Overview of Chapter 5
Chapter 5 addresses electrical installations in locations where conditions create risks beyond those found in ordinary occupancies. These include environments with flammable gases or dust, healthcare facilities where patients depend on electrical life-support equipment, and temporary construction sites. The rules in Chapter 5 supplement or modify the general requirements of Chapters 1 through 4.
Exam Tip: Hazardous location classification (Class, Division, Zone) and healthcare facility essential electrical systems are heavily tested topics. Focus on understanding the classification system rather than memorizing every specific rule.
Hazardous (Classified) Locations (Articles 500-516)
Hazardous locations contain concentrations of flammable gases, vapors, dust, or fibers that could ignite and cause an explosion or fire. The NEC provides two classification systems.
Class/Division System (Article 500)
- Class I: Locations where flammable gases or vapors are present.
- Class II: Locations where combustible dust is present.
- Class III: Locations where ignitable fibers or flyings are present.
Each class is divided into two divisions:
- Division 1: The hazardous material is present under normal operating conditions or frequently.
- Division 2: The hazardous material is present only under abnormal or fault conditions.
Zone System (Articles 505-506)
The Zone classification system is an alternative to the Class/Division system, aligned with international standards (IEC).
- Zone 0: Ignitable concentrations present continuously or for long periods.
- Zone 1: Ignitable concentrations likely under normal operation.
- Zone 2: Ignitable concentrations not likely under normal operation, only under abnormal conditions.
Wiring Methods in Hazardous Locations
- Division 1 locations typically require threaded rigid metal conduit (RMC) or mineral-insulated cable (MI).
- Division 2 locations permit a broader range of wiring methods including EMT and MC cable in certain conditions.
- All equipment must be approved for the specific class, division (or zone), and group of the hazardous material present.
Commercial Garages and Fuel Dispensing (Articles 511, 514)
Commercial Garages (Article 511)
Locations used for service and repair of self-propelled vehicles with volatile flammable liquids or gases require classified area designations:
- The area up to 18 inches above the floor is typically classified as Class I, Division 2 where lighter-than-air ventilation is not provided.
- Equipment located in classified areas must be suitable for the classification.
Motor Fuel Dispensing Facilities (Article 514)
- The area within the dispenser enclosure is Class I, Division 1.
- The area extending 20 feet horizontally from the dispenser and up to 18 inches above grade is Class I, Division 2.
- Underground wiring must be installed in threaded RMC or an approved alternative.
Healthcare Facilities (Article 517)
Article 517 establishes requirements to protect patients who may be connected to electrical equipment during medical procedures.
Essential Electrical Systems
Healthcare facilities require redundant power systems divided into branches:
- Life Safety Branch: Powers exit lighting, fire alarms, critical care lighting, and hospital communication systems. Must be restored within 10 seconds of power loss.
- Critical Branch: Supplies power to task illumination, receptacles in critical patient care areas, and selected equipment.
- Equipment System: Serves large equipment loads such as HVAC, elevators, and supply systems that can tolerate a brief delay before restoration.
Patient Care Areas
- General care areas: Require a minimum of two branch circuits, one from the normal system and one from the critical branch, plus an equipment grounding conductor.
- Critical care areas: Require additional redundancy with at least two branch circuits from the critical branch and a patient equipment grounding point at each bed location.
Key Requirement: The ground-fault protection required for service equipment is typically not permitted on the life safety branch to prevent nuisance tripping that could de-energize critical loads.
Assembly Occupancies (Article 518)
Assembly occupancies are buildings or portions of buildings designed for the gathering of 100 or more persons. Theaters, churches, restaurants, and conference halls fall under these provisions.
- Wiring methods are generally limited to metal raceways, nonmetallic raceways in concrete, MC cable, and MI cable.
- Nonmetallic-sheathed cable (NM) is generally not permitted in assembly occupancies.
- Portable switchboards and equipment used in theaters must have proper overcurrent protection and grounding.
Temporary Installations (Article 590)
Article 590 permits temporary electrical power and lighting during construction, remodeling, demolition, or similar activities.
- Temporary wiring is permitted for a period not to exceed 90 days for holiday decorative lighting and similar purposes.
- GFCI protection is required for all 125V, 15A and 20A receptacle outlets that are not part of the permanent wiring.
- Temporary wiring methods include NM cable, SE cable, and other approved methods, provided they are protected from physical damage.
Agricultural Buildings (Article 547)
Agricultural buildings present unique challenges due to corrosive atmospheres, moisture, and dust from animal confinement and feed processing.
- Wiring methods must be suitable for the corrosive environment and are often required to be nonmetallic or specifically rated for corrosive conditions.
- An equipotential plane is required in concrete-floor confinement areas to prevent dangerous step and touch voltages for livestock.
- A site-isolating device is required to disconnect the agricultural building from the main power source.
