Ex 2.0. Rail-Mounted Terminal Block Systems Electronic Components. for Applications in Hazardous Environments

Transcription

1 Ex 2.0 Rail-Mounted Terminal Block Systems Electronic Components for Applications in Hazardous Environments

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3 Contents Over 50 years of innovations worldwide 1 The world of spring clamp termination systems 1 WAGO*SYSTEM Flexible Future-proof 2 Zone 1 Zone 2 Zone 0 Zone 1 General technical information for electrical equipment in hazardous environments 2 Zone 0 Zone 0 3 Ex e Rail-mounted terminal blocks 3 4 Ex e Terminal strips Ex e PCB terminal blocks Ex e Push-wire connectors for junction boxes 4 5 Ex i Terminal blocks (overview) 5 6 Matrix patchboards Terminal blocks for matrix patching 6 7 Shield (screen) connecting system 7 8 WAGO*SYSTEM 8 9 Rail-mounted terminal blocks with overvoltage protection function with coupler function 9 Index 10 Technical information Addresses 10

4 1 Over 0 50 Years of Innovations Since its foundation in 1951, WAGO Kontakttechnik GmbH, in Minden, has been pioneering terminal blocks and connectors with spring clamp termination technology. The carbon steel available at that time was barely suitable for manufacturing the first spring clamp terminal blocks (patent ). In addition, there were no test specifications to which spring clamp terminal blocks could have been tested or even approved. However, the idea was born and presented to the professional public at the Hanover Fair in Precision designed and manufactured, they not only guarantee a faster and easier connection but also offer a higher safety level since the contact quality is largely independent of the skill of the installer. The connected wire is clamped safely and permanently by the pre-programmed clamping force that automatically adjusts to the conductor cross section. WAGO spring pressure connection technologies became an industrial standard. The WAGO spring clamp terminal blocks are appreciated for their quick and easy operation, long-term durability and resistance to vibrations. As a result, maintenance-free operation leads to higher equipment availability. This benefits WAGO customers in competition worldwide. Today, WAGO is the worldwide leader of spring clamp connection systems and a component provider for decentralized automation in industry and building. More than 3700 WAGO employees worldwide are at the service of the customer, in development, production and marketing. Global availability of our products and services is guaranteed by 9 WAGO production sites 27 WAGO companies and more than 30 representations 1951 The first WAGO spring clamp: patent No WAGO push-wire connectors for juntion boxes. The original! 1977 Terminal blocks 0.08 mm 2 35 mm 2 with CAGE CLAMP 1995

5 Worldwide Main production sites Minden/Germany Headquarters, development, production Sondershausen/Germany Logistics centre, production Domdidier/Switzerland Production 2005 TOPJOB S installation terminal blocks 2003 TOPJOB S rail-mounted terminal blocks with CAGE CLAMP S Compact connectors for all types of wires WINSTA connector system

6 1 02 The Wide Variety of Applications U2fNDa HJq:;{[&4 U2fDaH U2KfD8 ajq:;{[&4 In worldwide railway traffic For more than 25 years, WAGO CAGE CLAMP technology has been ensuring trouble-free clamping connections in electrical installations in trams, underground railways, carriages, locomotives, all ICE generations, magnetic levitation train prototypes and the Shanghai Transrapid. In addition to the WAGO rail-mounted terminal blocks, terminal strips and connectors, the WAGO X-COM -SYSTEM,a modular, rail-mounted connector system has proved its worth during assembly, wiring and maintenance work. Moreover, it saves time and money. In power generation and distribution In 1955, terminal blocks with spring clamp connection were already being used in the control room of a nuclear energy center. Today, WAGO railmounted terminal blocks, terminal strips, PCB terminal blocks, matrix patchboards, connectors, interface modules and the WAGO I/O SYSTEM are constantly used in power generation, distribution and measuring installations. Absolute reliability during operatio, easy servicing and long-term durability; with installations that have to run for decades, these are connection requirements that are hard to find in any other application. In addition to that, it might be that the switchgear cabinet enclosure is the only protection against the weather, in outdoor installations for example. WAGO products with CAGE CLAMP connection meet all these requirements. In car manufacture WAGO products with CAGE CLAMP such as rail-mounted terminal blocks, terminal strips, the MULTI CONNECTION SYSTEM or the WAGO I/O SYSTEM contribute to a high availability of the production facilities: In switch or control cabinets in the press plant, in the bodyshell production, final assembly or in the paint shop. The vibration-proof and maintenance-free CAGE CLAMP provides double savings: wiring is done quickly and the routine maintenance work to control the clamping units is no longer necessary.

