Section 695.7 includes a requirement limiting voltage drop to 15% under starting conditions and 5% when the motor is running at 115% of the full load rating of the motor.

This is one of the few actual rules about voltage drop defined in the NEC. The reason is that excessive voltage drop is a safety issue for fire pumps, not just a design issue, because the operation of the pump itself is a safety issue. If the voltage drop is too high, the motor may not start and run properly to protect the building and people by working to put a fire out.