    United States Court of Appeals
         FOR THE DISTRICT OF COLUMBIA CIRCUIT



Argued December 11, 2015             Decided August 12, 2016

                         No. 14-1170

               TILDEN MINING COMPANY, INC.,
                       PETITIONER

                              v.

    SECRETARY OF LABOR AND FEDERAL MINE SAFETY AND
              HEALTH REVIEW COMMISSION,
                     RESPONDENTS


         On Petition for Review of a Decision of the
     Federal Mine Safety and Health Review Commission


    Ralph Henry Moore II argued the cause for petitioner.
With him on the briefs was Patrick W. Dennison.

    Sara L. Johnson, Attorney, U.S. Department of Labor,
argued the cause for respondents. With her on the brief was
W. Christian Schumann, Counsel, Appellate Litigation. John
T. Sullivan, Attorney, Mine Safety and Health Review
Commission, entered an appearance.

    Before: GARLAND, Chief Judge ∗, MILLETT, Circuit
Judge, and WILLIAMS, Senior Circuit Judge.

∗
  Chief Judge Garland was a member of the panel at the time the
case was argued but did not participate in this opinion.
                               2
    Opinion for the Court filed by Circuit Judge MILLETT.

     MILLETT, Circuit Judge: As Benjamin Franklin knew,
equipment that conducts electricity is safest when
“grounded”—physically connected to the earth. 1 Among
other things, grounding prevents exposed metal in equipment
from remaining electrically charged in the event of a power
failure, thereby preventing accidental shock or electrocution.
Grounding works most effectively when every component of
an electrical circuit is continuous and has low resistance. See
Secretary of Labor v. Tilden Mining Company, LC, 36
F.M.S.H.R.C. 1965, 1967 (2014); see generally 8 McGraw-
Hill Encyclopedia of Science & Technology 237–238 (6th ed.
1987). Those two features allow any built-up electrical
charge to dissipate swiftly via a grounding conductor into the
earth the moment a power failure occurs.

     Miners operate all sorts of electrical equipment as part of
their work. The Secretary of Labor accordingly exercised his
authority under the Federal Mine Safety and Health Act of
1977, Pub. L. No. 95-164, 91 Stat. 1290, to promulgate
regulations that require mine operators to test the continuity
and resistance of “grounding systems” for mining equipment.
30 C.F.R. § 56.12028; see generally 30 C.F.R. Part 56,
Subpart K. The question in this case is whether the Secretary
properly determined that power cables and extension cords
are regulated parts of those “grounding systems.” We uphold
the Secretary’s decision because, under the regulations’ plain
language, power cables and extension cords are most
naturally considered components of “grounding systems.”




1
 See generally I. Bernard Cohen, Benjamin Franklin’s Science 66–
109 (1990).
                               3
                               I

                               A

     The Federal Mine Safety and Health Act of 1977 requires
the Secretary of Labor “to develop detailed mandatory health
and safety standards to govern the operation of the Nation’s
mines.” Donovan v. Dewey, 452 U.S. 594, 596 (1981); see
also 30 U.S.C. § 811(a). The Act also created the Mine
Safety and Health Administration within the Department to
carry out the Secretary’s mine-safety duties. 29 U.S.C.
§ 557a. Administration inspectors may issue citations to mine
operators who fail to abide by the Department’s standards. 30
U.S.C. § 814. Citations can result in civil penalties of up to
$50,000 for each violation. Id. § 820(a)(1). Mine operators
may contest any citations they receive before Department of
Labor administrative law judges, who conduct hearings and
make findings of fact. Mine operators can then appeal ALJ
rulings to the Federal Mine Safety and Health Review
Commission. Id. § 815(d). Commission decisions, in turn,
may be reviewed in this court. Id. § 816(a)(1).

