Approved
Acceptable to the authority having jurisdiction.

Arcing Device
A device, such as make/ break component, that under normal conditions produces an arc with energy sufficient to cause ignition of an ignitable mixture. See also "nonincendive circuit."

Associated Apparatus
Apparatus in which the circuits are not intrinsically safe themselves but affect the energy in the intrinsically safe circuits and are relied upon to maintain intrinsic safety. An example being an intrinsic safety barrier.

Authority Having Jurisdiction
The organization, office, or individual that has the responsibility and authority for approving equipment, installations, or procedures.

Automation System
The system which provides overall control and monitoring functions of a specific process or application. Generally consists of a network of computers, controllers, and I/O modules.

Certified Equipment
Equipment that has been evaluated by a recognized testing agency and confirmed to be in compliance with the applicable standard(s).

Class I, Division 1 Location
A location (1) in which ignitable concentrations of flammable gases or vapors can exist under normal operating conditions; (2) in which ignitable concentrations of such gases or vapors may exist frequently because of repair or maintenance operations or because of leakage; or (3) in which breakdown or faulty operation of equipment or processes might release ignitable concentrations of flammable gases or vapors and might also cause simultaneous failure of electrical equipment that could act as a source of ignition.

Class I, Division 2 Location
A location (1) in which volatile flammable liquids or flammable gases are handled,processed, or used, but in which the liquids, vapors, or gases will normally be confined within closed containers or closed systems from which they can escape only in case of accidental rupture or breakdown of such containers or systems, or in case of abnormal operation of equipment; (2) in which ignitable concentrations of gases or vapors are normally prevented by positive mechanical ventilation and might become hazardous through failure or abnormal operation of the ventilating equipment; or (3) that is adjacent to a Class I, Division 1 location and to which ignitable concentrations of gases or vapors might occasionally be communicated unless such communication is prevented by adequate positive-pressure ventilation from a source of clean air and effective safeguards against ventilation failure are provided. Electrical conduits and their associated enclosures separated from process fluids by a single seal or barrier are classified as a Class I, Division 2 location if the outside of the conduit and enclosures is a nonhazardous (unclassified) location.

Class II location
A location that is hazardous because of the presence of combustible dust.

Class II, Division 1 Location
A location (1) in which combustible dust is in the air under normal operating conditions in quantities sufficient to produce explosive or ignitable mixtures; (2) in which mechanical failure or abnormal operation of machinery or equipment might cause such explosive or ignitable mixtures to be produced and might also provide a source of ignition through simultaneous ( the word "simultaneous" is not included in the Canadian definition) failure of electric equipment, operation of protection devices, or from other causes; or (3) in which combustible dusts of an electrically conductive nature may be present in hazardous quantities.

Class II, Division 2 Location (United States)
A location in which combustible dust is not normally in the air in quantities sufficient to produce explosive or ignitable mixtures and dust accumulations are normally insufficient to interfere with the normal operation of electrical equipment or other apparatus, but combustible dust may be in suspension in the air as a result of infrequent malfunctioning of handling or processing equipment and where combustible dust accumulations on, in, or in the vicinity of the electrical or may be ignitable by abnormal operation or failure of electrical equipment.

Class II, Division 2 location (Canada)
A location in which combustible dusts are not normally in suspension in air likely to be thrown into suspension by the normal or abnormal operation or the failure of equipment or apparatus in quantities sufficient to produce explosive or ignitable mixtures, but in which:

a) deposits or accumulations of dust may be sufficient to interfere with the safe dissipation of heat from electrical equipment or apparatus; or

b) deposits or accumulations of dust on, in, or near electrical equipment may be ignited by arcs, sparks, or burning material from the electrical equipment.

Class III Location
A location that is hazardous because of the presence of easily ignitable fibers or flyings but in which such fibers or flyings are not likely to be in suspension in the air in quantities sufficient to produce ignitable mixtures.

