What must be done to prevent the circulation of warm air to a colder section of a raceway or sleeve subjected to different temperatures?

The appropriate method to prevent the circulation of warm air to a colder section of a raceway or sleeve that is subjected to differing temperatures is to fill it with an approved material. This practice helps to minimize air movement, thereby limiting the potential for temperature discrepancies that can lead to condensation and other issues within the raceway or sleeve.

Using an approved filling material can also serve other purposes, such as offering physical protection for the conductors inside the raceway and enhancing the overall structural integrity. This approach is aligned with National Electrical Code standards, which emphasize the importance of maintaining the integrity of electrical installations, particularly in environments where temperature variations might impact performance and safety.

Sealing the raceway with tape might not provide a reliable long-term solution as it may not adequately fill all voids or prevent air circulation entirely. Leaving it open for ventilation would contradict the very goal of preventing warm air from affecting the colder section. Insulating the outer layer could help in some scenarios but doesn't specifically address maintaining a controlled internal environment for the raceway. Therefore, filling the raceway with an approved material is the most effective solution in this context.