National Electrical Code Top Ten Tips: Article 511 -- Commercial Garages, Repair and Storage
- The occupancies covered by Article 511 include locations used for
the service and repair of self-propelled vehicles (such as cars and
buses) that use flammable liquids or gases for fuel or for power [511.1].
- Article 511 distinguishes between major repair garages and minor
repair garages. The requirements that follow differ,
depending on which of these is the location of the installation. Oddly enough, the definitions of major repair and minor repair were removed from 511.2 (there is not a 511.2 with the 2020 revision), but do not appear in Article 100 even though the index says they do. Major repairs are non-routine tasks such as engine rebuilding, painting, or body work. Minor repairs are things like lubrication, tune-ups, fluid changes, and similar routine maintenance.
- If you store, handle, or transfer Class I fuels in a given area,
you must install electrical equipment in that area per Class I requirements
- Parking garages can be unclassified [511.3(A)], as long as they
don't double as some other area that is classified (e.g., fuel
- Floors, pits, and depression are critical areas, because liquids
and heavier-than-air gases can pool in low areas.
- Ceilings and any "inverted depressions" (e.g., spaces between
joists) in them are critical areas, because lighter than air gases
can accumulate in them.
- Areas adjacent to classified areas can be unclassified, if
flammable vapors are unlikely to be released and certain other
conditions are met [511.3(E)(1)].
- If a garage location is Class I per 511.3, wire it per Article
501 [511.4(A)]. If a garage location is Class I per 511.3, install only
equipment that conforms to Article 501 [511.4(B)].
- Installations above Class I locations must also meet certain
requirements [511.7], so don't think only of equipment in those locations.
- Table 511.3(C) tells you the extent of the classified location based on several parameters such as the Division and Zone. Table 511.3(D) tells you the extent of the classified location for major repair garages with lighter than air fuel.