: That the outlet box is rated for fan support (not just luminaire support)
Fan-rated boxes are designed to handle the combined weight and dynamic movement loads of a ceiling fan; standard light fixture boxes are not.
CPI Installation Techniques & Procedures 3
During cable tray installation, what minimum clearance above a cable tray is typically required for maintenance access?