Check 2002 NEC, 312.5(C) Cables. Where cable is used, each cable shall be secured to the cabinet, cutout box, or meter socket enclosure.
Exception: Cables with entirely nonmetallic sheaths shall be permitted to enter the top of a surface-mounted enclosure through one or more nonflexible raceways not less than 450 mm (18 in.) or more than 3.0 m (10 ft) in length, provided all the following conditions are met:
(a) Each cable is fastened within 300 mm (12 in.), measured along the sheath, of the outer end of the raceway.
(b) The raceway extends directly above the enclosure and does not penetrate a structural ceiling.
(c) A fitting is provided on each end of the raceway to protect the cable(s) from abrasion and the fittings remain accessible after installation.
(d) The raceway is sealed or plugged at the outer end using approved means so as to prevent access to the enclosure through the raceway.
(e) The cable sheath is continuous through the raceway and extends into the enclosure beyond the fitting not less than 6 mm (1/4 in.).
(f) The raceway is fastened at its outer end and at other points in accordance with the applicable article.
(g) Where installed as conduit or tubing, the allowable cable fill does not exceed that permitted for complete conduit or tubing systems by Table 1 of Chapter 9 of this Code and all applicable notes thereto.
FPN:See Table 1 in Chapter 9, including Note 9, for allowable cable fill in circular raceways.
See 310.15(B)(2)(a) for required ampacity reductions for multiple cables installed in a common raceway.
Joe Tedesco, NEC Consultant