What is the common insulation type for underground feeder cables?

The correct answer is Type UF, which stands for Underground Feeder cable. This type of insulation is specifically designed for use in wet and underground environments, making it ideal for applications such as supplying power to outdoor buildings or submersible pumps. Type UF cables are constructed to be moisture-resistant and durable, allowing them to withstand the harsh conditions found underground.

Other types of insulation, such as Type THHN, Type NM-B, and Type SWA, are not suitable for direct burial in the ground without additional protection or methods of installation to ensure safety and longevity. Type THHN is commonly used for indoor residential wiring but is not rated for wet locations. Type NM-B is intended for use within buildings only. Type SWA (Steel Wire Armored) is used for wiring in exposed and industrial applications but is typically above ground rather than underground. Therefore, Type UF is the most suitable choice for underground feeder applications due to its specific design and rating.