Buildings or Structures Supplied by a Feeder or Branch Circuit
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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
Buildings or Structures Supplied by a Feeder or Branch Circuit
By Mike Holt
(A) Grounding Electrode. To provide a path to
earth for lightning, each building or structure must have its
disconnecting means [225.31] grounded (earthed) to one of the following
electrodes [250.50 and 250.52(A)]:
Where none of the above grounding electrodes are available at a
or structure, then one or more of the following must be used:
- Underground metal water pipe [250.52(A)(1)]
- Metal frame of the building or structure [250.52(A)(2)]
- Concrete-encased steel [250(A)(3)]
- Ground ring [250.52(A)(4)]
Exception: A grounding electrode isn't required where only one
circuit serves the building or structure. For the purpose of this
section, a multiwire branch circuit is considered to be a single branch
- Ground rod [250.52(A)(5)]
- Metal underground systems [250.52(A)(7)]
Bonding Requirements. To quickly clear a ground fault and
remove dangerous voltage from metal parts, the building or structure
disconnecting means must be grounded (bonded) to an effective
ground-fault current path in accordance with (1) or (2) [250.4(A)(3)].
(1) Equipment Grounding (Bonding) Conductor. The building or
structure disconnecting means can be bonded to an equipment grounding
(bonding) conductor, as described in 250.118, installed with the feeder
conductors. The equipment grounding (bonding) conductor, if of the wire
type, must be sized in accordance with 250.122, based on the rating of
the feeder protection device.
Caution: To prevent dangerous objectionable current
from flowing onto metal parts of the electrical installation, as well
metal piping and structural steel [250.6(A)], a building or structure
disconnecting means supplied by a feeder must not have the grounded
neutral conductor bonded to the building or structure disconnecting
to read the rest of this article.
Editor's note: This information was extracted from Mike Holt's
the National Electrical Code.
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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: Was this installer color blind?
By Mike Holt
Q. Do I have to use bonding jumpers around
Web site to see the answer.
By Steven Owen
Q. What is the proper size overload, and
branch-circuit, short-circuit, ground-fault protective device permitted
for a hermetic compressor with a nameplate rated-load of 38A, and a
branch-circuit selection current of 40A? The fusible disconnect is
to serve as the disconnecting means, the overload protective device,
the branch-circuit, short-circuit, ground-fault protective device.
Web site for the answer and explanation.
Code Quiz Correction
By Steven Owen
Although the answer to the question in the last
issue was correctly shown as: C) 70A, the ampere ratings in
the question were inadvertently reversed. The nameplate rated-load
current should have been shown as 38A, and the branch-circuit selection
current should have been listed as 40A.
We apologize for any confusion this may have caused.
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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 Systems Maintenance (special experts
excluded). This committee is responsible for NFPA 73, Electrical
Inspection Code for Existing Dwellings.
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Shows and Events
Visit the 2006 EC&M E-TradeShow, a Year-Long
Virtual Business Event
Don't miss these scheduled seminars on November 16 in the EC&M
Before attending these events, make sure you visit the 2006 EC&M
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- "Energy Storage Methods for Electric Power Systems," presented by
John DeDad (11:00 a.m. EDT and PDT). Learn about all the new energy
storage technologies now available, including ultracapacitors, fuel
cells, and flywheels by attending this live conference.
- Find out how to size residential electrical generators by sitting
on Generac's live conference scheduled for 9 a.m. EDT and PDT. If you
can't make these times, catch a special contractor's night live
conference at 8 p.m. EDT.
- If you're looking for information to include in your business
forecast for 2007, you'll certainly want to attend the 2007 electrical
market sales forecast, presented by Jim Lucy, Electrical
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You'll see forecasting statistics for residential, commercial,
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