CSLB C-10 Electrical ContractorWiring Methods and MaterialsMedium
A pilot light for an industrial control panel must be installed in a hazardous location where ignitable fibers are present. The wiring method must be suitable for such an environment. Which of the following wiring methods is generally NOT permitted in a Class III, Division 1 hazardous location?
- AThreaded Intermediate Metal Conduit (IMC)
- BElectrical Metallic Tubing (EMT)
- CRigid Metal Conduit (RMC)
- DType MC Cable with a gas/vapor-tight jacket
Show answer & explanationAnswer & explanation
Correct answer: B. Electrical Metallic Tubing (EMT)
Electrical Metallic Tubing (EMT) is generally not permitted in Class III, Division 1 hazardous locations because its slip-joint couplings and non-threaded connections do not provide the necessary explosion-proof or dust-ignition-proof protection required. RMC, IMC, and specific types of MC cable are typically suitable when installed correctly with appropriate fittings.
Why the other options are wrong
- A. Threaded IMC, when properly sealed, is permitted in Class III, Division 1 hazardous locations.
- C. RMC, when properly threaded and sealed, is permitted in Class III, Division 1 hazardous locations.
- D. Specific types of Type MC cable with a gas/vapor-tight continuous corrugated metallic sheath are permitted in Class III, Division 1 locations.
Hazardous Location Wiring
Wiring methods in hazardous locations must prevent ignition of flammable gases, vapors, liquids, combustible dust, or ignitable fibers, requiring specialized conduit, cable, and sealing techniques.
- Hazardous locations are classified by type (Class I, II, III) and degree of hazard (Division 1, 2).
- Wiring methods like RMC, IMC, and certain MC cables are often permitted.
- EMT and flexible conduit (unless specific types) are typically restricted due to lack of sealed integrity.
Memory trick: Hazardous zones demand tough wires and seals, no flimsy stuff, that's how it feels.