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2011 Changes to the NEC – 250.64
The following is an instructional page from our 2011 Changes to the NEC Textbook/DVD Package complete with graphics and video where applicable. As part of our on-going effort to provide free resources to help the industry, we will be sending this content as part of a series of newsletters. Each newsletter will feature pages taken directly from our textbooks. This can be a great training resource for your organization!
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.
250.64 Grounding Electrode Conductor Installation
Several changes to this section have been made for clarity and technical accuracy.
250.64 Grounding Electrode Conductor Installation. Grounding electrode conductors must be installed as specified in (A) through (F).
(A) Aluminum Conductors. Aluminum grounding electrode conductors must not be in contact with masonry, subject to corrosive conditions, or within 18 in. of the earth.
(B) Conductor Protection. Where installed exposed, grounding electrode conductors must be protected where subject to physical damage and are permitted to be installed on or through framing members. Grounding electrode conductors 6 AWG copper and larger can be installed exposed along the surface of the building if securely fastened and not subject to physical damage.
Grounding electrode conductors sized 8 AWG must be protected by installing them in rigid metal conduit, intermediate metal conduit, PVC conduit, electrical metallic tubing, or reinforced thermosetting resin conduit.
Author’s Comment: A ferrous metal raceway containing a grounding electrode conductor must be made electrically continuous by bonding each end of that type of raceway to the grounding electrode conductor [250.64(E)], so it’s best to use PVC conduit.
(C) Continuous. Grounding electrode conductor(s) must be installed without a splice or joint except:
(1) By irreversible compression-type connectors or exothermic welding.
(2) Sections of busbars connected together to form a grounding electrode conductor.
(3) Bolted, riveted, or welded connections of structural metal frames of buildings or structures.
(4) Threaded, welded, brazed, soldered or bolted-flange connections of metal water piping.
(D) Grounding Electrode Conductor for Multiple Service Disconnects. If a service consists of more than a single enclosure, grounding electrode connections must be made in one of the following methods:
(1) Common Grounding Electrode Conductor and Taps. A grounding electrode conductor tap must extend to the inside of each service disconnecting means enclosure.
The common grounding electrode conductor must be sized in accordance with 250.66, based on the sum of the circular mil area of the largest ungrounded service-entrance conductors. Figure 250–54
Figure 250-54 (Click on image to enlarge)
A grounding electrode conductor must extend from each service disconnecting means, sized not smaller than specified in Table 250.66, based on the area of the largest ungrounded conductor for each service disconnecting means.
The grounding electrode tap conductors must be connected to the common grounding electrode conductor, without splicing the common grounding electrode conductor, by one of the following methods:
(1) Exothermic welding
(2) Connectors listed as grounding and bonding equipment
(3) Connections to a busbar not less than 1⁄4 in. × 2 in. that’s securely fastened and installed in an accessible location.
(2) Individual Grounding Electrode Conductors. A grounding electrode conductor must be connected between the grounded conductor in each service equipment disconnecting means enclosure and the grounding electrode system, each sized in accordance with 250.66 based on the ungrounded service-entrance conductor(s) supplying the individual service disconnecting means. Figure 250–55
Figure 250-55 (Click on image to enlarge)
(3) Common Location. A single grounding electrode conductor is permitted from a common location, sized not smaller than specified in Table 250.66, based on the area of the ungrounded conductor at the location where the connection is made. Figure 250–56
Figure 250-56 (Click on image to enlarge)
(E) Ferrous Metal Enclosures Containing Grounding Electrode Conductors. To prevent inductive choking of grounding electrode conductors, ferrous raceways and enclosures containing grounding electrode conductors must have each end of the raceway or enclosure bonded to the grounding electrode conductor in accordance with 250.92(B) for installations at service equipment. Figure 250–57
Figure 250-57 (Click on image to enlarge)
For other than service equipment locations, ferrous raceways and enclosures containing grounding electrode conductors must have each end of the raceway or enclosure bonded to the grounding electrode conductor in accordance with 250.92(B)(2) through (B)(4).
Author’s Comment: Nonferrous metal raceways, such as aluminum rigid metal conduit, enclosing the grounding electrode conductor aren’t required to meet the “bonding each end of the raceway to the grounding electrode conductor” provisions of this section.
Caution: The effectiveness of a grounding electrode is significantly reduced if a ferrous metal raceway containing a grounding electrode conductor isn’t bonded to the ferrous metal raceway at both ends. This is because a single conductor carrying high-frequency induced lightning current in a ferrous raceway causes the raceway to act as an inductor, which severely limits (chokes) the current flow through the grounding electrode conductor. ANSI/IEEE 142, Recommended Practice for Grounding of Industrial and Commercial Power Systems (Green Book) states: “An inductive choke can reduce the current flow by 97 percent.”
Author’s Comment: To save a lot of time and effort, install the grounding electrode conductor exposed if it’s not subject to physical damage [250.64(B)], or enclose it in PVC conduit suitable for the application [352.10(F)].
(F) Termination to Grounding Electrode.
(1) Single Grounding Electrode Conductor. A single grounding electrode conductor is permitted to terminate to any grounding electrode of the grounding electrode system. Figure 250–58
Figure 250-58 (Click on image to enlarge)
(2) Multiple Grounding Electrode Conductors. When multiple grounding electrode conductors are installed [250.64(D)(2)], each grounding electrode conductor is permitted to terminate to any grounding electrode of the grounding electrode system. Figure 250–59
Figure 250-59 (Click on image to enlarge)
(3) Termination to Busbar. A grounding electrode conductor and grounding electrode bonding jumpers are permitted to terminate to a busbar sized not less than ¼ in. × 2 in. that’s securely fastened at an accessible location. The terminations to the busbar must be made by a listed connector or by exothermic welding. Figure 250–60
Figure 250-60 (Click on image to enlarge)
ANALYSIS:
Previous editions of the Code used the now obsolete term “grounding conductors” in this subsection, although the title of 250.64 is “grounding electrode conductor installation.” This change clarifies that the grounding electrode conductor is the topic.
With the new raceway systems that have been added to the NEC over the past few years, 250.64(B) was in need of an update. It’s now clear that both PVC conduit and RTRC conduit can be used for protecting the grounding electrode conductor, in addition to the other raceways that the Code already recognized.
Although the definition of “tap conductor” is found in 240.2, and therefore should only be used for conductors described in Article 240, most people in the industry think of an ungrounded conductor when they read the phrase “tap conductor.” In order to avoid this confusion, and to use terms consistently throughout the NEC, the term “tap conductor” in this section has been replaced with “grounding electrode conductor tap.”
The Code has long required that ferrous metal raceways containing the grounding electrode conductor be bonded at each end, in an effort to reduce the effects of “inductive choke” on the conductors. The manner in which the bonding is to be performed, however, has never been addressed. Revisions to this section now clarify that the bonding method must be recognized by 250.92(B) (service bonding) in order to meet this requirement. Considering that most electricians use bonding bushings with a bonding jumper, this revision probably isn’t that significant. |
2011 NEC Changes DVD Package |
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Don't let the scale of the code changes intimidate you, this package will get you up to speed on the most essential 2011 NEC changes quickly. The book is well-organized, easy to follow, and the full-color illustrations bring the material to life. The DVDs bring together a group of experts from the field to discuss the changes and how they apply in the real-world.
This program includes the following items:
- Changes to the NEC 2011 Textbook
- Changes to the NEC 2011 DVD 1 & 2 includes Articles 90 - 810
Product Code: 11CCDVD
Price: $198.00
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