Understanding NEC Article 515: Bulk Storage Plants

NEC Article 515 outlines safety requirements for electrical systems in facilities that store or blend flammable liquids in bulk for distribution. These facilities handle liquids received via tank vessels, pipelines, or vehicles and distribute them through various methods, such as tank vehicles or containers.

Scope of Article 515

Article 515 applies to:

• Indoor and outdoor bulk storage tanks.
• Facilities handling flammable liquids like gasoline or liquefied natural gas (LNG).
• Storage, loading, and offloading operations at tank vehicles, piers, and wharves.

Exclusions: Retail fuel dispensing stations fall under Article 514.

Key Requirements for Bulk Storage Plants

1. Area Classification
   Classified areas depend on the likelihood of flammable vapor presence:
   • Class I, Division 1 or Zone 1: Areas near equipment where flammable vapors are present during normal operations, such as inside tanks.
   • Class I, Division 2 or Zone 2: Adjacent areas where vapors may be present under abnormal conditions, such as 3 feet to 10 feet around tanks or vents.
   Unclassified Locations: Areas where sufficient barriers or ventilation mitigate vapor hazards.

2. Wiring and Equipment
   • Wiring methods must meet the requirements of Article 501 (Division system) or Article 505 (Zone system).
   • Fixed equipment near classified locations must be explosionproof or prevent the escape of sparks.
   • Underground wiring must use rigid metal conduit (RMC) or equivalent with appropriate seals to prevent vapor migration.

3. Sealing and Ventilation
   • Sealing is required at boundaries of classified areas and at underground wiring points.
   • Adequate ventilation can reduce the extent of classified locations.

4. Special Equipment
   • Tank Vehicles and Drums: Classifications apply during loading and unloading, with areas around domes or vents being Class I locations.
   • Pumps and Valves: Typically classified within a 3-foot radius.
   • Piers and Wharves: Additional classifications apply based on construction type (e.g., closed or open docks).

5. Grounding and Bonding
   • All metal raceways, enclosures, and equipment must be grounded to prevent static discharges.
   • Bonding is critical during loading and unloading operations to ensure continuous electrical connection.

Applications

Bulk storage plants serve industries like:

• Petroleum Distribution: Gasoline, diesel, and aviation fuel storage.
• Chemical Manufacturing: Large-scale solvent handling.
• LNG Terminals: Receiving and distributing liquefied gases.

Conclusion

NEC Article 515 provides a robust framework for managing electrical hazards in bulk storage plants. By addressing area classification, wiring, grounding, and sealing, the article ensures the safe handling and storage of flammable liquids.