Lighting and Electrical Equipment
for use in Hazardous Atmospheres to IEC standards
- A Useful Guide
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Lighting and Electrical Equipment for use in Hazardous Atmospheres to IEC standards - A Useful Guide |
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We offer a selection of lighting and power distribution equipment suitable for use in areas where flammable atmospheres may occur. The proper use of protected apparatus is a specialist subject and these notes must be treated as being informative only. Users must themselves study the relevant codes of practice and construction standards in addition to the Installation and Maintenance manuals enclosed with each product (available upon request).
Methods of Explosion Protection For Electrical Equipment
The ignition of flammable atmospheres can be initiated by sparks or hot surfaces arising from the use of electrical power. Other possible sources of ignition are electrostatic effects and frictional sparking. The hot surfaces involved can be those of enclosures, components and light sources. Under fault conditions electrical connections may become over-heated and cause arcs or sparks. In addition, sparks may be the result of the discharge of stored energy or from switching contacts. A number of standard methods of protection against ignition have been established and these have been codified in construction standards. These design codes enable manufacturers to make apparatus of a uniform type and have it tested by certification authorities for compliance with the standards.
The methods of protection are summarized in Table 1:
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Table 1 Methods of Explosion Protection |
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Method |
Type of Protection |
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Designed to prevent any ignition from arising |
Ex e Increased Safety Ex N or Ex nA Non Sparking |
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Designed to limit the ignition energy of the circuit |
Ex i Intrinsic Safety |
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Designed to prevent the flammable mixture reaching a means of ignition |
Ex m Encapsulation Ex p Pressurisation Ex o Oil immersion Ex N or Ex nR Restricted Breathing |
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Designed to prevent any ignition from spreading |
Ex d Flameproof Enclosure Ex q Powder Filling |
Ex o "Oil immersion" Protection EN 50015
This is an old technique primarily used for switchgear. The spark is formed under oil and venting is controlled. (The use of hydrocarbon oil has obvious disadvantages and the method of protection is confined to Zone 2).
Ex p "Pressurized Apparatus" Protection EN 50016
These are system methods. One maintains a positive static pressure inside the apparatus and the other a continuous flow of air or inert gas to neutralize or carry away any flammable mixture entering or being formed within the enclosure. Essential to these methods are monitoring systems and purging schedules to ensure their reliability.
Ex q "Powder Filling" Protection EN 50017
This involves the mounting of potentially incendive components in an enclosure filled with sand or similar inert powder and having a vent. It is primarily of use where the incendive action is the abnormal release of electrical energy by the rupture of fuses or failure of components such as capacitors. Usually it is used for components inside Ex e apparatus and for heavy duty traction batteries.
Ex d "Flameproof Enclosure" Protection EN 50018
The potentially incendive components are contained within an enclosure into which the flammable atmosphere can enter but which will contain any resultant explosion and prevent its transmission outside the enclosure.
Ex e "Increased Safety" Protection EN 50019
Normally sparking components are excluded. Other components are designed to substantially reduce the likelihood of the occurrence of fault conditions which could cause ignition. This is done by reducing and controlling working temperatures, ensuring the electrical connections are reliable, increasing insulation effectiveness, and reducing the probability of contamination by dirt and moisture ingress.
Ex i "Intrinsic Safety" Protection EN 50020
The circuit parameters are reliably controlled to reduce potential spark energy to below that which will ignite the specific gas mixture. This includes the occurrence of one (ib) or two (ia) component faults in the apparatus. It should be noted that this method does not protect entirely against the local over-heating of damaged connections or conductors and these should be kept sound and suitably enclosed against damage.
Ex m "Encapsulation" Protection EN 50028)
Potentially incendive components are encapsulated by a method which excludes the flammable atmosphere and controls the surface temperature under normal and fault conditions.
Ex s "Special" Protection BASEEFA SFA 3009
This method, being special, has no definite rules. In effect it is any method which can be shown to be safe in use. Much of the apparatus having 's' protection was designed with encapsulation and this has been superseded by EN 50028. In addition, the s coding is used when apparatus has been assessed to one of the individual parts of the CENELEC series but does not exactly comply with it. Ex s protection has been commonly used for Zone 0 and Zone 1 applications and its use was contained in BS 5345, the previous UK code of practice. The introduction of the ATEX directive removes the need for the continuing use of the 's' coding.
Ex N "Non Sparking" Protection BS 4533 Section 102.51 (Luminaires) Ex n "Non Sparking" protection EN 50021
Precautions are taken with connections and wiring to increase reliability, though not to as high a degree as for Ex e. Where internal surfaces are hotter than the desired T rating they can be tightly enclosed to prevent the ready access of a flammable atmosphere into the internal parts. This is the "restricted breathing enclosure" technique. Its employment also means that high ingress protection ratings of IP65 and above are built into the design. When tested to EN 50021, the coding Ex nR denotes that the protection method employs a restricted breathing enclosure. This enclosure may be restricted to the part of the enclosure containing the hot components such as lamps. Where the normal non-sparking construction is used the coding is Ex nA. The Ex N/Ex n methods have been developed specifically for the use of such equipment in the remotely hazardous area Zone 2.
