Explosion Protection Theory and Practice - Phoenix Contact

Explosion ProtectionTheory and Practice

PhoeNix CoNTACT

This brochure on explosion protection is

designed to help installation technicians,

design engineers and operators of plants

located in explosive atmospheres.

Most often hazardous areas are equated

to chemical and petrochemical industries.

A potential hazardous atmosphere could

exist with applications in food/beverage or

automative industries (paint applications)

which may usually seem harmless.

explosion protection is often seen in

connection with gases. however, explosive

atmospheres can also be generated by

dusts.

explosion protection worldwide with installation examples

Chemical and petrochemical industries

Off-shore plants

Coal-mining

PhoeNix CoNTACT

Contents Page

1. Physical Background 4

2. explosion Protection Standards, Regulations and Directives 5

3. installation and Protection Methods 7

4. Zones and Divisions 9

5. Types of Protection 11

6. identication and Marking 14

7. intrinsic Safety 17

8. Surge Voltage Protection in the hazardous Area (ex Area) 21

9. ex-Approved Modular Terminal Blocks 23

10. Cable/Conductor Routing and Conduit Systems 25

11. iP Protection Type, NeMA Classication 26

12. What is NAMUR? 27

13. Smart-Compatible Devices 28

14. Application/installation examples 29

15. Terms and Abbreviations 37

16. Principles of Signal Transmission 39

in the rst part of this brochure, the basics of explosion protection is explained with intention of making you aware of the particular risks involved. explosion protec-tion around the world is based mainly on european and American standards and directives.

The second part provides support for the user of elec-trical equipment for the hazardous area. There is a com-prehensive explanation of what explosion protection criteria must be observed.

in addition to information on MCR instrumentation devices for intrinsically safe circuits, you will also nd information on modular terminal blocks and surge vol-tage protection for the hazardous area.

You will nd additional information about the products listed in this brochure in the Phoenix Contact catalogs. Use the fax order form on the back cover of this bro-chure to order these catalogs.

02-25 Ex-Basics Seite 4 Mittwoch, 27. November 2002 8:13 08

4 Phoenix Contact

Sources of ignition

1. Physical Background

Complete CombustionComplete combustion is a rapid oxidation

process. It is also referred to as a "destructive re", a process in which a combustible material is decomposed exothermally where there is a sufcient supply of oxygen. As the speed with which the shock wave emanating increases, the process is referred to as deagration, explosion or detonation in this order.

In the case of complete combustion, the damage caused increases signicantly in proportion to speed of the shock wave emanating.

Speed of the shock wave emanating

Deagration cm/s

Explosion m/s

Detonation km/s

ExplosionAn explosion can occur if there is a

combination of a ammable material, oxygen and a source of ignition. If one component is missing no exothermal reaction will occur.

Prerequisites for an explosion

OxygenIf an explosive material is combined with

oxygen, an explosive mixture is created.In the case of gases, the ratio of

concentrations determines whether an explosion is possible. The mixture can only be ignited if the concentration of the material in air is within the lower (LEL) and upper (UEL) explosive limits.

Some chemically unstable materials (e.g. acetylene, ethylene oxide) can also enter into exothermal reactions without oxygen as a result of spontaneous decomposition. The upper explosive limit (UEL) shifts to 100 volume percent. In the case of gases under pressure, the explosive ranges change.

Dusts can also be grouped into a lower explosion or ammability limit (at approx. 2060 g/m3) and an upper explosion or ammability limit (at approx. 26 kg/m3).

Examples for explosive areas of gases under normal pressure

Lower explosion limit

Upper explosive limit

AcetoneAcetoneAcetoneAcetoneAcetone

AcetyleneAcetyleneAcetyleneAcetyleneAcetylene

AmmoniaAmmoniaAmmoniaAmmoniaAmmonia

ButaneButaneButaneButaneButane

Diesel fuelDiesel fuelDiesel fuelDiesel fuelDiesel fuel

Carbon monoxideCarbon monoxideCarbon monoxideCarbon monoxideCarbon monoxide

MethaneMethaneMethaneMethaneMethane

GasolineGasolineGasolineGasolineGasoline

Carbon disuldeCarbon disuldeCarbon disuldeCarbon disuldeCarbon disulde

HydrogenHydrogenHydrogenHydrogenHydrogen

Volume percent of combustible materialsVolume percent of combustible materialsV

Explosive material Oxygen

Source of ignition

Source of ignition Examples of reasons for explosionsSparks mechanically created sparks (e.g. caused by friction, impact or

abrasion processes), electric sparks

Arcs short circuit, switching operationsHot surfaces power in electric systems, heaters, metal-cutting, heating up

during operation

Flames and hot gases due to combustion reactions, sparks during welding

Electrical systems protective low voltages ( U < 50 V) can still generate enough energy to ignite an explosive atmosphere.opening/closing of contacts, loose contact

Static electricity separately arranged conductive parts, many plastic materials

Electrical equalizing currents reverse currents from generators, body/earth contact in the case of faults, induction

Electromagnetic waves in the range of 3 x 10113 x 1015 Hz laser beam for distance measurement, especially: focusing

High frequency 1043 x 1012 Hz radio signals, industrial high-frequency generators for heating, drying, cutting, etc.

Lightning strike atmospheric weather disturbancesIonizing radiation X-ray apparatus, radioactive material, absorption of energy leads

to heating up

Ultrasound absorption of energy in solid/liquid materials leads to heating up

Adiabatic compression and shock waves sudden opening of valvesExothermal reactions chemical reaction

Explosive materialA ammable material which is present as a

gas, vapor or dust is called an explosive material.

In the case of vapors or dusts, an explosive atmosphere is created if the drop or particle size is smaller than 1 mm. Vapors, aerosols and dusts occurring in practice have particle sizes between 0.001 and 0.1 mm. Dusts with larger particle sizes are not ammable.


Phoenix Contact 5

2. Explosion Protection Standards, Regulations and Directives

ATEX Free commodity trade in EuropeATEX Free commodity trade in EuropeATwo directives are relevant for explosion

protection in the European Union's "new approach".

Target group Directive Common designation*et group Directive Common designation*

Manufacturer 94/9/EC ATEX 100aATEX 100aAATEX 95ATEX 95A

Operator 1999/92/EC ATEX 118aOperator 1999/92/EC ATEX 118aATEX 137ATEX 137A

* The directive is based on an article of the treaty establishing the European Community. The number of the article has changed. The term ATEX is derived from French, "ATmosphre EXplosive".

The manufacturer directive through the times

01.03.1996 10.10.1997 30.09.199801.03.1996 10.10.1997 30.09.1998 30.06.200330.06.2003

Council directive 94/26/EC, adapted to technical progress; Council directive 79/196/EEC

(List of harmonized standards generation D)

Council directive 97/53/EC, adapted to technical progress; Council directive 79/196/EEC

(List of harmonized standards generation E)

Directive 82/130/EEC, adapted with directive 98/65/EC

(List of harmonized standards generation D and E)

Council directive 94/9/EC

Certication Putting on the market

North American Hazardous Location Systems

Based on the North American Hazardous Location System (Hazloc), fundamental rules are laid down for explosion protection. In the US, these are stated in the National Electrical Code (NEC), and in Canada in the Canadian Electrical Code (CEC)

Among the main institutions of the system are: Underwriters Laboratories Inc. (UL), CSA International (CSA), Institute of Electrical and Electronics

Engineers (IEEE), The Instrumentation, Systems and

Automation Society (ISA), Mine Safety and Health Administration

(MSHA), National Electrical Manufacturers

Association (NEMA), National Fire Protection Association

(NFPA), United States Coast Guard (USCG), Factory Mutual Research (FM).

Equipment group

Category Degree of protection

Protection guarantee Operating conditions

I M1 very high safety degree

In the case of failure of one installation protection measure, a second protection measure guarantees the necessary safety, or

That the necessary degree of safety is guaranteed when two independent errors occur.

For reasons of safety, it must be possible to continue operating a product even if the atmosphere is potentially explosive.

I M2 high safety degree

It must be possible to switch off these products if an explosive atmosphere occurs.

In normal operation, the protective measures must still guarantee the required safety even in difcult conditions, or if equipment is treated roughly or ambient inuences have changed.

II 1 very high Two Two T independent protective measures.

Safe if two faults occur independent from one another.

Equipment can still be used in zones 0, 1, 2 (G) and 20, 21, 22 (D) and continue to be operated.

II 2 high Safe in normal operation and if II 2 high Safe in normal operation and if II 2 high Safe in normal operation and if common faults occur.

Equipment can still be used in zones 1, 2 (G) and 21, 22 (D) and continue to be operated.

II 3 normal Safe in normal mode. Equipment can still be used in zones 2 (G) and 22 (D) and continue to be operated.

ATEX Manufacturer directive 94/9/ECATEX Manufacturer directive 94/9/ECAUntil now, certicates of conformity have

been issued by the testing agencies. The directives for devices of generations A to E are the basis for this. These directives will, however, be replaced by the directive 94/9/EC as of July 1st, 2003.

As early as 1997, Phoenix Contact supported the "new approach" of the European commission and approved all equipment in accordance with the directive 94/9/EC.

