Conductor Size for A/C and Refrigeration Equipment -- One Motor
Comments Sought on
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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
Conductor Size for A/C and Refrigeration Equipment -- One Motor
By Mike Holt
The branch-circuit conductors for air-conditioning and
refrigeration equipment must be sized not smaller than identified on
equipment's nameplate. If the equipment doesn't have a nameplate
specifying the branch-circuit conductors, the conductors must be sized
in accordance with 440.32.
If equipment doesn't have a nameplate identifying the minimum
circuit ampacity, the branch-circuit conductors to a single
motor-compressor must have an ampacity not less than 125% of the
motor-compressor rated load current or the branch-circuit selection
current, whichever is greater.
In accordance with 440.22(A), branch-circuit conductors must have
branch-circuit protection sized between 175% and 225% of the rated load
current to provide protection against short circuits and ground faults.
Let's review an example to better explain these requirements.
What size conductor and protection device is required for an 18A
Step 1. Refer to Table 310.16 to determine the proper size
18A x 1.25 = 22.5A
Therefore, you should use a 12AWG conductor, rated 25A at
Step 2. Refer to Sections 240.6(A) and 440.22(A) to determine the
proper size protection device.
18A x 1.75 = 31.5A
Use the next size down device, rated 30A.
If the 30A protection device isn't capable of carrying the starting
current, then the protection device can be sized up to 225% of the
equipment load current rating.
18A x 2.25 = 40.5A
Use the next size down device, rated 40A.
Editor's note: This information was extracted from Mike
Holt's textbook, Understanding
the National Electrical Code
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What's Wrong Here?
By Joe Tedesco
Think you know how this installation violates the
Web site to see the answer.
Hint: 7th floor problems.
By Mike Holt
Q. Is GFCI protection required for drinking
fountains in office buildings?
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By Steven Owen
Q. Which of the following methods for connecting
grounding and bonding conductors to equipment is the only one not
permitted by the NEC?
- listed pressure connectors
- exothermic welding process
- green-colored "tapcon" self-tapping concrete anchors drilled
directly through a metal box (no threads engaged), and used to connect
the grounding and bonding conductors
- thread-forming machine screws that engage not less than two
threads in the enclosure
Web site for the answer and explanation.
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Code News Update
Comments Sought on Proposed
As published in the March issue of NFPA News,
following Tentative Interim Amendment (TIA) has been proposed to the
NFPA 79-2007, Electrical Standard for Industrial
TIA Log No. 901
Submitter: Christine Livingston, Ford Motor Co.
1. Revise 22.214.171.124 to read as follows: "The color ORANGE or
YELLOW shall be used to identify ungrounded conductors that remain
energized when the main supply circuit disconnecting means is in the
position. This color identification shall be strictly reserved for this
2. Revise A.126.96.36.199 by removing the first sentence only.
Substantiation: Add the color yellow as an additional color
option for ungrounded conductors that remain energized when the main
disconnect is in the off position. This option was allowed in the 2002
edition, but was removed from the 2007 publication. Traditionally,
U.S.-based manufacturing has used the yellow color option exclusively
excepted circuits so there is a large installation base using this
Emergency Nature: By removing the yellow option from the list
of colors designated for excepted circuits in the standard, we have
opened the door for use of this color in other applications, creating
confusion and dangerous conditions.
This TIA has been published for public review and comment. Comments
should be filed with the Secretary, Standards Council by May 2, 2008.
You should identify the TIA number when submitting your comments. The
Standards Council will review the technical committees’ ballot
results, the public comments, and any other information that has been
submitted when it considers the issuance of the TIA at its July 22-24,
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