Types of Protection

Flameproof enclosures Ex da, db, dc according to EN IEC 60079-1 for electrical equipment Flameproof enclosures d according to
EN 13463-3 for non-electrical equipment
A type of protection in which the parts which could ignite an explosive atmosphere are located inside an enclosure which can withstand the pressure of an explosion of the explosive mixture inside, and prevents the transmission of the explosion to the explosive atmosphere surrounding the enclosure.
Technically unavoidable gaps are so long and narrow that hot gases jetting out will have lost their power to cause ignition by the time they reach the outside of the enclosure, or, alternatively, if the gaps are only required for the manufacturing process they might be sealed with adhesive.
Equipment where, during normal operation,sparks, electric arcs and/or hot surfaces are generated such as switchgear, slip rings, collectors, adjustable resistors, fuses,luminaires, heating elements, friction brakes.
Important design parameters
Mechanical strength in accordance with a defined safety factor to withstand internal explosion pressure.
As an orientation value, it may be assumed that inside a sphere approx. 0.8 MPa (8 bar) can be generated and that this sphere used as an Ex d
enclosure must be able to withstand a pressure of 1.2 MPa (12 bar).
Any gap between two parts of the enclosure must be kept so narrow and long that hot gas flowing out will not be able to ignite any explosive atmosphere which may be present in the potentially explosive atmosphere.
The parameters for the gaps preventing the transmission of the ignition, gap width/ gap length, are different for the explosion subgroups IIA, IIB and IIC. The most stringent requirements with regard to the gap parameters apply to enclosures in explosion subgroup IIC.
Ex d is in basis designed for level of protection ‘b‘, the additional level of protection ‘a‘ is applicable to catalytic sensors for combustible gas detectors only, just as level of protection ‘c‘ is applicable to enclosed break devices with internal volume limited to 20cm3
= 0,02 liter.

 Increased safety Ex eb according to EN IEC 60079-7
Additional measures provide a high level of protection "b". This ensures reliable prevention of unacceptably high temperatures and sparks or electrical arcs, both on the internal and on the external parts of electrical equipment whose normal operation does not involve unacceptably high temperature sparks or arching.
Installation material such as junction boxes,connection technology for heating systems,batteries, transformers and cage motors.
Important design parameters
For uninsulated, live parts, special protective requirements apply. Clearance and creepage distances are made wider than is generally the case in industry. Special requirements apply to the IP protection degree to be adhered to.
For windings, their design, mechanical strength and insulation, higher requirements apply and the windings must be protected from increased temperatures.
Minimum cross sections are stipulated for winding wire, the impregnation and reinforcement of coils and for thermal monitoring equipment.

Increased safety Ex ec according to EN IEC 60079-7 (previously non-sparking Ex nA according to EN IEC 60079-15)
A normal level of protection ‘c‘ is provided. The construction ensures reliable prevention of unacceptably high temperatures and sparks or electrical arcs, both on the internal and on the external parts of electrical equipment whose normal operation does not involve unacceptably high temperature sparks or arcing. Simplified version of type of protection eb.
Installation material such as junction boxes,connection cabinets, rotating electrical machines,special fuses, luminaires, cells and batteries,transformers and semi conductor technology.
Important design parameters
For uninsulated, live parts, special protective requirements apply.
Clearance and creepage distances are specified.
Special requirements must be fulfilled by certain types of equipment.

Constructional safety c with marking Ex h accordig to EN ISO 80079-37
The systems, equipment and components are constructed in a way which ensures that they cannot turn into an ignition source under normal operation or in cases of faults.
Coupling between pump and driving motor, fans.
Important design parameters
Requirements to enclosure material are applicable identical as with the other types of protection 
The material choice must be selected in a way which ensures that their heating-up, for example by means of friction, is excluded.
Friction occurring under normal operation is also not allowed to lead to electrostatic charging or frictional sparks.
The constructive requirements - derived from EN 1127-1 - must be verified with regard to possible ignition sources.

Pressurized enclosures Ex pxb, pyb according to EN IEC 60079-2
The ingress of the surrounding atmosphere into the enclosure of electrical equipment is prevented by maintaining a protective gas (clean dry air, inert or a different suitable gas) inside it at a pressure above atmospheric pressure. The overpressure is maintained with or without constant flushing of the protective gas.
Equipment where during normal operation sparks, electric arcs or hot surfaces are generated and complex industrial equipment (controls) which must be operated in a potentially explosive atmosphere protected by this type of protection.
Large machines, slip ring or collector motors,switch cabinets and control cabinets and analytical equipment.
Important design parameters
Strength of the enclosure; the purged enclosure must withstand 1.5 times the overpressure experienced during normal operation.
Purge (flush) before powering the electrical equipment (for EPL Gb only, so not for EPL Db).
Mandatory shut-down and alarm for EPL Gb or Db if the purging gas flow or overpressure fails.

