The connection of conductors to terminal parts must ensure a mechanically secure electrical connection and shall be made by means of _____.

The requirement for the connection of conductors to terminal parts to ensure a mechanically secure electrical connection is fundamental within the National Electrical Code (NEC). This includes a variety of methods that can effectively meet the criteria for securing electrical connections.

Solder lugs provide a means for attaching conductors securely by using solder, which can create a strong and reliable connection if done correctly. Pressure connectors, such as screw terminals or crimp connections, allow for tight mechanical attachment through the application of force, which also ensures a good electrical connection while facilitating easy installation and removal when needed.

Splices to flexible leads, which involve connecting conductors to flexible cabling or wires, also constitute an acceptable method when done according to NEC standards, as they can ensure that the electrical connection remains secure while accommodating movement or vibration.

Since all of these methods can be applied to secure electrical connections as per NEC requirements, this makes the answer to the question a comprehensive 'all of the above.' Each method addresses the need for a mechanical and electrical connection in a way that aligns with safety and performance standards outlined by the NEC.