What insulation type is designated by NM cables marked with "-B"?

• A. 60 degrees Celsius
• B. 75 degrees Celsius
• C. 90 degrees Celsius
• D. 105 degrees Celsius

Answer: (C)

The insulation type designated by NM cables marked with "-B" is 90 degrees Celsius. This specification indicates that the conductors are rated for a maximum operating temperature of 90 degrees Celsius. This higher temperature rating is significant because it allows for the safe operation of the cable in various applications, offering greater flexibility in terms of installation and usage, especially in environments where heat may accumulate.

Conductors with a lower temperature rating, such as 60 degrees Celsius and 75 degrees Celsius, would not be appropriate for applications requiring the performance characteristics associated with the 90 degrees Celsius rating. This distinction ensures that the cable can safely carry the required load without risk of insulation breakdown or failure, contributing to overall safety and reliability in electrical installations.