7 Years of Experience in Worldwide Applications U2fDa& Jq:;{[H4 YQ f:{[ rp ;:{4/ In shipbuilding, on and offshore installations Electrical installations in ships were among the first applications for WAGO rail-mounted terminal blocks with CAGE CLAMP connection. Vibrations are always present on ships. Time and again, these vibrations lead to loose connections in screw clamp terminal blocks since screws tend to untighten. This then requires time and cost intensive routine maintenance work. The CAGE CLAMP connection technology makes this work redundant. The WAGO I/O SYSTEM as well as WAGO terminal blocks and connectors are used successfully worldwide in the following: Sailing and motor boats, luxury liners, container and special vessels, high speed ferries, military catamarans, loading and container terminals, oil and gas platforms as well as different offshore applications. In building installation In 1974, WAGO revolutionized the wiring of distribution boxes in building installation with the WAGO push-wire connectors for junction boxes. Railmounted and installation multi-level terminal blocks with CAGE CLAMP connection, the WINSTA connector system and TOPJOB S rail-mounted terminal blocks with CAGE CLAMP S connection are other groundbreaking WAGO products that contribute to making building installation more economical and to increasing longterm durability of the installations. Special components, including radio modules that don t require an external power supply, add to the WAGO I/O SYSTEM and allow flexible and futureoriented decentralized building automation via LONWORKS or ETHERNET. The hardware is supported by intelligent software solutions to a universal programming environment in accordance with IEC In production and process automation Ex applications require special components. In addition to WAGO Ex railmounted terminal blocks with IECEx and ATEX 100a approvals, the WAGO I/O SYSTEM is also suitable for use in hazardous areas. For a long time, standard components have already been used in Zone 2 applications. Using intrinsic I/O modules it is possible to directly connect sensors and actuators from Zones 1 and 0 to Zone 2. The PROFIsafe modules are ideal for safety applications, which represent 10 20%, up to category 4 in accordance with EN or SIL 3 according to IEC and AK 6 (DIN V 19250). Standard, Ex and PROFIsafe components can be combined within one single fieldbus node. This means flexibility and economy.

8 1 WAGO Spring Clamp Termination Systems 04 Since the foundation of the company in 1951, terminal blocks and connectors equipped with innovative spring clamp termination technology have been manufactured by WAGO. Many of the spring clamp termination systems that have been developed and patented by Leaf spring clamping systems Clamping systems with leaf spring are available with or without operating device (push-button, screwdriver). These are simple push-wire connection systems, which are used for the connection of solid conductors with cross sections from 0.5 mm 2 to 6 mm 2. Conductors with lower stiffness solid wires with cross sections smaller than 0.5 mm 2 and flexible wires can also be connected to clamping systems equipped with an operating device, by actuating the clamp. Flexible conductors are only suitable to a limited extent (reduced rated current) for push-wire connection systems as these systems cannot bundle the wires. WAGO Spring Clamp Connection Technologies Leaf spring connection up to 2.5 mm 2 Push-wire connection up to 6 mm 2 IDC connection up to 1.0 mm 2 up to 1.5 mm 2