From July 1st, 2003, electrical equipment may only be allowed on the market for the rst time if it complies with directive RL 94/9/EC.

Equipment group and categoryIn order to determine the appropriate

procedure to be used for conformity assessment, the manufacturer must rst decide which equipment group and category the product belongs to, based on its intended use (see table below).

Equipment group I: Equipment for use in mining industries (coal-mining) and the related surface installations which are at risk from mine gases and/or combustible dusts.

Equipment group II: Equipment for use in all other areas that might be endangered by an explosive atmosphere.

The equipment groups are assigned to categories in the directive 94/9/EC. Categories M1 and M2 are determined for equipment group I. Three categories - 1, 2 and 3 are dened in equipment group II. The correlation between category and zones is made in the operator directive 1999/92/EC.

Equipment group IIEquipment group II " "Surface Surface installationinstallations"s"Hazardous areasHazardous areas

Equipment group IEquipment group I ""Mining installations"Mining installations"Areas with a redamp hazard = Areas with a redamp hazard = coal-miningcoal-mining


6 Phoenix Contact

Conformity assessmentThe classication of electrical equipment

according to equipment group and category is the basis for conformity assessment. The illustration shows this relationship. Except for category 3 equipment, an EC type examination is required for the conformity assessment.

The modules are tested by a notied body.

An example illustrates this fact:CE 0344CE: EC conformity,0344: notied body, here: KEMA.

EC type examinationThe EC type-examination certicate

certies that the test has been carried out by a notied body. Notied bodies are determined by the EU.

The certicate constitutes the documentation for the operator.

Group II

Category 1 Category 2 Category 3

Group IGroup I

Individual testccccccccccccccccccccccccccccccc 0344

EC type examination

Conformity assessment in acc. with 94/onformity assessment in acc. with 94/onformity assessment in acc. with 94 9/9/ /9/9 EC

Module DQA Productionor product testccccccccccccccccccccccccccccccc 0344

Module EQA Productor conformity with designccccccccccccccccccccccccccccccc 0344

Module AInternal production controlccccccccccccccccccccccccccccccc 0344

*

*

* possible as an option, similar procedure

M1 M2

Notied body in acc. with 94/4/EC (extract)

Testing body Country Identicationesting body Country IdenticationTesting body Country IdenticationT

PTB Germany 0102

DMT (BVS) Germany 0158DMT (BVS) Germany 0158

TV Nord Germany 0032

DQS Germany 0297DQS Germany 0297

IBExU Germany 0637

BAM Germany 0589BAM Germany 0589

BASEEFA(2001 Ltd)

Great Britain

SCS Great Britain 0518SCS Great Britain 0518

INERIS France 0080

LCIE France 0081LCIE France 0081

LOM Spain 0163

KEMA Netherlands 0344KEMA Netherlands 0344

CESI Italy 0722

DEMKO Denmark 0539DEMKO Denmark 0539

NEMKO Norway 0470


Phoenix Contact 7

ATEX operator directive 1999/92/ECATEX operator directive 1999/92/ECA

Extract from RL 1999/92/EC:

Areas with explosive atmospheresThe employer/operator: divides areas in which explosive

atmospheres may occur into zones. guarantees that the minimum

requirements are applied. marks the entrances to areas with

explosive atmospheres.

(1) Article 137 of the treaty provides that the Council may adopt, by means of Directives, minimum requirements for encouraging improvements, especially in the working environment, to guarantee a better level of protection of the health and safety of workers.(7) Directive 94/9/EC of the European Parliament and of the Council of 23 March 1994 on the approximation of the laws of the Member States concerning equipment and protective systems intended for use in potentially explosive atmospheres (5) states that it is intended to prepare an additional Directive based on Article 137 of the Treaty covering, in particular, explosion hazards which derive from a given use and/or types and methods of installation of equipment.

Note:In many areas, national law requires that

the plants be tested. This is carried out by independent experts.

Assessing the explosion riskThe operator of a plant must carry out a

detailed assessment. The assessment is based on the standards EN 60 079-10, EN 60 079-14 and EN 1127-1. The zones are determined on the basis of the assessment. The assessments must be recorded in the documentation.

Correlation in acc. with 1999/92/EC

Zone Category

0, 20 1

1, 21 1, 2

2, 22 1, 2, 3

Identication of hazardous areasThe hazardous area is identied by means

of a danger sign.

3. Installation and Protection Methods

Installation

GeneralIf systems are installed in hazardous

areas, a great number of measures must be taken. When selecting equipment, cables/conductors and construction, particular requirements must be met. In any case of doubt, we recommend including additional experts in the planning stage.

Risk assessmentPrior to installation, the operator of a

system must carry out a risk assessment. On the basis of the risk assessment, the zones must be laid down and the permitted equipment selected. Every plant must be examined for its specic characteristics.

Check list: (possible procedure)

Recognizing the risk

Which materials are processed in the plant?

Probability of an explosive atmosphere occurring

What are the conditions necessary for the raw materials, semi-nished and nished products to be present in an explosive concentration?The physical correlations described on page 4 must be taken into account.

Presence of ignition sources

Ignition sources that can cause materials in the process to ignite must be identied.Presence: permanent, frequent, seldom or very seldom.The interaction between individual parts of the system and the material being processed must be also be taken into account in the assessment.

Effects of the explosion

Possible risks

If an explosion occurs despite these measures, the possible risks must be examined. Can chain reactions occur, what is the extent of damage to the buildings and what effect does the explosion have on other parts of the plant. It is possible for interactions that could never occur in the individual system to occur with neighboring systems.

The risk assessment requires a high degree of experience and the correct evaluation. If there is any doubt, it is advisable to refer to other experts. Risk assessment is the basis for all other measures, including the operation of the system.

Warning signs for the hazardous area

Documentation of explosion protectionThe documentation is crucial for the safe

operation of the plant in the hazardous area. The documentation is created prior to installation and must be updated whenever there are alterations or additions.

If changes are made to the plant, all inuencing variables described must be taken into account.

Example for the structure of the documentation

Person responsible for the object

with name

Description of the structural and geographic characteristics

Plan of site and building, ventilation and air supply

Description of procedures Description of the plant from the point of view of explosion protection

Materials data List of data with characteristics of relevance to an explosion

Risk assessment see adjacent check list

Protection concepts Division into zones, safety categories applied

Organizational measures Training, written instructions, clearance for work

In directive 1999/92/EC, annex II, the correlation between the category in acc. with 94/9/EC and the zone is made.


8 Phoenix Contact

Overview of standard protection methods for electrical equipment

Worldwide overview of standardsWorldwide overview of standardsW

Installation, standards for operator

Designation EN standard IEC standardDesignation EN standard IEC standard(factually identical to EN)

China

Explosion protection part 1: basics and methods EN 1127-1 ---

Electrical operating equipment for potentially gas-explosive areas introduction of the areas

EN 60 079-10 IEC 60 079-10 GB3836.14EN 60 079-10 IEC 60 079-10 GB3836.14

Electrical operating equipment for potentially gas-explosive areas Electrical equipment in potentially explosive areas

EN 60 079-14 IEC 60 079-14 GB3836.15

Electrical operating equipment for use in areas with combustible dusts; part 1-2: selection, installation and maintenance

EN 50 281-1-2

Protection methods USA basis

Principle EN standard IEC standard Principle EN standard IEC standard (factually identical to EN)

FM(USA)

UL(USA)

CSA(Canada)

China

General requirements Basis for safety categories EN 50 015,EN 50 021, EN 50 028, EN 50 039

EN 50 014 IEC 60 079-0 FM 3600(ISA 12.00.01)

GB3836.1

Intrinsic safety EEX i Limiting energy EN 50 020Intrinsic safety EEX i Limiting energy EN 50 020AEx i NEC505 FM 3610 UL2279 Pt.11 CSA-E79-11FM 3610 UL2279 Pt.11 CSA-E79-11Ex i IEC 60 079-11 GB3836.4IEC 60 079-11 GB3836.4IEC 60 079-11 GB3836.4IEC 60 079-11 GB3836.4(IS) NEC504 FM 3610 UL913 CSA-157FM 3610 UL913 CSA-157

Increased safety EEx e Constructional measures through spacing and dimensioning

EN 50 019AEx e NEC505 FM 3600

(ISA 12.16.01)UL2279 Pt.11 CSA-E79-7

Ex e IEC 60 079-7 GB3836.3Non-incendive (NI) NEC500 Constructional measures through

spacingFM 3611 UL 1604 CSA-213FM 3611 UL 1604 CSA-213

Explosion-proof (XP) NEC500 Constructional measures through enclosure

FM 3615 e.g. Housing:UL 1203

Flameproof enclosure EEx d Constructional measures through enclosure

EN 50 018AEx d NEC505 FM 3600

(ISA 12.22.01)UL2279 Pt.1 CSA-E79-1

Ex d IEC 60 079-1 GB3836.2IEC 60 079-1 GB3836.2IEC 60 079-1 GB3836.2IEC 60 079-1 GB3836.2Encapsulation EEx m Exclusion of potentially explosive

atmosphereEN 50 028

AEx m NEC505 FM 3600(ISA 12.23.01)

