Grounding vs Bonding Online Training

This article was posted 12/30/2005 and is most likely outdated.

Grounding vs Bonding: 250.54 Supplementary Electrodes

December 30, 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.

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Grounding versus Bonding

PART III. GROUNDING ELECTRODE SYSTEM AND GROUNDING ELECTRODE CONDUCTOR

Page 6 of 14

Sections

250.54 Supplementary Electrodes.

A supplementary electrode is an electrode that is not required by the NEC. This electrode is not required to be bonded to the building or structure grounding electrode (earthing) system. Figure 250–103

The supplementary electrode is not required to be sized to 250.66, and it is not required to comply with the 25 ohm resistance requirement of 250.56. Figure 250–104

The earth cannot be used as an effective ground-fault current path as required by 250.4(A)(4).

Author’s Comment: Because the resistance of the earth is so high, very little current will return to the electrical supply source via the earth. If a ground rod is used as the ground-fault current path, the circuit overcurrent protection device will not open and metal parts will remain energized.

CAUTION: The requirements contained in 250.54 for a “supplementary” electrode should not be confused with the requirements contained in 250.53(D)(2) for the underground metal water pipe “supplemental” electrode.

Author’s Comment: Typically, a supplementary electrode serves no useful purpose, and in some cases it may actually create equipment or performance failure. However, in a few cases, the supplementary electrode is used to help reduce static charges on metal parts. For information on protection against static electricity in hazardous (classified) locations, see NFPA 77, Recommended Practice on Static Electricity.

Figure 250–103
(Click on image to enlarge)

Figure 250–104
(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

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Comments

Hello Mike,

I have a single phase load 200kW@480V in my system, and the rest of load is only 20kw@480V 3phase. What kind of transformer I can use for this? What I need to watch out for such a distribution system? The primary system is 600V@3phase.

Your help will be greatly appreciated!

Hao Sun
Reply to this comment

Reply from: Mike Holt
All questions of a technical nature shold be posted on our code forum. Simply go to www.mikeholt.com and click "Code Forum" in the left menu bar.

Thank you.
Reply to Mike Holt

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