Ampacities for Conductors Rated 0V to 2,000V
Time to Submit
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Top 2008 Code Changes
Ampacities for Conductors Rated 0V to 2,000V
By Mike Holt
A new subsection adds ambient temperature adjustments
for conduits installed on rooftops.
As per 310.15(B)(2)(c) Raceways Exposed to Sunlight on
Rooftops, the ambient temperature adjustment contained in Table
310.15(B)(2)(c) is added to the outdoor ambient temperature for
conductors or cables that are installed in raceways exposed to direct
sunlight on or above rooftops when applying ampacity adjustment
correction factors contained in Table 310.16.
FPN No. 1: See ASHRAE Handbook – Fundamentals for the
average ambient temperatures in various locations.
FPN No. 2: The temperature adders in Table 310.15(B)(2)(c) are based
on the results of averaging the ambient temperatures.
When adjusting conductor ampacity, use the conductor ampacity as
listed in Table 310.16, based on the conductor's insulation rating. In
this case, it's 75A at 90°F. Conductor ampacity adjustment is not
on the temperature terminal rating as per 110.14(C).
This new subsection requires the ambient temperature used for
ampacity correction to be adjusted where conductors or cables are
installed in conduit on or above a rooftop, and the conduit is exposed
to direct sunlight. The reasoning behind this change is that the air
inside conduits in direct sunlight is significantly hotter than the
surrounding air, and appropriate ampacity corrections must be made in
order to comply with 310.10.
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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: Hot tin roof
By Mike Holt
Q. Can a 45 kVA transformer be installed in the
ceiling space above the ceiling grid?
Visit EC&M's Web
site to see the answer.
By Steven Owen
Q. What is the minimum ampacity and minimum size
conductor required for a circuit that connects a capacitor to the
terminals of a 25 hp, 460VAC, 3-phase, air conditioner induction motor?
The rated current of the capacitor is 20A. The motor branch circuit
conductors are 8 AWG THHN/THWN. The terminal ratings of the capacitor
are 60°C. The motor terminals are rated at 75°C.
- 18.15A, 14 AWG THHN.
- 25A, 12 AWG THHN.
- 27A, 10 AWG THHN.
- 42.5A, 8 AWG THHN.
Web site for the answer and explanation.
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Code News Update
Time to Submit Those
The committee for NFPA 73, Electrical Inspection Code
for Existing Dwellings, is now accepting proposals for recommendations
on content changes. Proposals received by 5:00 p.m. ET on December 1,
2008 will be acted on by the committee, and the action will be
in the committee's report.
This code provides requirements for evaluating installed electrical
systems within and associated with existing dwellings. Its focus is to
identify safety, fire, and shock hazards, such as improper
installations, overheating, physical deterioration, abuse, and similar
conditions. It does not define installation requirements that might be
desired for convenience or utilitarian purposes.
Proposals must be submitted to Codes and Standards Administration on
proposal forms available in the back of this document or from NFPA
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Shows and Events
The Electric West Show, to be held March 18-20, 2009 at
the Las Vegas Convention Center in conjunction with the Power Quality
Reliability Conference, is the perfect place to brush up on the latest
NEC topics – and earn continuing education credits in the process.
Geared toward electrical contractors, consulting & specifying
electricians, and plant facility personnel, there’s something for
everyone at the Electric Show. The biggest electrical marketplace in
western United States, this event attracts 250 exhibiting companies and
more than 6,000 attendees every year. Here's a preview of some of the
NEC seminars planned for next year's event:
For more information, visit our Web
- One- and Two-Family Dwelling Unit Electrical Systems
- Changes to the 2008 NEC
- Swimming Pools and Similar Installations (NEC Article 680)
- Introduction to the 2009 NFPA 70E
Eliminate Red Tags
It takes more than the UL
Mark on a product to satisfy code requirements. Before your next
installation, use UL’s Code Compliance Database to identify the
correlation between model codes and UL Certified products, as well as
find manufacturers of certified products.
Click here today
find up-to-date UL Listed products at the UL Code Correlation
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