You're right to question the interpretation. Let's break down the NEC language and why your EMT idea might work

Understanding the NEC Section

The section you quoted is about supporting enclosures (boxes) that don't contain devices (other than splices) or support fixtures. It outlines the requirements for supporting these boxes solely by the entering raceways. The key phrases are: "It shall have threaded entries or identified hubs." This means the box must have threaded connections to accept the raceways. "It shall be supported by two or more conduits threaded wrenchtight into the enclosure or hubs." This specifies the method of support – the conduits must be threaded into the box and tightened securely.

Does it Require Threaded Raceway (e.g., Rigid Metal Conduit)? No, it does not explicitly say you must use threaded raceway. The requirement is for threaded connections at the box.

Your EMT Idea and Threaded Adapters

Here's why your EMT idea could work:1. Threaded Hubs

You choose a box that has threaded hubs (e.g., a rigid conduit box with threaded entries).2.

EMT Connectors

You use EMT connectors that are designed to thread into the threaded hubs of the box. These connectors provide a threaded connection to the box.3.

Proper Installation

The EMT connectors are threaded into the hubs of the box and tightened wrenchtight, fulfilling the "threaded wrenchtight into the enclosure or hubs" requirement.4.

Secure the EMT

The EMT is secured within 3 feet (or 18 inches if entries are on the same side) of the box as required.

Important Considerations and Potential Issues Listing and Suitability

The most crucial factor is whether the EMT connectors you're using are listed and suitable for creating a threaded connection in this manner. Look for connectors specifically designed for this purpose. Some EMT connectors are designed to thread into threaded hubs, providing a secure, code-compliant connection.

Tightening

Ensure the EMT connectors are tightened adequately to provide the required support. "Wrenchtight" implies a significant level of torque.

Local AHJ Interpretation

While the NEC language allows for this interpretation, the local Authority Having Jurisdiction (AHJ) has the final say. It's always best to consult with the AHJ before proceeding, especially when using methods that might be considered unconventional. Show them the specific connectors you plan to use and explain your rationale.

Grounding/Bonding

Be mindful of proper grounding/bonding practices when using EMT. Ensure a reliable grounding path is maintained.

Physical Protection

Consider the environment. If the installation is in a location where the raceway is subject to physical damage, a more robust raceway system (like RMC or IMC) might be more appropriate, regardless of the NEC's minimum requirements.

In Summary

While the NEC section doesn't explicitly mandate threaded raceway, it requires threaded connections to the box for support. Using EMT with properly listed and installed threaded connectors could be compliant, but it heavily depends on:1. Connector Listing and Suitability

Are the connectors specifically designed and listed for creating a threaded connection into a threaded hub?2.

Proper Installation

Are the connectors tightened sufficiently ("wrenchtight") to provide support?3.

AHJ Approval: Will the local AHJ accept this method? This is the most important factor.Always err on the side of caution and seek clarification from your local AHJ before implementing this approach. They can provide guidance and ensure your installation meets local requirements and interpretations of the NEC. Flag for review