Which type of connector does the NEC permit for connecting power to a 1900 box with flex conduit?

The National Electrical Code (NEC) allows for the use of a straight flex connector for connecting power to a 1900 box when using flexible conduit. This is because a straight flex connector provides the necessary stability and electrical continuity for the connection, ensuring that the wiring is securely anchored and protected.

The flexibility of these connectors accommodates the movement and vibration that can occur in installations, while maintaining the safety and integrity of the electrical system. Straight connectors are preferred in many applications because they often create a lower profile and can facilitate easier access for wiring.

Additionally, the code doesn't restrict the use of straight connectors exclusively; however, the context of the question suggests that the straight flex connector is the most applicable and commonly accepted option for this particular scenario. Thus, the straight connector aligns with the NEC safety guidelines and practical installation requirements for power connections to junction boxes.