What is the temperature rating limit for the ampacity of non-metallic sheathed cable?

The ampacity of non-metallic sheathed cable, commonly known as NM cable or Romex, is rated based on an ambient temperature limit, which is established to ensure both safety and performance. The correct temperature rating limit for this type of cable is set at 60 degrees Celsius, which aligns with the National Electrical Code (NEC) guidelines.

This rating is essential because it indicates the maximum temperature at which the cable can operate safely without risking damage to the insulation or posing a fire hazard. When calculating ampacity, it's crucial to consider not just the current flowing through the cable, but also the environment in which it operates; exceeding this temperature can lead to degraded cable performance or failure, potentially resulting in electrical fires.

In contrast, ratings like 50 degrees Celsius, 70 degrees Celsius, and 80 degrees Celsius do not pertain to the standard operating limits for non-metallic sheathed cables. Each of these ratings may reflect different types of conductors or insulation, but they do not represent the accepted limits set for NM cable as specified in electrical codes. Understanding these temperature ratings helps ensure the safe and efficient installation of electrical systems.