Which of the following is not a valid application for type SE conductors?

Type SE conductors, or Service Entrance conductors, are primarily used for the delivery of electrical power from the utility service to the service equipment in a building. The characteristic features that make SE conductors suitable for various environments include their capacity to withstand moisture and some exposure to the elements, but they are not specifically designed for submersion or consistent exposure to water conditions.

When evaluating the applicability of Type SE conductors, indoor installations, outdoor installations, and above-ground installations are generally acceptable due to the durability and insulation provided in their design. However, underwater installations involve unique challenges, such as the need for specialized sheathing to withstand high moisture and pressure levels without degrading. Type SE conductors lack the necessary waterproof characteristics and mechanical protection required for effective underwater usage, which is why they are not considered a valid application in that scenario.

Thus, identifying underwater installation as not a valid application highlights the limitations of Type SE conductors when it comes to environments with continuous or prolonged exposure to water.