Final answer:
The NEC stipulates a maximum fill ratio of 53% by cross-sectional area for a conduit with one cable, ensuring safe installation and adequate heat dissipation.
Step-by-step explanation:
The National Electrical Code (NEC), or NFPA 70, is a regionally adoptable standard for the safe installation of electrical wiring and equipment in the United States. It is part of the National Fire Code series published by the National Fire Protection Association (NFPA), a private trade association.
The NEC conduit fill chart specifies these maximum conduit fill percentages: Maximum fill for one conductor is 53% of the space in the conduit. Maximum fill for two conductors is 31%. Maximum fill for more than two conductors is 40% of the conduit.
This limit ensures that cables are not damaged during installation and that there is enough space within the conduit for heat dissipation. For installations using more than one cable, the maximum fill ratios change, typically decreasing as the number of cables increases.