What factor necessitates the need for single-phase over three-phase oil switches?

The factor that necessitates the use of single-phase over three-phase oil switches relates primarily to high voltage clearance. In certain applications, such as connections to overhead distribution lines or in situations where space is limited, the design of a single-phase oil switch can provide the required insulating properties and clearance distances to handle high voltage levels.

Single-phase switches can be installed with adequate spacing to ensure that they meet the necessary safety standards and voltage ratings. This is particularly important when dealing with high voltages, as improper clearance can lead to arcing or other electrical failures. By using single-phase switches, utilities can more easily manage the required clearances, ensuring the safety and reliability of the electrical system.

While factors like low voltage clearance, high current loads, and reduced maintenance costs are considerations in the selection of switches, they do not take precedence over the explicit need for adequate high voltage clearance. High voltage environments demand a specific attention to insulation and clearance, making this the primary reason for choosing single-phase over three-phase oil switches in certain contexts.