Yes, the NEC allows a sub-fed panelboard to be a Main Lug Only (MLO) panelboard if located within the same building as the main service panelboard.Here's why and the relevant NEC considerations: MLO panels are common

MLO panels are very commonly used as subpanels within a building. They are designed to receive power from a feeder circuit and distribute it to branch circuits.

Main Breaker is Not Required

An MLO panel does not require a main breaker if it is fed from a breaker in the main service panel (or another appropriately sized feeder breaker). The upstream breaker provides the overcurrent protection for the feeder conductors supplying the subpanel.

Feeder Overcurrent Protection

The NEC requires overcurrent protection (a breaker or fuses) for the feeder conductors feeding the subpanel. This overcurrent protection is typically located at the point where the feeder originates, which is usually in the main service panel.

Properly Sized Feeders

The feeder conductors supplying the subpanel must be properly sized according to NEC Article 215 and sized according to 310.16 and must be protected by the breaker size they are rated for.*

Grounding and Bonding

The grounding and bonding requirements of Article 250 must be followed carefully. Critically, the neutral and ground must be kept separate in the subpanel. The subpanel's grounding bus must be bonded to the enclosure and the equipment grounding conductor from the feeder. The neutral bus must be isolated from the enclosure.

In Summary:

As long as the subpanel is fed from a properly sized and protected feeder breaker in the main panel, and grounding/bonding requirements are met, an MLO panel is perfectly acceptable for use as a subpanel within the same building. Flag for review