Journeyman Electrician Exam (NEC)Wiring Methods and MaterialsHard
An industrial electrician is installing a new control circuit in a hazardous location identified as Class II, Division 1. Which wiring method is generally permitted for this installation, assuming the area is dusty and potentially explosive?
- ARigid Metal Conduit (RMC) with threaded explosionproof fittings
- BElectrical Metallic Tubing (EMT) with compression fittings
- CFlexible Metal Conduit (FMC) with standard connectors
- DType NM cable (nonmetallic-sheathed cable)
Show answer & explanationAnswer & explanation
Correct answer: A. Rigid Metal Conduit (RMC) with threaded explosionproof fittings
Class II, Division 1 locations involve combustible dusts that are normally in the air or present in quantities sufficient to be ignitable. For these locations, NEC 502.10(A)(1) specifies wiring methods such as RMC, Intermediate Metal Conduit (IMC), or dusttight wireways, with all fittings and boxes listed for Class II, Division 1. Threaded explosionproof fittings are essential for RMC in such environments to prevent ignition of external dusts.
Why the other options are wrong
- B. Incorrect. EMT with compression fittings is not permitted in Class II, Division 1 locations because it does not provide the necessary dust-ignitionproof integrity.
- C. Incorrect. FMC with standard connectors is not permitted in Class II, Division 1 locations, as it does not offer the required dust-ignitionproof protection.
- D. Incorrect. Type NM cable is not permitted in hazardous locations due to its lack of mechanical protection and inability to contain explosions or prevent dust ingress.
Class II, Division 1 Wiring Methods
Specific wiring methods permitted by the NEC for locations where combustible dust is normally present or present in ignitable quantities.
- Focus on preventing dust ingress and containing internal explosions.
- Requires robust, sealed wiring methods.
- NEC Article 502 governs these requirements.
Memory trick: Dusty Zones Demand Durable Ducts.