For which size of conductor is the connection by studs and nuts with upturned lugs not permitted?

In the context of electrical installations and wiring practices, certain size conductors have specific requirements and limitations regarding connections. For conductors sized 10 AWG and smaller, the use of studs and nuts with upturned lugs is generally not permitted due to the need for secure and reliable connections that can handle the electrical load without risk of overheating or disconnection.

The connection method using studs and nuts with upturned lugs is typically acceptable for larger conductors, as they can provide a robust mechanical and electrical connection. However, smaller conductors, such as 10 AWG, may not be able to accommodate the physical stresses that can occur from this type of connection method, which is essential for maintaining safety and performance in electrical systems.

Therefore, it's critical to utilize different connection methods specifically designed for the size and characteristics of smaller conductors to ensure compliance with safety standards and to prevent potential failures in the electrical system. This is why the use of studs and nuts with upturned lugs is not permitted for the 10 AWG size conductor.