Yes, the ampacity of the conductors must be derated when multiple non-metallic sheathed cables are run through the same hole in a wall stud, ceiling, or floor joist.According to Article 310.15(B)(3)(a) of the National Electrical Code (NEC), when multiple conductors are contained within the same enclosure, the allowable ampacity of each conductor must be reduced by an amount based on the number of conductors contained within the enclosure. For non-metallic sheathed cable, the reduction factors are as follows: 2 conductors: 80% of the allowable ampacity 3 conductors: 70% of the allowable ampacity 4 conductors: 60% of the allowable ampacity 5-9 conductors: 50% of the allowable ampacity 10-20 conductors: 40% of the allowable ampacity 21-30 conductors: 30% of the allowable ampacity 31-40 conductors: 25% of the allowable ampacity Over 40 conductors: 20% of the allowable ampacityThis derating is necessary to account for the increased heat that is generated when multiple cables are bundled together. The heat can cause the insulation on the cables to break down, which can lead to electrical fires.For example, if you are running three non-metallic sheathed cables through the same hole in a wall stud, the ampacity of each conductor must be reduced by 70%. This means that if the allowable ampacity of each conductor is 15 amps, the actual ampacity of each conductor when bundled together will be 10.5 amps (0.7 x 15 amps). Flag for review