CEI Hazardous Location Wiring 3 — Questions and Answers
Question 1: Which NEC article covers Class III hazardous locations involving ignitable fibers and flyings?
- Article 501
- Article 502
- Article 503 (Correct answer)
- Article 505
Correct answer: Article 503
Article 503 addresses Class III locations where easily ignitable fibers or flyings are present but not likely to be in suspension in hazardous quantities.
Question 2: In a Class I hazardous location, flexible connections to equipment must use which type of fitting?
- Standard liquid-tight flexible conduit
- Explosion-proof flexible fittings listed for the location (Correct answer)
- Standard flexible metallic conduit
- PVC-coated flexible conduit
Correct answer: Explosion-proof flexible fittings listed for the location
Flexible connections in Class I locations require fittings specifically listed as explosion-proof to maintain the integrity of the hazardous location wiring system.
Question 3: What is a Zone 0 hazardous location characterized by?
- Flammable gases present only during abnormal conditions
- Flammable gases present intermittently under normal operations
- Flammable gases present continuously or for long periods (Correct answer)
- No flammable gases expected
Correct answer: Flammable gases present continuously or for long periods
Zone 0 is the most hazardous zone where flammable concentrations exist continuously or for long periods during normal operation.
Question 4: When sealing Class I conduit runs, the sealing compound must have a minimum thickness equal to the trade size of the conduit or what minimum value?
- 5/8 inch (Correct answer)
- 3/4 inch
- 1 inch
- 1-1/4 inch
Correct answer: 5/8 inch
Per NEC 501.15(C), the sealing compound thickness must not be less than the trade size of the conduit and in no case less than 5/8 inch.
Question 5: Which type of motor is NOT permitted in a Class I, Division 1 location?
- Explosion-proof squirrel cage induction motor
- Totally enclosed pipe-ventilated motor
- Open drip-proof motor (Correct answer)
- Submerged motor in oil
Correct answer: Open drip-proof motor
Open drip-proof motors expose live parts and arcing contacts to the hazardous atmosphere and are not permitted in Class I, Division 1 locations.
Question 6: Class II, Group G hazardous locations involve which type of combustible dust?
- Metal dusts
- Carbon black and coal dust
- Grain dusts, flour, starch, and similar agricultural dusts (Correct answer)
- Sulfur and plastics
Correct answer: Grain dusts, flour, starch, and similar agricultural dusts
Group G includes grain dust, flour, starch, sugar, and other combustible dusts of agricultural origin that are less conductive than metal dusts.
Question 7: For a Class I, Division 2 location, which of the following wiring methods is acceptable?
- Type NM cable
- Threaded RMC or IMC (Correct answer)
- Type UF cable
- Open wiring on insulators
Correct answer: Threaded RMC or IMC
Threaded RMC or IMC is acceptable in Class I, Division 2 locations, along with other methods listed in NEC 501.10(B).
CEI Hazardous Location Wiring 3
Which NEC article covers Class III hazardous locations involving ignitable fibers and flyings?