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
A 120 V circuit has a total resistance of 24 Ω. Using Ohm's Law, what is the current in the circuit?
Answer: 5 A
I = V ÷ R = 120 ÷ 24 = 5 A.
Under NEC Article 220, the general lighting load for a dwelling unit is calculated using a unit load of:
Answer: 3 VA per square foot
NEC Table 220.12 specifies 3 VA per square foot for the general lighting load in dwelling units.
The impedance of a series RLC circuit at resonance is equal to:
Answer: The resistance R only
At resonance, XL = XC, so they cancel, and the impedance equals only the resistance R.
NEC 230.23 states that service entrance conductors installed as open individual conductors overhead shall not be smaller than:
Answer: 8 AWG copper
NEC 230.23(A) requires a minimum of 8 AWG copper for overhead service entrance conductors installed as open conductors.
What is the apparent power (in kVA) of a 3-phase load drawing 40 A at 480 V?
Answer: 33.3 kVA
3-phase apparent power S = √3 × VL × IL = 1.732 × 480 × 40 ≈ 33,254 VA ≈ 33.3 kVA.
NEC 250.66 governs sizing of the grounding electrode conductor (GEC). For a service with 3/0 AWG copper service-entrance conductors, the minimum GEC size is:
Answer: 4 AWG copper
NEC Table 250.66 specifies a 4 AWG copper GEC for service-entrance conductors up to 3/0 AWG copper.
Per NEC 110.14(C)(1), terminals of equipment rated 100 A or less and 14 AWG through 1 AWG conductors shall be rated for use with conductors at:
Answer: 60°C or 75°C
NEC 110.14(C)(1) limits conductors connected to 60°C or 75°C rated terminals on equipment rated 100 A or less, regardless of the conductor's insulation rating.