CEI Hazardous Location Wiring 2 — Questions and Answers
Question 1: In a Class I, Division 1 location, which wiring method is permitted for fixed equipment?
- Type NM cable
- Threaded rigid metal conduit (RMC) (Correct answer)
- Type AC cable
- Electrical metallic tubing (EMT)
Correct answer: Threaded rigid metal conduit (RMC)
Threaded RMC is specifically approved for Class I, Division 1 locations because its threaded connections provide explosion-proof integrity.
Question 2: What does the 'T' temperature code on explosion-proof equipment indicate?
- Type of enclosure
- Maximum surface temperature the equipment can reach (Correct answer)
- Thermal insulation rating
- Tensile strength of housing
Correct answer: Maximum surface temperature the equipment can reach
The T-code (T1–T6) specifies the maximum surface temperature of the equipment, which must be below the ignition temperature of the hazardous atmosphere.
Question 3: Which NEC article primarily covers Class I, Zone 0, Zone 1, and Zone 2 hazardous locations?
- Article 500
- Article 501
- Article 505 (Correct answer)
- Article 510
Correct answer: Article 505
Article 505 covers Class I, Zone 0, 1, and 2 locations using the IEC zone system as an alternative to the Division system in Article 501.
Question 4: A seal fitting in a Class I hazardous location conduit run must be installed within how many inches of an explosion-proof enclosure?
- 6 inches
- 12 inches
- 18 inches (Correct answer)
- 24 inches
Correct answer: 18 inches
Per NEC 501.15, seals must be installed within 18 inches of explosion-proof enclosures to prevent flame propagation through conduit.
Question 5: Which Group classification applies to acetylene in hazardous location wiring?
- Group A (Correct answer)
- Group B
- Group C
- Group D
Correct answer: Group A
Acetylene is classified as Group A, the most sensitive group, due to its extremely low ignition energy and wide flammability range.
Question 6: In a Class II, Division 1 location involving combustible metal dusts, which equipment group applies?
- Group E (Correct answer)
- Group F
- Group G
- Group H
Correct answer: Group E
Group E covers metal dusts including aluminum, magnesium, and their commercial alloys, which are the most hazardous Class II materials.
Question 7: What is the primary purpose of intrinsically safe (IS) equipment in hazardous locations?
- To operate at higher voltages safely
- To limit energy below ignition levels under normal and fault conditions (Correct answer)
- To provide explosion-proof enclosures
- To replace explosion-proof enclosures with lighter housings
Correct answer: To limit energy below ignition levels under normal and fault conditions
Intrinsically safe equipment limits electrical and thermal energy so that sparks or heat cannot ignite the hazardous atmosphere even under fault conditions.
CEI Hazardous Location Wiring 2
In a Class I, Division 1 location, which wiring method is permitted for fixed equipment?