     Pursuant to his statutory authority, the Secretary has
promulgated mandatory standards designed to address and
prevent electrical hazards at mines. Relevant here is a set of
four regulations that requires mine owners to ground certain
electrical devices and other objects to prevent electrical
shock. First, “[a]ll metal enclosing or encasing electrical
circuits shall be grounded or provided with equivalent
protection.” 30 C.F.R. § 56.12025. Second, “[m]etal fencing
and metal buildings enclosing transformers and switchgear
shall be grounded.” Id. § 56.12026. Third, “[f]rame
grounding or equivalent protection shall be provided for
mobile equipment powered through trailing cables.” Id.
§ 56.12027. Finally, 30 C.F.R. § 56.12028 directs that
“[c]ontinuity and resistance of grounding systems shall be
tested immediately after installation, repair, and modification;
                              4
and annually thereafter,” and records of those tests must be
preserved for federal inspection.

     Since at least 1993, the Secretary’s Program Policy
Manuals have expressly applied the continuity and resistance
testing requirement to power cables and extension cords,
explaining that “[t]he grounding conductors in trailing cables,
power cables, and cords which supply power to portable or
mobile equipment should be tested more frequently than
stationary grounding conductors.” Mine Safety and Health
Administration, Program Policy Manual Vol. IV (April 1993,
Release IV-12) at 52. Indeed, even five years earlier in 1988,
the Program Policy Manual had presumed that cables and
extension cords were subject to testing, explaining that “[t]he
annual test does not apply to grounding conductors in trailing
cables, power cables and cords which supply power to
portable or mobile equipment” because “[t]he grounding
conductors in these cables require more frequent testing.”
Mine Safety and Health Administration, Program Policy
Manual Vol. IV (July 1988, Release IV-1) at 52. Again, in
1994, the Manual underscored that “[g]rounding conductors
in trailing cables, power cables, and cords that supply power
to tools and portable or mobile equipment must be tested as
prescribed in the regulation.” Mine Safety and Health
Administration, Program Policy Letter No. P94-IV-1 (Jan. 31,
1994) at 2. The Secretary restated that language verbatim in
the 1996 and 2003 Program Policy Manuals. See Mine Safety
and Health Administration, Program Policy Manual Vol. IV
(February 2003, Release IV-21) at 45; Mine Safety and
Health Administration, Program Policy Manual Vol. IV
(April 1, 1996, Release IV-16) at 52.

                              B

     In April 2008, a Mine Safety and Health Administration
Inspector issued two citations to the Tilden Mine in Michigan
for failure to perform continuity and resistance testing on
                              5
certain equipment and extension cords. Tilden contested
those citations before an ALJ, arguing that power cables and
extension cords do not fall within the regulatory term
“grounding systems,” and that even if they did, the
Secretary’s application of the term to extension cords and
power cables was unlawful because that position was not
adopted through notice-and-comment rulemaking. The ALJ
upheld the citations, reasoning that, “[d]ue to their function
and the importance of preventing electric shock to miners,
continuity testing must be performed on all aspects of the
grounding system, including grounding conductors in
extension cords.” J.A. 16.

     The Commission affirmed. It held that “grounding
systems” was an ambiguous term and that the Secretary’s
interpretation was reasonable and entitled to deference. J.A.
6. Specifically, the Commission reasoned:

    Conducting a continuity test assures that the
    equipment being used is connected directly to the
    ground prong, and that the grounding circuit is
    complete. A grounding system is only as protective
    as its weakest link, which is why it is critical to
    ensure that all the necessary components of the
    grounding system are fully functional, including
    extension cords and cables.          Otherwise, the
    grounding system will cease to function.

Id. The Commission further explained that the Secretary’s
position does not unduly burden mine operators because
testing is only required annually and upon “installation,” 30
C.F.R. § 56.12028, which the Secretary has determined
means only when “an extension cord or cable is first put into
use, [not] every time the cord or cable is subsequently
plugged in.” J.A. 7 n.3.
                                6
     The Commission held, secondly, that the Secretary’s
reading of his regulation did not have to go through notice-
and-comment rulemaking because, whatever ambiguity the
1988 Manual’s discussion of testing frequency might have
created, no prior position of the Secretary had held that
extension cords were exempt from testing. J.A. 8–9.

