2011 Changes to the NEC – 250.4

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.

250.4(A)(1) Solidly Grounded Systems

The Informational Note regarding the length of grounding electrode conductors has been revised.

250.4 General Requirements for Grounding and Bonding.

(A) Solidly Grounded Systems.

(1) Electrical System Grounding. Electrical power systems, such as the secondary winding of a transformer are grounded (connected to the earth) to limit the voltage induced by lightning, line surges, or unintentional contact by higher-voltage lines.

Figure 250-2 (Click on image to enlarge)

Author’s Comment: System grounding helps reduce fires in buildings as well as voltage stress on electrical insulation, thereby ensuring longer insulation life for motors, transformers, and other system components.

Figure 250-3 (Click on image to enlarge)

Note: An important consideration for limiting imposed voltage is to remember that grounding electrode conductors shouldn’t be any longer than necessary and unnecessary bends and loops should be avoided.

Figure 250-4 (Click on image to enlarge)

ANALYSIS: With the deletion of the term “grounding conductor” from Article 100, this rule was in need of revision. The Code now makes it quite clear that the length of grounding electrode conductors is of concern for the proper application of 250.4(A)(1). Because of the high frequency of lightning, the length of the grounding electrode conductor becomes critical in order to reduce inductive reactance.

 

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