Code, Theory, and Calculations Flashcards
7 cards from real Licensed Electrical Contractor practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Code, Theory, and Calculations flashcards as text
According to NEC 430.52, what is the maximum rating of an inverse-time circuit breaker used as short-circuit protection for a 10 HP, 230 V, single-phase motor with a full-load current of 50 A?
Answer: 150 A
NEC Table 430.52 allows inverse-time breakers at 250% of FLC for single-phase motors; 50 A × 250% = 125 A, rounded up to the next standard size of 150 A.
What does the term 'demand factor' mean in electrical load calculations?
Answer: The ratio of the maximum demand to the total connected load
Demand factor is the ratio of the maximum demand of a system to the total connected load, accounting for the fact that not all loads operate simultaneously at full capacity.
Under NEC 700.12, emergency system power sources must be arranged to supply loads within:
Answer: 10 seconds
NEC 700.12 requires that emergency power sources supply power within 10 seconds of normal power failure.
Two capacitors of 20 µF and 30 µF are connected in series. What is the total capacitance?
Answer: 12 µF
Series capacitance: 1/Ct = 1/20 + 1/30 = 3/60 + 2/60 = 5/60, so Ct = 12 µF.
NEC 310.15(B)(3)(a) requires conductor ampacity correction when more than 3 current-carrying conductors are in a raceway. How does adding a 4th current-carrying conductor affect the allowed ampacity?
Answer: Reduce to 80% of the base ampacity
NEC Table 310.15(B)(3)(a) requires a 0.80 correction factor (80%) when 4 to 6 current-carrying conductors are bundled together.
In a 3-phase wye circuit, the relationship between line current (IL) and phase current (Iph) is:
Answer: IL = Iph
In a wye (Y) connection, each phase winding carries the full line current, so IL = Iph.
NEC 517.13 requires that patient care areas of health care facilities have a redundant grounding path using:
Answer: An insulated copper EGC in addition to the metal raceway
NEC 517.13 requires both the metal raceway AND an insulated copper EGC to provide a redundant grounding path in patient care areas.