Solution:


By NEC Section 725.27(A) Table 402.5 must be used to determine the ampacities of fixture wire sizes for No. 16 and No. 18 when used on Class 1 circuits as defined in Article 725.  The ampacity of a No. 16 TFFN is given in Table 402.5 as 8 amperes.
1232
By NEC Section 725.28(A) Class 1 circuit conductors must be derated according to Section 310.15(B)(2)(a) if the conductors carry loads in excess of 10 percent of the ampacity of each conductor and where the total number of conductors is more than three. 10 % X 8 = .8 amperes; 3 amperes exceeds .8 amperes therefore derating is required.

By Table 310.15(B)(2)(a) the derating Factor for 6 conductors (assuming no diversity) is 80 %. .8 X 8 = 6.4 amperes.  The derated ampacity of the conductors is 6.4 amperes.

 
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