9 1 15 WAGO are now used worldwide, for example, in rail-mounted terminal blocks, in PCB terminal blocks, connectors, electronic modules, in the WAGO-I/O-SYSTEM and in other products. 1 CAGE CLAMP connection systems The original CAGE CLAMP is suitable for all types of wires with a rated cross section from AWG 28 to 2 (0.08 mm 2 to 35 mm 2 ). Both CAGE CLAMP Compact and POWER CLAMP complement the CAGE CLAMP connection. On the route to miniaturization, the CAGE CLAMP Compact connects wires up to 2.5 mm 2 (AWG 14) and the POWER CLAMP is the largest spring clamp allowing conductors from 35 mm 2 (AWG 2) to 95 mm 2 (AWG 3/0) to be wired. The CAGE CLAMP S connection offers all the advantages of the CAGE CLAMP in the cross section range from 0.25 mm 2 (AWG 22) to 25 mm 2 (AWG 4) with the additional benefit that "solid wires from 0.5 mm 2 (AWG 20) to 16 mm 2 (AWG 6) and flexible conductors with ferrules from 0.75 mm 2 (AWG 18) to 16 mm 2 (AWG 6) can be simply pushed in. CAGE CLAMP up to 35 mm 2 CAGE CLAMP Compact up to 2.5 mm 2 CAGE CLAMP S up to 25 mm 2 POWER CLAMP 25 mm 2 up to 95 mm 2

10 1 06 The advantages of the CAGE CLAMP Easy and obvious handling 3. Front entry 1. The screwdriver is inserted with a rocking motion to the stop The screwdriver is captivated, holding the CAGE CLAMP open, while the wire is inserted The screwdriver is withdrawn and the wire is automatically clamped. Side entry 4. Side entry: Operation of the CAGE CLAMP from the top, wire entry from the side. Screw terminal blocks are generally delivered with open clamping units. Once the conductor has been inserted, the clamping screw must be tightened using the correct torque. This requires high "visual judgement" on the part of the installer or the use of well set and well maintained torque screwdrivers. The operator may forget to tighten the screw after inserting the conductor. Therefore, the quality of the connection depends on the skill of the operator. Using the CAGE CLAMP connection, the conductor is inserted by opening the clamp with a standard screwdriver. Once the clamp is released, the fully inserted conductor is clamped safely and permanently by the pre-programmed clamping force that automatically adjusts to the conductor cross section. The contact quality is virtually independent of the operator's skill. With side-entry wiring, operating the CAGE CLAMP and inserting the conductor is done at a right angle to each other similar to the screw type connection. The widely used front-entry wiring, i.e. operation of the CAGE CLAMP and wire entry are executed parallel to each other from the front, makes protection against splaying of flexible conductor strands, such as the crimping of ferrules, unnecessary. Fast and maintenance-free Public wiring competitions have proven a reduction of the wiring time by 75 % when comparing manual wiring of screw-clamp terminal blocks with CAGE CLAMP terminal blocks. Even when powered screwdrivers are used for tightening the clamping screws, there is still a time advantage for the CAGE CLAMP terminal blocks. Pushin connection technology makes protection against splaying of flexible conductor strands unnecessary so that further cost reduction can be achieved. Furthermore, the maintenance-free CAGE CLAMP connection indirectly min. Average wiring time for 100 connections each. contributes to significant cost reduction. Due to maintenance-free operation, which results from longterm consistency and vibrationproof design, higher equipment availability can be achieved. This benefits WAGO customers in competion worldwide Screw-clamp terminal blocks CAGE CLAMP terminal blocks