                                C

     Tilden timely petitioned for review. While that petition
was pending, the Supreme Court decided Perez v. Mortgage
Bankers Association, 135 S. Ct. 1199 (2015). Mortgage
Bankers held that “[b]ecause an agency is not required to use
notice-and-comment procedures to issue an initial interpretive
rule, it is also not required to use those procedures when it
amends or repeals that interpretive rule.” Id. at 1206. In
simple terms, the Court held that if an agency’s interpretation
of a statute or regulation does not require notice-and-comment
rulemaking procedures in the first instance, a change in that
interpretation does not require notice-and-comment
rulemaking procedures merely because it is a change. In light
of that decision, Tilden has appropriately abandoned its
argument that any arguable change in the Secretary’s
interpretation between the 1988 and 1994 versions of the
Program Policy Manual in and of itself required notice-and-
comment rulemaking. See Oral Arg. Tr. 3–4.

                               II

     Tilden argues that the Secretary’s application of the
testing requirements for “grounding systems” to power cables
and extension cords was an unreasonable interpretation of
Department regulations because extension cords and power
cables are “not logically included within the standard.” Pet’r
Br. 15. Tilden alternatively argues that the application of
testing requirements to power cables and extension cords is a
legislative, not an interpretive, rule that required the agency to
                              7
engage in notice-and-comment rulemaking. In Tilden’s view,
requiring the testing of cables and cords was legislative
because it is a “substantive change” that is “not logically
included within” the Secretary’s regulations. Id. at 31.
Tilden concedes, however, that if the testing requirement
instead is a logical and reasonable reading of the regulation,
that would “be the end of the case,” Oral Arg. Tr. 16, since
the Secretary’s position would neither be unreasonable nor
would it be a legislative rule requiring notice-and-comment
rulemaking procedures.

     Ordinarily, “[t]his Court affords great deference to an
agency’s interpretation of its own regulation.” Secretary of
Labor v. Twentymile Coal Co., 411 F.3d 256, 260 (D.C. Cir.
2005). We afford such deference based on the Supreme
Court’s decisions in Auer v. Robbins, 519 U.S. 452 (1997),
and Bowles v. Seminole Rock & Sand Co., 325 U.S. 410
(1945). However, we need not rely on Auer deference where
an agency’s interpretation is the fairest reading of a
regulation. See, e.g., Talk America, Inc. v. Michigan Bell
Telephone Co., 564 U.S. 50, 67–68 (2011) (Scalia, J.,
concurring) (“I have no need to rely on Auer deference,
because I believe the FCC’s interpretation is the fairest
reading.”); cf. International Internship Program v.
Napolitano, 718 F.3d 986, 987 n.1 (D.C. Cir. 2013) (“Because
we conclude that the agency’s interpretation of the statute is
the better reading, we need not determine whether the
agency’s interpretation is entitled to Chevron deference.”).

    In this case, the better and most natural reading of the
regulatory text includes power cables and extension cords
appended to electrical appliances as part of the regulated
“grounding systems.”

     We begin, and for the most part end, with the text of the
key regulation. See In re England, 375 F.3d 1169, 1177 (D.C.
Cir. 2004). Section 56.12028 reads:
                                8
    Continuity and resistance of grounding systems shall
    be tested immediately after installation, repair, and
    modification; and annually thereafter. A record of
    the resistance measured during the most recent tests
    shall be made available on a request by the Secretary
    or his duly authorized representative.

