How many threads should be seen protruding through the nut when installing nuts to hold a substation superstructure?

When installing nuts to secure a substation superstructure, the guideline for the number of threads visible protruding through the nut is typically two. This standard ensures that there is adequate engagement between the nut and the bolt, allowing for a secure connection that can handle the mechanical stresses encountered in a substation environment.

Having two threads visible indicates that the nut is properly installed and that there is sufficient thread engagement to prevent the nut from loosening due to vibration or other operational factors. It also reflects good engineering practice, as too few threads could lead to failure under load, while excessive protrusion may indicate that the bolt is too long or that the nut is not fully seated. Thus, the recommendation to have two threads protruding provides a balance between security and proper mechanical function in the installation of substations.