| CONTENTS
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250.92
Service Bonding
What's
Wrong
Here?
Code Q&A
Code Quiz
Eliminating
Confusion Over Rod Size
EC&M Code
Change Conferences
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Top 50 NEC Rules
250.92
Service Bonding
By Mike Holt
As per section A of this requirement, the following
metal parts must be service bonded to an effective ground-fault current
path in accordance with 250.92(B):
- Metal raceways containing service conductors.
- Enclosures containing service conductors.
- A metal raceway containing the grounding electrode
conductor.
The metal raceway containing the grounding electrode conductor must be
effectively bonded in accordance with 250.64(E). Raceways or enclosures
containing feeder and branch-circuit conductors are not required to be
service bonded in accordance with 250.92(B).
As per section B of this requirement, enclosures and raceways
containing service conductors must be bonded to an effective
ground-fault current path by one of the following methods:
- Grounded Neutral Conductor. Enclosures and raceways
containing service conductors are considered bonded to an effective
ground-fault current path by bonding to the grounded neutral service
conductor via the main bonding jumper. The bonding must be by
exothermic
welding, listed pressure connectors, listed clamps, or other listed
fittings [250.8].
A main bonding jumper is required to bond the service disconnect to
the grounded neutral service conductor [250.24(B) and 250.28]. At
service equipment, the grounded neutral service conductor is used to
provide the effective ground-fault current path to the power source
[250.24(C)]. Therefore, an equipment grounding (bonding) conductor
isn't
required to be installed within a non-metallic raceway containing
service-entrance conductors [250.142(A)(1) and 352.60, Ex. 2] (see
Figure).
- Threaded Fittings or Entries. Raceways containing service
conductors are considered bonded to an effective ground-fault current
path by threaded couplings or threaded entries on enclosures where made
up wrenchtight.
- Threadless Fitting. Raceways containing service conductors
are considered bonded to an effective ground-fault current path by
threadless raceway couplings and connectors where made up
tight.
- Bonding Fitting. When a metal service raceway terminates to
an enclosure with a ringed knockout, a listed bonding device, such as a
bonding wedge or bushing, must bond one end of the service raceway with
a bonding jumper sized in accordance with Table 250.66 [250.92(B)(4)
and
250.102(C)].
When a metal raceway containing service conductors terminates to an
enclosure without a ringed knockout, a bonding-type locknut can be used
instead of a bonding wedge or bushing. A bonding-type locknut differs
from a standard-type locknut in that it has a bonding screw with a
sharp
point that drives into the metal enclosure to ensure a solid
termination. Bonding one end of a service raceway in accordance with
250.92(B) provides the low-impedance fault-current path to the utility
electrical supply source.
Editor's note: This information was extracted from Mike Holt's
textbook, Understanding
the National Electrical Code
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Code Challenge
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: Do you hear a fire truck siren?
Code Q&A
By Mike Holt
Q. If the secondary conductors of a transformer
are less than 10 feet in length, do the secondary conductors have to
terminate in a main breaker?
Visit EC&M's
Web site to see the answer.
Code Quiz
By Steven Owen
Q. When cutting and threading rigid metal
conduit, intermediate metal conduit and stainless steel conduit in the
"field", which one of the aforementioned conduits is not required to
have its threads protected with an approved electrically conductive
corrosion-resistant compound?
A) Rigid metal conduit.
B) Intermediate metal conduit.
C) Stainless steel conduit.
D) None of these conduit types are required to be protected with
an approved electrically conductive corrosion-resistant compound.
Visit EC&M's
Web site for the answer and explanation.
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Code News Update
Eliminating Confusion Over Rod
Size
Installers and inspectors alike have been confused over
the requirements of 250.52(A)(5) -- more specifically with regard to
the
diameter of the rod. In an effort to eliminate this confusion,
Code-Making Panel 5 has accepted in principle proposal 5-160 for the
2008 NEC. If adopted, the new section would read as follows:
"Rod and pipe electrodes shall not be less than 2.44 m (8 ft) in
length and shall consist of the following materials.
(a) Grounding electrodes of pipe or conduit shall not be smaller
than
metric designator 21 (trade size 3/4), and where of steel, shall have
the outer surface galvanized or otherwise metal-coated for corrosion
protection.
(b) Grounding electrodes of stainless steel, copper, or zinc-coated
steel shall be at least 15.87 mm (5/8 in.) in diameter unless listed
and
not less than 12.70 mm (1/2 in.) in diameter."
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Shows and Events
EC&M Code Change
Conferences
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. Plans are currently underway to present seven Code
change
conferences 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
any
of our 2008 Code change conferences will receive Professional
Development Hours (PDHs), a requirement for re-licensing in many
states.
The conferences are also approved by every state that has a continuing
education requirement for contractors and electricians.
Hotel and registration information will be announced soon!
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