The wiring methods for a class 1 circuit need to be in a Chapter three wiring method and comply with the applicable Articles of Chapter 3. (See 725.25)
Typically the conduit fill can't exceed 40% for over two conductors. Take a look at the xxx.22 sections of the conduit articles for conductor fill, these will direct you to Table 1, Chapter 9.
60% fill is only allowed for short conduit nipples less than 24" in length. (See Note 4 to Table 1, Chapter 9.)
Also pay attention to Notes (5) and (9) of Table 1, Chapter 9.
Chris