Material Selection & Properties Flashcards
7 cards from real CAT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Material Selection & Properties flashcards as text
What characteristic of tinned copper wire makes it preferable to bare copper in marine or high-humidity alarm installations?
Answer: Corrosion resistance due to the tin coating protecting against oxidation
The tin plating on tinned copper wire acts as a barrier that prevents the copper from oxidizing when exposed to moisture and salt air.
In which scenario would a technician use armored cable (AC/MC) rather than standard NM cable for an alarm system run?
Answer: Commercial installation requiring physical protection from mechanical damage
Armored cable is used where cables are exposed to physical damage, such as in commercial mechanical rooms or exposed surface runs.
When a door contact reed switch is selected for a high-security application, which contact material offers the best resistance to arcing and contact erosion?
Answer: Rhodium or ruthenium-plated reed contacts
Rhodium and ruthenium platings on reed switch contacts provide exceptional hardness and resistance to arc erosion, extending contact life in demanding applications.
A technician installs a passive infrared (PIR) detector behind a glass window to protect an exterior area. Why will this typically not function as intended?
Answer: Standard glass blocks the 8–14 micron infrared wavelengths that PIR sensors detect
Standard glass is opaque to long-wave (8–14 µm) infrared radiation, which is the wavelength range PIR motion detectors sense, so the detector cannot see through it.
Which property determines how much a wire's resistance increases as its temperature rises?
Answer: Temperature coefficient of resistance (TCR)
The temperature coefficient of resistance (TCR) quantifies how much a conductor's resistance changes per degree of temperature change.
A cable specification calls for a foil shield with 100% coverage. What material is most commonly used for this foil?
Answer: Aluminum-polyester (Mylar) laminate tape
Aluminum-polyester (Mylar) laminate tape provides 100% coverage foil shielding that is lightweight and cost-effective for alarm and low-voltage cables.
Which type of conduit fitting must be used when transitioning rigid metal conduit (RMC) into a metal enclosure to protect wiring from sharp edges?
Answer: A conduit bushing or insulated throat fitting
A conduit bushing or insulated throat fitting covers the sharp cut edge of the conduit end inside the enclosure, protecting conductor insulation from abrasion.