Lesson 2: Article 500 - Understanding Class I, II, And III Locations Flashcards by Jordan Knutson

Solid particles ______ or smaller that can form an explosible mixture when suspended at standard pressure and temperature are defined as combustible dust.

a. 400 µm
b. 450 µm
c. 500 µm
d. 550 µm

NEC REF:

c. 500 µm

100

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A combustible gas detection system is a(n) ______ utilizing stationary gas detectors in industrial establishments.

a. apparatus
b. explosionproof enclosure
c. protection technique
d. none of the above

NEC REF:

c. protection technique

100

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Having electrical make-or-break contacts such that, if an internal explosion of the flammable gas or vapor that can enter it occurs, the device will withstand the internal explosion without suffering damage and without communicating the internal explosion to the external flammable gas or vapor is the definition of ______.

a. enclosed-break
b. explosionproof
c. nonsparking
d. none of the above

NEC REF:

a. enclosed-break

100

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Dust-ignitionproof equipment must be designed and built in a manner that excludes dusts and prevents arcs, sparks, or heat that may be generated or liberated inside of the enclosure from causing ignition of ______ of a specified dust on or in the vicinity of the enclosure.

a. atmospheric suspensions
b. exterior accumulations
c. interior accumulations
d. a. and b.
e. a., b., and c.

NEC REF:

d. a. and b.

100

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The ______ protection technique minimizes the risk of ignition in explosive atmospheres from optical radiation where visible or infrared radiation is confined inside optical fiber or other transmission medium under normal constructions or constructions with additional mechanical protection based on the assumption that there is no escape of radiation from the confinement.

a. inherently safe optical radiation “op is”
b. protected optical radiation “op pr”
c. optical system with interlock “op sh”
d. nonsparking

NEC REF:

b. protected optical radiation “op pr”

100

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Hermetically sealed equipment is sealed against the entrance of an external atmosphere, such that the seal is made by ______ of metal to metal, ceramic to metal, or glass to metal.

a. binding
b. bonding
c. fusion
d. joining

NEC REF:

c. fusion

100

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Sealed as applied to hazardous locations means that equipment is constructed such that it is sealed effectively against entry of a(n) ______ atmosphere and is not opened during normal operation or for any maintenance activities.

a. combustible
b. external
c. flammable
d. hazardous

NEC REF:

b. external

100

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Where ______ are the only materials used or handled, these locations are not covered by Article 500.

a. carbonaceous dusts
b. metal dusts
c. pyrophoric materials
d. uranium dusts

NEC REF:

c. pyrophoric materials

500.1(B)(4)

Note: Pyrophoric materials were addressed in 500.5(A) in the 2020 NEC, which violated the NEC Style Manual. The scope of articles is required to address what is and what is not covered in an article. The 2023 revision of 500.1 moved pyrophoric materials to the scope and removed it from 500.5(A).

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A Class I, Division 1 location is a location in which ______.

I. breakdown or faulty operation of equipment or processes might release ignitible concentrations of flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors
II. ignitible concentrations of flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors can exist under normal operating conditions
III. ignitible concentrations of such flammable gases, flammable liquid-produced vapors, or combustible liquids above their flash points might exist frequently because of repair or maintenance

a. I. and II.
b. I. and III.
c. I., II., and III.
d. II. and III.

NEC REF:

c. I., II., and III.

500.5(B)(1)

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An area adjacent to a Class I, Division 1 location without adequate positive-pressure ventilation from a source of clean air and to which ignitible concentrations of flammable gases, flammable liquid-produced vapors, or combustible liquid-produced vapors above their flash points might occasionally be communicated is considered as being unclassified.

True or False

NEC REF:

False

500.5(B)(2)(3)

Note: The question is one of the three conditions that constitute a Class I, Division 2 location.

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Documentation for areas designated as Hazardous (Classified) Locations shall be available to the/those ______.

I. authority having jurisdiction
II. building owner(s)
III. authorized to design electrical equipment at the location
IV. authorized to operate electrical equipment at the location

a. I. and II.
b. I., II., and III.
c. I., II., and IV.
d. I., III., and IV.

NEC REF:

d. I., III., and IV.

