What is the maximum conduit length from the finish surface to the box that does not require additional support for RMC installations?

The maximum conduit length from the finish surface to the box that does not require additional support for Rigid Metal Conduit (RMC) installations is 18 inches. This specification ensures that the conduit remains securely attached to the building structure while minimizing the risk of damage or displacement due to mechanical stress or environmental factors.

The support requirements are intended to maintain the integrity of the electrical installation and prevent any potential hazards associated with unsecured conduits. By adhering to this maximum length, electricians can efficiently install RMC in a manner that complies with safety standards and building codes. This consideration is crucial as it relates to both practical installation techniques and ensuring robust electrical infrastructure.

Other options represent lengths that exceed the maximum allowable limit without additional support, which could lead to instability and increased risk of failure in the installation.