You've covered the major points, but here's a more detailed breakdown of considerations, both code-related and practical

NEC Considerations:
240.24(A) Accessibility

You are correct. The NEC requires overcurrent devices to be readily accessible. This means they must be capable of being reached quickly for operation, renewal, or inspections without requiring those to climb over or remove obstacles or resort to portable ladders, and so on. Mounting overhead can be acceptable, but height and accessibility are key. Consider the maximum height allowed by the NEC and local amendments, as some jurisdictions are more strict with height requirements.

110.26 Working Space

You're right to demand the 3' working space (or more, depending on voltage and conditions). This space must be clear and extend the full width of the equipment (typically 30" or the width of the equipment, whichever is greater).

110.26(D) Illumination

Adequate illumination is essential in the working space. This often overlooked aspect is critical for safe maintenance. Consider whether the existing mezzanine lighting is sufficient or if dedicated fixtures are needed.

110.26(E) Headroom

Ensure at least 6'6" headroom above the working platform or the height of the equipment, whichever is greater. This is easily overlooked with overhead installations.

Panel Labeling (110.22)

The panel must be clearly and durably labeled to indicate its purpose and the circuits it controls.

Dedicated Equipment Space (110.26(F)(1)(a))

The space above and below the electrical equipment must be dedicated. No foreign systems (piping, ducts, etc.) should be located in this zone.

Non-Code Considerations (Practical & Safety)



Platform Surface

Insist on a solid surface (not open grate) in the working space. Dropped tools or parts through the grate are a significant hazard. You could potentially use solid metal plating over the grating just in the immediate working space. This also provides a more stable surface for ladders.

Fall Protection

If the working space is elevated (and it likely is on a mezzanine), fall protection is paramount. Ensure the mezzanine railings meet or exceed OSHA standards for height, spacing, and strength. Consider a self-closing gate at the access point.

Ladder Access

How will personnel safely access the panels for maintenance? A fixed ladder (with cage, if necessary), a mobile ladder, or a scissor lift might be needed. Factor in the space required for ladder placement and operation.

Lockout/Tagout (LOTO)

The location and accessibility of the panel impact LOTO procedures. Ensure it's easy for authorized personnel to safely disconnect power during maintenance.

Forklift Protection

While the panels are out of reach, consider potential damage from forklifts impacting the mezzanine structure itself. Guard rails or barriers might be needed to protect the mezzanine supports.

Environmental Conditions

Is the mezzanine area subject to excessive dust, moisture, or temperature fluctuations? Choose panels and enclosures rated for the environment.

Future Expansion

Consider whether additional panels might be needed in the future. Plan for extra space and conduit capacity.

Maintenance Procedures

Develop a clear maintenance plan that includes safe access procedures, required tools, and training for personnel.

Coordination with Other Trades

Ensure the panel location doesn't interfere with other equipment or systems on the mezzanine (e.g., HVAC ducts, plumbing, sprinklers).

Weight Distribution

Confirm with the Structural Engineer that the mezzanine widening and panel weight are considered holistically across the entire structure and not just locally where the panels are mounted. Concentrated weight on a mezzanine can have far-reaching structural implications.

Service Personnel Preference

Ask the maintenance personnel if they have any preference or concerns about the location. Their input is very valuable.

Documentation

Keep thorough records of the panel locations, circuit diagrams, and maintenance procedures.

Anchoring

Ensure the panels are properly anchored to the mezzanine structure to prevent movement or vibration.

Recommendation



Solid Working Platform

Make a solid working platform mandatory.

Lighting

Upgrade the lighting if necessary.

Access

Determine the safest and most practical access method (ladder, lift, etc.) and ensure adequate space.

Structural Approval

Get written confirmation from the Structural Engineer that the mezzanine can support the weight of the panels and all associated equipment and personnel.

Review Plans: Thoroughly review the final plans with the construction firm, structural engineer, maintenance personnel, and any relevant safety officers before installation.By carefully considering these code and non-code factors, you can ensure a safe, compliant, and practical installation. Remember to prioritize safety and accessibility for maintenance personnel. Flag for review