How many services can a structure have? Generally, only one [230.2]. But suppose you want to supply a fire pump. If so, you can run a separate service just for it [230.2(A)(1)]. This often makes sense for many reasons, including overcurrent protection issues, load issues (e.g., a big fire pump can mean a much larger main service), and the location of the pump. Voltage drop may be an issue if the pump is at the far edge of the property and distant from your main service.
Electrical Services, Part 2
If you want to supply a fire pump, you can run a separate service just for it [230.2(A)(1)].