UL2279 Pt.18 CSA-E79-18

Ex m IEC 60 079-18 GB3836.9Oil immersion EEx o Exclusion of potentially explosive

atmosphereEN 50 015

AEx o NEC505 FM 3600(ISA 12.16.01)

UL2279 Pt.6 CSA-E79-6

Ex o IEC 60 079-6 GB3836.6IEC 60 079-6 GB3836.6IEC 60 079-6 GB3836.6IEC 60 079-6 GB3836.6Powder lling EEx q Exclusion of potentially explosive

atmosphereEN 50 017 FM 3622

AEx q NEC505 FM 3600(ISA 12.25.01)

UL2279 Pt.5 CSA-E79-5

Ex q IEC 60 079-5 GB3836.7Pressurization (purged) EEx p Exclusion of potentially explosive

atmosphereEN 50 016

AEx p NEC505 --- --- CSA-E79-2--- --- CSA-E79-2Ex p IEC 60 079-2 GB3836.5IEC 60 079-2 GB3836.5IEC 60 079-2 GB3836.5IEC 60 079-2 GB3836.5Type X NEC500Type X NEC500T FM 3620 NFPA496Type Y NEC500Type Y NEC500T FM 3620 NFPA496Type Z NEC500Type Z NEC500T FM 3620 NFPA496

Protection Method "n" EEx n Improved industrial quality EN 50 021AEx n NEC505 FM 3600;

(ISA 12.12.02)UL2279 Pt.15 CSA-E79-15

Ex n IEC 60 079-15 GB3836.8Intrinsically safe electrical systems "i-Sys"

Power limitation in interconnected intrinsically safe circuits

EN 50 039 IEC 60 079-11 GB3836.4EN 50 039 IEC 60 079-11 GB3836.4EN 50 039 IEC 60 079-11 GB3836.4EN 50 039 IEC 60 079-11 GB3836.4EN 50 039 IEC 60 079-11 GB3836.4

Dust explosion protection Dust; protection through housing design EN 50 281-1-1Dust explosion protection Dust; protection through housing design EN 50 281-1-1(DIP) NEC500 NFPA 70

Abbreviations based on the NEC 500 in North America

XP Explosion-proofIS Intrinsically safe apparatusAIS Associated apparatus with intrinsically safe connectionsANI Associated non-incendive eld wiring circuitPX, PY, PZ PressurizedAPX, APY, APZ Associated pressurization systems/componentsNI Non-incendive apparatus and non-incendive eld wiring apparatusDIP Dust ignition-proof


Phoenix Contact 9

IEC/CENELEC Zone 0 Zone 1 Zone 2IEC/CENELEC Zone 0 Zone 1 Zone 2IEC/CENELEC Zone 0 Zone 1 Zone 2

USA: NEC 505 Zone 0 Zone 1 Zone 2USA: NEC 505 Zone 0 Zone 1 Zone 2USA: NEC 505 Zone 0 Zone 1 Zone 2

USA: NEC 500 Division 1 Division 2

Explosive material Class Group Explosive material Class GroupExplosive material Class Group Explosive material Class GroupExplosive material Class Group Explosive material Class GroupExplosive material Class Group Explosive material Class GroupExplosive material Class Group Explosive material Class Group

Gas / vaporor liquid I A, B, C, Dor liquid I A, B, C, D

Gas / vaporor liquid I A, B, C, Dor liquid I A, B, C, D

Dust II E, F, G Dust II F, GDust II E, F, G Dust II F, GDust II E, F, G Dust II F, GDust II E, F, G Dust II F, GDust II E, F, G Dust II F, G

Fibers III Fibers III Fibers III Fibers III Fibers III Fibers III Fibers III Fibers III Fibers III Fibers III

CLASS I (gases and vapors) Group A (acetylene)

Group B (hydrogen)

Group C (ethylene)

Group D (propane)

CLASS II (dusts) Group E (metal dust)

Group F (coal dust)

Group G (grain dust)

CLASS III (bers) No subgroups

North America

4. Zones and Divisions

EuropePotentially explosive areas are allocated to

standard zones that are distinguished according to two types: potentially gas-explosive areas and potentially dust-explosive areas.

The zones are dened for gases in EN 60 079-14 and for dusts in EN 50 281-1-2. Furthermore, the standard EN 1127-1 was created on the basis of the mandate of the European Commission (KEU) and the European Free Trade Zone (EFTA) to the European Standardization Committee (CEN). This is to support the EC directives (ATEX) 94/9/EC and 1999/92/EC.

The zones are divided based on the frequency of the occurrence of potentially explosive atmospheres. Gases and dust can also occur at the same time. The zones were assigned precise time specications for gases in the explosion protection rules of the Trade Association for Chemicals in Germany These values are not mentioned in the standards, because it appears that it is not possible to make a generally valid statement. For this reason, one must weigh up how to judge the frequency of occurrence in every individual risk assessment.

Potentially gas-explosive areas

Zones Type of danger

Zone 0 continuous, long periods, frequent

Zone 1 occasional

Zone 2 normally not, only for a short period

Potentially dust-explosive areas*

Old division in Germany

New division in Germany

Type of dangerType of dangerT

Zone 10 Zone 20 continuous, long periods, frequent

Zone 21 occasional

Zone 11 Zone 22 normally not, only for a short period

* General assignment, must be checked in individual cases.

In Germany, dusts were previously divided into two zones. When standards were revised as a result of European directives, the zone division was also divided into three zones for dusts as well, throughout Europe. However, it must be taken into account that zones 10 and 11 cannot be transferred to the new zone division without checking.

National Electrical Code (NEC) in the USA

Article Contents

500 General requirements for divisions of class I, II and III

501 Requirements for division of class I

502 Requirements for division of class II

503 Requirements for division of class III

504 Requirements for division of class I, II and III in relation to intrinsic safety (IS)

505 General and special requirements for the zone of class I

Canadian Electrical Code (CEC) in Canada

Regulation Contents

18-000 General requirements for class I / zone and class II and III / division

18-090 Requirements for class I, zone 0 requirements

18-100 Requirements for zone 1 and 2, class I

18-200 Requirements for division of class II

18-300 Requirements for division of class III

Appendix J General and special requirements for the division of class I

In the USA, zones or divisions are divided up according to the National Electrical Code (NEC). The comparison with the IEC/CENELEC zone division can only be regarded as a general approximation. The conversion must be checked in individual cases.

Electrical operating equipment can be used especially for division 2. The same operating equipment can only be used in zone 2 with additional testing and certication. The possibilities are shown in the simplied assignment diagram.

The basis for explosion protection in North America is the National Electric Code (NEC) in the USA and the Canadian Electrical Code (CEC) in Canada. The listed excerpts of the NEC and CEC refer to explosion protection.


10 Phoenix Contact

Simplied assignment diagram for the USA

Operating equipment marked with *: Permissible areas of application

NEC class I, div. 1 OK in NEC class I, zone 1 and 2

NEC class I, div. 2 OK in NEC class I, zone 2

NEC class I, zone 1 Not permissible in NEC class I, div. 1

NEC class I, zone 2 OK in NEC class I, div. 2

NEC AEx OK in NEC zone 0, 1, 2, as marked

NEC AEx Not permissible for NEC class I, div. 1

NEC AEx OK in NEC class I, div. 2

IEC zone 1 Not permissible for NEC purview

IEC zone 2 Not permissible for NEC purview

IEC EEx or Ex Not permissible for NEC purview

* When this mark is given, it can be used to derive the permissible area of application. Assignment is only possible in the indicated direction.

Understanding classes and divisions

Division Explosive atmosphere

Class I, division 1 Gas, liquid and vapor Can also occur under normal operating conditions, can occur frequently during repair, maintenance or due to lack of sealing, or can become a source of ignition in the case of an operation failure.

Class I, division 2 Gas, liquid and vapor Normally in closed systems in which ammable concentrations are prevented by ventilatioClass I, division 2 Gas, liquid and vapor Normally in closed systems in which ammable concentrations are prevented by ventilation or connected to the area that is assigned to class I, division 1, for which the danger exists that ammable concentrations can occur.

Class I, zone 0 Gas, liquid and vapor Continuous, long periods, frequently present.

Class I, zone 1 Gas, liquid and vapor Occurs under normal conditions, can occur frequently during repair, maintenance or due to lClass I, zone 1 Gas, liquid and vapor Occurs under normal conditions, can occur frequently during repair, maintenance or due to lack of sealing, can become a source of ignition in the case of an operation failure or is connected to the area that is assigned to class, zone 0, for which the danger exists that ammable concentrations can occur.

Class I, zone 2 Gas, liquid and vapor Normally not, only for short periods in connection with the area that is assigned to class 1, zone 1, for which the danger exists that ammable concentrations can occur.

Class II, division 1 Dust Can also occur under normal conditions, frequently during repair, maintenance or due to lack of sealingClass II, division 1 Dust Can also occur under normal conditions, frequently during repair, maintenance or due to lack of sealing. Can become a source of ignition in the case of an operation failure, or electrically conductive dust occurs in a dangerous amount.

Class II, division 2 Dust Normally not present in a ammable concentration in the air, does not endanger the normal operation of the electrical plant.Occurs during seldom operation failures of the plant, or dust hinders reliable heat discharge.