30 C.F.R. § 56.12028.

     The regulation then defines “electrical grounding [to]
mean[] to connect with the ground to make the earth part of
the circuit.” 30 C.F.R. § 56.2. The term “grounding systems”
thus encompasses all of the related parts of the electrical
circuit—all of the parts in the system—that together are
grounded to the earth. For that reason, extension cords and
power cables are naturally understood to be components of
the grounded electrical circuit. If the equipment is not
plugged into an electrical power source through a cable or
extension cord, there is no continuous electrical circuit and
therefore no grounding system. On the other hand, when the
cable or cord is plugged in, the entire functional point of the
cable or cord is to facilitate the movement of electricity from
the power source to the piece of equipment, which creates a
continuous, grounded electrical circuit.

     That makes the testing of power cables and extension
cords textually logical. “A grounding system is only as
protective as its weakest link,” so it is “critical to ensure that
all the necessary components of the grounding system are
fully functional, including extension cords and cables.” J.A.
6 (Commission decision). As a Department of Labor
inspector elaborated during the agency proceedings:

    The idea behind grounding is to protect the people
    who use metal-encased equipment from electric
    shock. * * * If an extension cord is being used, it,
    too, must be grounded for the same reasons that the
                               9
    metal-encased equipment itself should be grounded.
    The extension cord has now extended the circuit to
    the end of the extension cord. Conducting a
    continuity test assures one that the extension cord is
    connected directly to the ground prong and thus, the
    grounding circuit is complete, including the
    extension cord.

Id. at 79. In short, the fairest reading of the text mirrors its
purpose: miners cannot be protected from electrical shock if a
necessary component of a grounded electrical circuit has high
resistance or is not continuous.

     Tilden argues that “the terms extension cord or power
cable are not found in the standard.” Pet’r Br. 16. True
enough. But outlets, power sources, and other conductors of
electricity are not mentioned by name either, yet Tilden does
not and could not dispute that they are indispensable
components of a grounding system. What is critical is that the
cords and cables fall within the natural compass of the phrase
“grounding system,” an expansive term that includes multiple
constituent components. Cf. Massachusetts v. EPA, 549 U.S.
497, 529 (2007) (“On its face, the definition [of ‘air
pollutant’] embraces all airborne compounds of whatever
stripe.”); CSX Transportation, Inc. v. Alabama Dep’t of
Revenue, 562 U.S. 277, 284 (2011) (Though “the statute [does
not] place any matters within, or exclude any matters from,
the term’s ambit, * * * the meaning of ‘tax’ is expansive.”).

     The Secretary’s Program Policy Manual confirms that
“grounding systems” encompasses power cables and
extension cords through its identification of categories of
devices that are included within “grounding systems.” The
2003 Manual (like all preceding iterations) explains that
“[g]rounding systems typically include” three components:
(i) “grounding electrodes,” (ii) “grounding electrode
conductors,” and (iii) “equipment grounding conductors.”
                               10
Mine Safety and Health Administration, Program Policy
Manual Vol. IV (February 2003, Release IV-21) at 44. As the
name suggests, grounding electrodes are the end device in the
system where the grounding occurs: they are “usually driven
rods connected to each other by suitable means, buried metal,
or other effective methods located at the source, to provide a
low resistance earth connection.” Id. The grounding
electrodes then connect to “grounding electrode conductors,”
which in turn connect to “equipment grounding conductors.”
Id.    And, most relevantly here, “equipment grounding
conductors” are defined as “the conductors used to connect
the metal frames or enclosures of electrical equipment to the
grounding electrode conductor.” Id.

     Power cables and extension cords, at a minimum, qualify
as equipment grounding conductors: they are part of a series
of conductors that link electrical equipment (through
attachment to its outside metal frame or its enclosure) to the
grounding electrode conductor—a connection that typically
occurs at a circuit breaker or fuse box. That grounding
electrode conductor then links up directly to the grounding
electrode in the earth. Voilà—a grounding system.

