Hidden within the rewrite of Articles 511 and 514—which cover repair garages for motor vehicles and motor fuel dispensing stations, respectively, in the 2005 National Electrical Code (NEC)—is a major change in the concept of hazardous (classified) locations. Gone are any references in these two articles to raceways buried beneath a concrete floor or directly buried in the earth as being in a hazardous (classified) location.
In a commercial garage, for example, Section 511.4(A)(1) of the 2002 NEC considered raceways embedded in a masonry wall or buried beneath a floor to be within the Class I location above the floor, if there were any connections or extensions that lead into or through the classified area.
There was no consideration for underground raceways located beneath the floor of a repair garage where the raceway penetrated the floor, entered into the garage area, but was unbroken for its entire length through the classified area.
Even though there was no probable way for gas, vapor or liquid to enter the raceway, the raceway was still assumed to be in a classified area. In other words, any raceway that penetrated the floor and then entered into this hazardous (classified) location was considered as being in a hazardous location.
An interesting side note to this requirement was located in an exception directly following Section 511.4(A)(1). This exception permitted rigid nonmetallic conduit that was buried under not less than 24 inches of cover to emerge through the concrete using threaded rigid metal or steel intermediate metal conduit for the last 24 inches or more.
This raceway was also considered to be subject to the requirements of a Class I location since it entered into the classified area. However, where the rigid nonmetallic conduit or any raceway, for that matter, was buried under the concrete floor and did not emerge through the floor, this raceway was not considered to be in a Class I area. This inconsistency was difficult to explain unless one assumed any flammable liquids that were spilled on the floor migrated through the floor and entered into the raceway somewhere in the sub-base under the concrete.
There were similar inconsistencies found in Section 514.8 in the 2002 NEC for any underground wiring in a motor fuel dispensing facility (gas station). This section stated that any portion of electrical wiring that is below the surface of a Class I, Division 1 or a Class I, Division 2 area was considered to be in a Class I, Division 1 location that shall extend to the emergence above grade.
In this particular case, just having the raceway installed underground below the Class I area meant this raceway was also considered to be subject to the classified area requirements.
In the 2005 NEC, both of these requirements have disappeared. The NFPA Technical Committee on Automotive and Marine Service Stations, the committee with jurisdiction of NFPA 30A, Code for Motor Fuel Dispensing Facilities and Repair Garages, has determined that “the space below the surface of a Class I, Division 1 or 2 location does not meet the literal definition of a Class I, Division 1 location, unless a pocket or void is left in the earth to collect air.”
In other words, there must be a certain amount of fuel mixed with the proper quantity of air to form an ignitable concentration in order to be a Class I, Division 1 location. In addition, there must be a source of ignition present to cause ignition of the mixture. Take any one of these items away and ignition will not occur.
If a flammable liquid were to migrate through the concrete and accumulate in proximity to the raceway, there still must be enough air to form an ignitable mixture. Properly compacted dirt or sub-base will not normally contain pockets or voids containing air.
Using the concept developed by the NFPA 30A Committee, Code-Making Panel 14 removed the hazardous classification requirements for underground raceway installations in Section 511.4 for repair garages and Section 514.8 for fuel dispensing locations.
Do not, however, mistakenly assume that raceways installed partially underground and partially above ground in a hazardous (classified) location are not subject to the requirements in Class I, Division 1 or 2 locations. This concept change only applies to the underground portion of the raceways.
Where any portion of electrical wiring is below the surface of a Class I, Division 1 or 2 locations, Section 514.8 still requires seal-off devices to be installed within 10 feet of the point of emergence of the raceway above grade.
Comparing the actual text in the 2005 NEC to the text in the 2002 NEC in Articles 511 and 514 should provide an electrical installer with an accurate understanding of the changes to these sections. EC
ODE is a staff engineering associate at Underwriters Laboratories Inc., in Research Triangle Park, N.C. He can be reached at 919.549.1726 or at firstname.lastname@example.org.