Class III, division 1 Fibers Areas in which easily ammable bers are processed or transported. Class III, division 1 Fibers Areas in which easily ammable bers are processed or transported.

Class III, division 2 Fibers Areas in which easily ammable bers are stored or transported.

Example for zone division

ValveValveV

Zone 1Zone 1

Zone 2Zone 2

Zone 0Zone 0

Sink

Example: Tank for ammable liquids (acc. to EN 60 079-10)


Phoenix Contact 11

Clearance and creepage distancesClearance and creepage distances must

be maintained for intrinsic safety, increased safety and type of protection "n".

5. Types of Protection

The basis for the standardized protection methods are the requirements for the surface temperature, clearance and creepage distances, the identication of electrical operating equipment, the assignment of the electrical operating equipment to the area of application and the degrees of protection.

Everything that goes beyond the basic requirements are specied in the respective protection method.

Classication in groupsDue to its characteristics, coal mining is

assigned group I. This group was previously characterized by the term "susceptible to redamp".

All other potentially explosive areas are assigned to group II. Examples include the petrochemical industry, the chemical industry and silo plants with ammable dusts. The term "potentially explosive" (old abbreviation "Ex") stands for the electrical operating equipment of the current group II.

For intrinsic safety, ame-proof enclosures and type of protection "n" subgroups IIA, IIB,

Permissible surface temperature of group I[C]

Condition

150 with deposits of coal dust on the operating equipment

450 without deposits of coal dust on the operating equipment

Temperature class of group IITemperature class of group IITThe explosive atmosphere can be

prevented from igniting when the surface temperature of the operating equipment is lower than the ignition temperature of the surrounding gas. The surface temperature is valid for all parts of an electrical apparatus that can come into contact with the explosive material.

The majority of the gases can be assigned to the temperature classes T1 to T3.

In the USA its referred as the T rating.

Permissible surface temperatures [C] for group II: temperature classes in Europe and the USA

Temperature limits with dustTemperature limits with dustTIn the case of potentially dust-explosive

areas, the maximum surface temperature is given as a temperature value [C].

There is no classication into groups . The permissible temperatures for each type of dust normally have to be determined through experiments.

Clearance distanceClearance distance

Creepage distanceCreepage distance

Clearance and creepage distance

The term clearance distance is dened as the shortest connection between two potentials through the air. The creepage distance is the shortest connection between two potentials over a surface. A minimum distance must be maintained, depending on the comparative tracking index of the material.

The minimum distances for clearance and creepage distances are specied in the corresponding protection methods.

TTemperature class group Iemperature class group ITemperature class group ITTemperature class group ITThe temperatures are designed for the

requirements in coal mining. Methane is present as a gas and dust results from the coal.

and IIC are distinguished in group II. Group IIC contains gases with the highest ammability.

In the case of intrinsic safety and protection method "nL", the classication is determined by the minimum ignition current (MIC). The gap (MESG) determines the subgroups for "ame-proof enclosures" and for protection method "nC".

Note:The ATEX directive 94/9/EC refers to device groups. These are identical to the groups according to EN standard.

Group IIGroup II "Surface installations" "Surface installations"PPotentially explosive atmospheresotentially explosive atmospheres

Group IGroup I "Underground installations" "Underground installations"Areas with a redampAreas with a redamphazard = coal mininghazard = coal mining

Example:

Modular terminal blocks are used in a housing in safety category EEx e IIC T6. In this case, the maximum permissible current strength must be calculated so that the temperature class T6 is also maintained at the modular terminal blocks. The housing is designed with the IP protection type IP 54, but the explosive gas can still intrude into the housing. For this reason, it is not sufcient only to regard the surface temperature of the housing.


12 Phoenix Contact

Increased safety Ex eIn protection method "increased safety",

voltages up to 11 kV can be brought into the potentially explosive area. Increased safety is especially suitable for supplying motors, lights and transformers. The protection principle

is based on constructional measures.Clearance and creepage distances are

determined for the live parts, divided into voltage levels. This prevents electrical sparks. In addition, at least the IP protection type (EN 60529) IP 54 must be fullled.

Limiting the surface temperature ensures that explosive atmosphere cannot be ignited at any place, even inside the housing, during operation. The housing does not prevent gas from entering.

Flame-proof Enclosures Ex dIn ame-proof enclosures an explosion is

contained.An explosion that occurs inside is not able to ignite the explosive atmosphere surrounding the housing. This leads to very robust

housings.The housings have covers and insertion

points to accommodate cables and lines. The maximum permitted gap that is present is dimensioned in such a way that it prevents the explosion from being carried over from inside the housing to the surrounding explosive atmosphere.

In the case of cable and conductor leads in the protection type Ex d, it is not permitted to grease the thread or remove rust with a wire brush. The gap could be changed as a result and the protection principle destroyed. The manufacturers specications must be observed. In the USA a similar method used is called explosion proof. (xp) (see page 8)

Encapsulation, powder lling or oil emersion Ex m, Ex q, Ex o

The principle of the protection methods "molded encapsulation", "sand encapsulation" and "oil encapsulation" safety categories is to surround possible sources of ignition in

an electrical apparatus with the potting compounds, sand or oil. This prevents the ignition of the explosive atmosphere.

Voltages from 1011 kV can also be Voltages from 1011 kV can also be Vreached with these protection methods. Details can be found in the standards (see page 8).

Pressurization (purged) Ex pThe positive pressure or inert gases

describes methods that use overpressure to prevent an explosive atmosphere from entering the housings or the control room. The ambient pressure around the

housing is always lower than inside.Three forms of pressurization are possible

(see table at the bottom left). In the case of static pressurization, the housing must be hermetically sealed. No loss of pressure occurs. More common, however, are methods in which the pressurization is maintained by compensating the leakage losses or by constant circulation. The overpressure is usually created by simple compressed air.

Pressurization (purged) methods Ex p requires a monitoring unit that reliably switches off the electrical operating equipment inside the housing as soon as sufcient pressurization is no longer present. The monitoring unit must be designed in a different protection method, so that it can also be operated without pressurization.

Operating equipment can now be operated inside the enclosure.Nevertheless, a source of ignition must not develop if the pressurization decreases, as a result of the temperature of the operating equipment. In the USA this method used is referred to as purged with three forms X,Y,Z. (see page 8)

Possibilities of pressurization

Pressurization Static With compensation of the leakage Pressurization Static With compensation of the leakage losses

With continuous circulation

Compressed air Without correction Compensation of the leakage losses Continuous correction

Operating states --- Pre-purging phase: Operating states --- Pre-purging phase: The housing is purged and any explosive atmosphere that is present is removed from the housing.

Operating phase:The overpressure in the housing is monitored. If it decreases, the electrical operating equipment inside the housing is switched off.

Intrinsic safety protection method Ex iThe intrinsic safety category, as opposed

to other categories (e.g. increased safety), refers not only to individual equipment, but to the entire circuit that is

intrinsically safe. The protection is in the circuit and not in the housing. A circuit is described as intrinsically safe if no spark or thermal effect can cause an explosive atmosphere to ignite.

Suitable measures must guarantee that the energy in intrinsically safe operating equipment is so low that an explosive atmosphere cannot be ignited even in the case of a defect.

In the case of intrinsically safe electrical apparatus, all circuits are intrinsically safe and depending on their overall protection method, this equipment can be used directly in the designated zones or divisions.

Associated apparatus has both intrinsically safe and non-intrinsically safe circuits. They are generally implemented in the safe area but the connecting lines do extend into the hazardous area.

Therefore, the associated apparatus must also comply with the above-mentioned categories, i.e. associated apparatus which is connected with a sensor or actuator in zone 0, Div. 1 must be equipment from category 1.


Phoenix Contact 13

Type of protection "n"Type of protection "n"TProtection method "n" can be described as

an improved industrial quality that is designed for normal operation. A fault scenario examination as with the intrinsic safety category is not performed. This can only be applied for group II and the use of electrical operating equipment in zone 2. The manufacturer species the technical data for normal operation.

In the method "n", ve different versions are distinguished, which can be derived in part from the well-known increased safety, intrinsic safety, ame-proof encapsulation, pressurization and encapsulation and molded encapsulation safety categories.

This method was developed based on the US protection method "non-incendive" (NI) and was introduced in Europe as a standard in 1999.

Classication of protection method "n": EEx n in Europe

Abbreviation Meaning Comparable to Method Divisions of Abbreviation Meaning Comparable to Method Divisions of Abbreviation Meaning Comparable to Method Divisions of Abbreviation Meaning Comparable to Method Divisions of group II

A Non-sparking EEx e Occurrence of arcs, sparks or hot surfaces is minimized

None

C Sparking equipment

partly EEx d, EEX m

Enclosed break deviceNon-incendive componentsHermetically sealed, sealed or encapsulated installations

IIA, IIB, IIC

R Restricted breathing housing

--- Intrusion of explosive gases is limited None

L Power-limited EEX i Power limitation so that neither sparks nor er-limited EEX i Power limitation so that neither sparks nor thermal effects cause an ignition

IIA, IIB, IIC

P Simplied pressurized encapsulation

EEx p Intrusion of explosive gases is prevented by overpressure, monitoring without disconnection

None

* different in North America and Europe

Dust explosion protection in EuropeThe dust explosion protection for group II

acc. to EN 50 281-1-1 limits the entrance of dust into housings by requiring an IP protection for housings acc. to the standard EN 60 529. In addition, the maximum surface temperature that can ignite the dust is specied. Higher temperatures can occur inside the housing, however. In these cases, special instructions are necessary for opening the housing.

