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FAQ Process industry

Q: How often do ex isolating spark gaps need to be tested and what are the criteria?

A: If the Ex isolating spark gaps are applied within the scope of the specified technical data, they are maintenance-free. Inspection is usually carried out at the intervals defined for the plant by the operator. All information on inspection intervals and criteria can be found in DEHN Form "Inspection of Ex Isolating Spark Gaps".


Q: What are the criteria for testing lightning protection systems in potentially explosive areas?

A: How to test lightning protection systems in hazardous areas is laid down in the standard IEC 62305-3. The DEHN Form "Testing of lightning protection systems in explosion hazardous areas" provides a test procedure which conforms with the standard.


Q: What kind of earth-termination systems should be installed for plants and systems in hazardous areas?

A: The only earth-termination systems approved by IEC 62305-3 for use in potentially explosive areas are type B earth-termination systems. These are, as a rule, ring or foundation earth electrodes.


Q: How dangerous is a direct lightning strike in ex zone 1?

A: When lightning strikes an explosive atmosphere, it always ignites it. Strong currents also flow away from the point of strike and can cause sparking along the discharge path. Lightning strikes are one of the sources of ignition in explosive atmospheres defined in EN 1127-1.

A risk analysis according to regulations on health and safety at work and the ordinance on hazardous substances must be conducted to assess whether there is a real possibility of ignition by lightning in the area in question. If the risk cannot be excluded, appropriate measures must be taken. One possible measure is to erect a suitable lightning protection system which effectively prevents direct lightning strikes to the relevant zone.


Q: Which requirements must be fulfilled by screw connections for equipotential bonding in ex zones 1 and 2?

A: Screw connections in ex zones 1 and 2 must fulfil the minimum requirements in IEC 60079-14. Namely, they must be secured against self-loosening and corrosion resistant. Secured against self-loosening means, for example, using spring washers.

A further requirement in ex zone 1 is that equipotential bonding and also connections and links with metal parts of the system should be executed in such a way that no sparks or unacceptably high heat can develop when lightning current passes through.


Q: Can any equipotential bonding bar be installed in the ex zone?

A: No, in addition to the conventional test parameters laid down in the product standard (DIN VDE 0618-1), the equipotential bonding bar must also fulfil the minimum requirements of IEC 60079-14. Namely, be secured against self-loosening and corrosion resistant. This safeguards permanently effective equipotential bonding.


Q: May spark gaps of type EXFS C1 (Part No. 923070) or EXFS C1 KU (Part No. 923071) still be used?

A: Yes – these types of spark gap can still be used in existing systems in zone 1/21 and zone 2/22 as long as they are still fully functional.
The following spark gaps are available as successors to EXFS C1 and EXFS C1 KU:
EXFS 100 (Part No. 923100) / EXFS 100 KU (Part No. 923101). 


Q: May spark gaps of type EXFS L (Part No. 923005 / 923006) still be used?

A: Yes – this type of spark gap can still be used in existing systems in zones 1 and 2 as long as only 8/20 µs impulses are to be expected in these systems. There is no lightning current test (10/350 µs) for this type!
The following spark gaps are available as successors to Part Nos. 923005 and 923006:

  • For use in zone 2 only:
    EXFS L100 (Part No. 923060), EXFS L200 (Part No. 923061), EXFS L300 (Part No. 923062)
  • For use in all ex zones:
    EXFS 100 (Part No. 923100)



Test reports in the process industry: oil, gas, chemical and pharmaceutical industries


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