In equipment bonding jumper connections, which option is not permitted according to Section 250.8?

In equipment bonding jumper connections, the use of sheet metal screws is not permitted according to Section 250.8 of the NEC. This section specifies the acceptable methods for making bonding connections, emphasizing the need for secure and reliable methods that ensure good electrical conductivity and mechanical strength.

Sheet metal screws do not provide a reliable or secure electrical connection, as they can be prone to loosening over time due to vibration or thermal expansion and contraction. They also present the risk of corrosion that can compromise the integrity of the bond. In contrast, methods such as exothermic welding, listed pressure connections, and listed clamps are specifically designed for bonding, ensuring durability and compliance with safety standards.

The approaches mentioned in the other options are authorized for creating secure connections that maintain effective electrical bonding, which is essential for safety and to reduce the risk of electrical faults.