A master electrician is performing an installation in a Class I, Division 2 hazardous location. The location is an outdoor area where flammable liquids are handled, but only in closed containers or systems, and are released only under abnormal conditions. Which of the following wiring methods is permitted in this specific hazardous location?
- AType NM cable (nonmetallic-sheathed cable) with proper sealing fittings.
- BRigid metal conduit (RMC) with threaded connections and explosionproof fittings.
- CType MC cable (metal-clad cable) with a gas/vaportight continuous corrugated metallic sheath and listed fittings.
- DOpen wiring on insulators with adequate spacing.
Show answer & explanationAnswer & explanation
Correct answer: C. Type MC cable (metal-clad cable) with a gas/vaportight continuous corrugated metallic sheath and listed fittings.
For Class I, Division 2 locations, NEC 501.10(B)(1) permits Type MC cable with a gas/vaportight continuous corrugated metallic sheath, an overall jacket, and listed termination fittings. RMC (Option B) is also permitted, but the description of 'explosionproof fittings' is typically associated with Division 1, although threaded connections are required. Type NM cable (Option A) and open wiring (Option C) are not permitted in hazardous locations.
Why the other options are wrong
- A. Type NM cable is generally not permitted in hazardous (classified) locations due to its lack of mechanical protection and inherent gas/vapor sealing capabilities.
- B. Rigid Metal Conduit (RMC) is permitted in Class I, Division 2 (501.10(B)(1)(2)), and threaded connections are required, but 'explosionproof fittings' are particularly emphasized for Division 1. For Division 2, sealing fittings are critical, but 'explosionproof' is a higher standard than strictly necessary for all fittings in Div 2.
- D. Open wiring is never permitted in hazardous (classified) locations due to the risk of ignition.
Class I, Div 2 Wiring (NEC)
In Class I, Division 2 hazardous locations (where flammable gases/vapors are present only under abnormal conditions), the NEC permits specific wiring methods like threaded rigid metal conduit or certain types of metal-clad (MC) cable designed to prevent ignition.
- Flammable gases/vapors present under abnormal conditions.
- Wiring methods prevent ignition from arcs/sparks.
- Permitted methods include RMC, IMC, certain types of MC and MI cable.
- Sealing fittings are crucial where conduits pass from hazardous to nonhazardous areas.
Memory trick: Hazardous Wiring: Division 2 means robust cable or threaded pipe, sealed where it counts.