For complete details, reference the National Electrical Code (NEC), NFPA 70 or the appropriate NFPA or UL Standard.
A Class I, Division 1 location is a location where ignitable concentrations of flammable gases, vapors
or liquids:
- can exist under normal operating conditions;
- may exist frequently because of repair or maintenance operations or because of leakage; or
- may exist because of equipment breakdown that simultaneously causes the equipment to become a source of ignition
Equipment intended for use in a Class I , Division 1 area is usually of the explosion
proof, intrinsically safe, or purged/pressurized type.
Explosion proof apparatus:
"Apparatus enclosed in a case that is capable of withstanding an explosion of a specified gas or
vapor that may occur within it and of preventing the ignition of a specified gas
or vapor surrounding the enclosure by sparks, flashes, or explosion of the gas
or vapor within and that operates at such an external temperature that a
surrounding flammable atmosphere will not be ignited thereby."(See NFPA 70)
Intrinsically safe apparatus:
"Apparatus in which all the circuits are intrinsically safe." (See UL 913)
Intrinsically safe circuit:
"A circuit in which any spark or thermal effect is incapable of causing ignition of a mixture
of flammable or combustible material in air under prescribed test conditions." (See UL 913)
Purging:
"The process of supplying an enclosure with a protective gas at a sufficient flow and
positive pressure to reduce the concentration of any flammable gas or vapor
initially present to an acceptable level." (See NFPA 496)
Pressurization:
"The process of supplying an enclosure with a protective gas with or without continuous flow at sufficient
pressure to prevent the entrance of a flammable gas or vapor, a combustible dust, or an ignitable fibre." (See NFPA 496)
A Class I, Division 2 location is a location:
- where volatile flammable liquids or flammable gases or vapors exist, but are normally confined within closed containers;
- where ignitable concentrations of gases, vapors or liquids are normally prevented by positive mechanical ventilation; or
- adjacent to a Class I, Division 1 location, where ignitable concentrations might be occasionally communicated.
Equipment intended for use in a Class I, Division 2 area is usually of the nonincendive,
non-sparking, purged/pressurized, hermetically sealed, or sealed device type.
Nonincendive circuit:
"A circuit in which any arc or thermal effect produced under intended operating conditions of the
equipment is not capable, under the test conditions specified, of igniting the specified flammable gas- or vapor- air mixture. "(See UL 1604)
Nonincendive component:
"A component having contacts for making or breaking an incendive circuit and the contacting
mechanism shall be constructed so that the component is incapable of igniting
the specified flammable gas- or vapor-air mixture. The housing of a nonincendive
component is not intended to:
- exclude the flammable atmosphere, or
- contain an explosion." (See UL 1604)"
Nonincendive field circuit:
"A circuit that enters or leaves the equipment enclosure and that under intended operating
conditions is not capable, under the test conditions specified, of igniting the
specified flammable gas- or vapor-air mixture or combustible dust." (See UL
1604)"
Non-sparking apparatus:
"Apparatus that has no normally arcing parts or thermal effects capable of ignition. Examples of
normally arcing parts are relays, circuit breakers, servo-potentiometers
adjustable resistors, switches, non-latching type connectors and motor brushes.
(See UL 1604)"
Purging:
See definition under Class I, Division 1
Pressurization:
See definition under Class I, Division 1
Hermetically sealed component:
"A component that is sealed against entrance of an external atmosphere and in which the seal
is made by fusion, such as soldering, brazing, welding, or the fusion of glass
to metal." (See UL 1604)
Sealed device:
"A device that is constructed so that it cannot be opened, has no external
operating mechanisms, and is sealed to restrict entry of an external atmosphere
without relying on gaskets. The device may contain arcing parts or internal hot
surfaces." (See UL 1604)
A Class I, Zone 0 location is a location where ignitable concentrations of flammable gases,
vapors or liquids:
- are present continuously; or
- are present for long periods of time.
Equipment intended for use in a Class I, Zone 0 area is usually of the intrinsically safe,
"ia," type.
Intrinsically safe:
See definitions under Class I, Division 1
A Class I, Zone 1 location is a location where ignitable concentrations of flammable gases,
vapors or liquids:
- are likely to exist under normal operating conditions;
- may exist frequently because of repair or maintenance operations or leakage; or
- may exist because of equipment breakdown that simultaneously causes the equipment to
become a source of ignition; or
- are adjacent to a Class I, Zone 0 location from which ignitable concentrations could be
communicated.
Equipment intended for use in a Class I, Zone 1 area is usually of the flameproof,
purged/pressurized, oil immersed, increased safety, encapsulated or powder
filled type.
Flameproof:
"The enclosure of the equipment will withstand an internal explosion, and prevent
passage of flame to the surrounding atmosphere. Care must be taken to maintain
the length and clearance (gap) of flameproof joints in service." (See UL
2279)
Purged/pressurized:
See definitions under Class I, Division I.
Oil immersion:
"Arcing contacts are immersed in a protective liquid." (See UL 2279)
Increased safety:
"The equipment contains no normally arcing parts, and additional measures (such as larger spacings among
wiring connections) are taken to prevent the possibility of high temperatures or
sparks. A minimum IP rating of IP 54 is required." (See UL 2279)
Encapsulation:
"Arcing contacts are completely surrounded by an encapsulating
material." (See UL 2279)
Powder filling:
"Arcing contacts are surrounded by a filling material (glass or quartz
powder)." (See UL 2279)
A Class I, Zone 2 location is a location:
- where ignitable concentrations of flammable gases, vapors or liquids are not
likely to occur in normal operation or, if they do occur, will exist only
for a short period;
- where volatile flammable liquids, or flammable gases or vapors exist, but are
normally confined within closed containers
- where ignitable concentrations of gases, vapors, or liquids are normally prevented
by positive mechanical ventilation;
- adjacent to a
Class I, Zone 1 location from which ignitable concentrations could be
communicated.