For group I, which is designed for coal-mining, the dust explosion protection (coal dust) is already covered by the standards EN 50 014 ff.

Requirements for housings of group II, dust (D)

Category 1 2 3Category 1 2 3Category 1 2 3

IP protection (EN 60 529) IP6X IP6X IP5X

Housing Dust-proof Dust-proof Dust-protectedHousing Dust-proof Dust-proof Dust-protectedHousing Dust-proof Dust-proof Dust-protected

Ambient temperature -20C to + 40C -20C to + 40C -20C to + 40C

Max. surface temperature* of the housing

Measurement based on ambient temperature 40C



* A temperature value is given in Celsius.

Subdivision of type of protection "n" in North America

Designation acc. to NEC

Energy limited, "nC" *

Hermetically sealed, "nC"

Non-incendive, "nC"

Non-sparking, "nA"

Restricted breathing, "nR"

Sealed device, "nC"

Simplied pressurization, "nP" **

* different in North America and Europe** referred to as type X, Y and Z in the USA

US type of protection acc. to NEC 500504

Explosion-proof For operating equipment of this protection type, additional requirements are made for explosion protection. The temperature is specied to a value that is considered safe in relation to the surroundings. This includes products such as: Motors and generators Monitoring devices for industrial and process control applications (industrial control equipment, process

control equipment) Electrically operated valves

Dust ignition-proof The ignition of dust or dust accumulation by arcs, sparks or heat is prevented.

Non-incendive A short circuit or thermal effect is not able to ignite a ammable gas-air or vapor-air mixture that is specied by the manufacturer under certain operating conditions.

Non-sparking The electrical operating equipment does not have any parts that normally cause arcs, sparks, or thermal effects with which an explosive atmosphere can be ignited.

Hermetically sealed The electrical operating equipment is completely sealed so that no explosive atmosphere can enter from outside. This is realized by welding or other melting methods.

Sealed device The operating equipment is designed in such a way that it cannot be opened, has no function parts on the outside and is totally sealed. Sparking parts or hot surfaces can be located inside the equipment.


14 Phoenix Contact

Current year of manufactureType-examination in acc. Type-examination in acc. Twith 94/9/EC (ATEX)

Associated apparatus

Xccccccccccccccccccccccccccccccc 02 II (1) GDX02 II (1) GDX0102

Atmosphere(G = Gas, D = Dust)

Category

Equipment group

Notied body, production (e.g. PTB)

TV 01 ATEX 1750

Certicate no.

Type-examination in acc. Type-examination in acc. Twith 94/9/EC (ATEX)

Year of EC type-examination Year of EC type-examination Ycerticate

Notied body


[E Ex ia] IIC

Group

Protection method

Explosion-protected

Certied toCENELEC standard EN 50


X02 II 2 GDX02 II 2 GDX0102


Category

Equipment group


Components are excepted from the ccccccccccccccccccccccccccccccc marking.

TV 01 ATEXATEXA 1750 U

Certicate no.


Year of EC type-Year of EC type-Yexamination certicate

Notied body

E Ex e II T6

Temperature classTemperature classT(for electrical equipment used directly in the Ex area)Group

Protection method

Explosion-protected


6. Identication and Marking


Electrical equipment

Xccccccccccccccccccccccccccccccc 02 II 1 GDX02 II 1 GDX0102


Category

Equipment group


TV 01 ATEX 1750

Certicate no.



Notied body

Electricalequipment

E Ex ia IIC T6

Temperature classTemperature classT(for electrical equipment used directly in the Ex area)Group

Protection method

Explosion-protected


Electrical apparatusIdentication acc. to ATEX EC type-examination certicate Identication acc. to EN 50 014

Associated apparatusIdentication acc. to ATEX EC type-examination certicate Identication acc. to EN 50 014

ComponentIdentication acc. to ATEX EC type-examination certicate Identication acc. to EN 50 014

Identication in Europe acc. to ATEX and EN standards


Phoenix Contact 15


Xccccccccccccccccccccccccccccccc 02 II 1 DX02 II 1 DX0102

Atmosphere(D = Dust)

Category

Equipment group


TV 01 ATEX 1750

Certicate no.



Notied body

IP 66 T = 180C

TemperatureTemperatureT

IP protection in acc. with EN 60 529

Dust explosion protection for electrical equipmentIdentication acc. to ATEX EC type-examination certicate Identication acc. to EN 50 281-1-1

Associated apparatusIdentication

ComponentIdentication


16 Phoenix Contact

Identication US Standard in acc. with NEC 505

Deviation in ambient temperature

I / 1 / AEx ia / IIB / T6, T5 Ta = 70C; 699008; IP 54

Type of housingType of housingT

Control document

Temperature classTemperature classT

Group, Gas group

Degree of protection

American National Standard approved

Zone

Class


Identication US Standard in acc. with NEC 500

Certifying body in the USA: here UL; c for Canada; us for the USA

Fibers

Can be used in Div 2* for Class I: Gases

Gases

Dusts suitable for circuits in Div 1*

* Acc. to NEC 500

Class III, Hazardous Locations

Suitable for Class I, Div. 2, Groups A, B, C and D installation;

Class I, Div. 1, Groups A, B, C and D;

Class II, Groups E, F and G; and

providing intrinsically safe circuits for use in

Classication of the electrical equipment

A: AcetyleneB: HydrogenC: EthyleneD: Propane

1M68

UListed

Identication USA

CD-No: 12345678 Control drawing no. (Control document)

Deviation in ambient temperature

IS / II,I / 1 / CDEFG / T6, T5 Ta = 70C; 699008; Type 4X, 6P

Type of housingType of housingT

Control document

Temperature classTemperature classT

Group

Division

Class

Safety category


Phoenix Contact 17

Electrical equipment and associated apparatus

An intrinsically safe circuit consists of at least one electrical equipment and one associated apparatus.

The circuits of the electrical equipment fulll the requirements of intrinsic safety. Electrical equipment may only be connected to circuits without intrinsic safety via associated apparatus. Associated apparatus has both intrinsically safe circuits and circuits without intrinsic safety. The circuits are isolated using Zener barriers or galvanic isolators. In EN 50 020, the term "safety barrier" is used to refer to this technique.

Intrinsically safe electrical equipment and intrinsically safe parts of associated apparatus are classied according to EN 50 020 in categories "ia" and "ib".

Category "ia" is always safer than "ib". Category "ia" or "ib" denes whether

protection is maintained with one or two faults in the protective circuit.

For intrinsically safe circuits going into zone 0, standard (EN 60079-14 chap. 12.3) recommends the preferential use of category

Category* Faults Per-Category* Faults Per-missible zones

ia Under normal operating conditions, not able to cause ignition if one fault or a combination of two faults occurs.

0, 1, 2

ib Under normal operating conditions, not able to cause ignition if one fault occurs.

1, 2

* Category, in acc. with EN 50 020, is not identical with the term used in directive 94/9/EC

"ia" in conjunction with galvanic isolation.Intrinsic safety is based on the

consideration of faults in order to rule out the danger of explosion. This does not, however, provide any conclusions as to the operational safety. This means that a total functional failure of the equipment can be permissible as seen from the point of view of explosion protection.

Electrical equipment can be used in zone 0, Div. 1 according to the category. Associated apparatus is usually installed in the safe area. Only the intrinsically safe circuits are routed into the hazardous area, according to the category.

Signal system around 1910

Block diagram for limiting voltage and current.

The Zener diode becomes conductive at a dened voltage level. The higher voltage is discharged over the Zener diode and the voltage in the electrical circuit is limited in the Ex area.

A resistor connected in series limits the current in the hazardous area.

Imax = Io =UoR

Intrinsic safety does not reduce the Intrinsic safety does not reduce the ammable material and/or the oxidizer.

The ignition of an explosive mixture is prevented if electrical sparks and thermal effects are ruled out. In order to keep the electrical spark below the ignition limit, the voltage is limited. The thermal effect, in other words, excessively hot surfaces, is ruled out by limiting the current.

Limiting the energy prevents the electrical equipment and its surfaces from becoming too hot. This is also true of the sensors connected to the intrinsically safe circuits. Energy may be stored in capacitors (condensers) or inductors (coils) within the intrinsically safe circuit.

The principle of intrinsic safety> voltage limited> current limited> stored energy limited

Electrical equipment, intrinsic safety Associated apparatus, intrinsic safetyElectrical equipment, intrinsic safety Associated apparatus, intrinsic safetyElectrical equipment, intrinsic safety Associated apparatus, intrinsic safetyElectrical equipment, intrinsic safety Associated apparatus, intrinsic safety

Hazardous area Safe areaHazardous area Safe areaHazardous area Safe areaHazardous area Safe areaHazardous area Safe area

When limiting voltage and current, the following applies for the maximum power:

The maximum permissible values are determined by the ignition limit curves according to in EN 50 020. There are a total of four ignition limit characteristic curves for the gas groups I, IIA, IIB and IIC. They are grouped according to the ignition energy.