Classification of Hazardous Areas and the Use of Protected Apparatus
Codes of practice have been established for the classification of the potential hazards, the selection of suitable equipment to protect against the hazards, and their installation and their maintenance. The codes of practice will list the methods of protection which, used individually or in combination, may be employed to attain an acceptable degree of safety.
The hazardous areas are classified in Table 2 according to EN 60079-10:
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Table 2 Hazardous Area Classification |
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| Zone | Description |
| Zone 0 |
Zone in which an explosive atmosphere is continuously present for long periods. |
| Zone 1 | Zone in which an explosive atmosphere is likely to occur in normal operation, typically between 10 and 100 hours per year. |
| Zone 2 | Zone in which an explosive atmosphere is not likely to occur in normal operation, and if it occurs it will exist only for a short time, typically less than 10 hours per year. (Zone 2 is often referred to as the remotely hazardous area.) |
Deployment of protected apparatus in the areas according to EN 60079-14 is summarized in Table 3:
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Table 3 Selection of Protected Apparatus in Hazardous Areas |
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| Zone | Description |
| Zone 0 |
Ex ia |
| Zone 1 |
Any type of protection
suitable for Zone 0 and
Ex d, Ex ib, Ex p, Ex e, Ex s, Ex m |
| Zone 2 |
Any type of protection suitable for Zone 0 or Zone 1 and Ex N or Ex n Ex o Ex q Also see notes on Ex s protection |
The
relevant directives of the EU are:
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99/92/EC Minimum requirements for improving the safety and health protection of
workers potentially at risk from explosive atmospheres.
The
manufacturer must make a declaration of compliance with the equipment directive
and apply the CE mark before the product can be placed on the market in the EU.
The individual governments of the member states appoint “notified bodies” to
carry out testing and certification. Apparatus is divided into Equipment Groups
(I for mining and II non-mining), the ignitable component of the explosive
atmosphere, Gas (G) and Dust (D) and Categories 1, 2 and 3. The Categories
provide respectively, very high, high and normal levels of protection against
ignition. The Categories should be considered as achieving the level of
protection obtained by applying the existing protection techniques (Ex d, Ex e
etc). Alternatively, the existing techniques can be replaced or supplemented by
new concepts and engineering judgements made by the manufacturers in the design
and construction of the apparatus. Where required, this would be validated by
notified bodies performing an EC type examination of the product.
In
practice, the Categories are equated to suitability for Zones. The actual
category of apparatus specified by the user for a Zone will depend on the
overall risk assessment. The Zoning considers only the probability of the
occurrence of an explosive atmosphere, its extent and duration. It does not
consider the consequential effects of an ignition having taken place or of the
environment. Apparatus will be marked with the Grouping and Category in addition
to the marking required by the individual protection standards.
For
example, the Chalmit Lighting range of products falls within Group II for
industrial applications and covers designation as Category 2 or 3. This means
that products will generally be suitable for use in Zone 1 and 2 areas as
defined by the codes of practice for zoning such as EN 60079-10 (IEC 60079-10)
and selection, EN 60079-14 (IEC 60079-14) etc.
Currently EN 60079-14 does not refer to categories so the protection code of the apparatus is used as listed in the standard or the category can be equated as being suitable for a specific Zone as detailed in the directive. These codes of practice provide the user with guidance in selecting apparatus needed to obtain the degree of safety that is required for the particular hazardous area application.
The
Euro-norms (EN) have been updated for ATEX but as the updating mainly consisted
of a cross reference to the ATEX categories this did not affect the standards
technically except where co-incidental technical amendments were made.
Compliance with the Euro-norme gives a presumption of compliance with those
aspects of the directive covered by the standard. These are “The Essential
Health and Safety Requirements” EHSR’s. Lists of standards giving a presumption
of compliance with the directive are published in the official journal (OJ) of
the EU. The European Commission web site contains a large quantity of material
concerning the directives along with the actual directive itself and the
guidelines for its application.
An EC
type examination by a notified body is mandatory for Category 1 and 2 electrical
equipment but not for Category 3. Chalmit have chosen to obtain a certificate of
compliance from a third party for Category 3 equipment in order to promote
customer confidence and continue the long standing practice that Chalmit has
used for Ex N apparatus. The designation EC can not be used for certification of
Category 3 apparatus. In the data. the term “type examination” rather than “EC
type examination” is used for Category 3 apparatus.