Class III, Division 1 Location
A location in which easily ignitable fibers or materials producing flyings are handled, manufactured or used.

Class III, Division 2 Location
A location in which easily ignitable fibers are stored or handled (except in the process of manufacture).

Code of Practice
An International term referring to a document that describes basic safety features and methods of protection and recommends the selection, installation, and maintenance procedures that should be followed to ensure the safe use of electrical apparatus.

Control Drawing
A drawing or other document provided by the manufacturer of the intrinsically safe or associated apparatus that details the allowed interconnections between the intrinsically safe and associated apparatus.

Dust, Combustible
Dust that (when mixed with air in certain proportions) can be ignited and will propagate a flame. The combustible properties of dust are dependent upon test conditions and dust particle size, chemical structure, and other particle characteristics.

Dust-ignitionproof
A term used in the United States to describe an enclosure that will exclude ignitable amounts of dusts that might affect performance or rating and that, when installed and protected in accordance with the original design intent, will not permit arcs, sparks, or heat otherwise generated or liberated inside the enclosure to cause ignition of exterior accumulations or atmospheric suspensions of a specified dust.

Dust layer, combustible
Any surface accumulation of combustible dust that is thick enough to propagate flame or will degrade and ignite.

Dust-protected enclosure
An international term describing an enclosure in which the ingress of dust is not totally prevented, but dust does not enter in sufficient quantity to interfere with the safe operation of the equipment or accumulate in a position within the enclosure where it is possible to cause an ignition hazard.

Dust-tight
An enclosure so constructed that dust will not enter the enclosing case under specified test conditions.

Encapsulation
An international term describing a type of protection in which the parts that could ignite an explosive atmosphere by either sparking or heating are enclosed in an encapsulant in such a way that this explosive atmosphere cannot be ignited. This type of protection is referred to By CENELEC as "Ex m" in draft Standard EN50028.

Explosionproof enclosure
An enclosure that is capable of withstanding an explosion of a gas or vapor within it and of preventing the ignition of an explosive gas or vapor that may surround it and that operates at such an external temperature that a surrounding explosive gas or vapor will not be ignited thereby. This type of enclosure is similar to a flameproof enclosure.

Explosionproof equipment (apparatus)
Equipment or apparatus enclosed in an explosionproof enclosure.

Fault (as applicable to intrinsically safe systems)
A defect or electrical breakdown of any component, spacing, or insulation that alone or in combination with other defects or breakdowns may adversely affect the electrical or thermal characteristics of the intrinsically safe system. If a defect or breakdown leads to defects or breakdowns in other components, the primary and subsequent defects and breakdowns are considered to be a single fault. Certain components may be considered not subject to fault when analyses or tests for intrinsic safety are made.

Fibers and flyings, easily ignitable
Fibers and flyings that are easily ignitable including rayon, cotton (including cotton linters and cotton waste), sisal or henequen, , jute, hemp, tow, cocoa fiber, oakum, baled waste kapok, Spanish moss, excelsior, and other materials of similar nature.

Flameproof Enclosure
An International term describing an enclosure that can withstand the pressure developed during an internal explosion of an explosive mixture and that prevents the transmission of the explosion to the explosive atmosphere surrounding the enclosure and that operates at such an external temperature that a surrounding explosive gas or vapor will not be ignited thereby. This enclosure is similar to an explosionproof enclosure. This type of protection is referred to by IEC as "Ex d."

Galvanic Isolation
A form of isolation which meets stringent standards for intrinsically safe circuits.

Ground
A conducting connection, whether intentional or accidental, between an electrical circuit or equipment and the earth or to some conducting body that serves in place of the earth.

Group
A classification of flammable materials of similar hazard. Consists of Groups A, B, C, D, E, F, and G to NEC and CEC standards and Groups I, IIA, IIB, and IIC to IEC standards.

Group A
Acetylene Atmospheres

Group B
Atmospheres containing Butadiene, ethylene oxide, propylene oxide, acrolein, or hydrogen (or gases or vapors of equivalent hazard to hydrogen, such as manufactured gas.)

