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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
By Mike Holt
When cables and raceways are run underground, they must
have a minimum "cover" in accordance with Table 300.5. Note 1 to Table
300.5 defines cover as the distance to the top of the underground cable
or raceway to the surface of finish grade. The cover requirements
contained in 300.5 do not apply to signaling or communications wiring.
These requirements are found in other sections of the Code.
Cables and insulated conductors installed in enclosures or raceways
underground must be listed for use in wet locations. Cables run under a
building must be installed in a raceway that extends past the outside
walls of the building.
Direct buried conductors and cables must be protected from damage in
accordance with (1) through (4).
Direct buried conductors or cables can be spliced or tapped underground
without a splice box [300.15(G)], if the splice or tap is made in
accordance with 110.14(B).
- Emerging from grade. Direct buried cables or conductors that
emerge from the ground must be installed in an enclosure or raceway to
protect against physical damage. Protection isn't required to extend
more than 18 inches below grade, and protection above grade must extend
to a height not less than 18 feet.
- Conductors entering buildings. Conductors that enter a
building must be protected to the point of entrance.
- Service conductors. Service conductors that aren't under the
exclusive control of the electric utility, and are buried 18 inches or
more below grade, must have their location identified by a warning
ribbon in the trench not less than 1 foot above the underground
installation. Note: It's impossible to comply with the service
conductor identification location requirement when service conductors
are installed using directional boring equipment.
- Enclosure or raceway damage. Where direct buried cables,
enclosures, or raceways are subject to physical damage, the conductors
must be installed in rigid metal conduit, intermediate metal conduit,
Schedule 80 rigid nonmetallic conduit.
Backfill material for underground wiring must not damage the
underground cable raceway or contribute to the corrosion of the metal
raceway. Large rocks, chunks of concrete, steel rods, mesh, or other
sharp-edged objects cannot be used for backfill material because they
can damage the underground conductors, cables, or raceways.
Where moisture could enter a raceway and contact energized live
parts, seals must be installed at one or both ends of the raceway. This
is a common problem for equipment located physically downhill from the
supply or in underground equipment rooms. See 230.8 for service raceway
seals and 300.7(A) for different temperature area seals. A Fine Print
Note in 300.5(G) explains that hazardous explosive gases or vapors make
it necessary to seal underground conduit or raceways that enter the
building in accordance with 501.15. It isn't the intent of this FPN to
imply that seal-offs of the types required in hazardous (classified)
locations must be installed in unclassified locations, except as
required in Chapter 5. This also doesn't imply that the sealing
provides a watertight seal, but only that it prevents moisture from
Raceways that terminate underground must have a bushing or fitting
the end of the raceway to protect emerging cables or conductors.
All conductors of the same circuit, including the
(bonding) conductor, must be inside the same raceway or in close
proximity to each other. See 300.3(B). There are two Exceptions
associated with this rule. The first notes that conductors can be
installed in parallel in accordance with 310.4. The second exception
states individual sets of parallel circuit conductors can be installed
in underground nonmetallic raceways, if inductive heating at raceway
terminations is reduced by complying with 300.20(B) [300.3(B)(1) Ex.
1]. Installing phase and neutral wires in different nonmetallic
makes it easier to terminate larger parallel sets of conductors, but it
will result in higher levels of electromagnetic fields (EMF), which can
cause computer monitors to flicker in a distracting manner.
Direct buried conductors, cables, or raceways subject to movement by
settlement of frost, must be arranged to prevent damage to conductors
equipment connected to the wiring.
Cables or raceways installed using directional boring equipment must
be approved by the authority having jurisdiction (AHJ) for this
Editor's note: This information was extracted from Mike
the National Electrical Code
Fluke 117 Electrician's Multimeter with
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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: Count the prongs.
By Mike Holt
Q. What are the requirements for supporting
outlet boxes above/to suspended ceilings?
Visit EC&M's Web
site to see the answer.
By Steven Owen
Q. When installing a high-impedance grounded
neutral system, for a 480V, 3-phase system, the following question has
arisen. Which of the following choices best describes the proper
for the grounded conductor of the system?
