Grounding vs Bonding Online Training

This article was posted 10/07/2005 and is most likely outdated.

Grounding vs Bonding: 250.30 Grounding and Bonding of Separately Derived AC Systems

October 7, 2005

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 [ 8MB ]

Below is the full course page which includes these videos:

Grounding versus Bonding

PART II.

Page 7 of 13

Sections

250.30 Grounding and Bonding of Separately Derived AC Systems.

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 250–67

Generators that supply a transfer switch that opens the grounded neutral conductor would be considered separately derived [250.20(D) FPN 1]. Figure 250–68

(A) Grounded Systems. Separately derived systems must be system bonded and grounded in accordance with the following:

A neutral-to-case bond must not be on the load side of the system bonding jumper, except as permitted by 250.142(B).

(1) System Bonding Jumper. Bonding the metal parts of the separately derived system to the secondary grounded neutral terminal by the installation of a system bonding jumper ensures that dangerous voltage from a secondary ground fault can be quickly removed by opening the secondary circuit’s overcurrent protection device [250.2(A)(3)]. Figure 250–69

DANGER: During a ground fault, metal parts of electrical equipment, as well as metal piping and structural steel, will become and remain energized providing the potential for electric shock and fire if the system bonding jumper is not installed. Figure 250–70

The system bonding jumper must be sized in accordance with Table 250.66, based on the area of the largest ungrounded secondary conductor [250.28(D)].

Question: What size system bonding jumper is required for a 45 kVA transformer, where the secondary conductors are 3/0 AWG? Figure 250–71

(a) 4 AWG (b) 3 AWG (c) 2 AWG (d) 1 AWG

Answer: (a) 4 AWG, Table 250.66

Figure 250–67
(Click on image to enlarge)

Figure 250–68
(Click on image to enlarge)

Figure 250–69
(Click on image to enlarge)

Figure 250–70
(Click on image to enlarge)

Figure 250–71
(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

Re: "All transformers, except autotransformers, are separately derived because the primary circuit conductors do not have any direct electrical connection to the secondary circuit conductors." -- This statement is untrue. Y-y transformers with solidly bonded primary-secondary neutrals are a perfect example, such an installation is NOT a separately derived system. Any transformer with an intentional bond from a primary neutral or phase conductor to a secondary neutral or phase conductor is NOT a separately derived system.

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