Pressurized enclosures Ex pzc according to EN IEC 60079-2
Use of a protective gas preventing ignition inside an enclosure to prevent the formation of an explosive atmosphere inside the enclosure by maintaining a pressure greater than the that in the surrounding atmosphere.
Equipment where during normal operation sparks, electric arcs or hot surfaces are generated and complex industrial equipment (controls) which must be operated in a potentially explosive atmosphere protected by this type of protection.
Large machines, slip ring or collector motors, switch cabinets and control cabinets and analytical equipment.
Important design parameters
Strength of the enclosure.
Purge flush before powering the electrical equipment (for EPL Gc only, so not for EPL Dc). 
Major difference to Ex pxb, Ex pyb: mandatory alarm only, if the purging gas flow or overpressure fails.

Restricted breathing Ex nR according to EN IEC 60079-15 for electrical equipment
Flow restrictive fr according to EN 13463-2 for non-electrical equipment
The enclosures are designed in such a way that the ingress of gases is restricted.
Switchgear, measuring and monitoring instrumentation and information equipment (electrical).
Luminaires (electrical).
Important design parameters
The powerloss in the enclosure may, if it contains sparking components, only lead to a temperature increase on outside surface of ≤ 20 K compared to ambient temperature. 
Equipment with these enclosures must allow monitoring of the gas and vapour tightness ,when brand new from factory as well as after installation and maintenance. 
It must not be possible for elastomeric seals to become mechanically damaged under normal operating conditions; they must maintain their sealing properties over the service life of the equipment.
Cast seals must permit a continues operating temperature (COT) ≥ 10 K compared to the maximum service temperature.

Intrinsically safe Ex ia, ib, ic according to EN IEC 60079-11 (Ex ic = previous Limited Energy Ex nL according to EN IEC 60079-15)
Intrinsically safe circuits are circuits in which a spark or thermal effect occurring under the test conditions laid down in the standard is not able to ignite the explosive atmosphere of subgroups IIA, IIB and IIC or air/dust mixture of group III. The test conditions cover normal operation and certain fault conditions which are stipulated in the standard.
Measuring and monitoring instrumentation and control.
Sensors working on the basis of physical, chemical or mechanical principles and at limited power.
Transmitters and remote I/O technology based on several fieldbus applications.
Enterprise Mobility equipment like mobile computers, tablets, camera’s and smartphones.
Important design parameters
Use of certain (unfallible) components for electrical and electronic circuits.
Lower permitted load on the components than in ordinary industrial applications with regard to
voltage related to electric strength
current related to heat
Voltage and current, including a safety margin, are kept permanently so low that no unacceptable temperatures can occur, and, in the event of open circuit or short-circuit, sparks and electric arcs possess so little energy that they are unable to ignite an explosive atmosphere.
An impression of this type of protection is provided by the fact that explosive atmospheres of subgroup IIA require only a few 100 μJ and those of subgroup IIC only 10 μJ for ignition.
Control of ignition sources b with marking Ex h according to EN ISO 80079-37
Monitoring of possible ignition sources or early determination of dangerous conditions, such as heating up during normal operation, in malfunction or even rare malfunction, certain counter measures in critical situations are initiated.
plain bearing, pump, agitator, vacuum pumps, gas turbines
Important design parameters
Use of sensor/actuator devices to monitor various physical-technical variables (temperature, pressure, flow, speed, vibrations etc.)
To limit the risk of ignition, an evaluation is done of the quality (function) of the ignition sources at the mechanical equipment and the corresponding sensor/actuator monitoring equipment.
The functional reliability (minimum quality) of the sensor/actuator monitoring equipment is specified in the form of ignition prevention types.

Encapsulation Ex ma, mb, mc according to EN IEC 60079-18
Parts that could ignite an explosive atmosphere by means of sparks or heat are potted so as to prevent ignition of the explosive atmosphere. This is achieved by encapsulating (molding) the components in a casting compound, resistant to physical - especially electrical, thermal and mechanical - and chemical influences.
Static coils in ballasts, solenoid valves, relays and other control gear of limited power and complete PCBs with electronic circuits.
Important design parameters
Breakdown strength
Low water absorption 
Resistance to various influences
Casting compound must be of the stipulated thickness all round 
Cavities are only permitted to a limited extent
As a rule the casting compound is only penetrated by the electrical wiring entries
The load on the components is limited or reduced
Increased clearance between live parts

Non-incendive component Ex nC according to EN IEC 60079-15 (clause 7)
Variant of the Ex n type of protection with contacts which close and open a circuit potentially able to trigger an explosion, where the contact mechanism is designed in such a way that the ignition of a mixture of subgroup IIA, IIB or IIC in the surrounding environment is prevented as long as defined operating conditions apply.
Contact systems
Important design parameters
The contact arrangements will extinguish any incipient flame
Limited maximum rating to 254 V and 16 A AC as well as DC
L and C are part of the test
Explosion subgroups IIA, IIB and IIC are to be treated differently.