- It shall be run (installed) in the same raceway with the other
phase conductors. This is the only choice. No other options are
- It shall be run (installed) in a non-metallic raceway with the
other phase conductors, following the requirements of
- It shall be permitted to be run (installed) in the same raceway
the other phase conductors if desired; however, it shall also be
permitted to be installed in a separate raceway by itself with any
routing chosen by the installer.
- It must be insulated, bare, or covered, and installed so as not to
be easily damaged, with or without a raceway for protection.
Web site for the answer and explanation.
Need help defining the parameters of your facility's next Arc
Flash Hazard Evaluation? ESA's electrical engineers have written a
detailed, customizable specification to help you determine what you
for your study. This Arc Flash tool is provided in a Word document that
can be easily updated with your facility's unique requirements. Request
your Free Arc
Flash Study Specification.
Code News Update
Code Committee Call-Up
Got some extra time on your hands? Looking to put some
of your vast knowledge of the electrical field to use? NFPA is looking
for new members for several of its committees, including the
Anyone interested in serving can download the application form at NFPA's Web
- Committee on Electrical Equipment in Chemical Atmospheres. This
committee is responsible for NFPA 496, Standard for Purged and
Pressurized Enclosures for Electrical Equipment; NFPA 497,
Recommended Practice for the Classification of Flammable Liquids,
Gases, or Vapors and of Hazardous (Classified) Locations for Electrical
Installations in Chemical Process Areas; and NFPA 499,
Recommended Practice for the Classification of Combustible Dusts and
of Hazardous (Classified) Locations for Electrical Installations in
Chemical Process Areas
- Committee on Electrical of Industrial Machinery (seeking members in
all categories except end users or manufacturers). This committee is
responsible for NFPA 79, Electrical Standard for Industrial
- Committee on Electrical Equipment Evaluation (seeking members in
- Committee on Electrical Systems Maintenance (special experts
excluded). This committee is responsible for NFPA 73, Electrical
Inspection Code for Existing Dwellings.
- Committee on Health Care Facilities -- Electrical Systems. This
committee is responsible for chapters within NFPA 99, Standard for
Health Care Facilities.
Cool Electronic Cabinets
Beat the heat and prevent hot weather failures. UL Listed Cabinet
Coolers from EXAIR produce 20 degree Fahrenheit air from an ordinary
supply of compressed air to cool electrical controls. Thermostat
minimizes air usage. Maintains the NEMA 4, 4X (stainless steel) and 12
rating of the enclosure. Web site offers detailed information,
downloadable drawings and PDF literature.
Shows and Events
Let's Go Racing! Win a Free Road
America Race Weekend for Two
EC&M magazine and Generac Power Systems have
teamed up to offer an expenses-paid weekend (August 10-12, 2007)
featuring two of the world's fastest racing series. The third annual
Generac Power Weekend is one thrilling day of American LeMans series
racing (the Generac 500) and an equally exciting day of Champ Car
at its finest (the Generac Grand Prix). It's your chance to see both
series compete in a single weekend at one of North America's most
beautiful tracks. Located in the hilly heart of Wisconsin's scenic
Kettle Moraine area, Road America is a four-mile permanent road course
that tests drivers with 14 challenging turns.
Enter by July 10, 2007. Visit the Generac Power Systems virtual
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E-Tradeshow. Full contest rules are available online in the Generac
E-Tradeshow booth. For more information about the Generac Power
go to www.roadamerica.com.
EC&M Code Change
Where do you turn when you need accurate information on
changes to the National Electrical Code? Acknowledged as the leaders in
providing information on the NEC, EC&M magazine and EC&M
Seminars have been the preferred sources of this information for more
than 60 years. Seven Code change conferences have been scheduled in the
fall of 2007. Host cities include: Atlanta, Boston, Dallas, Orlando,
Philadelphia, St. Louis, and Seattle.
As an approved provider with the National Council of Examiners for
Engineering and Surveying (NCEES), through its Registered Continuing
Education provider Program (RCEPP), professional engineers attending
of our 2008 Code change conferences will receive Professional
Development Hours (PDHs), a requirement for re-licensing in many
The conferences are also approved by every state that has a continuing
education requirement for contractors and electricians.
For additional information on the dates and locations of these
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