11 Suitable for all copper conductors 1 conductor per clamping unit A universal system: suitable for all copper wires from AWG 26 (0.08 mm 2 ) up to AWG 2 1. solid, 2. stranded, 3. flexible 4. flexible wigh ferrule (gastight crimped) (35 mm 2 ). Special conductor preparation not necessary but possible. No load transfer to the insulation material Front-entry wiring makes it possible to place any number of CAGE CLAMP clamping units on a current bar. This has several advantages: a) It meets the safety requirement one conductor per clamping unit of the relevant standards, b) Conductors can be exchanged without interfering with the existing wiring, c) Additional connection points offer cost and space savings without the need for adjacent jumpers or additional terminal blocks and d) It offers spare capacity for future expansion. This can be practically implemented by using 3- and 4-conductor terminal blocks The CAGE CLAMP spring of the CAGE CLAMP connection secures itself to the current bar without support. During manufacturing, the springs are attached to the current bar and this self-contained assembly is then inserted into the insulated plastic housing. The separation of the mechanical from the electrical requirements allows the optimum choice of materials: high-grade stainless steel for the spring and high conductivity copper, tin-plated, for the current bar. This combination provides the best of both worlds. The WAGO CAGE CLAMP Clamping of the wire without damage through unique design CAGE CLAMP terminal block Pressure-blade, screw-type terminal block Screw-type terminal block with wire protection Screw-type terminal block without wire protection The CAGE CLAMP spring clamps the connected wire with pre-programmed clamping force that adjusts automatically to the conductor cross section. The flat clamping face of the spring presses the wire against the current bar without damaging the conductor. Any deformation or movement of the conductor is compensated, thus eliminating the risk of a loose connection. Each of the photos above show an 0.18 mm 2 and 1.5 mm 2 wire that was connected to both CAGE CLAMP as well as different screw-clamp connection systems. The tightening torque used for the screw-clamp terminal blocks was the torque specified by VDE In practical use this value is dependent upon the operator and generally higher. However, with the CAGE CLAMP connection, the clamping force automatically adjusts to the conductor cross section independent of the operator and is consistent everytime. Clamping force F in N 35 mm 2 An unlikely connection demonstrates the capability: a conductor of AWG 24 (0.2 mm 2 ) on the left and the nominal cross section of AWG 6 (16 mm 2 ) on the right in an AWG 6 (16 mm 2 ) terminal block. 1,5 mm 2 1,0 2,0 3,0 4,0 5,0 6,0 7,0 Displacement f in mm

12 1 08 Gastight contact area between conductor and current bar The corrosion-resistant CAGE CLAMP spring, manufactured of CrNi spring steel, presses the conductor into a defined contact zone against the slightly curved tin-plated current bar made of electrolytic copper. The conductor is embedded into the soft tin surface of the current bar with a high specific pressure. The contact area is hence protected permanently against corrosion. Due to this concentration of the clamping force in a defined contact area between conductor and current bar, the value of the contact pressure is comparable with that of screwclamp terminal blocks with the screws correctly tightened, as shown in the following example: Contact pressure P: Screw connection: CAGE CLAMP connection: P= Force F Area A P= 550 N 4 mm 2 = N/mm 2 55 N P= = N/mm mm 2 CAGE CLAMP connections are suitable for high current applications as well as for the transmission of low voltages and low currents in the mv and ma range for electronic and process control applications. Maintenance-free The maintenance-free operation results from the good long-term consistency of the electrical and mechanical characteristics of the terminal block - or more precisely the clamping unit. The voltage drop test allows quality assessment of the clamping unit under stress such as vibration, temperature change, and corrosive conditions, so that the gas tightness of the contact area can be checked. The long-term consistency of WAGO terminal blocks and connectors has been demonstrated both through the laboratory experiments of international approval agencies and from worldwide applications. As a result, their maintenance-free operation leads to higher equipment availability. This benefits WAGO customers in competition worldwide. Short circuit protected The short-circuit test according to IEC , paragraph 7.2.3, specifies that 120 A per square mm has to be applied for a period of one second, which means 4200 A for a 35 mm 2 terminal block. CAGE CLAMP connections pass this test without damage or impairment of their function. The figure shows an impractical test situation (in practice, fuses would switch off the current long before): The cur- rent through a 4 mm 2 terminal block is increased until the conductor glows red. Even under such test conditions, the terminal block remains undamaged.

