E2 Special Occupancies 2 — Questions and Answers
Question 1: In a Class I, Division 1 location, which wiring method is specifically permitted by the NEC?
- Type NM cable in conduit
- Threaded rigid metal conduit (RMC) with listed fittings (Correct answer)
- Type MC cable with standard connectors
- PVC conduit with expansion fittings
Correct answer: Threaded rigid metal conduit (RMC) with listed fittings
NEC Article 501 requires threaded RMC or threaded steel intermediate metal conduit with listed fittings in Class I, Division 1 locations.
Question 2: Which of the following best describes a Class II, Division 1 location under NEC Article 502?
- An area where flammable gases exist continuously under normal conditions
- An area where combustible dust is in suspension in the air under normal operating conditions (Correct answer)
- An area where ignitable fibers are stored in open containers
- An area adjacent to a Class I location where vapors may occasionally drift
Correct answer: An area where combustible dust is in suspension in the air under normal operating conditions
Class II, Division 1 locations have combustible dust in suspension in the air continuously or intermittently under normal operating conditions.
Question 3: Under NEC Article 504, an intrinsically safe system is one in which any spark or thermal effect is incapable of causing ignition under which condition?
- Normal operation only
- Both normal and abnormal conditions as specified (Correct answer)
- Abnormal conditions only
- Startup and shutdown sequences only
Correct answer: Both normal and abnormal conditions as specified
Article 504 defines intrinsically safe systems as those where no spark or thermal effect can cause ignition under both normal and specified abnormal conditions.
Question 4: In a Class I, Zone 0 location per NEC Article 505, flammable concentrations of gases are present:
- Intermittently under abnormal conditions
- Only during equipment failure
- Continuously or for long periods under normal conditions (Correct answer)
- Periodically during maintenance operations
Correct answer: Continuously or for long periods under normal conditions
Zone 0 is the most hazardous classification under the Zone system, where flammable concentrations are present continuously or for long periods.
Question 5: When sealing fittings are required in a Class I conduit system at a boundary, where must the seal be installed?
- Within 36 inches of the enclosure
- Within 18 inches of the enclosure (Correct answer)
- At the panel or switchboard only
- At the midpoint of the conduit run
Correct answer: Within 18 inches of the enclosure
NEC 501.15 requires seals in Class I, Division 1 locations to be within 18 inches of the enclosure.
Question 6: Equipment installed in a Class I hazardous location must be marked to show which information as required by NEC 500.8?
- Voltage rating and ampacity only
- Class, Division or Zone, Group, and temperature class (T-code) (Correct answer)
- Manufacturer name and UL listing number only
- Conduit fill percentage and conductor insulation type
Correct answer: Class, Division or Zone, Group, and temperature class (T-code)
NEC 500.8 requires equipment markings to include the Class, Division or Zone, Group, and temperature class to ensure compatibility with the specific hazard.
Question 7: Class III locations under NEC Article 503 involve which type of hazard?
- Flammable liquids stored above their flash point
- Combustible metal dusts such as magnesium
- Ignitable fibers or flyings not likely to be in suspension (Correct answer)
- Vapors from paint mixing operations
Correct answer: Ignitable fibers or flyings not likely to be in suspension
Class III locations are those that are hazardous because of the presence of easily ignitable fibers or flyings but are not likely to be in suspension in air.
E2 Special Occupancies 2
In a Class I, Division 1 location, which wiring method is specifically permitted by the NEC?