Group C
Atmospheres containing Cyclopropane, ethyl ether, ethylene, hydrogen sulfide, or gases or vapors of equivalent hazard.

Group D
Atmospheres such as acetone, alcohol, ammonia, benzine, benzol, butane, gasoline, hexane, lacquer solvent vapors, methane, naphtha, natural gas, propane, or gases or vapors of equivalent hazard.

Group E
Atmospheres containing combustible metal dusts regardless of resistivity or other combustible dusts of similarly hazardous characteristics having resistivity of less than 102 ohm-centimeter (magnesium, aluminum, bronze powder, etc.)

Group F
Atmospheres containing carbon black, charcoal, coal, coke dusts that have more than 8% total volatile material ( coal and coke dusts per ASTM 3175-82) or atmospheres containing these dusts sensitized by other materials so that they present an explosion hazard and having resistivity greater than 102 ohm-centimeter but equal to or less than 108 ohm-centimeter.

Group G
Atmospheres containing combustible dusts ( flour, starch, pulverized sugar and cocoa, dairy powders, dried hay, etc.) having resistivity of less than 108 ohm-centimeter or greater.

Group I
Below ground installations in which methane may be present.

Group IIA
Above ground installations with propane or equal atmospheres. This group most closely matches Group D in the United States and Canadian classifications.

Group IIB
Above ground installations with ethylene or equal atmospheres. This group most closely matches Group C in the United States and Canadian classifications.

Group IIC
Above ground installations with acetylene, hydrogen or equal atmospheres. This group most closely matches Group A in the United States and Canadian classifications.

Hazardous (Classified) Location
A location in which fire or explosion hazards may exist due to flammable gases or vapors, flammable liquids, combustible dust, or easily ignitable fibers or flyings.

Hazardous Materials
Gases, vapors, combustible dusts, fibers, or flyings which are explosive under certain conditions.

Hermetically Sealed Device
A device that is sealed against the entrance of an external atmosphere and in which the seal is made by fusion. Continuous soldering, brazing, welding and the fusion of glass to metal are examples of recognized methods.

I/O Module
A module which provides basic input and output functions between the automation system and the field devices. Disregarding specialty modules, there are four basic types available from various vendors - analog input, analog output, discrete input, and discrete output.

Ignitable Gas Mixture
A gas -air mixture that is capable of being ignited by an open flame, arc or spark or high temperature.

Ignition (autoignition) Temperature
The minimum uniform temperature required to initiate or cause self-sustained combustion of a solid, liquid, or gaseous substance (independent of any other ignition source).

Increased Safety
An international term that describes a type of protection in which various measures are applied so as to reduce the probability of excessive temperatures and the occurrence of arcs or sparks in the interior and on the external parts of electrical apparatus that do not produce them in normal service.

Indoor Locations
Areas which are protected from exposure to the weather.

Intrinsic Safety
A type of protection in which a portion of the electrical system contains only intrinsically safe equipment (apparatus, circuits, and wiring) that is incapable of causing ignition in the surrounding atmosphere. No single device or wiring is intrinsically safe by itself (except for battery-operated self-contained apparatus such as portable pagers, transceivers, gas detectors, etc., which are specifically designed as intrinsically safe self-contained devices) but is intrinsically safe only when employed in a properly designed intrinsically safe system. This type of protection is referred to by IEC as "Ex i."

Intrinsic Safety Barrier
A component containing a network designed to limit the energy (voltage and current) available to the protected circuit in the hazardous (classified) location under specified fault conditions.

Intrinsically Safe Circuit:
A circuit in which any spark or thermal effect, produced either normally or in specified fault conditions, is incapable of releasing sufficient electrical or thermal energy to cause ignition of a specific hazardous atmospheric mixture in its most easily ignitable concentration.

