Standard Ampere Ratings
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Top 50 NEC Rules
Standard Ampere Ratings
By Mike Holt
The standard ratings in amperes for fuses and
inverse-time breakers are: 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80,
90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500,
600, 700, 800, 1,000, 1,200, 1,600, 2,000, 2,500, 3,000, 4,000, 5,000
and 6,000. Additional standard ampere ratings for fuses include 1, 3,
10, and 601.
Fuses rated less than 15A are sometimes required for the protection
of fractional horsepower motor circuits [430.52], motor control
[430.72], small transformers [450.3(B)], and remote-control circuit
The ampere rating of an adjustable circuit breaker is equal to its
maximum long-time pickup current setting.
The ampere rating of adjustable-trip circuit breakers that have
restricted access to the adjusting means is equal to their adjusted
long-time pickup current settings.
Editor's note: This information was extracted from Mike
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: Something seems to be missing here.
By Mike Holt
Q. What type of fitting can I use to terminate
ground wires in a metal box?
Web site to see the answer.
By Steven Owen
Q. What is the maximum number of 12 AWG THHN
insulated conductors permitted in a strut-type channel raceway that is
1/2 inches by 1 1/2 inches and of unlimited length? The channel
is defined as indoors and dry. The ambient temperature does not exceed
30°C. The raceway sections of this strut-type channel are joined
with external joiners.
Web site for the answer and explanation.
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Call for Comments
The following Tentative Interim Amendment (TIA Log No.
822) to the 2005 NEC has been proposed to the NFPA. The TIA is now open
for public review and comment. All comments on this proposed change
should be filed with the Secretary, Standards Council, by September 20,
2006. The Standards Council will review any and all information
submitted and then determine whether or not to issue the TIA at its
November 3, 2006 meeting.
The TIA proposes new wording for the ampacity of conductors in
cellular metal floor raceways. The existing wording and proposed
are shown here for your benefit.
"374.17 Ampacity of Conductors. The ampacity adjustment factors in
310.15(B)(2) shall apply to conductors installed in cellular metal
"374.17 Ampacity of Conductors. In addition to all other requirements
Article 374 of the NEC, the ampacity adjustment factors in 310.15(B)(2)
shall apply to current-carrying conductors installed in headers with
internal dimensions of less than 9 square inches.
"The ampacity adjustment factors in 310.15(B)(2) shall also apply to
current-carrying conductors installed in cells, except that cells
internal dimensions in excess of 5.5 square inches shall be permitted
contain up to 30 current-carrying conductors of #10 size without
ampacity reduction, and cells having internal dimensions in excess of
square inches shall be permitted to contain up to 75 current-carrying
conductors of #10 size without ampacity reduction."
The submitter's reason behind this proposed change is noted in the August
2006 issue of NFPA News (page 3).
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