Which of the following does not typically describe duct systems?

Duct systems are often used to contain and protect various types of cables, providing a structured way to organize wiring in buildings. While duct systems do often vary in size, accommodating different cable types and quantities, they can also be made from materials such as metal or plastic, making option A a possible description of duct systems.

Regarding the location of duct systems, while it is common to find them above ground, it is not exclusive to that position. Duct systems can also be installed below ground or in walls, depending on the application and building design. This flexibility in placement makes it appropriate to indicate that they are not strictly found above ground. Therefore, due to the variety in installation options, the assertion that duct systems are usually found above ground does not accurately describe them.