    At oral argument, Tilden argued that extension cords are
grounding electrode conductors. See Oral Arg. Tr. 7. No
matter. Either way the cords are a recognized component of a
“grounding system” under the regulation.

     Tilden also argues that interpreting “grounding systems”
to include extension cords and power cables does not comport
with the broader regulatory scheme. But Tilden’s structural
objections do not hold up. First, Tilden says that, because the
rule requires testing “after installation,” 30 C.F.R. § 56.12028,
the Secretary’s position would mean that power cables and
extension cords have to be tested every single time they are
plugged in.       Not so.      The Secretary has interpreted
“installation” in this context to “only require[] that continuity
                               11
and resistance testing be done when an extension cord or
cable is first put into use, as opposed to every time the cord or
cable is subsequently plugged in.” J.A. 7 n.3; see also Supp.
App. 47 (documenting Secretary’s position before the
Commission). That is because the threat a power cable or
extension cord poses to a grounding system derives not from
being plugged in improperly, but from internal wiring that is
flawed or damaged by vibration, flexing, or corrosive
environments like those found in mines. Accordingly, testing
the integrity of the installed wiring need not occur every time
the cord is plugged in.

    Changing tacks, Tilden argues (Pet’r Br. 19) that
extension cords and power cables require no “installation.”
But the “installation” referenced in the regulation is of the
“grounding system,” 30 C.F.R. § 56.12028, and in that
context the cords are installed when they are first connected to
equipment and conductors creating a grounding system.

     Anyhow, both of those arguments go to the ambiguity of
the term “installation” not “grounding systems.” Whatever
ambiguity or confusion Tilden perceives in the Secretary’s
interpretation of “installation,” that does nothing to detract
from the logical compass of the phrase “grounding systems.”

     Second, Tilden argues that the application of the
“grounding systems” language to extension cords and power
cables makes no sense because the regulation requires both
continuity and resistance testing of grounding systems, yet
only continuity—not resistance—testing is required for power
cables and extension cords. No again. In fact, testing
resistance is very much necessary for extension cords because
a high resistance would mean that “it would take longer for
[a] message to get back to the circuit breaker or fuse box * * *
when the equipment is energized through [an] electrical
fault.” Oral Arg. Tr. 31–32. Moreover, the Secretary
explained that only resistance—not continuity—is directly
                              12
recorded during testing, because the resistance reading
simultaneously shows whether the electrical circuit is
continuous. Id. at 32–34.

      Third, Tilden argues that power cables and extension
cords, as temporary pieces of equipment, do not fit
comfortably within the regulations’ categories of permanent
pieces of equipment for which direct grounding is required:
(i) “[a]ll metal enclosing or encasing electrical circuits,” 30
C.F.R. § 56.12025, (ii) “[m]etal fencing and metal buildings
enclosing transformers and switchgear,” id. § 56.12026, and
(iii) “mobile equipment powered through trailing cables,” id.
§ 56.12027. But those provisions identify which equipment
must be connected to the ground; they do not purport to list
every object that must be tested as part of a grounding system.

     Moreover, the fact that the “mobile equipment powered
through trailing cables,” 30 C.F.R. § 56.12027, can be
detached from electrical systems—a point Tilden conceded at
oral argument, see Oral Arg. Tr. 14—means that Tilden’s
proposed distinction between temporary and permanent
installations does not hold together.

     Finally, Tilden argues that the plain meaning of the term
“grounding systems” cannot include extension cords and
power cables because the industry did not understand that
term to include those devices. But a regulation’s ambit comes
from the natural import of its text. Disavowals by those on
the receiving end of regulation cannot, by themselves, alter a
regulation’s natural meaning.

                              III

     In sum, because the fairest reading of the regulation
embraces power cables and extension cords used as part of an
electrical grounding system, the Secretary’s reading of the
regulation was reasonable and non-legislative, making notice-
                         13
and-comment rulemaking unnecessary.   The petition for
review is denied.

                                           So ordered.
