Grounding vs Bonding Online Training 12

This article was posted 09/02/2005 and is most likely outdated.

Many of you have completed our Online Continuing Education Courses which include video instruction and know this is a very fast way to obtain your CEU credits from the comfort of the chair you're sitting in. For the rest of you we are sending a weekly series of newsletters featuring an instructional page complete with videos.

To view the videos you will need to download the free Real Player plugin for your browser - if you don't already have it. After installing Real Player, you can view the videos by clicking on one of these icons:

Click on this icon to view the video

Below is the full course page which includes these videos:

Grounding versus Bonding

PART II.

Page 2 of 13

Sections

250.20 Systems Required to be Grounded and Bonded Continued

(D) Separately Derived Systems. Separately derived systems that are required to be grounded (bonded) by 250.20(A) or (B), must be grounded and bonded in accordance with 250.30(A).

Author’s Comment: A separately derived system is a premises wiring system with no direct electrical connection to conductors originating from another system [Article 100 definition and 250.20(D)]. All transformers except autotransformers are separately derived because the primary circuit conductors do not have any direct electrical connection to the secondary circuit conductors. Figure 250–46

Generators that supply a transfer switch that opens the grounded neutral conductor are also considered separately derived. Figure 250–47

FPN 1: A generator isn’t a separately derived system if the grounded neutral conductor from the generator is solidly connected to the electrical supply source.

Author’s Comment: In other words, if the transfer switch doesn’t open the grounded neutral conductor, then the generator isn’t a separately derived system. Therefore, a neutral-to-case bond (system bonding jumper) cannot be made at the generator because it will cause objectionable current to flow on metal parts in violation of 250.6(A). Figure 250–48

FPN 2: If a grounded neutral conductor is supplied at a transfer switch, and the transfer switch doesn’t open the grounded neutral conductor, then the grounded neutral conductor must be sized:
To carry fault current back to the generator in accordance with 445.13. Figure 250–49
Not smaller than required to carry the unbalanced load in accordance with 220.61.

(E) Impedance Grounded Neutral Systems. Impedance grounded (bonded) neutral systems must be grounded and bonded in accordance with 250.36.

Author’s Comment: The NEC refers to the practice of deliberately placing resistance between the system winding and the metal case as an impedance grounded neutral system. Figure 250–50

Figure 250–46
(Click on image to enlarge)

Figure 250–47
(Click on image to enlarge)

Figure 250–48
(Click on image to enlarge)

Figure 250–49
(Click on image to enlarge)

Figure 250–50
(Click on image to enlarge)

Grounding versus Bonding Library - DVDs

Grounding and bonding problems are at epidemic levels. Surveys repeatedly show a high percentage of power quality problems are due to poor grounding and bonding. Electrical theory has been applied to this difficult to understand Article, making it easier for students to grasp the concepts of grounding and bonding. Additionally, Mike has color coded the graphics so you can easily differentiate between grounding and bonding. For a limited time, you can order the Entire Grounding versus Bonding Library including the textbook, 2 videos, MP3 Audio CD and the Online Program for this great price. You save over $200!

Product Code: 05GBDVD
ISBN: N/A
MultiMedia: Tape & CDROM & DVD

DVD/CD Return Policy: Unopened sealed DVD's or CD's may be returned within 10 days and we will credit your credit card or issue a refund for the price of the item(s). Opened items may not be returned unless they arrive defective.

Table of Contents

Sample Pages

Sample Graphic

Comments

To say that "All transformers except autotransformers are separately derived" is a bit of an overstatement -- for example, a Y-y transformer with the primary & secondary neutrals solidly bonded does NOT constitute a separately derived system.

Reply to this comment

Mike I really appreciate the information I recieved through your e-mails. Mike! I need to know more about motor control systems and their relationship with system grounding and bonding, with 480 votes 3 phaze systems.

Reply to this comment

Add Your Comments to this Newsletter


* Your Name:	Your name will appear under your comments.
* Your Email:	Your email address is not displayed.
* Comments:	This newsletter is closed to new comments. Email Notification Options: Notify me when a reply is posted to this comment Notify me whenever a comment is posted to this newsletter