Electrician's Licensing Practice Exam

In NEC regulations, how many threads must machine screw-type fasteners engage?

1. At least two threads

2. At least three threads

3. At least four threads

4. No specific requirement

The correct answer is: At least two threads

In the context of NEC (National Electrical Code) regulations, the requirement for machine screw-type fasteners to engage a minimum of two threads is based on ensuring adequate mechanical strength and structural integrity in the assembly of electrical equipment. Engaging at least two threads helps to ensure that the fastener can withstand the mechanical stresses placed upon it during use, such as vibrations or movements, which can be common in electrical installations. Engaging two threads provides a balance between sufficient strength and practicality. It avoids the potential for stripping the threads or insufficient contact that might lead to failure. This requirement is particularly relevant in ensuring reliability in electrical installations, as any loose connections can lead to increased resistance, overheating, or even electrical failures. The other approaches indicated in the options would not provide the same level of assurance. For example, requiring fewer than two threads may not offer enough grip, leading to potential safety hazards. More than two threads, while generally safe, are not typically necessary for standard applications per NEC guidelines, making the two-thread requirement both the minimum standard and an efficient use of fasteners in many scenarios.