Which conduit type is generally not suitable for underground installations?

The choice of EMT Conduit as generally not suitable for underground installations is correct. EMT, or Electrical Metallic Tubing, is a lightweight, thin-walled conduit made of steel that is primarily designed for above-ground applications where protection against physical damage is needed, but not direct exposure to moisture and other environmental factors.

When it comes to underground installations, conditions such as moisture, soil acidity, and the potential for damage from ground movement require conduits to have certain durability and protection features. EMT does not provide the necessary water resistance and corrosion protection needed for underground environments.

In contrast, Rigid PVC Conduit is specifically designed for underground applications as it is resistant to moisture and chemicals. Rigid Metal Conduit is also suitable since it offers excellent protection against physical damage and corrosion when properly installed with protective coatings. Flexible Metal Conduit, while primarily used for areas where flexibility is required, can be used for some underground applications as long as it is properly encased or protected.

This distinction is essential for electrical installations, as using a conduit type not suited for specific conditions can lead to failures, safety hazards, or non-compliance with electrical codes.