13 Vibration and shock resistant The CAGE CLAMP spring itself has very little mass in relation to the high force it produces. Additionally, the CAGE CLAMP is mounted on the current bar and clamps the conductor in such a way that a favorable division of masses is obtained The interaction of these factors results in a connection which has high resistance to vibration and shock, as confirmed in many approval tests and in practical use. WAGO has tested the CAGE CLAMP connection for vibration up to 2000 Hz with accelerations up to 20 G. Independent agencies have tested and passed CAGE CLAMP for shock and vibration up to 2000 Hz with accelerations up to 109 G in each of three axes. The CAGE CLAMP connection also meets the vibration test requirements of VDE 0611 which incorporate a pull test while vibration is present. The UL "waggle" test also puts a rotational force on the wire while a pullout force is applied. Conductor retention forces Pull-out tests of different IEC / EN standards are used to determine the retention forces of conductors. The values specified by these standards are the same for both screw-clamp and spring-clamp terminal blocks. The table shows the pull-out forces required by IEC / EN / VDE 0611, part 1, rail-mounted terminal blocks for copper conductors and IEC / EN /VDE 0609, part 1, table 3 as well as IEC / EN , table 2, in comparison with the conductor retention forces measured on CAGE CLAMP terminal blocks. Rated cross section mm AWG/ MCM Conductor retention forces acc. to IEC N N Conductor retention forces measured on CAGE CLAMP terminal blocks /EN IEC /EN Solid Flexible Stranded N N N

14 1 100 FIELDBUS INDEPENDENT PROFIBUS INTERBUS ETHERNET TCP/IP DeviceNet CANopen CAL MODBUS \ II /O-LIGHTBUS Firewire CC-Link ETHERNET Controller Bit CPU programmable acc. to IEC /100 Mbit/s ETHERNET Controller programmable acc. to IEC Mbit/s SCALABLE SOLUTIONS ETHERNET coupler Modbus TCP 10/100 Mbit/s programming and commissioning with I/O-Pro and I/O-Check

15 Flexible Future-proof 1 11 I/O IPC Pentium MMX kompatible CPU optional Profibus Master MODULAR DOWN TO THE BIT 1 LOCAL TO OPERATION

16 control fieldbus

17 One solution many applications

18 2 0 General Technical Information for Electrical Equipment in Hazardous Environments Prerequisite for a potential explosion danger is the realization of an explosion endangered atmosphere. This can occur wherever inflammable gases or liquids are produced, processed, transported or stored. Such hazardous environment can form, for example, in chemical plants, refineries, tank farms, vehicles, sewage treatment plants, airports, grain mills or sea ports. GUIDELINE FOR THE BASIC PRINCIPLES OF EXPLOSION PROTECTION: General requirement The European Standard EN VDE classification 0170/0171 part 1 contains the general requirements for the construction and testing of electrical apparatus, which are determined for use in potentially explosive atmospheres. It has to be ensured, that this equipment does not cause an explosion of the surrounding atmosphere. In addition to the EN specification, the European Standards (see opposite page) which relate to specific standards of protection have to be considered. Electrical equipment Electrical equipment is any part which serves as a whole or in parts for the application of electrical energy. Amongs these are equipment for the production, transmission, distribution, storage, controlling and use of electrical energy, including telecommunication systems. Ex-components Ex-components are parts of an electrical equipment for hazardous environments and are marked with the symbol U. It is not allowed to use them alone in hazardous environments and, in case they should be used in these environments and in electrical equipment, an additional certificate is required. Types of ignition protection Only explosion protected equipment may be used in areas in which a dangerous, explosive atmosphere may still be expected despite the implementation of primary explosion protection measures. Electrical, explosion protected equipment can have various types of protection according to the construction regulations of the series of standards EN following (DIN VDE 0170/0171 Part 1 - following). The type of protection used by the manufacturer for apparatus essentially depends on the type and function of the apparatus. From a safety point of view, all standardized types of protection should be seen as being equal. Ignition protection n describes exclusively the use of explosion protected electrical components in zone 2. This zone encompasses areas where explosive atmospheres can only be expected to occur rarely or short-term. It represents the transition between the area of zone 1, which requires an explosion protection and safe area in which for instance welding is allowed at any time. Regulations covering these electrical components are being prepared on a world-wide scale. The standard EN allows electrical component manufacturers to obtain certificates from the corresponding authorities for instance KEMA in the Netherlands or the PTB in Germany, certifying that the tested components meet the above mentioned standards draft. Type "n" ignition protection additionally requires electrical components to be marked with the following extended identification: A non spark generating (function modules without relay /without switches) AC spark generating, contacts protected by seals (function modules with relays /without switches) L limited energy (function modules with switch) The table on the opposite page shows an overview of the standardized types of ignition protection and describes their basic principle as well as usual applications.

