Free E2 Hazardous (Classified) Locations Questions and Answers 1 — Questions and Answers
Question 1: According to NEC Article 500, a Class I, Division 1 location is a location in which ignitable concentrations of flammable gases or vapors can exist under which condition?
- Only during equipment maintenance or repair.
- Under normal operating conditions. (Correct answer)
- Only in the event of a catastrophic container failure.
- If they are stored in approved containers.
Correct answer: Under normal operating conditions.
NEC 500.5(B)(1) defines a Class I, Division 1 location as one where ignitable concentrations of flammable gases, vapors, or liquids can exist under normal operating conditions. Division 2 locations are those where such concentrations are present only under abnormal conditions, such as container failure or equipment breakdown.
Question 2: In a Class I, Division 1 location, a conduit seal shall be installed within what distance of a terminal or junction box that contains a switch, circuit breaker, or other arcing device?
- 6 inches
- 12 inches
- 18 inches (Correct answer)
- 24 inches
Correct answer: 18 inches
NEC 501.15(A)(1) requires that in Class I, Division 1 locations, a conduit seal shall be placed within 18 inches of any enclosure that contains arcing or high-temperature devices. This seal is critical to prevent an explosion from propagating through the conduit system.
Question 3: What does the temperature marking, or 'T-Code', on a piece of equipment used in a hazardous location signify?
- The maximum ambient temperature in which the equipment can operate.
- The type of hazardous material it is approved for.
- The maximum surface temperature the equipment will develop. (Correct answer)
- The time it takes for the equipment to cool down after shutdown.
Correct answer: The maximum surface temperature the equipment will develop.
As per NEC 500.8(C), the T-Code indicates the maximum surface temperature the equipment can reach during operation. This temperature must be less than the autoignition temperature of the specific hazardous substance present in the atmosphere to prevent ignition.
Question 4: Which of the following wiring methods is permitted in a Class II, Division 1 location?
- Electrical metallic tubing (EMT)
- Threaded rigid metal conduit (RMC) (Correct answer)
- Type MC cable without an overall nonmetallic jacket
- Open wiring on insulators
Correct answer: Threaded rigid metal conduit (RMC)
NEC 502.10(A) lists the permitted wiring methods for Class II, Division 1 locations, which involve combustible dust. Threaded rigid metal conduit (RMC) or intermediate metal conduit (IMC) are primary methods to prevent dust ingress and contain any potential internal issues.
Question 5: The fundamental principle of an intrinsically safe system as defined in NEC Article 504 is to:
- Contain any explosion within a robust enclosure.
- Limit the electrical energy to a level below that required to ignite a hazardous atmosphere. (Correct answer)
- Purge the enclosure with clean air to prevent hazardous gases from entering.
- Use only non-arcing components.
Correct answer: Limit the electrical energy to a level below that required to ignite a hazardous atmosphere.
NEC 504.2 defines an intrinsically safe circuit as one in which any spark or thermal effect is incapable of causing ignition of a mixture of flammable or combustible material in air. This is achieved by limiting the electrical energy (voltage and current) to levels below what is needed to cause ignition.
Question 6: A Class III location is hazardous because of the presence of:
- Flammable gases or vapors
- Combustible dust
- Flammable liquids
- Easily ignitable fibers or flyings (Correct answer)
Correct answer: Easily ignitable fibers or flyings
NEC 500.5(D) defines Class III locations as those that are hazardous because of the presence of easily ignitable fibers or flyings. These materials are not likely to be in suspension in the air in quantities sufficient to produce ignitable mixtures but can still pose a fire hazard.
Free E2 Hazardous (Classified) Locations Questions and Answers 1
According to NEC Article 500, a Class I, Division 1 location is a location in which ignitable concentrations of flammable gases or vapors can exist under which condition?