Yes, you are correct. NEC 210.4(C) (as of the 2020 code cycle, and likely applicable in later editions) permits the use of multiwire branch circuits (MWBCs) with a common neutral for all three phases provided that the circuit is supplied from a three-phase system and the branch-circuit overcurrent device opens all ungrounded conductors of the multiwire branch circuit simultaneously.Here's a breakdown and important considerations for your specific application: 210.4(C) Connection to a Three-Phase System

This section explicitly allows for a MWBC consisting of three ungrounded conductors and a shared neutral conductor fed from a three-phase system that has a neutral conductor.

Simultaneous Disconnection

The key requirement is that the overcurrent device (in your case, the 3-pole circuit breaker) must disconnect all ungrounded (hot) conductors simultaneously. This is crucial for safety. This is typically achieved with a 3-pole circuit breaker (or a handle tie).

277V LED Street Lighting

Since your street lighting uses 277V, you're already in a commercial/industrial environment where MWBCs are common and appropriate. 277V is a line-to-neutral voltage, so your MWBC would be derived from a 480Y/277V system.

Neutral Sizing

Pay close attention to neutral sizing. In the vast majority of scenarios involving standard loads (like lighting), the neutral will carry a current roughly equal to the highest current on any of the phase conductors. However, if you have significant non-linear loads or harmonic currents (which some LED drivers can produce), the neutral current can be higher than the phase currents. Consult your equipment manufacturer's specifications and consider over-sizing the neutral conductor if harmonic content is a concern.

Disconnecting Means

Ensure the disconnecting means for the lighting is readily accessible and clearly labeled.

Local Codes and Amendments

Always check with your local Authority Having Jurisdiction (AHJ). They may have amendments or additional requirements to the NEC. Don't assume NEC compliance is automatically sufficient.

In summary: Using a 3-phase MWBC with a common neutral and a 3-pole breaker for your 277V LED street lighting is generally permissible under the NEC, provided you adhere to all the requirements of 210.4(C), especially regarding simultaneous disconnection and neutral sizing. Always confirm with your local AHJ. Flag for review