The ignition limit curves are determined by means of spark test apparatus as described in EN 50 020.

Po = Uo2

4R

PrincipleSafety category "Intrinsic safety" Ex i is

based on the principle of limiting the current, voltage and stored energy within an electric circuit.

7. Intrinsic Safety

)

* )

* *


18 Phoenix Contact

Without electrical isolation: Zener barrier

With electrical isolation: Galvanic isolator barriers

Associated apparatus can be designed in a further safety category in order for it to be installed in zone 2, Div. 2 or maybe even in zone 1, Div. 1.

Simple electrical equipmentSimple electrical equipment does not

require certication. It must be assigned to a temperature class and conform with any other applicable requirements of EN 50 020.

The maximum temperature can be calculated from power Po of the associated apparatus and the temperature class determined.

Simple electrical equipment (EN 50 020)

Type Condition Examplesype Condition ExamplesType Condition ExamplesT

passive compo-nents

No energy contribution Resistor, switch, potentiometer, distributor box, simple semi-conductor components, Pt 100

Energy storing devices

Precisely dened characteristics, the values of which must be taken into account in the overall safety of the system.

Coil, Capacitor

Energy sources

Maximum values: U 1.5 V, I 100 mA, P 25 mW

Thermocouple,Photocell

Associated apparatus with/without galvanic isolation

Simple electrical equipment, intrinsic safety Associated apparatus, intrinsic safetySimple electrical equipment, intrinsic safety Associated apparatus, intrinsic safetySimple electrical equipment, intrinsic safety Associated apparatus, intrinsic safetySimple electrical equipment, intrinsic safety Associated apparatus, intrinsic safety

Hazardous area Safe areaHazardous area Safe areaHazardous area Safe areaHazardous area Safe areaHazardous area Safe area

Ex side Safe areaEx side Safe areaEx side Safe areaEx side Safe area

Ex side Safe areaEx side Safe area

Intrinsic safety installations

The central idea with regard to installation

The entire intrinsically safe circuit must be protected against energy from other sources entering, and against electrical and magnetic elds. The installation technician or operator is responsible for the intrinsic safety installation, and not the manufacturer.

Identication of hazardous areasThe hazardous area is identied by means

of a warning sign.

Warning signs for the hazardous area

)))

*** )))

*** ***

Potentially explosive area

Safe area

Common designations Europe USACommon designations Europe USA

For electrical equipment:Max. permissible voltageMax. permissible currentInternal capacitanceInternal inductance

UiIiCiLi

VmaxImaxCiLi

For associated apparatus:Max. open-circuit voltageMax. short-circuit currentMax. permissible capacitanceMax. permissible inductance

UoIoCoLo

VocIscCaLa

Dimensioning of intrinsically safe circuitsDimensioning of intrinsically safe circuitsDimensioning of intrinsically safe circuitsDimensioning of intrinsically safe circuitsDimensioning of intrinsically safe circuits

PLC420 mA

Intrinsically safe circuits

with associated apparatusTo aid planning and installation, it is

advisable to keep the operating instructions and EC type-examination certicates of the associated apparatus used at hand. These must be referred to for the necessary parameters. The rst step is to verify the data according to the following table.


Phoenix Contact 19

Grounding in intrinsically safe circuitsPotential differences can arise when

intrinsically safe circuits are grounded. These must be taken into account when considering the circuits.

Intrinsically safe circuits may be isolated to ground. The danger of electrostatic charging must be considered. The connection via a resistance R = 0.21 M to discharge electrostatic charges is not a ground connection.

An intrinsically safe circuit may be connected to the equipotential bonding system if this is only done at one point within the electrically isolated, intrinsically safe circuit. This condition is fullled by an electrical isolator.

Systems with Zener barriers must be grounded to them. Mechanical protection against damage must also be provided if necessary. These circuits may not be grounded at another point.

All electrical operating equipment that does not pass the voltage test with at least 500 V to ground must be grounded.

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX-NoteIf a grounding is necessary at the sensor/

actuator due to the function, this must be done immediately outside of zone 0.

In the case of galvanic isolation of supply and signal circuits, the faults and/or transient currents in the equipotential leads must be taken into account.

Permitted conductor cross sections for connection to earth

Number of conductors

Conductor cross section

Condition

At least two separate conductors

min. 1.5 mm2 Each individual conductor can carry the greatest possible current

One conductor

min. 4 mm2

Galvanic isolator barriers versus Zener barriers

Comparison of galvanic isolator barriers and Zener barriers

Condition Galvanic isolator barriers:

Zener barriers

Sensor, actuator can be connectedto ground, but not in zone 0

cannot be connected to ground

Equipotential bonding not necessary necessaryEquipotential bonding not necessary necessary

Faults in measurement (ground loops)

not possible possible

Leakage currents in Zener diodes

not possible possible

Temperature coefcients Temperature coefcients Tin limiting resistors

none present

Different potentials for intrinsically safe circuit and evaluation circuit

permitted not permitted

Installation work less higher due to reliable grounding

The next step is to check the electrical data of the intrinsically safe circuit (voltage, current, power, capacitance and inductance).

The system parameters are seen as complying if the system has certication.

In the intrinsically safe circuit, all capacitances and inductances must be taken into account and compared with capacitance Co and inductance Lo of the associated apparatus. In practice, it is particularly important to observe the capacitance, since this can considerably restrict the length of cables or conductors. As a reference value, capacitance CC can be taken to be approx. 140200 nF/km and inductance LC approx. 0.81 mH/km. Where there is any doubt, always assume the worst case.

In order to prevent difculties during installation that can occur due to grounding, the IS products from Phoenix Contact always have electrical isolation.

Service and maintenanceNo special authorization (e.g. re

certicate) is required for servicing intrinsically safe circuits. The conductors of the intrinsically safe circuit can be short-circuited or interrupted without causing an explosion. Electrical equipment can be replaced (or modules unplugged) without the system having to be switched off. Soldering is not permitted.

No dangerous contact currents or voltages occur in intrinsically safe circuits, so they pose no danger to people.

The measurement of intrinsically safe circuits requires approved, intrinsically safe measuring instruments. If the data from these measuring instruments is not taken into account, additional energy can enter into the intrinsically safe circuit. The permissible maximum values may be exceeded and the requirements for intrinsic safety will no longer be fullled. The same holds true for all testers that are to be used.

Intrin-sically safe circuits

Circuits to the PLC in the safe area

Light blue cable in hazardousarea

Distance between EEx i and Non-Ex

Structure of a control cabinet with intrinsically safe circuits

with several pieces of associated apparatusThe interconnection of several associated

apparatus is not permitted for use in zone 0. If an intrinsically safe circuit for

applications in zone 1 and zone 2 contains more than one associated apparatus, proof must be provided from theoretical calculations or test with the spark tester (in acc. with EN 50 020). It must be taken into account whether a current addition is present. It is therefore recommended to have the evaluation performed by an expert.

Examples for the interconnection of several intrinsically safe circuits with a linear current-voltage characteristics are listed in appendix A and B of EN 60 079-14. When associated operating equipment with non-linear characteristics are interconnected, the evaluation on the basis of the open-circuit voltage and the short-circuit current does not lead to the result. The calculations can be performed on the basis of the PTB report PTB-ThEx-10 "Interconnection of non-linear and linear intrinsically safe circuits". However, here graphic methods are used to evaluate the intrinsic safety up to zone 1.

Checking the use in the hazardous area

Criteria Electrical equipment


Equipment group,

II, G, D II, G, D

Category 1, 2, 3 (1), (2), (3)Category 1, 2, 3 (1), (2), (3)

Group IIA, IIB, IIC IIA, IIB, IIC

Zone 0, 1, 2 0, 1, 2Zone 0, 1, 2 0, 1, 2

Type of Type of Tprotection

EEX ia, EEx ib [EEX ia], [EEx ib]

Temperature Temperature Tclass

T1T6 --

D_02_25 Ex-Basics Seite 20 Dienstag, 25. Mrz 2003 12:53 12

20 Phoenix Contact

Special requirements in zone 0, Europe

The standard EN 50 284 "Special requirements for the construction, testing and labeling of electrical equipment for equipment group II, category 1G" (corresponding to the ATEX directive 94/9/EC) supplements EN 50 014 ff. This describes further requirements for using operating equipment with other protection method as intrinsic safety in zone 0.

The following also hold true for intrinsically safe circuits, outside of the potentially explosive area as well: Protection against the intrusion of external

power. Protection against external electrical or Protection against external electrical or Protection against e

magnetic elds. Possible cause: High-voltage overhead conductor or single-phase high-voltage conductors.

Single-core non-sheathed conductor of intrinsically safe and non-intrinsically safe circuits may not be routed in the same conductor.