Equipment that is intended for use in a Class I, Zone 2 area is usually of the nonincendive,
non-sparking, restricted breathing, hermetically sealed or sealed device type.
Nonincendive:
See definitions under Class I, Division 2
Non-sparking:
See definition under Class I, Division 2
Restricted breathing:
"The enclosure relies on tight seals and gaskets to prevent diffusion of the explosive atmosphere into
the equipment enclosure. Provision for checking that the restricted breathing
properties of the enclosure are maintained is provided." (See UL 2279)
Hermetically sealed:
See definition under Class I, Division 2
Sealed device:
"A device that is constructed so that it cannot be opened and is sealed to
restrict entry of an external atmosphere. The device may contain arcing parts or
internal hot surfaces." (See UL 2279)
A Class II, Division 1 location is a location where:
- ignitable concentrations of combustible dust can exist in the air under normal
operating conditions;
- ignitable
concentrations of combustible dust may exist because of equipment breakdown
that simultaneously causes the equipment to become a source of ignition; or
- electrically
conductive combustible dusts may be present in hazardous quantities.
Equipment intended for use in a Class II, Division 1 area is usually of the
dust-ignition-proof, intrinsically safe, or pressurized type.
Dust-ignition-proof:
"Enclosed in a manner that will exclude dusts and, where installed and
protected in accordance with the NEC, will not permit arcs, sparks or heat
otherwise generated or liberated inside of the enclosure to cause ignition of
exterior accumulations or atmospheric suspensions of a specified dust on or in
the vicinity of the enclosure." (See NFPA 70)
Intrinsically safe:
See definitions under Class I, Division 1.
Pressurization:
See definition under Class I, Division 1.
A Class II, Division 2 location is a location where:
- combustible dust is not normally in the air in ignitable concentrations;
- dust accumulations are normally insufficient to interfere with normal operation
of electrical equipment;
- dust may be in suspension in the air as the result of infrequent malfunctioning of
equipment; or
- dust accumulation may be sufficient to interfere with safe dissipation of heat or
may be ignitable by abnormal operation.
Equipment intended for use in a Class II, Division 2 area is usually of the dust tight,
nonincendive, non-sparking, or pressurized types.
Dust tight:
"Constructed so that dust will not enter the enclosing case under specified
test conditions. An example of such conditions would be a UL Type 12
enclosure." (See NFPA 70)
Nonincendive:
See definitions under Class I, Division 2
Non-sparking:
See definition under Class I, Division 2
Pressurization:
See definition under Class I, Division 1.
A Class III, Division 1 location is a location where easily ignitable fibres
or materials producing combustible flyings are handled, manufactured or used.
Equipment intended for use in a Class III, Division 1 area is usually of the
dust tight or intrinsically safe type (both previously defined).
A Class III, Division 2 location is a location where easily ignitable fibres
are stored or handled.
Equipment intended for use in a Class III, Division 1 area is usually of the
dust tight or intrinsically safe type (both previously defined).
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Division 1:
Where ignitable concentrations of flammable gases, vapors
or liquids can exist all of the time or some of the time under normal
operating conditions.
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Zone 0:
Where ignitable concentrations of flammable gases, vapors
or liquids are present continuously or for long periods of time under
normal operating conditions.
Zone 1:
Where ignitable concentrations of flammable gases, vapors
or liquids are likely to exist under normal operating conditions.
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Division 2:
Where ignitable concentrations of flammable gases, vapors
or liquids are not likely to exist under normal operating conditions.
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Zone 2:
Where ignitable concentrations of flammable gases, vapors
or liquids are not likely to exist under normal operating conditions.
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Division 1 and 2
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Zone 0, 1 and 2
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(acetylene)
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IIC
(acetylene & hydrogen)
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B
(hydrogen)
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C
(ethylene)
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IIB
(ethylene)
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D
(propane)
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IIA
(propane)
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Division 1 and 2
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Zone 0, 1 and 2
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T1 (450°C)
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T1 (450°C)
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T2 (300°C)
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T2 (300°C)
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T2A, B, C, D
(280, 260, 230, 215°C)
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| T3 (200°C)
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T3 (200°C)
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T3A, B, C
(180, 165, 160°C)
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| T4 (135°C)
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T4 (135°C)
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| T4A (120°C)
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| T5 (100°C)
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T5 (100°C)
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| T6 (85°C)
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T6 (85°C)
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| Area
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Division Protection Methods
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Area
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Zone Protection Methods
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| Division 1
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- Explosionproof
- Intrinsically safe
(2 fault)
- Purged/pressurized
(Type X or Y)
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Zone 0
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- Intrinsically safe, 'ia' (2 fault)
- Class I, Division 1 Intrinsically safe (2 fault)
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| Zone 1
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- Encapsulation,'m'
- Flameproof, 'd'
- Increased safety, 'e'
- Intrinsically safe, 'ib' (1 fault)
- Oil immersion, 'o'
- Powder filling, 'q'
- Purged/pressurized,'p'
- Any Class I, Zone 0 method
- Any Class I, Division 1 method
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Division 2
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- Hermetically sealed
- Nonincendive
- Non-sparking
- Oil immersion
- Sealed device
- Purged/
pressurized (Type Z)
- Any Class I, Division 1 method
- Any Class I, Zone 1 or 2 method
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Zone 2
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- Energy Limited, 'nC'
- Hermetically sealed, 'nC'
- Nonincendive,'nC'
- Non-sparking,'nA'
- Restricted breathing, 'nR'
- Sealed device, 'nC'
- Any Class I, Zone 0 or 1 method
- Any Class I, Division 1 or 2 method
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