Section 6: Outside Branch Circuits and Feeders

6.1 Number of Supplies
6.2 Disconnecting Means
6.3 Location
6.4 Clearances over Roadways, Walkways, Rail, Water, and Open Land

6.1 Number of Supplies
In general, only one feeder is permitted to supply a building.

NEC Article 225.30 permits only one feeder or branch circuit to supply a building or structure.  This is similar to the requirement in NEC Article 230.2 that permits only one service to supply a building or structure.  Limiting the power sources makes it safer for maintenance or emergency personnel to remove all power from a building when necessary.

There are a number of conditions permitting additional branch circuits and feeders for the following:

  • Special Conditions: Multiple branch circuits or feeders are permitted for fire pumps, emergency systems, legally required and optional standby systems, paralleled power production systems, and installations designed for more than one source of supply for increased reliability.
  • Special Occupancy’s: Building with no space for supply equipment to be available to multiple occupants; and a building or structure so large that multiple services are necessary.
  • Capacity Requirements:  Feeders operated at 1000 volts or less are permitted to be supplied by multiple branch circuits or feeders when the capacity requirements are more than 200 amps.
  • Different System Characteristics: Multiple feeders or branch circuits are permitted to supply different voltages, frequencies, or phases.
  • Documented Switching Procedures: Multi-building installations under single management are permitted to be supplied by more than one branch circuit or feeder when switching procedures are documented to ensure safety during maintenance and emergency situations.  For example, this is common with multi-building industrial facilities and on multi-building campuses.

Review Question Section 6.1

37. Considering only the Capacity Requirement, what is the minimum calculated load required for a building to be supplied by more than a single outside feeder?

6.2 Disconnecting Means

Part II of NEC Article 225 is labeled, Buildings or Other Structures Supplied by a Feeder(s) or Branch Circuit(s) and deals with outside feeders and branch circuits supplying more than one building or structure.  Unless an installation is exempted by one of the 4 exceptions to the general requirement in NEC Article 225.31, the NEC requires a means to disconnect all ungrounded conductors or a feeder or branch circuit that supplies or that passes through a structure or building.

The four exceptions to this rule are:

1) If documented safe switching procedures are established, maintained, and monitored by qualified persons, the disconnecting means can be located elsewhere on the premises [225.32 Ex 1].

2) The building or structure qualifies under the provisions of Art. 685 [225.32 Ex 2].

3) For towers or poles used as lighting standards, the disconnecting means is permitted to be located elsewhere on the premises [225.32 Ex 3].

4) For a pole or similar structure used only for the support of signs installed in accordance with Art. 600, the disconnecting means is permitted to be located elsewhere on the premises [225.32 Ex 4].

For example a factory with a free standing structure such as a materials silo supplied by a 277/480 volt, 400 amp, 3-phase feeder from the switchgear in the factory requires a disconnecting means at the free standing silo.

Regardless of the voltage or amperage of the circuit, NEC article 225.31 requires the disconnect at the freestanding building or structure to open all ungrounded conductors in the feeder or branch circuit.

Review Question Section 6.2

38. A 3-phase 200 amp, outside feeder is fed from the main building and supplies a second building used for tool storage. Without application of any exception, which of the following statements is true?

Feeders that supply buildings or structures require a disconnecting means that disconnects all ungrounded conductors.

6.3 Location
The disconnect for the supply is permitted either inside or outside the structure served.

The requirements in NEC article 225.32 for the location of disconnects supplied by feeders or branch circuits is similar to the requirement in NEC article 230.70(A) for services.  Both sections require the disconnect to be both readily accessible and to be located immediately inside or outside the building at the nearest point of entrance of the supply conductors.

In some cases, deciding what is the closest or nearest point that is readily accessible is a judgment call that should have been discussed with the AHJ prior to installing the disconnect.

Review Question Section 6.3

39. An outside feeder supplies a building. The disconnecting means is required to be installed:

6.4 Clearances over Roadways, Walkways, Rail, Water, and Open Land

The minimum clearance of high voltage outside feeder conductors up to 22kV is listed in NEC Table 225.60.  The required clearance depends on the area the high voltage conducts pass over.  Areas subject to pedestrian traffic do not require as much clearance as areas subject to vehicles.  Areas that pass over railroad tracks require more clearance than walkways.


Review Question Section 6.4

40. What is the minimum clearance above a roadway for a high voltage feeder rated 12,460 volts?

Minimum overhead clearance depends on location.