In the case of proven, metal-sheathed or shielded cables/conductors, intrinsically safe and non-intrinsically safe circuits can be laid in one and the same cable duct.In the control cabinet, the intrinsically safe

circuits should be as clearly marked as possible. The standard does not stipulate a uniform process, but only indicates that identication should preferably be in light blue. The neutral conductors of power cables are also usually identied with blue. In this case, intrinsically safe circuits should be identied in a different way, to prevent mix ups. A clear arrangement and spatial separation is advantageous in the control cabinet.

Conductive shields may only be grounded at a place that is usually in the non-explosive area. See also the section "Grounding in intrinsically safe circuits" (see page 19). Three special cases are allowed in which the shield can be grounded several times.

Special cases for grounding conductive shields in intrinsically safe circuits

Reason Conditions

a Shield has a high resistance, additional shielding against inductive interferences

Sturdy ground conductor (min. 4 mm2),insulated ground conductor and shield: insulation test 500 V, both grounded at one point,Ground conductor fullls the requirements for intrinsic safety and is taken into account in the proof

b Equipotential bonding between both ends

High guarantee that the equipotential bonding is guaranteed

c Multiple grounding via small capacitors

Total capacitance not over 10 nFTotal capacitance not over 10 nFT

Several intrinsically safe circuits can be routed in multi-conductor cables.

The cables and conductors must be selected accordingly for intrinsically safe circuits:

Cables/conductors for zone 1 and 2

Cable/conductor

Requirement

Fixed operating equipment

Sheath Thermoplastic,thermosetting plastic, elastomer or metal-insulated with a metal sheath

Portable, transportable equipment

External sheath

Heavy plolychloroprene, synthetic elastomer, heavy rubber tubing or comparable sturdy structure

Minimum cross-sectional area

1.0 mm2

Flexible Version Light rubber tubing without/with polychloroprene sheathing

Heavy rubber tubing without/with polychloroprene sheathing

Plastic-insulated conductor, comparable heavy rubber tubing

Selection criteria for cables/conductors for the intrinsic safety

Criterion Condition NoteCriterion Condition Note

Isolated cables/conductors

Test voltage Test voltage T 500 V AC

Conductor-ground, conductor-shield and shield-ground

Diameter of individual conductors

0.1 mm For ne-strand conductors as well

Fine-strand conductors

Protect against unsplicing

e.g. with ferrules

Multi-strand cables/conductors

Permitted Take into account the error monitoring from EN 60 079-14

Parameters (CC and LC) or (CC and LC/RC)

if in doubt: worst-case

Cables/conductors for zone 0, 1 and 2When cables/conductors are installed,

they must be protected against mechanical damage, corrosion, chemical and thermal effects. This is a binding requirement in the intrinsic safety category.

The accumulation of explosive atmosphere in shafts, channels, tubes and gaps must be prevented. Flammable gases, vapors, liquids and dusts must not be able to spread over them.

Within the potentially explosive area, cables/conductors should be laid without interruption wherever possible. If this cannot be done, the cables/conductors may only be connected in a housing that is designed with a protection type that is approved for the zone. If this is also not possible due to installation reasons, the conditions from the standard EN 60 079-14 must be fullled. These conditions will not be discussed here.

Distances to connection terminal blocks

Between different intrinsically safe circuits

The clearance distances between terminal blocks of different intrinsically safe circuits must be at least 6 mm. The clearance distances between the conductive parts of the connection terminal blocks and conductive parts that can be grounded must be at least 3 mm. Intrinsically safe circuits must be clearly identied.

Between intrinsically safe and other circuits

At modular terminal blocks, the distance between the conductive parts of intrinsically safe circuits and the conductive parts of non-intrinsically safe circuits must be at least 50 mm. The spacing can also be created using a separating plate made of insulation material or a grounded metal plate.

Cables/conductors of intrinsically safe circuits may not come into contact with a non-intrinsically safe circuit, even if they should become separated from the modular terminal block. The cables/conductors must be correspondingly shortened during installation.

Spacing acc. to EN 50 020, ch. 6.3.1 or g. 1.

IN OUT

42

31


Phoenix Contact 21

Protection devices of the product series MCR-PLUGTRAB are especially user-friendly. The decoupling elements (resistors) are contained in the base element and remain in the circuit regardless of whether the protective plug is plugged into the base element or not.

For use in potentially dust-explosive areas, the surge voltage protection devices must be installed in housings with a protetion level of at least IP 6X, directly before the volume to be protected. In the potentially gas-explosive area, an IP 4X housing is sufcient.

If signal conductors of an intrinsically safe circuit lead into the inside of a container in which ammable liquids are stored, the surge voltage protection devices must be installed in a metal housing directly before the tank wall in accordance with TRbF 100 (Technical Regulations for Flammable Liquids). This must be connected with the tank in such a way that a secure equipotential bonding can be assumed. In order to prevent direct strikes in already protected conductors, the conductors must be routed between the housing and tank, for example in metal tubes.

8. Surge Voltage Protection in the Hazardous Area

Surge voltagesSurge voltages are an important topic

where functional endurance and the availability of electrical equipment are concerned. Increasing automation, in conjunction with more and more powerful electronic components, involves a higher susceptibility to transient surge voltages. These interferences are disturbing pulses that quickly change through time and can reach amplitudes of several kV in a few microseconds. The most frequent cause for the occurrence of surge voltages is not lightning, as generally assumed, but switching transients at the facility. Electrostatic is also a considerable cause in many areas.

Once a surge voltage has occurred, then malfunctioning, short-term functional interruptions or in the worst case, complete failures due to destruction can often occur.

Protection circuit of the modular terminal block TT-EX(I)-24DC and the basic terminal blocks TT-PI-EX-TB

unprotected protectedunprotected protected

Basic terminal block with integrated surge voltage protectionTT-PI-EX-TB

The function principle can be easily explained using the above protection circuit as an example. When a surge voltage occurs, the suppressor diode operates rst as the fastest component. The protection circuit is designed so that when the amplitude increases, the discharge current passes to the upstream discharge path, i.e. to the gas-lled surge arrester, before the suppressor diode can be destroyed. With this design, it is possible to attain a surge arresting capacity of 10 kA (8/20)s with a very low and precise voltage threshold. If the discharge current remains low, then the upstream gas-lled surge arrester does not operate. This circuit provides the advantages of fast operating surge arresters with a low voltage threshold as well as a high surge arresting capacity at the same time in the case of a powerful surge voltage coupling.

Surge voltage protection devices help to control this threat and thereby increase the life span of the protected installation.

In instrumentation and data processing, the protection devices are connected into the signal circuit directly before the device interface to be protected. The connections of the surge arresters are labeled with "IN" and "OUT". During installation, make sure that "IN" points in the direction from which the surge voltage is expected. This enables the accurate functionality of multi-stage protection circuits function correctly.

Modular terminal block with integrated surge voltage protection TT-EX(I)- 24DC

100 m

+ 24 VDC- GND

420 mA

+ - - + - +

420 mA

IN OUT9,2

RCU L

100 m

+ 24 VDC- GND

420 mA

+ - - + - +

420 mA

IN OUT9,2

RCU L


22 Phoenix Contact

100 m100 m100 m

+ 24 VDC- GND

420 mA

+ - - + - ++ - - + - ++ - - + - ++ - - + - ++ - - + - +

420 mA

IN OUT9,29,2

RCU L

Cconductorconductorconductorconductorconductorconductorconductor = 20 nF = 20 nF = 20 nF = 20 nF = 20 nF = 20 nFLconductorconductorconductorconductorconductorconductorconductor = 2 x 100 = 2 x 100 = 2 x 100 = 2 x 100 = 2 x 100 = 2 x 100 F

Proof of intrinsic safety! ! !

1. Uo Ui Io Ii Po Pi!

2. Co1 + Ci2 + Cconductor + Ci3 Co!

i3!

i3

3. Lo1 + Li2 + Lconductor + Li3 Lo

Ci 30 VIi 200 mAPi 1 WCi1 = 0 nFLi1 20 nH

PT 2X EX (I)-24 DCCi3 < 5 nFLi3 < 1 H

TT-EX (I)-24 DCCi2 < 2.5 nFLi2 < 1 H PI-EX-RPSS-I/IUo = 28 V Co = 83 nF

Io = 93 mA Lo = 4.3 mHPo = 650 mW

Level measurement: Protection of the controller by TERMITRAB TT-EX(I)-24DC and basic terminal block PI-EX-TB

100 m100 m100 m

+ 24 VDC- GND

420 mA

+ - - + - ++ - - + - ++ - - + - ++ - - + - ++ - - + - +

420 mA

IN OUT9,29,2

RCU L

Cconductorconductorconductorconductorconductorconductorconductor = 20 nF = 20 nF = 20 nF = 20 nF = 20 nF = 20 nFLconductorconductorconductorconductorconductorconductorconductor = 2 x 100 = 2 x 100 = 2 x 100 = 2 x 100 = 2 x 100 = 2 x 100 F

Proof of intrinsic safety! ! !