19 2 1 Ignition protection types Symbol Standard Explanation Application area o EN Oil immersed apparatus: Zone Electrical equipment or parts of same immersed in oil. p IEC Pressurized apparatus: Zone EN The ingress of the surrounding (explosive) atmosphere into the housing of electrical equipment is avoided by keeping the ignition protection gas inside under pressure. 2 q EN Powder filled apparatus: Zone Filling of the electrical equipment housing with fine grain sand prevents the ignition of a surrounding explosive atmosphere by an electric arc generated in the housing. d IEC Flameproof enclosure: Zone EN Equipment which could ignite an explosive atmosphere is encapsulated in a housing which can resist an explosion pressure within the housing. e IEC Increased safety: Zone EN Measures have been undertaken in order to achieve an increased degree of safety by the avoidance of inadmissibly high temperatures and the creation of sparks or electric arcs. i IEC Intrinsic safety: Zone EN Current circuit following in which no sparks or special thermal effects can occur and cause testing an ignition of a certain explosive zone 0 atmosphere. n IEC Non-sparking: Zone 2 EN Electrical equipment of group II for use in areas in which an explosive mixture of gas, vapor or mist is unlikely to occur during normal operation and if it does it will be for a short period. m IEC Cast encapsulation: Zone EN Dangerous electrical equipment is embedded in a cast mass. This corresponds approximately to the known special protection type Ex s. IEC Intrinsically safe electrical systems Zone EN Assembly of interconnected electrical equipment following in which the circuits intended for use, special as a whole or in part, in hazardous environments testing are intrinsically safe. It is documented zone 0 accordingly in the system description. IEC / TS FISCO standard Electrical apparatus for explosive gas atmospheres - Part 27: Fieldbus intrinsically safe concept (FISCO) and Fieldbus non-incendive concept (FNICO).

20 2 2 Continued General Technical Information for Electrical Equipment in Hazardous Environments Hazardous environments Hazardous environments are areas in which the atmosphere may become explosive. Explosive atmosphere is defined as a mixture of ignitable substances in the form of gases, apors or mixtures with air under atmospheric conditions in critically mixed ratios such that excessive high temperature, arcs or sparks may cause an explosion. According to EN , endangered areas are classified into zones according to the probability of the existence of a dangerous explosion prone atmosphere as follows: ➊ Zone 2 ➊ Areas explosion endangered as a result of combustible gases, vapours or mist Zone 0 encompasses areas in which an explosive gas/air mixture is continuously present or present for long periods. Zone 1 encompasses areas in which an explosive mixture can occur during normal operation. Zone 1 Zone 0 Zone 0 Zone 0 Zone 1 Zone 2 encompasses areas in which an explosive mixture is unlikely to occur under normal operation and if it does it will be for a short period. ➋ Zone 22 ➋ Areas explosion endangered due to combustible dust Zone 20 Area in which an explosive mixture in the form of dust in air is continuously present or present for long periods. Dust deposits of a known thickness or of an excessive thickness may build up. Dust deposits alone are not synonymous with Zone 20. Zone 21 Zone 21 Area in which an explosive mixture in the form of dust in air can occur during normal operation. Deposits of combustible dust exist in general. Zone 20 Zone 22 Area in which an explosive mixture in the form of dust in air is unlikely to occur during normal operation and if it does it will be for a short period or in which deposits of combustible dust exist.

