APB for......'pipe electrode'

[ToolHound]

The illustration is potentially misleading in a way that has come up in other threads. You can only count a ufer if it runs through a wall footing rather than just through a flat foundation slab. The rods that go through the slab add to the quality of the ground as long as there is not a waterproofing membrane under it, but it is the footing portion that is mandatory.

Thanks GoldDigger. The more insight, the better. Here's the 2011 Code subsection for Concrete-Encased Electrodes, with the location specifications emphasized:

Chapter 2 Wiring and Protection
ARTICLE 250 Grounding and Bonding
III. Grounding Electrode System and Grounding Electrode Conductor

250.52 Grounding Electrodes.

(A) Electrodes Permitted for Grounding.

(3) Concrete-Encased Electrode. A concrete-encased electrode shall consist of at least 6.0 m (20 ft) of either (1) or (2):

(1)

One or more bare or zinc galvanized or other electrically conductive coated steel reinforcing bars or rods of not less than 13 mm (? in.) in diameter, installed in one continuous 6.0 m (20 ft) length, or if in multiple pieces connected together by the usual steel tie wires, exothermic welding, welding, or other effective means to create a 6.0 m (20 ft) or greater length; or

(2)

Bare copper conductor not smaller than 4 AWG

Metallic components shall be encased by at least 50 mm (2 in.) of concrete and shall be located horizontally within that portion of a concrete foundation or footing that is in direct contact with the earth or within vertical foundations or structural components or members that are in direct contact with the earth. If multiple concrete-encased electrodes are present at a building or structure, it shall be permissible to bond only one into the grounding electrode system.

Informational Note: Concrete installed with insulation, vapor barriers, films or similar items separating the concrete from the earth is not considered to be in “direct contact” with the earth.

And the related Handbook Commentary sez, quote:

To qualify as a grounding electrode, the horizontal or vertical installation of the steel reinforcing rod or the 4 AWG bare copper conductor within the concrete encasement is to be in one continuous 20 ft length so that there is a 20 ft long electrode in contact with the earth. Shorter lengths of reinforcing rod can be connected together to form an electrode 20 ft or longer using the connection methods identified in this requirement. Section 250.52(A)(3) only requires that a single concrete-encased electrode be incorporated into the grounding electrode system. Some buildings or structures may have discontinuous segments of a footing or foundation that individually qualify as grounding electrodes per this section, and once one has been bonded to the grounding electrode system, the remaining ones are exempt from any bonding or grounding requirements. Exhibit 250.23 shows an example of a concrete-encased electrode embedded horizontally. As indicated in the informational note, direct contact with the earth means that there is no medium between the concrete and the earth that impedes the grounding connection or insulates the concrete from being in direct contact with the earth.

Links to some other posts related to concrete-encased electrode are:

http://forums.mikeholt.com/showthread.php?t=83790
http://www.mikeholt.com/forum/Forum1/HTML/002508.html

 

[ToolHound]

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[GlennH]

pipe electrodes

pipe electrodes

Worked with an oldtimer who used to tell me that back in "his day" they would smash the end of a pipe and drive it into the ground. This would allow the inspector to stick his footrule down to measure the depth that you drove it down.

 

[ToolHound]

Worked with an oldtimer who used to tell me that back in "his day" they would smash the end of a pipe and drive it into the ground. This would allow the inspector to stick his footrule down to measure the depth that you drove it down.

Making it easier for the Inspector to do his/her job...sounds like a smart idea. 'Oldtimers' usually have smart ideas.