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2011 Changes to the NEC – 250.92
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.
250.92 Bonding Equipment for Services
The requirements for the bonding of service equipment were editorially revised, and the bonding of equipment containing service conductors has been revised for clarity and accuracy.
250.92 Bonding Equipment for Services.
(A) Bonding Requirements for Equipment for Services. The metal parts of equipment indicated below must be bonded together in accordance with 250.92(B). Figure 250–62
Figure 250-62 (Click on image to enlarge)
(1) Metal raceways containing, enclosing, or supporting service conductors.
(2) Metal enclosures containing service conductors.
Author’s Comment: Metal raceways or metal enclosures containing feeder and branch-circuit conductors are required to be connected to the circuit equipment grounding conductor in accordance with 250.86. Figure 250–63
Figure 250-63 (Click on image to enlarge)
(B) Methods of Bonding. Bonding jumpers around reducing washers or oversized, concentric, or eccentric knockouts are required. Standard locknuts are permitted to make a mechanical connection of the raceway(s), but they can’t serve as the bonding means required by this section. Figure 250–64
Figure 250-64 (Click on image to enlarge)
Electrical continuity at service equipment, service raceways, and service conductor enclosures must be ensured by one of the following methods:
(1) Neutral Conductor. By bonding the metal parts to the service neutral conductor. Figure 250–65
Figure 250-65 (Click on image to enlarge)
Author’s Comments:
• A main bonding jumper is required to bond the service disconnect to the service neutral conductor [250.24(B) and 250.28].
• At service equipment, the service neutral conductor provides the effective ground-fault current path to the power supply [250.24(C)]; therefore, an equipment grounding conductor isn’t required to be installed within PVC conduit containing service-entrance conductors [250.142(A)(1) and 352.60 Ex 2]. Figure 250–66
Figure 250-66 (Click on image to enlarge)
(2) Threaded Fittings. By terminating metal raceways to metal enclosures by threaded hubs on enclosures if made up wrenchtight. Figure 250–67
Figure 250-67 (Click on image to enlarge)
(3) Threadless Fittings. By terminating metal raceways to metal enclosures by threadless fittings if made up tight. Figure 250–68
Figure 250-68 (Click on image to enlarge)
(4) Other listed devices, such as bonding-type locknuts, bushings, wedges, or bushings with bonding jumpers.
Author’s Comments:
• A listed bonding wedge or bushing with a bonding jumper must be used to bond one end of the service raceway to the service neutral conductor. The bonding jumper used for this purpose must be sized in accordance with Table 250.66, based on the area of the largest ungrounded service conductors within the raceway [250.102(C)]. Figure 250–69
Figure 250-69 (Click on image to enlarge)
• When a metal raceway containing service conductors terminates to an enclosure without a ringed knockout, a bonding-type locknut can be used. Figure 250–70
Figure 250-70 (Click on image to enlarge)
• A bonding locknut differs from a standard locknut in that it’s a bonding screw with a sharp point that drives into the metal enclosure to ensure a solid connection.
• Bonding one end of a service raceway to the service neutral provides the low-impedance fault current path to the source. Figure 250–71
Figure 250-71 (Click on image to enlarge)
ANALYSIS: This change was made mainly for the sake of using more accurate terminology. Previous editions of the Code used the terms “bonding of services” as the title of 250.92(A), which isn’t really accurate. This requirement addresses the bonding of equipment related to the service, not the bonding of the actual service. Additionally, this change clarifies that meter enclosures containing service conductors must be bonded, a fact that could have been argued in previous editions of the NEC.
The term “bosses” has been changed to “hubs,” as that term is far more understood by the industry.
By adding the term “oversized” to the requirements of 250.92(B), it becomes clear that this rule applies to any knockout that isn’t the correct size, whether it’s the result of concentric or eccentric knockouts, or simply a mistake made in the field.
An additional change to the language in this section clarifies that while standard locknuts can’t be used to satisfy this rule, they’re allowed to be used in addition to the requirements of this subsection. |
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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