21 The specification EN defines two groups of electrical equipment for hazardous environments: Group l: Electrical equipment for mines. Group ll: Electrical equipment for hazardous environments other than mines. This group is further subdivided by pertinent combustible gases in the environment. Subdivision IIA, IIB and IIC take into account that different materials/substances/gases have various ignition energy characteristic values. For this reason the three subgroups are assigned representative types of gases: IIA Propane IIB Ethylene IIC Hydrogen Publication of the WBK Mining Authority of March Quotation:... terminal blocks for which the type of protection EEx e ll has been certified will also be accepted for use in group I Electrical equipment of the type of protection Increased safety e. The table shows a comparison between the existing practice according to ElexV, DIN VDE and the new EN : Group II This statement can also be found in point 12 of the EC Examination Certificate stating that terminal blocks are approved for Group I as well as for Group II. Temperature Max. surface class temperature C T1 450 T2 300 T3 200 T4 135 T5 100 T6 85 Depending on the maximum surface temperature of the equipment, the electrical equipment of group ll is defined in temperature classes T1 up to T 6. The ambient temperature, which has to be considered, is fixed at 40 C (104 F). (Modifications of this value are possible under certain conditions) Terminal blocks for the type of protection lncreased safety e are generally classed in T6. When using terminal blocks in equipment of temperature class T1 up to T 5 it has to be ensured, that the highest temperature on the insulating parts does not exceed 85 C (185 F). The highest measured temperature rise on the surface of the equipment shall not exceed 40 K. The resistance to heat of the insulating material shall at least be 20 C (68 F) above the highest operating temperature. Minimum ignition energy of representative types of gases: Explosion group I IIA IIB IIC Gas Methane Propane Ethylene Hydrogen Ignition energy Category Type of Adequate Comparable with New acc. to protection safety with existing practice EN Ex atmosphere highest 2 protection Group II, Zone 0 is very probable, measures Zone 0 Zone 20 dust in air 2 errors Zone 10 2 From time to time increased equipment Group II, Zone 1 Ex atmosphere failure Zone 1 Zone 21 or error 3 Low probability of normal trouble-free Group II, Zone 2 Ex atmosphere, operation Zone 2 Zone 22 settled dust Zone 11 The resistance to low temperature is sufficient if the insulating material withstands a 24-hour storage at a temperature of up to minus 60 C ( 76 F) without destroying this type of protection. Specific requirements Increased safety EEx e The European Standard EN VDE 0170/0171 part 6 contains the special requirements for the construction and testing of electrical equipment for the type of protection Increased safety e, which are intended for use in explosive atmospheres. This specification is a supplement to EN and relates to such equipment or parts thereof, which do not produce arcs, sparks or dangerous temperatures under normal operating conditions. This standard describes special measures, which have to be observed to obtain a safety degree according to the type of protection - Increased safety e. Paragraph 4.2 Terminal blocks for external conductors relates to electrical equipment, such as railmounted terminal blocks. The following are the most important design requirements for terminal blocks for external electrical conductors: They shall be sufficiently large to permit the reliable connection of external conductors with cross section of at least the size related to the nominal current of the equipment; they must be protected against selfloosening and designed in such a way that the external conductors cannot slip out of their clamping units; they must be designed in such a way that sufficient contact pressure is ensured without damaging the conductors; their design must ensure that the contact pressure does not change with temperature cycling; for the connection of stranded conductors they must be designed with a spring connecting link; terminal blocks for conductor cross section up to 4 mm 2 /AWG 12 shall be so designed that smaller conductor cross sections may be connected safely