Hermetically sealed device Ex nC according to EN IEC 60079-15
The equipment may include cavities. It is constructed in such a way that the external atmosphere cannot enter.
Spark generating equipment or components like interface relays.
Important design parameters
Sealing by means of soldering, welding or fusion of metal to metal or glass to metal are considered as meeting the requirements for sealed devices without test.

Sealed device Ex nC according to EN IEC 60079-15 (clause 9)
The equipment may include cavities, which are fully enclosed similar to the encapsulation type of protection so that ingress of the outer atmosphere is prevented.
Contact systems, static coils in solenoid valves and complete PCBs with electronic circuits. 
Important design parameters
Construction in such a way that it cannot be opened in normal operation. 
Internal free volume ≤ 100 cm3.
Flying leads or terminals in type of protection Ex ec must be available as external connections
It must not be possible for elastic seals to become mechanically damaged under normal operating conditions; they must maintain their sealing properties over the service life of the equipment.

Liquid immersion Ex ob, oc according to EN IEC 60079-6 (electrical equipment), Liquid immersion k with marking Ex h according to EN ISO 80079-37 (non-electrical equipment)
Parts which might ignite an explosive atmosphere are immersed in oil or other non-flammable, insulating liquid so that gases and vapours above the oil level and outside the enclosure cannot be ignited by electric arcs or sparks generated below the liquid level, or by hot residual gases from the switching process or by hot surfaces - for example on a resistor. 
Large transformers, high power switchgear, starting resistors and complete starting controllers. 
Gearboxeswith electronic circuits.
Important design parameters
Stipulated, insulating liquids, for example oil Protection of the liquid from contamination and moisture.
Non-electrical equipment
Wet surfaces (when partial immersed)
Assurance and possibility of monitoring that the oil level is safe 
When heated up or cooled 
For identification of leaks
Restricted to equipment for fixed installation only.

Protection by enclosures Ex ta, tb, tc according to EN IEC 60079-31 (also applicable to non-electrical equipment)
The enclosure is sealed so tight, that no combustible dust can enter. The surface temperature of the external enclosure is limited.
Various equipment where during normal operation sparks, electric arcs or hot surfaces occur and complex industrial designs(controllers) which by means of this type of protection can be utilised in the potentially explosive dust atmosphere.
Important design parameters
Minimum degree of protection in accordance with EN IEC 60529 ≥ IP 5X or IP6X, depending on Group and level of protection Ex ta requiring supplementary IP 6X enclosures for sparking parts inside the overall equipment enclosure 
Consideration of dust accumulating on the surface and reduction of permissible surface temperature with dust layer ≥ 5 mm are applicable according to EN IEC 60079-14 
Surface temperature of the equipment is considered for Ex tb and Ex tc, where for Ex ta the surface temperatures of internal components is considered as well.

Powder filling Ex q according to EN IEC 60079-5
By filling the enclosure with a finely grained powder from for example quartz glass, an arc within the enclosure is unable, with correct use, to ignite the explosive atmosphere outside. There must be no risk of ignition by flames, nor by increased temperarutes at the surface of the enclosure.
Capacitors, electronic assembly groups like HMI systems or even mobile computers which are used in a potentially explosive atmosphere. Often components where sparks or hot surfaces occur but whose functioning is not affected by the finely grained filling.
Important design parameters
The filling such as sand, glass balls etc. has to fulfil specific requirements, as must the design of the enclosure. The filling must not be able to leave the enclosure, neither during normal operation, nor as the result of electric arcs or other processes inside the powder-filled enclosure.
Special protection Ex sa, sb, sc according to CLC/TR 60079-33 or IEC 60079-33
Devices which do not fully comply with a type of protection but assure comparable safety.
New developments like flameproof enclosures with explosion vents and pressure reduction grid plates in the side wall.
Important design parameters
Depending on which level of protection is required one or more independent verifiers are required to verify the compliance of the equipment. Further details see IEC 60079-33.

Optical Radiation Ex op is, op pr, op sh according to EN IEC 60079-28
Optical radiation can be either limited in radiation energy, or protected by a medium, or protected by an interlock.
Optical laser sensors, auto identification systems, fibre optic couplers for data transmission. 
Design parameters
Three options:
Lasers having convergent optical beams have to be inherent safe in energy when openly radiating in the hazardous area (Ex op is).
When the laser goes through a medium like a fibre optic it can either be equipped with a mechanical protected system (Ex op pr) or 
by an interlock which has a safe guarding by a handshaking method. When transmitted output not being acknowledged by the receiver over the receiving line it will stop transmitting (Ex op sh).

Electrical Resistance Trace Heating Ex 60079-30-1 according to EN IEC/IEEE 60079-30-1
Safety requirements according to above mentioned standard. The marking is deviating from other types of protection by indicating on heating cables Ex 60079-30-1 as indication for the type of protection.
Winterization or Process Heating by the use of trace heating cables on piping or vessels.
Important design parameters
Ex Trace Heating cable has to be equipped with an earthed braid.
Temperature being limited in either a stablized design or a controlled design.


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