Wiring Methods and Protection Flashcards
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Read the first 7 Wiring Methods and Protection flashcards as text
What is the minimum wire fill percentage allowed for a conduit containing three or more conductors per NEC Chapter 9, Table 1?
Answer: There is no minimum fill percentage
NEC Chapter 9, Table 1 only specifies maximum fill percentages (40% for 3+ conductors); there is no minimum fill requirement.
Underground service entrance conductors installed in rigid PVC conduit must have a minimum burial depth of how many inches in a residential application?
Answer: 24 inches
NEC Table 300.5 requires a minimum 24-inch cover for service entrance conductors installed in PVC conduit.
Per NEC 300.20, when AC circuits are installed in metal raceways, why must all conductors of the same circuit be in the same raceway?
Answer: To prevent inductive heating of the metal raceway
NEC 300.20 requires all conductors of a circuit in the same metal raceway to prevent inductive heating caused by unbalanced magnetic fields around the conduit.
Intermediate metal conduit (IMC) is distinguishable from RMC primarily by which characteristic?
Answer: IMC uses thinner walls and is lighter weight
IMC has thinner walls than RMC, making it lighter while still suitable for use in the same applications per NEC Article 342.
What is required when Type UF cable is used for direct burial and passes under a road or driveway?
Answer: The cable must be enclosed in Schedule 80 PVC or equivalent protection
NEC 340.10 and Table 300.5 require additional mechanical protection such as RMC, IMC, or Schedule 80 PVC when direct-buried cable is subject to vehicular traffic.
Where must bushings be installed when conductors enter a metal enclosure through a knockout?
Answer: At every knockout regardless of conductor size
NEC 300.4(G) requires an insulating fitting or bushing at every point where conductors enter a metal enclosure through a knockout to protect insulation from sharp edges.
When installing cable trays containing power conductors, what is the minimum clearance required above the tray for maintenance access per NFPA 70?
Answer: No specific clearance is mandated by the NEC
The NEC (Article 392) does not mandate a specific overhead clearance above cable trays, though OSHA and local codes may apply; the NEC focuses on fill, support, and installation rules.