What type of cover would you use for a 4-S box?

A blank cover is the appropriate choice for a 4-S box. This type of cover is used to close off an electrical box that does not have any devices or fittings installed in it. A 4-S box, which is typically a square box, may be used in applications where you need a junction point for wires but have no current need for switches, outlets, or other devices. The blank cover serves to keep out dust, dirt, and debris, ensuring a clean and safe installation.

Using the correct type of cover is essential for maintaining the integrity and safety of the electrical system. It also helps prevent accidental contact with live wires or connections that may be inside the box, reducing the risk of electrical shock or short circuits. Other cover types like a socket cover or active cover imply the presence of active components or devices, which would not be applicable in this context where a blank cover is used to simply close off unused boxes.