De-rating of conductors

[tonype]

Does 310-15 apply to a bundle of cables tied together, tightly, with zip ties that are not in a conduit, cable tray or running through floor joists? My interpretation is yes. I saw an installation where up to 19 Type-NM's (minimum 12) were bundled together and routed above a garage door and along side the entire main beam in to the home. Total length was about 40 feet.

 

[augie47]

THey added a bit of wording in '08 {310.15(B)(2)} to help clarify that:

(a) More Than Three Current-Carrying Conductors in a Raceway or Cable. Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are installed without maintaining spacing for a continuous length longer than 600 mm (24 in.) and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(2)(a). Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor.

 

[infinity]

Does 310-15 apply to a bundle of cables tied together, tightly, with zip ties that are not in a conduit, cable tray or running through floor joists? My interpretation is yes. I saw an installation where up to 19 Type-NM's (minimum 12) were bundled together and routed above a garage door and along side the entire main beam in to the home. Total length was about 40 feet.

Sounds like bundling to me; therefore derating would need to be applied or the cables would need to be reinstalled with spacing between them.