Final answer:
The correct spacing for the first EMT strap from the box is 300 mm, as mandated by the National Electrical Code to ensure stability and safety in the installation.
Step-by-step explanation:
When performing an installation using Electrical Metallic Tubing (EMT), it is crucial to adhere to specific rules regarding the placement of straps to secure the conduit to the building structure. According to the National Electrical Code (NEC), the first strap needs to be secured within a certain distance from the box to ensure proper support and prevent sagging or movement of the conduit.
The correct answer to the question is that the spacing of the first strap from the box must be within 300 mm of the box. This requirement is designed to provide stability to the installation and to minimize the forces that connections and terminations are subjected to. Failure to adhere to this spacing can lead to code violations and may compromise the safety and functionality of the electrical system.