CSLB C-10 Electrical ContractorEquipment and InstallationHard
A contractor is installing wiring for equipment inside a paint spray booth classified as a Class I, Division 1 hazardous location due to flammable vapors present under normal operating conditions. Which wiring method is required for this area per NEC Article 501?
- ANonmetallic-sheathed cable (Romex) in surface raceway
- BRigid metal conduit (RMC) or intermediate metal conduit (IMC) with threaded, explosion-proof sealed fittings
- CElectrical metallic tubing (EMT) with standard set-screw fittings
- DMetal-clad cable (MC) with standard connectors
Show answer & explanationAnswer & explanation
Correct answer: B. Rigid metal conduit (RMC) or intermediate metal conduit (IMC) with threaded, explosion-proof sealed fittings
NEC 501.10(A) requires that wiring methods in Class I, Division 1 locations be threaded rigid metal conduit or threaded intermediate metal conduit, with boxes, fittings, and joints made explosion-proof and sealed per 501.15 to prevent ignition of flammable vapors.
Why the other options are wrong
- A. Nonmetallic cable is prohibited in Class I, Division 1 due to fire/explosion risk from flammable vapors.
- C. EMT with set-screw fittings is not approved for Class I, Division 1 due to insufficient explosion containment.
- D. Standard MC cable connectors are not rated for explosion-proof sealing required in Division 1 areas.
Class I Division 1 Wiring
Locations where flammable gases/vapors are present under normal operating conditions require explosion-proof wiring methods per NEC Article 501.
- Threaded RMC or IMC required per 501.10(A)
- Seals required per 501.15 to prevent flame/gas propagation
- Division 2 areas allow some additional wiring methods with restrictions
Memory trick: Explosive vapors demand threaded, sealed steel conduit.