Grounding (Earthing) Electrodes
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The designations "National Electrical Code” and “NEC” refer to the
National Electrical Code®, which is a registered
trademark of the
National Fire Protection Association.
Top 50 NEC Rules
Grounding (Earthing) Electrodes
By Mike Holt
Electrodes permitted for grounding include:
Electrodes not permitted for grounding include:
- An underground metal water pipe in direct contact with earth for 10
feet or more
- The metal frame of a building or structure, where any of the
following methods exist:
(a) 10 feet or more of a single structural
metal member is in direct contact with the earth or encased in concrete
that is in direct contact with the earth.
(b) The structural metal
bonded to an electrode as defined in 250.52(A)(1), (3), or (4).
The structural metal is bonded to two ground rods if the ground
resistance of a single ground rod exceeds 25 ohms [250.52(A)(5) and
(d) Other means approved by the authority having
- A concrete-encased grounding electrode. Steel reinforcing bars not
smaller than 1/2-inch in diameter or 4 AWG copper conductor can serve
as a grounding electrode if the steel or copper conductor has a total
conductive length of 20 feet, is encased in not less than 2 inches of
concrete, and is located near the bottom of a foundation or footer that
is in direct contact with earth.
- A ground ring encircling a building or structure, in direct contact
with earth consisting of not less than 20 feet of bare copper conductor
not smaller than 2 AWG copper.
- A ground rod not less than 8 feet long, with no less than 8 feet of
length in contact with the soil.
- A grounding plate. A buried iron or steel plate with not less than
1/4-inch of thickness, or a nonferrous (copper) metal plate not less
than 0.06 inch thick, with an exposed surface area not less than 2
- A metal underground system such as piping systems, underground
tanks, or an underground metal well casing that isn't effectively
to a metal water pipe system.
Editor's note: This information was extracted from Mike Holt's
the National Electrical Code.
- Underground metal gas piping systems or structures.
- Aluminum electrodes. Aluminum can't be used as a grounding
because it corrodes more quickly than copper.
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What's Wrong Here?
By Joe Tedesco
Think you know how this installation violates the
NEC? Visit EC&M's Web
site to see the answer.
Hint: Is this a new faux wood-approved electrical
By Mike Holt
Q. What are the limitations on the use of rigid
nonmetallic conduit in an underground application serving a gasoline
Web site to see the answer.
By Steven Owen
Q. In a Class 1 location of a spray application
(Art. 516) area, portable equipment such as portable electric lamps or
other utilization equipment shall be permitted in which of the
A) Never permitted.
B) Portable electric lamps identified for Class 1, Division 1 or
Class 1, Zone 1 locations where readily ignitable residues may be
present. This is intended for operations in spaces not readily
illuminated by fixed lighting within the spraying area.
C) Where portable electric drying apparatus is used in
refinishing spray booths, and the additional requirements of 516.4(D),
Exception No. 2, (a) through (d) are met.
D) Both B and C.
Web site for the answer and explanation.
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- Electrical Power Engineering: Industry Shortcomings and Possible
- MV Cable Basics: Construction, Testing, Ground Fault
- Ten Trends That Will Shock the Electrical Market
- Good Project Management: Enhancing the Bottom Line
- Insulation Resistance Testing
- Short Term, Long Term Energy Storage Methods for Standby Power
- 2007 Construction Market Forecast
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