A commercial electrician is installing a new circuit in a Class I, Division 1 hazardous location. Which of the following wiring methods is NOT permitted for use in this type of hazardous location?
- AType MC cable with a gas/vapor-tight continuous corrugated metallic sheath
- BExplosionproof flexible metal conduit
- CThreaded rigid metal conduit (RMC)
- DLiquidtight flexible metal conduit (LFMC)
Show answer & explanationAnswer & explanation
Correct answer: D. Liquidtight flexible metal conduit (LFMC)
NEC 501.10(A) specifies the wiring methods permitted in Class I, Division 1 locations. Rigid metal conduit (RMC), intermediate metal conduit (IMC), and specific types of Type MC cable (with a gas/vapor-tight continuous corrugated metallic sheath, an overall jacket, and identified for the purpose) are permitted. Liquidtight flexible metal conduit (LFMC) is generally not permitted in Class I, Division 1 locations, except for specific short sections for flexibility where approved fittings are used, but it's not a primary wiring method for the full installation.
Why the other options are wrong
- A. Permitted. Specific types of MC cable are allowed, identified for the purpose, with a continuous corrugated metallic sheath and overall jacket (NEC 501.10(A)(1)(c)).
- B. Permitted. Explosionproof flexible metal conduit (typically using fittings listed for the purpose) is allowed for short flexible connections (NEC 501.10(A)(2)).
- C. Permitted. Threaded RMC is a common and approved wiring method for Class I, Division 1 locations (NEC 501.10(A)(1)).
Class I, Division 1 Wiring
Wiring methods in Class I, Division 1 hazardous locations must be explosionproof and designed to prevent the ignition of flammable gases or vapors.
- NEC 501.10(A) lists permitted wiring methods.
- Rigid metal conduit (RMC) and Intermediate metal conduit (IMC) with threaded connections are primary methods.
- Specific types of Type MC cable are also permitted.
- Flexible connections generally require explosionproof flexible fittings or listed flexible conduit.
Memory trick: RMC, IMC, MC are tough, LFMC is not enough!