Intrinsically Safe Equipment (apparatus, circuits, and wiring)
Equipment and wiring that, under normal or abnormal conditions, are incapable of releasing sufficient electrical or thermal energy to cause ignition of a specific hazardous atmospheric mixture in its most easily ignitable concentration.

Intrinsic Safety Ground Bus
A grounding system that has a dedicated conductor separate from the power system so that ground currents will not normally flow and that is reliably connected to a ground electrode (e.g., in accordance with Article 250 of NEC, ANSI/NFPA 70, or Section 10 of CEC Part I, CSA C22.1).

Intrinsically Safe System:
An assembly of interconnected intrinsically safe apparatus, associated apparatus, and interconnecting cables in which those parts of the system that may be used in hazardous (classified) locations are intrinsically safe circuits.

Knockout
A portion of the wall of an enclosure so fashioned that it may be removed readily by a hammer, screwdriver, and pliers at the time of installation in order to provide a hole for the attachment of an auxiliary device or raceway, cable, or fitting.

Labeled Equipment
Equipment or materials, to which has been attached a label, symbol , or other identifying mark of an organization concerned with product evaluation, that may maintain periodic inspection of the production of labeled equipment or materials, and by whose labeling the manufacturer indicates compliance with appropriate standards or performance in a specified manner.

Listed
Equipment or materials, included in a list published by an organization concerned with product evaluation, that maintains periodic inspection of production of listed equipment or materials and whose listing states either that the equipment or materials meets appropriate standards or has been tested and found suitable for use in the specified manner.

Maintenance, Corrective
Any maintenance activity that is not normal in the operation of the equipment and requires access to the equipment's interior. Such activities are expected to be performed by qualified personnel who are aware of the hazards involved. Such activities typically include locating causes of faulty performance, replacement of defective components, adjustment of internal controls, and the like.

Maintenance, Operational
Any maintenance activity, excluding corrective maintenance, intended to be performed by the operator and required in order for the equipment to serve its intended purpose. Such activities typically include the correcting of "zero" on a panel instrument, changing charts, record keeping, adding ink, and the like.

Maximum Surface Temperature
The highest temperature attained by a surface accessible to flammable gases, vapors, or combustible dusts under conditions of operation within the ratings of the apparatus (including recognized overloads and defined fault conditions.

Nonhazardous (unclassified) Location
A location in which fire or explosion hazards are not expected to exist specifically due to the presence of flammable gases or vapors, flammable liquids, combustible dusts, or ignitable fibers or flyings. Internationally, such a location is referred to as a safe area.

Nonincendive Circuit
A circuit in which any arc or thermal effect produced in normal operating conditions of the equipment is not capable, under prescribed conditions, of igniting the specified flammable gas, vapor-in-air mixture, combustible dusts, or ignitable fibers or flyings.

Nonincendive Component
A component having contacts for making or breaking a specified incentive circuit in which the contacting mechanism is constructed so that the component is not capable of ignition of the specified flammable gas or vapor-in-air mixture when tested as specified by appropriate test procedure. The housing of a nonincendive component is not intended to (1) exclude the flammable atmosphere or (2) contain an explosion.

Nonincendive Equipment
Equipment having electrical/electronic circuitry and components that are incapable under normal conditions, of causing ignition of a specified flammable gas or vapor-in-air mixture due to arcing or thermal effect. this type of protection is referred to by IEC as "Ex n." Ex n protection is limited to gas and vapor hazards.

Nonincendive Field Wiring
Wiring that enters or leaves an equipment enclosure and, under normal operating conditions of the equipment, is not capable, due to arcing or thermal effects, of igniting a specified flammable gas or vapor-in-air mixture or combustible dust-in-air mixture. Normal operation includes opening, shorting, or grounding the field wiring.

