Bare Copper Conductor in Concrete
Some professionals are reluctant to use bare copper conductor embedded in concrete. They argue that the basic nature of concrete would be a source of corrosion. However this is not a proven argument and different codes and standards have allowed the use of bare copper embedded in concrete as a ground electrode.
The following excerpts of codes can clarify this issue\;
NEC
National electrical code Article 093, Section E.5 only rules out Aluminum conductor for direct burial in concrete for grounding purposes:
“5. Metals used for grounding, in direct contact with earth, concrete, or masonry, shall have been proven suitable for such exposure.
NOTE 1: Under present technology, aluminum has not generally been proven suitable for such use.
NOTE 2: Metals of different galvanic potentials that are electrically interconnected may require protection against galvanic corrosion.”
NEC article 094, section B.6 specifically refers to copper conductor for use as concrete encased electrode application:
“A metallic wire, rod, or structural shape, meeting Rule 93E5 and encased in concrete, that is not insulated from direct contact with earth, shall constitute an acceptable ground electrode. The concrete depth below grade shall be not less than 300 mm (1 ft), and a depth of 750 mm (2.5 ft) is recommended. Wire shall be no smaller than AWG No. 4 if copper, or 9 mm (3/8 in) diameter or AWG No. 1/0 if steel. It shall be not less than 6.1 m (20 ft) long, and shall remain entirely within the concrete except for the external connection. The conductor should be run as straight as practical.”
CSA
Canadian electrical code Section 10 item 10-700 accepts concrete encased copper conductor as a grounding electrode.
“10-700 Grounding electrodes (see Appendix B)
(3) A field-assembled grounding electrode shall consist of
(a) a bare copper conductor not less than 6 m in length, sized in accordance with Table 43 and encased within the bottom 50 mm of a concrete foundation footing in direct contact with the earth at not less than 600 mm below finished grade”
Also in item 10-806:
“(6) Notwithstanding Subrule (2), a grounding conductor No. 6 AWG or larger shall be permitted to be embedded in concrete provided that the points of emergence are located or guarded so as not to constitute exposure to mechanical damage.”
And in table 43, the size of bare copper conductor is specified for different ampacities of the service conductor:
Table 43
Minimum conductor size for concrete-encased electrodes
(See Rule 10-700.)
Ampacity of largest service conductor or equivalent for multiple conductors, A
|
Size of bare copper conductor, AWG
|
165 or less
|
4
|
166–200
|
3
|
201–260
|
2
|
261–355
|
0
|
356–475
|
00
|
Over 475
|
000
|
