Section 225.30/Number of Supplies to a Building or Structure
NEC 225.30 limits each building or structure to a single feeder or branch circuit unless one of the specific exceptions for multiple supplies applies.
A building or structure must be supplied by a maximum of one feeder or one branch circuit unless additional supplies are permitted by exceptions. The permitted exceptions include: buildings with multiple occupancies where each occupancy has its own service; additional supplies for fire pumps, emergency systems, legally required standby systems, optional standby systems, or parallel power production systems; buildings large enough in area to qualify for multiple services under Section 230.2; and separate feeders required for different voltage systems, different frequencies, or different phases. Where multiple feeders supply a single building, a permanent plaque or directory must be installed at each feeder disconnect location indicating the location of all other feeder disconnects for the building. Each feeder disconnect must be grouped and identified per Section 225.32 through 225.40.
Why this section exists
Limiting the number of supplies to a building simplifies the disconnect and lockout/tagout procedures for emergency responders and maintenance personnel. When a building has a single feeder, opening one disconnect de-energizes the entire building. Multiple supplies create the risk that a worker believes the building is de-energized after opening one disconnect while another supply remains energized. The plaque requirement for multiple supplies addresses this risk by alerting anyone working on the system that additional sources exist.
What plan reviewers look for
Plan reviewers check the site electrical plan for the number of feeders serving each building. If multiple feeders are shown, they verify one of the exceptions applies and is documented. They check for the permanent plaque or directory requirement at each disconnect location. For buildings with fire pumps or emergency systems, they verify the separate feeder is identified on the one-line diagram.