Grounding vs Bonding Online Training

This article was posted 02/10/2006 and is most likely outdated.

Grounding vs Bonding: 250.66 Grounding Electrode Conductor—Size

February 10, 2006

View Comments | Add Comments

PART III. GROUNDING ELECTRODE SYSTEM AND GROUNDING ELECTRODE CONDUCTOR

VIEWING Video FILE requires Real Media Player [ FREE ]

Page 12 of 14

Sections

250.66 Grounding Electrode Conductor—Size.

Except for a ground rod electrode [250.66(A)], a concrete-encased electrode [250.66(B)], or a ground ring electrode [250.66(C)], the grounding electrode conductor must be sized based on the largest service-entrance conductor or equivalent area for parallel conductors in accordance with Table 250.66

Question: What size grounding electrode conductor is required for a 1,200A service that is supplied with three parallel sets of 600 kcmil conductors per phase? Figure 250–116

(a) 1 AWG (b) 1/0 AWG (c) 2/0 AWG (d) 3/0 AWG

Answer: (d) 3/0 AWG

The equivalent area of three parallel 600 kcmil conductors is 1,800 kcmil per phase [Table 250.66].

FPN: Because the grounded neutral service conductor is required to serve as the low-impedance ground-fault current path back to the source, it must be sized no smaller than that shown in Table 250.66 [250.24(C)(1)]. Of course, it must be sized to carry the maximum unbalanced load as calculated by 220.61.

(A) Ground Rod. Where the grounding electrode conductor is connected to a ground rod, that portion of the grounding electrode conductor that is the sole connection to the ground rod isn’t required to be larger than 6 AWG copper. Figure 250–117

Author’s Comment: See 250.52(A)(5) for the installation requirements of a ground rod electrode.

(B) Concrete-Encased Grounding Electrode (Ufer Ground). Where the grounding electrode conductor is connected to a concrete-encased electrode, that portion of the grounding electrode conductor that is the sole connection to the concrete-encased electrode isn’t required to be larger than 4 AWG copper. Figure 250–118

Author’s Comment: See 250.52(A)(3) for the installation requirements of a concrete-encased electrode.

(C) Ground Ring. Where the grounding electrode conductor is connected to a ground ring, that portion of the conductor that is the sole connection to the ground ring isn’t required to be larger than the conductor used for the ground ring.

Author’s Comment: A ground ring encircling the building or structure in direct contact with earth must consist of not less than 20 ft of bare copper conductor not smaller than 2 AWG [250.52(A)(4)].

Figure 250–116
(Click on image to enlarge)

Figure 250–117
(Click on image to enlarge)

Figure 250–118
(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

My viewpoint of a Ufer ground is that for a service over 200 amps the length of metal that is in the footer should be increased to more than 20 feet and the wire size should be increased as well.

So far I have inly installed 1 electrical service that used a Ufer ground because most of the work that I do does NOT involve residential new construction. In this case I was building a 400 amp residential sevice using two 200 amp service switches. To avoid using crimpers I used two #4 copper wires each 24 feet long in the footer running in opposite directions. This way I could bond the 2 grounding electrode conductors together using a clamshell terminal.

Mike Cole, mc5w at earthlink dot net

Michael R. Cole

Reply from: Mike Holt
Michael, please don't take my response to be rude, but do you have anything to support your theory or do you just think it's a good idea?

Reply to this comment


* 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