1. Uo Ui Io Ii Po Pi!

2. Co1 + Ci2 + Cconductor + Ci3 Co!

i3!

i3

3. Lo1 + Li2 + Lconductor + Li3 Lo

Ci 30 VIi 200 mAPi 1 WCi1 = 0 nFLi1 20 nH

TT-EX (I)-24 DCCi2 < 2.5 nFLi2 < 1 H PI-EX-RPSS-I/IUo = 28 V Co = 83 nF

Io = 93 mA Lo = 4.3 mHPo = 650 mW

Basic terminal block with integrated surge voltage protection TT-PI-EX-TBCi3 = 3 nFLi3 = 1 F

Level measurement: Protection of the controller by the basic terminal block TT-PI-EX-TB with integrated surge voltage protection

Example: Holding tankIn a tank farm for chemical products,

disruptive errors can develop in the system software that cause the uncontrolled or simultaneous triggering of several valves and thus produce intense reactions.

In order to prevent the inadmissibly high potential differences, an equipotential bonding is rst set up between the control board and the holding tanks.

If a lightning bolt discharges with iB (t) = 30 kA(10/350 s), it is calculated according to IEC 61312-1 that only approx. 50% of the lightning current will be discharged into the ground if no risk analysis has been performed. If one assumes that the remaining 15 kA(10/350) s initially only ows over the equipotential lead, the following maximum ohmic potential difference between the control board and the holding tank with a copper cross section of 95 mm2 :

At rst glance, the combination of equipotential leads and the required insulation strength of 500 V seems to offer sufcient protection from partial lightning currents in intrinsically safe systems.

However, in addition to the resistance per unit length, every conductor also has an inductance per unit length L.

For a round copper conductor, a cross-section-independent inductance per unit length L 1 H/m is assumed in practice. Furthermore, a lightning current of the curve form (10/350) s reaches its amplitude (here: 15 kA) in approx. 10 s and is reduced to 50% after approx. 350 s. This yields a rate of front current rise of

The inductive voltage drop that occurs along the equipotential lead is calculated

R = RCU with RCU = IA

and

= R

= RB = RB = R = R2

= 17.3 m mm2

m

R = 30 kA

2m mm2

m 17.3

100 m95 mm2

R = 273 V

diB(part)dt

iB(part)t

= iB(part)

tB(part)

T1=

B2 T1

= 30 kA

2 10 s

= 1.5iB(part)

tkAs

according to Faradays law:

Intrinsically safe circuits that run between the holding tank and the control board are thereby destroyed.

The potential difference at the protected volume can only be limited to harmless values by the consistent use of surge voltage protection devices.

uL (t) = - L diB(part)

dt

L - L I iB(part)

t

L -1Hm

100 m 1.5kAs

L -150 kV


Phoenix Contact 23

Increased safety Ex eModular terminal blocks must also meet

the requirements for the connection of external conductors. The standards for the increased safety form the basis for the test. The most important requirements for modular terminal blocks can be summarized as follows: Modular terminal blocks for external

conductors must be generously dimensioned.

Modular terminal blocks must be secured against loosening, fastened and designed so that the conductors cannot become undone.

Modular terminal blocks must be designed to guarantee sufcient contact pressure without the conductors being damaged. This is particularly important in the case of multiple-wire (ne-strand) conductors that are used in terminal blocks for connecting conductors directly.

Modular terminal blocks must be designed so that their contact pressure during normal operation is not altered by a change in temperature. Under no circumstances may insulating material parts be used to transmit the contact pressure.

Modular terminal blocks that are intended for the connection of multi-wire conductors must be tted with an intermediate elastic element. The technical data for modular terminal

blocks in the hazardous area are specied by the type-examination and documented in the certicate. The basic data for the use of modular terminal blocks and accessories are: working voltage, nominal current, connectable conductor cross-sections, temperature range, temperature class.

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX--NoteThe standard modular terminal blocks with

screw, spring-cage and fast connection technology from Phoenix Contact are approved worldwide for applications in the hazardous area.

Further information can be found at:www.phoenixcontact.com

9. Hazardous ApprovedModular Terminal Blocks

Modular terminal blocks are used as approved components in the potentially explosive area. They are used in connection spaces of Ex equipment. The use in zone 1 and 2 for gases and in 21 and 22 for dusts is therefore allowed. The requirements for IP protection are fullled by the connection space in accordance with the respective safety category.

The approval of components serves as the basis for certifying a device or protection system. The modular terminal block is identied as a component by the certicate number (sufx "U" according to European standard) or the approval mark (e.g. UL: recognition mark A).

Modular terminal blocks with the "increased safety" category must have identication. Information on the details can be found on page 14 in the section "Components".


24 Phoenix Contact

Ex e and Ex i in the same housingIn electrical equipment, such as e.g.

terminal boxes, both intrinsically safe (Ex i) and (Ex e) circuits with increased safety can be combined. In this case, safe mechanical and, if necessary, also visual separation is stipulated. It must be taken into account that individual conductors do not come into contact with live parts of the other circuits when the wiring is disconnected from the modular terminal block.

The distance between the modular terminal blocks must be at least 50 mm. Conventional wiring procedures must be

Intrinsic safety Ex iWith intrinsic safety, no special

requirements are made for conductor connections concerning secured screws, solder connections, plug connections etc.

This is due to the fact that the current, voltage and power values are so low in circuits proven to be intrinsically safe, that there is no danger of explosion.

No special type tests or identications are planned for passive components such as e.g. modular terminal blocks and plug connectors.

Blue is the usual color for terminal

followed to make contact between the circuits improbable even if a conductor were to come loose. In control cabinets with a higher wiring density, this separation is achieved by either insulating or grounded metallic partition plates. The distance between intrinsically safe and non-intrinsically safe electric circuits must also be 50 mm. Measurements are made in all directions around the partition plates. The distance may be less if the partition plates come within at least 1.5 mm of the housing wall. Metallic partition plates must be grounded and must be sufciently strong and rigid. Metallic partition plates must be at least 0.45 mm thick; non-metallic insulating partition plates must be at least 0.9 mm thick.

The Ex e circuits must be additionally protected in the housing by a cover (at least IP 30) if the end cover is allowed to be opened during operation. Otherwise, it is only permissible to open the end cover when the Ex e circuits are switched off. Corresponding warning signs must be provided.

Clearance distance through separating plate between intrinsically safe circuits and other circuits

Clearance distances to intrinsically safe circuits and other circuits must also be observed even when there are several mounting rails.

Separating plate between mounting rail to ensure clearance distance

housings to clearly identify intrinsically safe electric circuits. This is why almost all modular terminal blocks from Phoenix Contact are also available in blue housings. Strict demands are placed on the clearance distances between adjacent terminal blocks and between terminal blocks and grounded metal parts. The clearance distance between the external connections of two neighboring intrinsically safe circuits must be at least 6 mm. The minimum clearance distance between non-insulated connections and grounded metal parts or other conductive parts, on the other hand, need only be 3 mm.

Clearance and creepage distances as well as distances through rigid insulation are specied e.g. in EN 50 020, section 6.3 and table 4.

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX-NoteIn the data sheets, Phoenix Contact not

only documents data for intrinsic safety, but also for the protection method "increased safety".


Phoenix Contact 25

Conduit systemIn the USA, value is especially placed on

high mechanical protection of the cables/conductors. For this reason, the conduit system has become very common in the USA.

10. Cable/Conductor Leads and Conduit Systems

Two installation techniques are used worldwide.

In Europe, cable/conductor leads protection method "ame-proof Ex d in encapsulation" or "increased safety" are most commonly used. In the USA and Canada, the conduit system is traditionally used.

Comparison of cable/conductor leads with conduit system

In comparison with the cable/conductor leads, the disadvantages of the conduit system can be seen in the time-consuming assembly. If the ignition lock is not properly sealed, then protection cannot be guaranteed. The cable/conductor leads, on the other hand, is designed so that the assembly does not depend on the respective tting. During installation, the position of the opening is also decisive for the sealing compound.

In addition, condensation can form very easily in conduit systems. This can lead to ground faults and short circuits as a result of corrosion.

Cable system with indirect entry

Cable system with direct entry

Conduit system

Ignition lock (seal)

Mineral ber wool(asbestos-free)

Sealing compound

Conductors(single wires)

Conductorprotection tube

(Ex d)Cable/conductor leads

The cable/conductor leads are designed in protection method "pressure-tight encapsulation". This is ame-proof and is used in conjunction with ame-proof encapsulated housings.

Designs can also be available with protection method "increased safety". The cable/conductor leads fulll the requirements for IP protection here. They are used together with housings in protection method "increased safety".


26 Phoenix Contact

IP protection IP 5 4

Firstcharac-teristic numeral

Degrees of protection against access to dangerous parts and solid foreign bodies

Secondcharac-teristic numeral

Degree of protection against water

Short description Denition Short description DenitionShort description Denition Short description DenitionShort description Denition Short description DenitionShort description Denition Short description Denitionteristic Short description Denition Short description Denitionteristic n

Short description Denition Short description Denitionnumeral

Short description Denition Short description Denitionumeral

0 Not protected 0 Not protected

1 Protected against touching dangerous parts with the back of ones hand.

The access probe, a sphere 50 mm in diameter, must be at a sufcient distance from dangerous parts.

1 Protected against dripping water.

Vertically falling drops must not have any detrimental effect.

Protected against solid foreign bodies of 50 mm diameter and larger.

The object probe, a sphere of 50 mm diameter, may not enter entirely 1The object p

Documents

Explosion Protection Theory and Practice - Phoenix Contact