The
relationship between Categories and applications is shown in Table 4.
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Table 4 ATEX Categories and Applications |
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Category |
Degree of Safety |
Design Requirement |
Application |
Expected Zone of Use |
| 1 |
Very High level |
Two independent means of protection or safe with two independent faults | Where explosive atmospheres are present continuously or for lengthy periods |
Zone 0 (gas) and Zone 20 (dust) |
| 2 | High level | Safe with frequently occurring disturbances or with a normal fault | Where explosive atmospheres are likely to occur |
Zone 1 (gas) and Zone 21 (dust) |
| 3 |
Normal level |
Safe in normal operation | Where explosive atmospheres are likely to occur infrequently of for short duration |
Zone
2 (gas)
and Zone 22 (dust) |
Marking of ATEX product and CE mark
The product carries the ATEX
marking which includes the CE mark,
,
the Group, the Category and the Category sub-group G or D. The product also
carries the normal coding, Ex d etc. and the surface temperature and ambient
temperature (Tamb) ratings. The Group also forms part of the marking in the
product standards and pre-dates ATEX. The Category is additional to the previous
marking. This means that all of the familiar marking is still present.
All
products carry the general product safety and electromagnetic compatibility CE
mark on the product, installation manual or packaging, as appropriate. The
marking attests that the product meets the requirements of the Low Voltage and
Electro-Magnetic Compatibility (EMC) directives of the EU as transposed into
Products
exported directly outside of the European Community are not required to carry
any CE marking but local marking regulations may apply.
Surface Temperature Rating And Gas Groupings
Any flammable mixture can be classified for explosion protection under two main characteristics; temperature of ignition by a hot surface and the spark energy to ignite the mixture. The spark energy of ignition is also related to the intensity of explosion. This property is crucial to the design of the joints in flameproof enclosures (Ex d) and the energy level of intrinsically safe (Ex i) apparatus. Other characteristics are the specific gravity and flash point, which are used in the determination of the area classification.
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Surface Temperature For Ignition
The surface temperature rating is measured in the most onerous design
attitude at the most severe supply voltage condition within the design
tolerance. Usually this is +10% of rated voltage for lighting and with
any fault or overload condition which could normally occur in service. A
normal overload condition for motors is the starting or stalled
condition and, for luminaires, the end of life of a lamp. In the case of
Ex d, Ex m, Ex q and also restricted breathing Ex nR and dust proof
enclosure methods, the maximum temperature is measured on the external
surface. In other methods of protection the maximum internal temperature
of the apparatus is measured. The
explosive mixtures are allocated into broad bands giving the Temperature
Classes shown in Table 5
For dust protection using the enclosure methods the surface temperature is limited to a given value in ºC, the T grouping is not used. |
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Gas Grouping The gas and vapor mixtures are classified as shown in below. The list shown is only representative as the possible number of chemical compounds is extensive. The classification shown is that associated with the IEC and CENELEC harmonized standards.
The apparatus sub-groupings: A, B and C are only applicable to the design and marking of flameproof and intrinsically safe, energy limited and non incendive apparatus. |
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Ingress Protection
The surface temperature classification and gas grouping are the primary safety considerations. A major secondary parameter is protection against the ingress of solid bodies and liquid, IP. In some cases the degree of IP protection forms part of the standard requirement of the explosion protection method. Where apparatus is used in dirty or wet conditions the resistance to ingress contributes to the reliability of explosion protection in that electrical faults within the apparatus are often the result of water ingress. Where our products are concerned, the latest edition of the appropriate standards are EN 60529 (IEC 60529). The definitions of the IP code are summarized below. It will be noted that many luminaires have both IP66 and IP67 ratings which is because the IP66 test can be more severe than IP67 for some constructions. The minimum enclosure rating is IP54 for explosion-protected electrical products.
