Select the best answer. For the first three questions, assume both a 120/240V and a 480Y/277V service drop feed a building at two sets of distribution equipment (one for each voltage) located adjacent to each other.
1. For general loads, how many sets of service conductors could you install from this equipment? There are no overcurrent devices. Assume the equipment serves a single occupancy.
2. How many would you get if there were a fire pump fed from this equipment? Use the first question’s answers.
3. How many would you get if the equipment supplies a mixed-use building, with the single-phase service for five units of multifamily housing with a common alarm system, and the other service for commercial purposes (assuming no other loads)? Use the first question’s answer set.
4. Assuming 75°C copper conductors and terminations, what is the minimum size service entrance conductor allowable for a single-circuit load, such as a telephone booth?
a. No. 14
b. No. 12
c. No. 10
d. No. 8
e. No. 6
5. Assume a gas-heated cottage has a general–purpose lighting circuit, laundry circuit, bathroom receptacle circuit, and two small-appliance branch circuits, with a total load of 8400VA. What’s the smallest allowable 120/240V service for this building?
6. Which of the following devices could you use (within an enclosure) to splice No. 6 service conductors?
a. Twist-on wire connectors
b. Hydraulic-crimped butt splices
c. Landing lugs
d. Split-bolt connectors
e. Two of the above
f. More than two of the above
7. Which of the following wiring methods could you not use to wire a service riser above a meter socket. The socket sits above a small section of lawn adjacent to a walkway running between the garage and a single-family house.
a. SE cable
b. Schedule 40 PVC rigid nonmetallic conduit
c. Schedule 80 PVC rigid nonmetallic conduit
d. Two of the above
e. All of the above
f. None of the above
Answers and Discussion
1. b, Sec. 230-2(d); Sec. 230-40. You can always supply a building with multiple classes of service through separate services, each following the basic rule in Sec. 230-40. None of the exceptions applies here.
2. c, Sec 230-40 Ex. 5. Long overdue, this section now correlates with long-standing allowances in Sec. 230-82 for special loads permitted to be tapped from the principal service conductors. In this case, the fire pump load adds one to the total allowable number of service entrance conductor sets. Note that the reference (in the exception) to item “(3)” is an erratum in the first printing and has been corrected for subsequent printings; it should refer to “(4)”.
3. e, Sec. 230-40 Ex. 1 and 4. The first exception allows for a set of conductors to each occupancy: The fourth allows for the additional set you’ll need to install to the common area panel for the multifamily housing as covered in Sec. 210-25.
4. a, Sec. 230-42(b). Instead of the No. 12 minimum historically required, the 1999 NEC deleted all special sizing rules at this point, in favor of referring to Sec. 230-79. This causes some unexpected results, and this question is a good example. Sec. 230-79(a) requires a minimum disconnecting means of 15A for these circuits, and that effectively drags the minimum size downward from No. 12 to No. 14.
5. d, Sec. 230-79(c). Although this load profile would have qualified for generations for a 60A service, the 1999 NEC concluded the number of qualifying houses that might use this allowance was dwindling to the vanishing point. Now, the minimum size is 100A.
6. e, Sec. 230-46. Although you have a lot more flexibility in tapping service conductors in the 1999 NEC, you do need to use clamped or bolted connections. The phrase “clamped or bolted” also appeared in the 1996 NEC (in former Ex. 1) in the context of metering equipment. For underground connections, you need to use a splicing kit specifically listed for that duty.
7. f, Sec. 230-50(a). A cable riser above a lawn at a single-family home would be an unlikely subject for physical damage. The former wording, which specifically mentioned walkways, now only refers to a likelihood of damage. The inspector makes this determination in the field, but if you could use Type SE cable anywhere on this property, it would probably be here.