64 Modern Commercial Wiring Copyright Goodheart-Willcox Co., Inc. 5.1.1 Rules for Buried Conductors Conduit, cables, and other raceways that are bur- ied must meet specifi c criteria. The conductors must be protected so that damage does not occur. Table 300.5 of the Code lists the minimum burial depth for conductors 1000 volts nominal or less. The table in Figure 5-3 is a condensed version of Table 300.5. Deeper burial is not uncommon due to soil conditions, interferences with other utilities, and structural footings. Cables under buildings must be installed in a raceway, and the raceway must extend past the exterior walls of the building. Further, where buried conductors and cables emerge from the ground, protection must be provided by race- ways that extend from the minimum cover dis- tance to at least 8′ above grade or to the point of entry into a building. See Figure 5-4. At the point where underground conductors emerge from a raceway, the raceway should be fi tted with a bushing or sealed. Regardless of the method of wiring used, all underground installations must be grounded and bonded as required by the Code. Refer CODE ALERT Protection for Underground Raceway According to Section 300.5(D)(4), where the enclo- sure or raceway is subject to physical damage, the conductors shall be installed in rigid metal conduit, intermediate metal conduit, RTRC-XW, or Schedule 80 PVC, or equivalent. to Chapter 10 of this text and Article 250— Grounding and Bonding of the Code. Splices and taps are permitted in buried con- ductors and cables. Be sure to use materials that are suitable for underground use. All splicing materials must be suitable for the conditions and environment in which they are installed. Goodheart-Willcox Publisher Figure 5-3. Condensed version of Table 300.5 from the Code. Minimum Burial Depths (1000 V or less) Location of Wiring Method or Circuit Cables or Conductors IMC or Rigid Metal Conduit Rigid Nonmetallic Conduit Below streets, alleys, and parking lots 24″ 24″ 24″ Below building slab or foundation (in raceway) 0″ 0″ 0″ In trench below 2″ thick concrete or equivalent 18″ 6″ 12″ Under one- or two-family dwelling driveway 18″ 18″ 18″ Conduit extends 8′ above ground or to point of entry into building Conduit extends down to minimum cover requirement (18″ max.) Bushing Goodheart-Willcox Publisher Figure 5-4. Conduit must be installed to protect cables and conductors emerging from underground.