One-piece porcelain pin insulators are commonly used at voltages less than what value in kV?

One-piece porcelain pin insulators are typically designed for medium voltage applications, often specifically for voltages under 23 kV. This type of insulator is favored for its durability and reliability in environments where the voltage is within the lower range. Its construction allows it to support overhead lines effectively while also maintaining the necessary electrical insulation.

When considering the other options, it's important to note that while insulators may be used in higher voltage applications, one-piece porcelain pin insulators are not sufficiently robust for long-term use at voltages greater than 23 kV. At higher voltages, the electrical stresses increase significantly, which requires different designs, materials, and insulating properties to ensure safety and efficiency, such as using composite or larger multi-piece insulators tailored for those demands. Thus, determining the correct voltage threshold for one-piece porcelain pin insulators emphasizes the significance of selecting the right type of insulator based on the application's specific voltage needs.