Electrical Contractor

AWG copper, but installing an aluminum grounding electrode conductor is not permitted. In accordance with 250.52(B), aluminum shall not be used as a grounding electrode. Another section in Article 250 also has something to say about aluminum in or near the earth. Bare aluminum or copper-clad aluminum grounding electrode conductors shall not be used where in direct contact with masonry or the earth or where subject to corrosive conditions [250.64(A)]. Where used outside, aluminum or copper-clad aluminum grounding electrode conductors shall not be terminated within 18 inches of the earth.

There are times when finding the
aluminum equivalent to copper is not
necessary. For example, where raceways
contain 4 AWG or larger insulated circuit
conductors, and these conductors enter a
cabinet, a box, an enclosure or a raceway,
the conductors shall be protected by an
identified fitting that provides a smoothly
rounded insulating surface, unless the
conductors are separated from the fit-
ting or raceway by identified insulating
material that is securely fastened in place
[300.4(G)]. With this requirement for
conductor protection, it does not matter
if the conductor is copper or aluminum.
Whether the raceway contains 4 AWG
(or larger) insulated copper or 4 AWG (or
larger) insulated aluminum, the conduc-
tors shall be protected by an identified
fitting that provides a smoothly rounded
insulating surface, unless the conductors
are separated from the fitting or raceway
by identified insulating material that is
securely fastened in place (see Figure 3).

As stated in 110.6, conductor sizes are
expressed in AWG or in circular mils.
Because “AWG” is in the Code more than
600 times, it is necessary to explain the
abbreviation. Section 110.6 explains that
AWG is the abbreviation for American
Wire Gage. It is interesting to note that
this section is the only place the full term
shows up in the Code. The most com-
mon AWG sizes in the Code are 18 AWG
through 4/0 AWG. This section states
that conductor sizes are also expressed
in circular mils. Because circular-mil
sizes are needed in some calculations,
the circular-mil area of various conduc-
tors are shown in Chapter 9, Table 8. The
circular-mil area is shown for all of the
conductors in Table 8, even for the con-
ductors expressed as AWG conductors.
For example, what is the circular-mil area
for the following conductors: 12 AWG, 6
AWG and 4/0 AWG? In accordance with
Table 8 in Chapter 9, the circular-mil
area for 12 AWG is 6,530 circular mils;
the circular-mil area for 6 AWG is 26,240
circular mils; and the circular-mil area
for 4/0 AWG is 211,600 circular mils.
Although it is not mentioned in 110.6, a
common abbreviation used throughout
the Code is “kcmil,” which stands for
one-thousand circular mils. In the cir-
cular mils column in Table 8, no circular
mils are shown for conductors larger than
4/0 AWG. This is because the number or
name of the conductor is the circular-mil
area of the conductor. For example, the
circular-mil area for a 500 kcmil conduc-
tor is 500,000 circular mils. Out in the
field, conductors are usually referred to
as “MCM” instead of “kcmil.” MCM also
stands for one-thousand circular mils.
M is the Roman numeral for 1,000. The
letters CM is an abbreviation for circular
mil. Therefore, the circular-mil area for
a 500 MCM conductor is 500,000 circu-
lar mils. In the 1990 edition of the NEC,
MCM was replaced with kcmil. Because
the Code contains International System
of Units (SI), Roman numerals were
replaced with metric symbols. The metric
prefix for 1,000 is kilo, and the symbol is
k. The letters cmil are an abbreviation for
circular mil. Therefore, the circular-mil
area for a 500 kcmil conductor is 500,000
circular mils. Metric units were first
introduced in the 1981 edition of the NEC.

Next month’s column continues the discussion of Article 110.

MILLER, owner of Lighthouse Educational Services, teaches custom-tailored seminars on the National Electrical Code and NFPA 70E. He is the author of “Illustrated Guide to the National Electrical Code” and “Electrician’s Exam Prep Manual.” He can be reached at 615.333.3336, charles@charlesRmiller.com, and www.charlesRmiller.com. Connect with Charles R. Miller on LinkedIn.

CODE IN FOCUS FIGURE 3 CHANGING THE SIZE MAY NOT BE NECESSARY

Where raceways contain 4 AWG or larger insulated circuit conductors, and these conductors enter a cabinet, a box, an enclosure or a raceway, the conductors shall be protected by an identified fitting providing a smoothly rounded insulating surface, unless the conductors are separated from the fitting or raceway by identified insulating material that is securely fastened in place [300.4(G)].

With the requirement
for conductor protection
in 300.4(G), it does not
matter if the conductor is
copper or aluminum.

Whether the raceway contains 4 AWG (or larger) insulated copper or 4 AWG (or larger) insulated aluminum, the conductors shall be protected by an identified fitting that provides a smoothly rounded insulating surface, unless the conductors are separated from the fitting or raceway by identified insulating material that is securely fastened in place.