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.
The fire pump is one of six types of “Special Conditions” in which you can run an additional service. Three others are emergency systems, legally required standby systems, and optional standby systems. The other two are parallel power production systems and systems designed for connection to multiple sources of supply (for enhanced reliability).
An example of this last one is a data center that has incoming power lines coming from two different geographic directions.
Special Conditions aren’t the only exceptions to the “one building, one service” rule. We’ll look at the other three exceptions as this series continues.
