Free TN LLE Services, Feeders, Branch Circuits Questions and Answers — Questions and Answers
Question 1: An overhead service drop, with a voltage not exceeding 300V between conductors, passes over a residential roof with a 3-in-12 pitch. According to NEC 230.24(A), what is the minimum vertical clearance that must be maintained above the roof surface?
- 18 inches
- 3 feet
- 8 feet (Correct answer)
- 10 feet
Correct answer: 8 feet
NEC 230.24(A) generally requires an 8-foot vertical clearance over roofs. An exception exists for roofs with a slope of 4 in 12 or greater, which allows a reduction to 3 feet. Since the roof pitch is 3-in-12 (less than 4-in-12), the general requirement of 8 feet applies.
Question 2: An electrician is installing a 120/240V multiwire branch circuit to supply two separate kitchen countertop receptacle circuits. Which of the following is an NEC requirement for this type of circuit?
- The neutral conductor must be one size larger than the ungrounded conductors.
- The circuit must be protected by two single-pole breakers on the same phase.
- A means must be provided to simultaneously disconnect all ungrounded conductors. (Correct answer)
- The circuit is not permitted to supply kitchen countertop receptacles.
Correct answer: A means must be provided to simultaneously disconnect all ungrounded conductors.
NEC 210.4(B) requires that for multiwire branch circuits, a means must be provided to simultaneously disconnect all ungrounded conductors where the circuit originates. This is typically accomplished with a two-pole circuit breaker or two single-pole breakers with an approved handle tie.
Question 3: What is the minimum feeder conductor ampacity required for a load consisting of a 40-amp continuous load and a 30-amp noncontinuous load?
- 70 amps
- 80 amps (Correct answer)
- 87.5 amps
- 100 amps
Correct answer: 80 amps
According to NEC 215.2(A)(1), the feeder ampacity must be not less than the noncontinuous load plus 125% of the continuous load. Calculation: (1.25 x 40A) + 30A = 50A + 30A = 80A.
Question 4: According to NEC 230.70(A)(1), where must the service disconnecting means for a one-family dwelling be located?
- In the center of the building for shortest branch circuit runs.
- Only inside the attached garage.
- In a locked cabinet in the basement.
- At a readily accessible location either outside or inside nearest the point of conductor entrance. (Correct answer)
Correct answer: At a readily accessible location either outside or inside nearest the point of conductor entrance.
NEC 230.70(A)(1) mandates that the service disconnect be installed in a readily accessible location. This can be on the exterior of the building or just inside, nearest the point where the service conductors enter, to limit the amount of unprotected service conductor inside the structure.
Question 5: When calculating the load for a branch circuit supplying a fixed multioutlet assembly (e.g., plugmold) in a commercial building where appliances are not likely to be used simultaneously, what is the standard load allowance per section?
- 180 VA for every 1-foot section
- 180 VA for every 5-foot section or fraction thereof (Correct answer)
- 1500 VA for the entire assembly
- 600 VA for the first 10 feet and 180 VA for each additional 5 feet
Correct answer: 180 VA for every 5-foot section or fraction thereof
NEC 220.14(H)(1) specifies that for a fixed multioutlet assembly where simultaneous use is unlikely, each 5-foot section (or any fraction of a 5-foot section) is calculated at 180 volt-amperes.
Question 6: A main-lug-only (MLO) panelboard is installed as a subpanel in a workshop. According to NEC 408.36, which of the following is required?
- It must have a maximum of six circuit breakers.
- It must be protected by an overcurrent device on its supply side. (Correct answer)
- It must be located within sight of the service disconnect.
- It can only be used in residential occupancies.
Correct answer: It must be protected by an overcurrent device on its supply side.
NEC 408.36 requires that each panelboard be protected by an overcurrent protective device (OCPD). For a main-lug-only panel, this OCPD must be located on the supply side of the panelboard, typically the breaker in the main panel that feeds the subpanel.
Free TN LLE Services, Feeders, Branch Circuits Questions and Answers
An overhead service drop, with a voltage not exceeding 300V between conductors, passes over a residential roof with a 3-in-12 pitch.
According to NEC 230.24(A), what is the minimum vertical clearance that must be maintained above the roof surface?