Which method is not permissible for connecting equipment grounding conductors?

Connecting equipment grounding conductors is crucial for ensuring safety in electrical systems, as it helps to prevent electric shock and ensures that fault currents have a safe path to ground. The permissible methods for connecting these conductors include methods that maintain a reliable, low-resistance connection.

Using solder to connect equipment grounding conductors is not permissible because solder joints can become unreliable over time due to factors such as thermal cycling, vibration, and the physical characteristics of solder itself. Soldered connections can also introduce resistance into the grounding system, which can affect the performance and safety of electrical equipment.

On the other hand, twisting, welding, and mechanical connectors are accepted methods as they provide solid connections that can withstand environmental and mechanical stresses. Twisting can maintain a good physical connection, welding offers a permanent and durable bond, and mechanical connectors are designed specifically to ensure low-resistance connections that can endure various conditions.

Understanding the properties and limitations of different connection methods is essential in electrical practice to ensure both safety and reliability in grounding systems.