CAT Material Selection & Properties 2 — Questions and Answers
Question 1: Which insulation material is most commonly used on wiring inside alarm control panels due to its flame-retardant properties?
- PVC (polyvinyl chloride) (Correct answer)
- Natural rubber
- Cotton braid
- Polyethylene foam
Correct answer: PVC (polyvinyl chloride)
PVC insulation is standard in alarm control panels because it is inherently flame-retardant and resists moisture.
Question 2: When selecting wire for a buried outdoor loop detector circuit, which material property is most critical?
- High tensile strength
- Direct burial-rated jacket with moisture resistance (Correct answer)
- Low capacitance
- Braided shielding
Correct answer: Direct burial-rated jacket with moisture resistance
Buried wiring must have a direct burial-rated jacket that resists moisture, soil chemicals, and physical abrasion.
Question 3: A technician needs conduit for an installation passing through a corrosive chemical storage area. Which material is the best choice?
- Rigid steel EMT
- PVC Schedule 40 conduit (Correct answer)
- Aluminum rigid conduit
- Flexible metallic conduit (FMC)
Correct answer: PVC Schedule 40 conduit
PVC conduit is chemically inert and will not corrode in environments with harsh chemicals.
Question 4: What is the primary reason THWN wire is preferred over THW wire for wet-location conduit runs?
- THWN has a higher ampacity rating
- THWN has a nylon outer jacket that resists moisture and pulling abrasion (Correct answer)
- THWN uses aluminum conductors
- THWN is rated for higher voltage
Correct answer: THWN has a nylon outer jacket that resists moisture and pulling abrasion
The 'N' in THWN stands for nylon, which adds a tough outer jacket suitable for wet locations and easier conduit pulling.
Question 5: Which conductor material has the highest electrical conductivity per unit cross-section?
- Aluminum
- Copper (Correct answer)
- Steel
- Tinned copper
Correct answer: Copper
Copper has higher electrical conductivity than aluminum, steel, or coated variants, making it the preferred conductor in alarm wiring.
Question 6: A motion detector mounting surface is a metal HVAC duct that vibrates. Which mounting hardware material best minimizes false alarms caused by vibration transmission?
- Zinc die-cast anchors
- Hard nylon standoffs
- Rubber-grommet isolation mounts (Correct answer)
- Stainless steel screws directly into duct
Correct answer: Rubber-grommet isolation mounts
Rubber-grommet isolation mounts absorb vibration, preventing mechanical movement from being transferred to the detector.
Question 7: For a fire alarm initiating device circuit (IDC) run in a plenum ceiling, the cable jacket must be rated as:
- CMR (Riser)
- CMP (Plenum) (Correct answer)
- CMG (General use)
- CM (Communications)
Correct answer: CMP (Plenum)
CMP-rated (Plenum) cable is required in air-handling spaces because it produces minimal smoke and toxic gases if burned.
CAT Material Selection & Properties 2
Which insulation material is most commonly used on wiring inside alarm control panels due to its flame-retardant properties?