When installed in thermal insulation, the ampacity of armored cable conductors relates to what rating?

The correct answer is based on the standard practices regarding the ampacity ratings of conductors when they are installed in thermal insulation. Specifically, when conductors are surrounded by thermal insulation, the ampacity must be considered lower due to the potential for heat buildup, which can lead to overheating of the conductors.

For armored cables, the generally accepted practice is to reference the ampacity ratings that correspond to the lowest temperature rating of the wire insulation material when in thermal insulation. In this case, 60-degree Celsius rated conductors represent a conservative measure for ensuring safety and reliability.

Higher temperature ratings, such as those for 75, 90, or 100-degree Celsius conductors, would typically indicate a capacity for carrying higher currents without overheating under free air conditions or other less restrictive scenarios. However, once you place conductors in thermal insulation, you must ensure you do not exceed the ampacity limits specified for the conductor system, which is why the 60-degree Celsius rating becomes the relevant standard in this context.

This understanding is essential in electrical installation practices to ensure compliance with safety standards, avoiding potential hazards associated with overheating.