500.4

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A location where combustible dust accumulations on, in, or in the vicinity of the electrical equipment could be sufficient to ______ electrical equipment, or could be ignitible by abnormal operation or failure of electrical equipment would be considered Class II, Division 2.

a. cause deterioration of
b. interfere with the normal operation of
c. interfere with the safe dissipation of heat from
d. none of the above

NEC REF:

c. interfere with the safe dissipation of heat from

500.5(C)(2)(3)

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Locations where metal combustible fibers/flyings are present shall be classified as ______.

a. Class II, Division 1, Group D
b. Class II, Division 1, Group E
c. Class II, Division 2, Group D
d. Class III, Division 1, Group E

NEC REF:

b. Class II, Division 1, Group E

500.5(D)(1)(a)

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Locations where ignitible fibers/flyings are handled, manufactured, or used shall be classified as ______.

a. Class II, Division 1
b. Class II, Division 2
c. Class III, Division 1
d. Class III, Division 2

NEC REF:

c. Class III, Division 1

500.5(D)(1)(b)

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Group B materials are flammable gas, flammable liquid-produced vapor, or combustible liquid-produced vapor mixed with air that may burn or explode, having either a maximum experimental safe gap (MESG) value less than or equal to 0.45 millimeters or a minimum igniting current ratio (MIC ratio) less than or equal to ______.

a. 0.30
b. 0.35
c. 0.40
d. 0.45

NEC REF:

c. 0.40

500.6(A)(2)

Note: NEC 500.6(A)(2) is extracted text from NFPA 497 Section 3.3.5.1.2.

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Group E includes atmospheres containing combustible metal dusts, including aluminum, magnesium, and their commercial alloys, or other combustible dusts whose ______, abrasiveness, and conductivity present similar hazards in the use of electrical equipment.

a. explosive characteristics
b. flashpoint
c. particle size
d. none of the above

NEC REF:

c. particle size

500.6(B)(1)

Note: Section 500.6(B)(1) is extracted text from NFPA 499 Section 3.3.8.1.1.

Atmospheres containing combustible carbonaceous dusts that have more than 8% total entrapped volatiles or that have been sensitized by other materials so that they present an explosion hazard are categorized as ______.

a. Group E
b. Group F
c. Group G
d. None of the above

NEC REF:

b. Group F

500.6(B)(2)

Zirconium, thorium, and uranium dusts have extremely low ignition temperatures (as low as _______) and minimum ignition energies lower than any material classified in any of the Class I or Class II groups.

a. 21°C
b. 21°F
c. 68°C
d. 68°F

d. 68°F

Note: See NEC 500.6(B)(1) Informational Note.

The group having either a maximum experimental safe gap (MESG) value greater than 0.45 mm and less than or equal to 0.75 mm, or a minimum igniting current (MIC) ratio greater than 0.40 and less than or equal to 0.80 is ______.

a. Group B
b. Group C
c. Group D
d. Group E

NEC REF:

b. Group C

500.6(A)(3)

The purged and pressurized protection technique shall be permitted for equipment in any Hazardous (Classified) Location for which it is ______.

a. designed
b. identified
c. labeled
d. listed

NEC REF:

b. identified

500.7(D)

Note: Article 100 definition of “Identified (as applied to equipment). Recognizable as suitable for the specific purpose, function, use, environment, application, and so forth, where described in a particular Code requirement.” The terms listed, labeled, approved, and identified are used throughout Articles 500 through 516. It is important to understand the definitions of all the terms. A discussion of the terms should also include 90.7, 110.2, and 110.3.

The oil immersion protection technique shall be permitted for ______ in Class I, Division 2 locations as described in 501.115(B)(1)(2).

a. current-interrupting contacts
b. explosionproof enclosures
c. listed equipment
d. none of the above

NEC REF:

a. current-interrupting contacts

500.7(I)

Nonsparking equipment is designed to reduce arcs and sparks that would be capable of becoming an ignition source during abnormal operation.

