A:  “As cables are bundled together, the inner conductors are not in free air and their ampacity is similar to conductors in a raceway. Therefore, to be conservative, a cable bundle of three cables should be subject to the ampacity limitations of Table 310.15(B)(16) which is used for up to three conductors in a raceway. Since outdoor ambient design temperatures are generally above 30 degrees C for most of the United States, an additional correction factor for temperature should be applied according to Table 310.15(B)(2)(a).

For more than three cables in a bundle, Table 310.15(B)(3)(a) should adjust the ampacity further. This may be a conservative interpretation, but the NEC is not specific on this issue.” Further detailed information on this subject is covered on page 9 in Bill Brooks White Paper.  – Bill Brooks, P.E., White Paper: Cable Management in Solar PV Arrays, Page 9, Jan. 16, 2014