Part VII of Article 230 provides the requirements for overcurrent protection of service equipment. Here are some highlights from this part of the NEC that are worth reviewing.
You must provide an overcurrent protection device (OCPD) in series with each ungrounded service conductor. Its rating or setting can’t exceed the ampacity of the protected conductor [230.90]. Of the five exceptions, perhaps the most critical is that for fire pumps. The fire pump OCPD must comply with 695.4