You're right to question the design team's approach. Here's a breakdown of the relevant code sections and why your understanding is likely correct

Key Code References (NFPA 20 and NFPA 70):
NFPA 20 (Standard for the Installation of Stationary Fire Pumps)

This standard is the primary driver for fire pump installations.

NFPA 70 (National Electrical Code - NEC)

This provides the electrical safety requirements.

NFPA 20 Requirements (most critical)



9.6.
2.1(2022 Edition) Alternate Power Source

"The alternate source shall be located so that fire within the building is not likely to damage the alternate power source and its supply conductors." (This is why generator location and wiring protection is so important)

9.6.6(2022 Edition) Branch Circuit Overcurrent Protective Device

The overcurrent protective device(s) shall be accessible only to authorized personnel. (Usually locked or sealed)

9.6.7(2022 Edition) Wiring



9.6.
7.1

Power wiring shall be in rigid metal conduit, intermediate metal conduit, electrical metallic tubing, liquidtight flexible metal conduit, or cable listed for fire pump service.

9.6.
7.2

The supply conductors shall have a fire resistance rating of not less than 2 hours or shall be concrete encased to a minimum of 2 inches (50.8 mm).

9.6.
7.3

(Deals with pump room wiring, not relevant to the feeder discussed here)

9.6.8(2022 Edition) Supervision. The supply to the fire pump shall be supervised to indicate loss of normal power.

Analysis of Your Situation


Generator to Switchboard Feeder (Your Concern)

The code requires protection of the branch circuit conductors, not the feeder from the generator to the switchboard. The intent of the code is to ensure the fire pump has a reliable power supply during a fire. Damage to the conductors between the generator and the switchboard would cause the generator breaker to trip, but the fire pump is still be backed up by the normal power. Unless some special conditions exist.2.

Branch Circuit from Switchboard to Fire Pump ATS



This is where the 2-hour fire-rated cable (or concrete encasement) is required. The branch circuit starts at the overcurrent device (300A breaker in your case) in the generator switchboard that is dedicated to the fire pump. The reasoning is that if a fire were to occur the branch circuit will still be able to feed the fire pump.

Justification for Challenging the Design Team



Code Focus

The code language explicitly focuses on the branch circuit supplying the fire pump, starting at the overcurrent protection device.

Cost and Benefit

The 2-hour rated cable is expensive. Applying it to the feeder from the generator to the switchboard doesn't add significant fire protection because the switchboard would be backed up by normal power unless the incoming utility is lost.

Practicality

Implementing 2-hour fire-rated cable for the parallel feeder would be much more complex, potentially requiring significant structural changes.

Recommendations


Formal Interpretation Request

To get absolute clarity, consider submitting a formal interpretation request to the relevant AHJ (Authority Having Jurisdiction). This provides written confirmation and protects you.2.

Review Shop Drawings

The fire protection engineer responsible for the fire protection system should sign and stamp shop drawings for the electrical installation. Ensure these drawings clearly delineate the extent of the 2-hour rated wiring.3.

Documentation

Thoroughly document your interpretation of the code, the design team's rationale, and any AHJ guidance.4.

Consider Local Amendments

Always double-check for any local code amendments that might be stricter than the national codes.

In summary, your assessment is likely correct. The 2-hour rated cable should be required only for the branch circuit from the generator switchboard overcurrent device to the fire pump ATS, not for the feeder from the generator to the switchboard. Flag for review