Normal Conditions
As related to intrinsically safe and nonincendive systems, equipment is under normal conditions when it conforms electrically and mechanically with its design specifications and is used within the limits specified by the manufacturer. Normal conditions for intrinsically safe systems include the following:

a) Supply voltage at maximum rated value.
b) Environmental conditions within the ratings given for the apparatus or associated apparatus.
c) Tolerances of all components at their most unfavorable conditions.
d) Adjustments at their most unfavorable conditions.
e) Opening of any one, shorting of any two, and grounding of any one of the field wires of the intrinsically safe circuit(s).

Normal conditions for nonincendive equipment include the following:
a) Supply voltage, current, and frequency at rated values.
b) Environmental conditions within the ratings given for the apparatus.
c) All tool-removable parts (i.e. covers) in place.
d) Adjustments at their most unfavorable settings.
e) All operator accessible adjustments at their most unfavorable settings.
f) Opening, shorting, and grounding of the nonincendive field wiring.

Outdoor Locations
Areas which are exposed to the weather

Purging
The process of supplying an enclosure with clean air or inert gas at a specified flow rate and a positive pressure to reduce the concentration of any flammable gas or vapor initially present to an acceptably safe level and to maintain this safe level by positive pressure with or without continuous flow. Refer to 5.2.1 and 5.2.1.2 and definitions of Type X,Y, and Z purging.

Purging, Type X
In the United States and Canada, a method of reducing the classification within an enclosure from Division 1 to Nonhazardous (unclassified).

Purging, Type Y
In the United States and Canada, a method of reducing the classification within an enclosure from Division 1 to Division 2.

Purging, Type Z
In the United States and Canada , a method of reducing a classification within an enclosure form Division 2 to Nonhazardous (unclassified)

RS-232
An EIA standard which specifies the electrical, mechanical, and functional characteristics for serial communications. Used in point-to-point applications.

RS-485
An EIA standard which specifies the electrical characteristics of a balanced-voltage digital interface. Used in multi-point applications.

Safe Area
A nonhazardous location.

Seal, Cable, Explosionproof
A cable terminator filled with compound and designed to contain an explosion in the enclosure to which it is attached or to minimize passage of flammable gases or vapors from one location to another. A conduit seal may also be used as a cable seal. This method differs from the international practice, which requires cable glands.

Seal, Conduit, Explosionproof
A sealed fitting, poured with a cement-like potting compound, designed to contain an explosion in the enclosure to which it is attached and to minimize passage of flammable gases or vapors from one location to another.

Serial Interface
A method of digitally transmitting data between devices over a pair of conductors. See RS-232 and RS-485.

Short-Circuit Proof
The ability of an intrinsic safety barrier or isolator to withstand the shorting of its' intrinsically safe connections to ground. Determined by dividing the rated voltage by its' internal resistance. If the resulting value is less than the fuse rating, the barrier is said to be short-circuit proof.

Simple Apparatus (as applied to intrinsic safety)
A device that will not generate nor store more than 1.2V, 100mA, 25mW, or 20µJ. Examples are switches, thermocouples, light-emitting diodes, and resistance temperature devices.

Temperature Identification Number (Temperature Class)
A system of classification by which one of 14 temperature identification numbers (internationally, six temperature classes) is allocated to an electrical apparatus. The temperature identification number represents the maximum surface temperature of any component that may come in contact with the flammable gas or vapor mixture.

Termination Panel
A mechanical assembly which resides in front of the I/O system and performs signal conditioning, electrical isolation, and other functions.

Zone
The international method of specifying the probability that a location is made hazardous by the presence, or potential presence, of flammable concentrations of gases and vapors. The term Division is used in the United States and Canada.

Zone 0
An area in which an explosive gas-air mixture is continuously present or present for long periods. Equal to a Division 1 hazardous location in the United States and Canadian classifications.

Zone 1
An area in which an explosive gas-air mixture is likely to occur in normal operation. Equal to a Division 1 hazardous location in the United States and Canadian classifications.

Zone 2
An area in which an explosive gas-air mixture is not likely to occur and if it does occur, will only exist for a short time. Equal to a Division 2 hazardous location in the United States and Canadian classifications.