Which of the following methods is NOT acceptable for making equipment bonding jumper connections?

The method of using sheet metal screws for making equipment bonding jumper connections is not acceptable. Equipment bonding involves ensuring that all conductive parts are connected to maintain grounding. The primary purpose is to ensure electrical continuity and avoid any potential differences in voltage that could lead to arcing or shock hazards.

Using sheet metal screws can compromise this important function since they may not provide a reliable electrical connection over time, especially under conditions where vibration or thermal expansion may occur. They can loosen, corrode, or fail to maintain a secure bond, which is critical in bonding applications where safety is paramount.

In contrast, the other methods mentioned—exothermic welding, listed pressure connections, and listed clamps—are recognized for their reliability and effectiveness in maintaining solid electrical connections. Exothermic welding creates a permanent connection that can withstand harsh conditions, while listed pressure connections and listed clamps are designed specifically to ensure that the bond is secure and durable, meeting safety standards set forth in electrical codes.