A pilot light for an industrial control panel must be installed in a hazardous location where flammable gases are present during normal operations. Which wiring method is generally required for such a location, according to NEC Article 500?
- ARigid PVC Conduit (PVC)
- BFlexible Metal Conduit (FMC)
- CElectrical Metallic Tubing (EMT)
- DSealed Rigid Metal Conduit (RMC)
Show answer & explanationAnswer & explanation
Correct answer: D. Sealed Rigid Metal Conduit (RMC)
Hazardous locations with flammable gases present during normal operations (Class I, Division 1) require robust wiring methods to contain explosions and prevent ignition. NEC Article 501.10(A) generally mandates the use of threaded RMC or IMC, or other listed wiring methods, with all joints made up tight and explosionproof fittings. EMT, PVC, and FMC are typically not permitted in such locations without extensive additional protection or specific listing, which is rare for general purpose variants.
Why the other options are wrong
- A. PVC conduit is generally not permitted in Class I, Division 1 locations as it is not explosionproof.
- B. FMC is generally not permitted in Class I, Division 1 locations, as it does not provide the necessary explosion containment.
- C. EMT is not permitted in Class I, Division 1 locations due to its non-threaded connections and thin walls.
Hazardous Location Wiring (Class I, Div 1)
Wiring methods in Class I, Division 1 hazardous locations (where ignitable concentrations of flammable gases or vapors exist under normal operating conditions) must be explosionproof to contain internal explosions and prevent ignition of the surrounding atmosphere.
- Governed by NEC Article 501
- Requires explosionproof wiring methods
- Threaded RMC/IMC with explosionproof fittings is common
Memory trick: In Class One, Division One, only Robust, Resilient Raceways Rule.