Temporary Wiring -- Art. 305
Choose the best answer:
1. If you must provide a 60A, 120/240V temporary feeder for work on the 15th floor of a high-rise building under construction, which of the following cabled wiring methods could you use?
a. Type MC cable
b. Type NM cable
c. Type G cord
d. Two of the above
e. All of the above
2. On the construction site in the previous question, how could you wire temporary lighting?
a. Type SJT cord
b. Single-conductor festoon-style assemblies
c. Type NM cable
d. Two of the above
e. All of the above
3. How could you secure the temporary lighting conductors in Question 2, and at what minimum intervals?
a. Cable ties, as per applicable article
b. Cable ties, as required to prevent damage
c. Staples, as per applicable article
d. Staples, as required to prevent damage
e. Both “a” and “c”
f. Both “b” and “d”
4. If you’re in charge of running the temporary wiring for Christmas decorations in your town, which of the following requirements doesn’t apply if you’re planning to reuse last year’s single-conductor festoon make-ups?
a. Voltage to ground not over 150V
b. Installed out of range of likely damage
c. Remove in less than 90 days.
d. None of the above; they all apply.
5. Which of the following statements applies to a 30A, 120V branch circuit for a table saw supplied by the feeder in the first question?
a. Outlet (or cord) must have GFCI protection.
b. GFCI device (if not part of the branch-circuit protection) must open if grounded conductor loses continuity.
c. Both of the above
d. None of the above
6. Suppose you have 60A, 480V pin-and-sleeve receptacles for specialized maintenance equipment you must connect at various places within an industrial plant. What protective arrangements must you make? Answer based on a practical, not theoretical basis.
a. GFCI protection
c. Either “a” or “b”
d. Neither “a” nor “b”
Answers and Discussion
1. e, Sec. 305-4(b). Any of those wiring methods work, since none of them involves single conductors. This subsection specifically recognizes flexible cord suitable for hard or extra hard usage, as well as Type NM cable—regardless of the building height.
2. d, Sec. 305-4(c). Here again, a similar rule as the one for feeders disallows methods using single conductors. The restriction even applies to factory make-ups using molded taps and plastic cages around the light bulbs.
3. f, Sec. 305-4(j). For temporary wiring, use any support interval that works to keep the cord or cables off the floor and out of trouble. You can use staples or cable ties to do this, as well as strapping or other methods that don’t damage the wiring.
4. d, Sec. 305-4(c), Sec. 305-3(b). When the Code disallowed single-conductor make-ups for temporary lighting in the 1996 NEC, the substantiation focused on construction sites. The 1996 NEC rule, however, inadvertently applied to all temporary use except use for emergencies and tests. The 1999 NEC corrected this by restoring a limited allowance for the seasonal use category.
5. c, Sec. 305-6(a). The threshold for mandated GFCI protection goes up in the 1999 NEC from 125V 20A to 125V 30A. In addition, the GFCI protection, if downstream from the branch circuit or permanently wired outlet protection, has to be listed and “identified for portable use.” This means, unlike conventional GFCI devices, it includes a normally open relay that fails open if the grounded conductor opens. For example, if you put a conventional GFCI receptacle in a handy box and feed it with a cord, you haven’t complied with this provision. If the grounded conductor opens, the conventional GFCI fails closed, with shock potential still at the tool. Meanwhile, the worker likely assumes that since the tool isn’t operating, the GFCI must have tripped, and it’s safe to work on the tool.
6. b, Sec. 305-6(b). Forget conventional GFCI approaches. At this voltage, 5mA currents exceed safe values for shock protection. Lower values, however, would frequently nuisance trip. Although there are residual current devices available for 480Y/277V systems, they trip in the range of 30mA, and you can’t use them for shock protection. AEGCP is the only option.