NEMA Standards Publication No. 250-1997 Enclosures for Electrical Equipment (1000Volts maximum) comparison to IEC 60529 Degrees of Protection provided by Enclosure IP Classification Designation (cannot be used to convert IEC classification designations to NEMA type numbers)
The IEC IP 56 rating is often specified for marine offshore applications of electrical enclosures, and corresponds to NEMA 4 and 4X enclosures which are intended for indoor and outdoor use primarily to provide a degree of protection against windblown dust and rain, splashing water, hose-directed water, and damage from external ice formation. The ANSI/NEMA 250 standard also contains tests for corrosion resistance. For example, NEMA 4X designates that the enclosure also resists corrosion. For more information on Comparision Between NEMA Enclosure Type Numbers and IEC Enclosure Classification Designations, please visit the Hubbell Wiring Device website and click on Technical Data: http://www.hubbell-wiring.com/library/pdf-catalog.htm
Resistance To Mechanical Damage The individual protection standards also contain minimum levels of resistance to mechanical damage as measured by test methods producing an impact energy measured in Joules or Newton/meters. 10 Newton meters is, in effect, 1 Kilogram dropped from a height of 1 meter. Chalmit equipment generally exceeds the minimum level by a substantial margin. The standards contain two levels of impact resistance appropriate to high and low risk of impact. If the apparatus is only suitable for low impact the certificate is suffixed X or the information is included in the installation information. Compliance With General Product Standards Luminaires comply with basic construction standards such as EN 60598, where these requirements do not conflict with those in the protection standard. This also applies to internal components such as lamp holders, terminals and control gear. Apparatus complying with the individual product standard will have its internal components operating inside their rated performance when operated in the maximum rated ambient temperature. This contributes to the reliability and, ultimately, the safety of the installation. Compliance with product standards is the normal way of claiming compliance with the Low Voltage Directive for non Ex apparatus. Operational Temperatures The operational temperature limits are based on both product function and Ex protection standards. The normal lower limit for Ex d products is -20ºC unless otherwise noted on the certificate or literature. This is the standard lower level given in EN 50014. The normal upper limit is 40ºC but some equipment is rated at other temperatures which may be linked to the surface temperature rating. The maximum ambient temperature is coded as T ambient. Lower limits of operation and starting for lamps and batteries can be obtained from the sales department. A usual guide is -40ºC for SON, -30ºC for MBF/MBI, -25ºC for fluorescents and -10ºC for battery operated equipment. Generation Of Certificate Many certificates contain a letter showing the "generation" of the certificate. The letters B, C and D show the amendment status of the standard to which the product is certified, E indicating the second editions of the standards. ‘X' Suffix On Certificate Some products carry a suffix ‘X’ after the certificate number. This denotes "special certification conditions". These are given on the certificate and on the installation leaflet. The conditions usually relate to cable entry, operation, lamps, installation position and location or maintenance, and must be observed by the user. Opening TimesIn those cases where internal temperatures are greater than the T rating or where energy is stored in electrical components, a time limit will be given to be observed following electrical isolation. This allows for cooling and discharge of energy. It applies to Ex d and e apparatus. For Zone 2 apparatus, opening times are not generally given as it is inferred that a flammable atmosphere is unlikely to arise during maintenance operations.
CE Marking
Chalmit hazardous area products carry the CE mark on the product, installation leaflet or packaging, where appropriate. Some products exported directly outside the European Community may not carry the marking. The marking attests that the product meets the requirements of the Low Voltage and Electro-Magnetic Compatibility directives of the EU as put into UK law. Except where stated otherwise the marking covers compliance with the hazardous atmospheres (ATEX) directive for which the transition period is from 1996 to 2003 unless specifically applied.
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International Standards Two
distinct groups of apparatus standards used world-wide are the IEC/EN (Euronorme)
series of standards and those used in the
The
practice in the
The
only basic technical difference between these and the equivalent IEC/EN
standards is that the ANSI/UL844 ‘non-sparking’ technique, known as
‘enclosed and gasketed’, does not use the restricted breathing method.
This is one factor which accounts for the generally higher surface
temperature ratings of ANSI/UL844 listed apparatus and the practical need
for a greater number of temperature sub-divisions. Another factor is that
the standard specifies higher test pressures for flameproof equipment. In
the case of HID luminaires this results in the lamp glass being smaller
and the surface temperature inevitably hotter. The
construction and testing of dust protected enclosures is different to EN
but is currently partially incorporated as an additional alternative in
the IEC standards. In
both codes the gases and compounds are classified by surface temperature
of ignition and grouped into ignition groups for the dimensioning of
flameproof joints and for intrinsic safety. The classification and
grouping are broadly similar to IEC/EN but differ in detail. The
classification and protection cannot be mixed and must be used as
complementary pairs. A general comparison between IEC/EN and NEC practice
for gas hazard protection is shown in Tables 7 and 8. The
The
NEC has now introduced the Zone classification concept for gas hazards as
an alternative to the Division method. The wiring methods currently remain
unchanged. To support this, UL and ISA have now introduced their own IEC
based protection standards for use in the alternative Zones. These
standards are intended to become single ANSI documents. The objective is
that the two systems will run in parallel until the older
Products may be marked for both divisions and zones. Where product
complies with the
The Canadian practice has been a hybrid of USA and European concepts. The mining industry in Canada was much influenced by Europe which led to the use of European methods elsewhere. Through the joint accreditation system with the USA (NRTL) there is a degree of overlap but the detail of this cannot be addressed properly in this introduction. Canada has now adopted the zone system for new construction. Table 7 Comparison of Surface Temperature Classification IEC and NEC
Table 8 Comparison of Representative Gases in CENELEC and NEC Gas Groups
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