Choose the best answer:
1. Assume qualified engineering staff and well-trained electrical maintenance personnel. How could they, as a practical matter, provide power for plastic shaping equipment that moves back and forth over a 5-ft span in a Class I Div. 1 environment? a. Liquidtight flex. metal conduit b. Fixed-length flexible Class I connection fittings c. Type SO cord d. More than one of the above
2. If the electrical supply (for Question 1) originates in another building and isn't regrounded at the building disconnect, even though there is a grounding electrode and grounding electrode conductor at that point, where could the facility use EMT with connectors and locknuts without additional bonding? The voltage is 208Y/120V. a. A branch circuit to the room b. A branch circuit for an unclassified area c. The feeder to the room panel d. The feeder to the building e. More than one of the above
3. Dust-ignitionproof (D-IP) enclosures in Class II locations must be installed such that dust won't get in. Which of the following methods can be used? a. Raceways running out of the classified location b. Raceways > 5 ft run downward c. Horizontal raceways > 10 ft d. Raceways running to other D-IP enclosures e. Raceways running up, but with sealing putty f. Four or fewer of the above g. All of the above
4. Suppose the room in the second question is classified Class I Div. 2 in all areas beyond the actual equipment. The owners import similar equipment, but listed Zone 1, for use in one corner of the room. What, at minimum, must happen next? a. Send the new equipment back b. Set up a Zone 1 area within the existing Div. 2 area c. Reclassify the entire room under the Zone system d. Answers "b" or "c" above
5. Assume the new equipment in the preceding question is marked "Ex e" (the designation for "increased safety") for Zone 1 use. Little, if any, of the machine components seem designed to contain explosions like Class I Div. 1 wiring. Which of the following wiring methods could be used for the supply to the new machine? a. Intermediate metal conduit b. EMT c. Rigid nonmetallic conduit d. Two of the above e. All of the above
6. Which of the wiring methods in the preceding question could be used within the floor slab of a new six-bay muffler and brake shop? The wiring will extend through the concrete slab comprising the garage floor, and then up to surface-mounted receptacles and other equipment.
ANSWERS AND DISCUSSION
1. c, Sec. 501-11. Formerly, this section allowed cord for portable lighting and equipment only. Now, with qualified engineering, maintenance, and supervision, it can be used on fixed equipment as well, provided there isn't a practical alternative for accommodating the amount of movement required. The cord can't be spliced, and it must be guarded.
2. b, Sec 501-16(a) (FPN No. 2). The point of the rule is to assure a highly reliable ground return path from the classified area in all points of the circuit where the equipment grounding conductor is part of that path. In this case, that is everywhere downstream of the main bonding jumper at the service. The local grounding electrode connection at the building disconnect serves other purposes.
3. g, Sec. 502-5. The seal function in dust environments is much different from what's required around gases and vapors. Dusts simply can't be allowed into these enclosures; gases and vapors are assumed to enter and periodically explode within their enclosures. This means Class I seals must contain an explosion. A Class II seal or one of the other methods judged equivalent by Code needs only exclude the dust.
4. c, Sec. 505-3. This is a trick question, since it relies on a tentative interim amendment (TIA) to the Code. It applies where locally adopted, or where the Code is adopted by reference. It accomplishes the stated panel intent that the Zone system is a stand-alone system. Div. 2 and Zone 2 boundaries may only touch but not overlap; a Zone 1 boundary can't touch or overlap a Div. 1 or Div. 2 area. The entire room, however, could be reclassified under the Zone system. This might be practical, since existing Div. 1 equipment can be used in Zone 1 locations, per Sec. 505-20(b) Ex. The reclassification must be controlled by a qualified PE, per Sec. 500-3.
5. a, Sec. 505-15(b). Class I Div. 1 wiring methods need to be used, even though the Zone 1 equipment typically, although not necessarily, won't be explosionproof.
6. d, Sec. 511-4 Ex. Now you can run rigid nonmetallic conduit within or under a floor slab in these locations, similar to gasoline stations (Sec. 514-8 Ex. 2) and bulk storage plants [Sec. 515-5(a)]. Unlike Sec. 501-4(a) Ex. 1, the conduit doesn't need to be encased in concrete.