2011 Changes to the NEC – 250.32

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There are some important features in this text which help to highlight the changes that you should be aware of:

• Each Code section which contains a change includes a summary of the change, followed by a paraphrase of the NEC text affected by the change. Any specific change is denoted by underlined text and in the corresponding chapter color
• Graphics with green borders and 2011 CC icons next to the heading are graphics that contain a 2011 change; graphics without a green border or icon are graphics that support the concept being discussed, but nothing in the graphic was affected by a 2011 Code change.

250.32 Buildings or Structures Supplied by a Feeder or Branch Circuit

The exception dealing with existing installations has been clarified, and a new subsection was added to address buildings supplied by a separately derived system.

250.32 Buildings or Structures Supplied by a Feeder or Branch Circuit.

(B) Equipment Grounding Conductor.

(1)  Supplied by a Feeder or Branch Circuit. To quickly clear a ground fault and remove dangerous voltage from metal parts, the building/structure disconnecting means must be connected to the circuit equipment grounding conductor, which must be one of the types described in 250.118. If the supply circuit equipment grounding conductor is of the wire type, it must be sized in accordance with 250.122, based on the rating of the overcurrent device. Figure 250–42

Figure 250-42 (Click on image to enlarge)

Caution: To prevent dangerous objectionable neutral current from flowing onto metal parts [250.6(A)], the supply circuit neutral conductor isn’t permitted to be connected to the remote building/structure disconnecting means [250.142(B)]. Figure 250–43

Figure 250-43 (Click on image to enlarge)

Ex: The neutral conductor can serve as the ground-fault return path for the building/structure disconnecting means for existing installations in compliance with previous editions of the Code where there are no continuous metallic paths between buildings and structures, ground-fault protection of equipment isn’t installed on the supply side of the circuit, and the neutral conductor is sized no smaller than the larger of:

(1) The maximum unbalanced neutral load in accordance with 220.61.
(2) The minimum equipment grounding conductor size in accordance with 250.122.

(2) Supplied by Separately Derived System.

(a) With Overcurrent Protection. If overcurrent protection is provided where the conductors originate, the supply conductors must contain an equipment grounding conductor in accordance with 250.32(B)(1).

(b) Without Overcurrent Protection. If overcurrent protection isn’t provided for the supply conductors to the building/structure as permitted by 240.21(C)(4), the installation must be grounded and bonded in accordance with 250.30(A).

ANALYSIS: The 2008 NEC contained a significant change to this section by requiring that an equipment grounding conductor be installed for buildings or structures supplied by feeders or branch circuits. With this change, an exception was added to the 2008 Code, clarifying that existing premises wiring systems need not comply with this new rule. Because most NEC changes don’t come with an exception that gives exemption for existing installations, confusion ensued. For example, when the AFCI requirements were expanded, there wasn’t an exception for existing buildings, because the Code isn’t retroactive (90.2(A) tells us that the NEC is an installation standard, not a maintenance standard). Because of this, when the exception was added, many Code users had no idea what it really pertained to. The change in this NEC revision cycle, however, clarifies that this exception applies only to existing buildings or structures that met the previous Code requirements and continue to meet the previous requirements, such as not having continuous grounded metal paths between the two buildings or structures. Previous NEC editions required a building or structure supplied by a feeder or branch circuit to be supplied with an equipment grounding conductor. When a building or structure is supplied by a separately derived system, with no overcurrent protection at the source, there’s no equipment grounding conductor by definition. This revision clarifies that when this occurs, a supply side bonding jumper must be run to the building or structure, and it’s to be installed in accordance with 250.30(A).

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