A major revision to article 511, covering commercial repair and storage garages, appears in the 2008 National Electrical Code (NEC). The revision provides several new definitions, as well as major changes to Section 511.3 covering area classification of service and repair facilities for self-propelled vehicles in which volatile flammable liquids or gases are used for fuel. These self-propelled items include, but are not limited to, passenger automobiles, buses, trucks, tractors, motorcycles, four-wheeled all-terrain vehicles and similar vehicles.

Two definitions have been added to 511.2, one covering minor repair garages and one covering major repair garages. A minor repair garage is a building or portion of a building used for lubrication, inspection, and minor automotive maintenance work. Minor work includes engine tune-ups, replacement of parts, brake repairs, tire rotation, and fluid changes, such as oil, antifreeze, transmission fluids, brake fluids, and air conditioning refrigerants.

Major repair garages include buildings or portions of a building used for engine overhauls, painting, body and fender work and for repairs that require draining of the vehicle fuel tanks. Both major and minor repair garages may include floor spaces used for offices, parking or showrooms.

Based on Section 511.3, parking garages only used for parking or storage of vehicles are permitted to be unclassified, even though the vehicles contain flammable gases or liquids. In other locations, where Class I liquids or gaseous fuels are stored, handled or transferred, the electrical wiring and electrical equipment must be designed for a Class I, Division 1 or 2 hazardous (classified) location.

Where a commercial garage has an office, associated parking area or showroom that is adjacent to a Class I location, the Class I location does not extend beyond a wall, roof or solid partition that is not pierced by an opening that could permit gas or vapor to intrude into the unclassified area.

Major and minor repair garages, where motor fuels, flammable gases (natural gas, hydrogen or liquefied petroleum gas), and flammable liquids with a flash point below 38°C (100°F), such as gasoline, are dispensed into the fuel tanks of vehicles shall comply with Table 514.3(B)(1) in addition to any classification required by Article 511. At a minimum, the area extending in all directions from 3 feet of any fill or dispensing point at a major or minor repair garage is classified as a Class I, Division 2 area but also must comply with Article 514 for motor fuel dispensing facilities.

In major repair garages, the floor area can be considered to be unclassified where there is mechanical ventilation providing a minimum of four air changes per hour or 1 cubic foot per minute of exchanged air for each square foot of floor area across the entire floor area. This exhaust air must be taken at a point within 12 inches of the floor.

If ventilation is not provided, the entire floor up to 18 inches above the floor must be classified as Class I, Division 2. Where lighter-than-air gaseous fueled (natural gas or hydrogen) vehicles are repaired or stored, the area within 18 inches of the ceiling may be classified or not, depending on proper ventilation.

Where ventilation is provided, the ceiling area can be unclassified from a point not less than 18 inches from the highest point in the ceiling, if the ceiling has an exhaust of 1 cubic foot per minute per square foot of ceiling area at all times the building is occupied or when vehicles using lighter-than-air gaseous fuels are parked below this area. If proper ventilation is not provided, the area within 18 inches of the ceiling is classified as Class I, Division 2.

In minor repair garages, floor areas without pits, below-grade or subfloor work areas can be unclassified. Where pits, below-grade or subfloor work areas exist in service or lubrication rooms, ventilation may or may not be provided. Where mechanical ventilation is provided by a minimum of four air changes per hour or 1 cubic foot per minute of exchanged air for each square foot of floor area across the entire floor area, the area can be unclassified. This exhaust air must be taken at a point within 12 inches of the floor.

If ventilation is not provided, the floor area up to 18 inches above the pits, below-grade, or subfloor work areas and within 3 feet of the edge are classified as Class I, Division 2 areas. Unless gaseous fuels are being transferred, the ceiling areas are unclassified. Pit areas and subfloor areas also are unclassified where properly ventilated at 1 cubic foot per minute per square foot.

Because of all of these revisions, it’s vital that electrical contractors study Article 511 before attempting an installation in commercial garages.

ODE is a staff engineering associate at Underwriters Laboratories Inc., in Research Triangle Park, N.C. He can be reached at 919.549.1726 and [email protected].