True or False

False

A nonincendive circuit is a circuit, other than ______ wiring, in which any arc or thermal effect produced under intended operating conditions of the equipment, is not capable, under specified test conditions, of igniting the flammable gas-air, vapor-air, or dust-air mixture.

a. Class II
b. control
c. field
d. intrinsic safety

NEC REF:

c. field

100

The ______ type of protection is used to minimize the risk of ignition in explosive atmospheres from optical radiation where visible or infrared radiation is incapable of producing sufficient energy under normal or specified fault conditions to ignite a specific explosive atmosphere.

a. inherently safe optical radiation “op is”
b. optical system with interlock “op sh”
c. protected optical radiation “op pr”
d. none of the above

NEC REF:

a. inherently safe optical radiation “op is”

100

A detection system for flammable gases shall be permitted as a means of protection in ______. a. all Class I locations b. Class I, Division 1 locations c. Class I, Division 2 locations d. restricted industrial establishments NEC REF:

d. restricted industrial establishments 500.7(K)

A restricted industrial establishment is one with restricted public access, where the conditions of maintenance and supervision ensure that only qualified ______ service the installation. a. electricians b. maintenance staff personnel c. persons d. none of the above NEC REF:

c. persons 100 Note: The definition of restricted industrial establishment [as applied to Hazardous (Classified) Locations] was added to Article 100 in the 2023 revision. Prior to moving to Article 100, the term and the definition were included in each relocation where industrial establishments were required for an installation requirement.

The interior of a control panel equipped with instrumentation or other equipment that use or measure flammable liquids, gases, or vapors is permitted to have Class I, Division 2 equipment, installation methods, and wiring where it is protected by a detection system for flammable gases and it is provided with an alarm that will sound at not more than ______ of the lower flammable limit. a. 10% b. 20% c. 30% d. 40% NEC REF:

d. 40% 500.7(K)(4)

Suitability of identified equipment shall be determined by ______. I. Equipment listing or labeling II. Evidence acceptable to the installer such as a manufacturer’s self-evaluation or an owner’s engineering judgment III. Evidence of equipment evaluation from a qualified testing laboratory or inspection agency concerned with product evaluation a. I. b. I. and II. c. I., II., and III. d. I. and III. NEC REF:

d. I. and III. 500.8(A)

Equipment that depends on a single compression seal, diaphragm, or tube to prevent flammable or combustible fluids from entering the equipment shall be ______ for a Class I, Division 2 location, even if installed in an unclassified location. a. approved b. identified c. labeled d. listed NEC REF:

b. identified 500.8(B)(4)

For equipment installed in a Class II, Division 1 location, the temperature class or operating temperature shall be based on operation of the equipment when blanketed with the maximum amount of dust ______. a. that can accumulate on the equipment b. the equipment is designed for c. the equipment is listed for d. none of the above NEC REF:

a. that can accumulate on the equipment 500.8(C)(4)

The temperature marking specified in NEC 500.8(C) for Class II equipment shall be less than the ignition temperature of the specific dust to be encountered and in the case of organic dusts that may dehydrate or carbonize, it shall not exceed the lower of either the ignition temperature or ______. a. 165°C b. 165°F c. 329°C d. 329°F e. a. and d. NEC REF:

e. a. and d. 500.8(D)(2)

Conduit and fittings shall be made wrenchtight to prevent sparking when fault current flows through the conduit system, and to ensure the ______ conduit system where applicable. a. explosionproof integrity of the b. integrity of the equipment grounding path provided by the c. mechanical integrity of the d. a. and b. NEC REF:

a. explosionproof integrity of the 500.8(E)

NPT-threaded entries into explosionproof equipment shall be made up with at least ______ threads fully engaged unless they are joints with factory-threaded NPT entries in listed explosionproof equipment. a. 4 b. 5 c. 6 d. 8 NEC REF:

b. 5 500.8(E)(1)

Markings for material classification groups shall specify the ______ material classification group(s) or specific gas, vapor, dust, or fiber/flying in accordance with Section 500.6. a. applicable b. appropriate c. identified d. relevant NEC REF:

a. applicable 500.8(C)(3)

Where metric-threaded fittings are installed into explosionproof equipment, they shall have a class fit of 6g/6H and there must be a minimum of ______ threads fully engaged. a. 4 b. 5 c. 6 d. 8 NEC REF:

b. 5 500.8(E)(2)

An optical fiber cable, with or without current-carrying conductors (hybrid optical fiber cable), shall be ______ to address the associated fire hazard and sealed to address the associated explosion hazard in accordance with Part II of Articles 500, 501, 502, or 503, as applicable. a. installed b. labeled c. located d. tested NEC REF:

a. installed 500.8(F)

A Class III, Division 1 location is a location in which easily ignitible fibers/flyings are handled, ______, or used. a. manufactured b. processed c. stored d. none of the above NEC REF:

a. manufactured 500.5(D)(1)(b)