What does the letter "W" indicate in the memory device for cables RHW and THW?

The letter "W" in the memory device for cables RHW and THW signifies "wet," indicating that these types of cables are rated for use in wet locations. This means they can safely be used in environments where they may be exposed to moisture without degrading their performance or insulating properties. This characteristic is particularly critical in installations where cables may be subject to water exposure, ensuring safety and reliability in electrical systems.

Other choices may relate to other properties of cables, but "W" specifically highlights the moisture resistance aspect of RHW and THW cables, making them suitable for outdoor or similarly challenging environments.