What percentage fill is permissible when a conduit contains only one conductor?

When determining permissible conduit fill for a single conductor, the National Electrical Code (NEC) provides specific guidelines. For one conductor, the maximum fill percentage allowed is 53%. This limit is designed to ensure that there is adequate space for heat dissipation and to prevent overheating of the conductor. If more than one conductor were present, the allowable fill percentage would decrease due to the increased density within the conduit, which can lead to higher temperature rise and potential safety hazards.

Therefore, the permissible fill of 53% for a single conductor is reflective of the need for safety and functionality in electrical installations, making it the correct choice in this scenario.