4.5 Feeder Installation & Buildings Supplied by a Feeder (0301)
Key Takeaways
- 215.6 requires a feeder that supplies branch circuits needing equipment grounding conductors to include or provide an equipment grounding conductor to which those branch-circuit grounding conductors connect.
- 215.12 requires the ungrounded conductors of a feeder to be identified by phase or line and system where the premises has more than one nominal voltage system, with the identification posted at each feeder panelboard.
- 225.30 generally permits only one feeder or branch circuit to supply an additional building or structure, subject to the same exception families used for services in 230.2.
- 225.31 and 225.32 require a disconnecting means for each building or structure supplied by a feeder, located at a readily accessible point nearest the point of entrance of the conductors.
- 250.32 requires a grounding electrode at each separate building or structure supplied by a feeder, with the equipment grounding conductor run with the feeder and the neutral kept isolated.
Feeders Carry Grounding as Well as Power
215.6 is short and decisive: where a feeder supplies branch circuits in which equipment grounding conductors are required, the feeder must include or provide an equipment grounding conductor, complying with 250.118, to which the branch-circuit equipment grounding conductors connect. In practice that means a feeder to a subpanel cannot rely on a break in the grounding path — the metal raceway must qualify under 250.118 or a wire-type equipment grounding conductor must be run.
This is the rule behind one of the most common commercial defects: a feeder run in flexible metal conduit longer than 6 ft with no wire-type equipment grounding conductor. FMC qualifies as an equipment grounding conductor under 250.118(5) only under specific conditions — the circuit conductors protected at 20 A or less, the length of the ground-fault path not exceeding 6 ft, and the fittings listed for grounding. A 100 A feeder in 10 ft of flex needs a wire.
Feeder Identification — 215.12
Where a premises wiring system has feeders supplied from more than one nominal voltage system — the ordinary commercial case of 208Y/120 V panels and 480Y/277 V panels in the same building — each ungrounded feeder conductor must be identified by phase or line and system at all termination, connection, and splice points. The means of identification may be separate color coding, marking tape, tagging, or other approved means, and it must be documented in a manner readily available or permanently posted at each feeder panelboard or similar distribution equipment.
The posting requirement is the part inspectors write up. A building may use any color scheme it likes, but the legend has to be on the panel.
Related identification rules:
- 200.6 — grounded conductors 6 AWG and smaller are identified by a continuous white or gray outer finish or three continuous white or gray stripes; 4 AWG and larger may be identified at terminations by white or gray marking that encircles the conductor.
- 200.6(D) — where grounded conductors of different systems are in the same raceway or enclosure, each system's grounded conductor must be distinguishable, with the means posted at each panel.
- 110.15 / 230.56 — on a 4-wire delta-connected system where the midpoint of one phase winding is grounded, the conductor with the higher phase voltage to ground (the high leg, nominally 208 V on a 240/120 V system) must be durably and permanently marked by an outer finish that is orange, or by other effective means, at every point where a connection is made and the grounded conductor is present. 408.3(E) further fixes the high leg in the B phase position in panelboards and switchboards.
A Second Building on the Same Property — Article 225
The moment a feeder leaves one building and supplies another building or structure on the same property, Article 225 Part II applies, and it reads very much like Article 230:
| Rule | Requirement |
|---|---|
| 225.30 | Only one feeder or branch circuit may supply a building or structure, with exceptions that parallel 230.2 — special conditions such as fire pumps and emergency systems, special occupancies, capacity requirements, and different characteristics such as voltage or use |
| 225.31 | A disconnecting means must be provided for all ungrounded conductors supplying or passing through the building or structure |
| 225.32 | The disconnect must be installed at a readily accessible location nearest the point of entrance of the conductors, either outside the building or inside nearest the point of entrance |
| 225.33 | Not more than six switches or circuit breakers may make up the disconnecting means |
| 225.34 | The disconnects must be grouped and each marked to indicate the load served |
| 225.36 | The disconnecting means must be suitable for use as service equipment where it is the building disconnect, except that a snap switch or set of three-way or four-way switches may serve as the disconnect for garages and outbuildings on residential property |
| 225.38 | The disconnect must be capable of being locked in the open position, and must simultaneously disconnect all ungrounded conductors |
On a commercial campus — a main building, a maintenance shop, a guard house, a parking-lot light pole base — every one of those structures needs its own disconnect at the point of entrance, and the inspector should be able to find it without walking back to the main building.
Grounding at the Second Building — 250.32
250.32(A) requires a grounding electrode at each building or structure supplied by a feeder or branch circuit, connected to the building disconnecting means. The exception is a single branch circuit supplying the structure that includes an equipment grounding conductor.
250.32(B)(1) is the rule that changed decades ago and still gets installed the old way: where a feeder supplies a separate building, an equipment grounding conductor must be run with the supply conductors and connected to the building disconnecting means and to the grounding electrode. The grounded (neutral) conductor must not be used as an equipment grounding conductor at the second building, and the neutral must not be bonded to the enclosure or the equipment grounding conductor there.
That means a separate building fed by a feeder gets:
- Ungrounded conductors
- A neutral, isolated at the building disconnect
- An equipment grounding conductor run with them
- A grounding electrode at the building, connected to the equipment grounding bar
The old three-wire feeder with a bonded neutral at the outbuilding — legal under earlier editions — is not permitted for new work. When you find it on an existing installation, the correction is to pull an equipment grounding conductor and remove the bond, not to add another electrode.
Why the neutral bond at a second building is dangerous. With the neutral bonded at both buildings, normal load current divides between the neutral conductor and every other metal path between the two structures — the equipment grounding conductor, a water line, a fence, the earth itself. Current on those paths creates voltage differences between metal parts in two separate buildings, and the fault-clearing path becomes unpredictable.
A 100 A feeder to a subpanel is run in 10 ft of flexible metal conduit with no wire-type equipment grounding conductor. What is the problem?
A feeder supplies a separate maintenance building on the same commercial property. Under 250.32(B)(1), how is the grounded (neutral) conductor treated at that building?
On a 240/120 V, 4-wire delta-connected system, how must the conductor with the higher voltage to ground be identified?