arpadveress 
An electrical / non.electrical equipment, within the operational parameters specified by the manufacturer, ensures a very high Level of Protection that includes rare faults malfunctions related to the equipment or two faults malfunctions occurring independently of each other.
NOTE A malfunction may result from a failure of the component parts of the electrical equipment or from anticipated externally applied influences. Two independent malfunctions which may occur more frequently and which, separately, would not create an ignition hazard but which, in combination, could create a potential ignition hazard, should be are regarded as occurring together to form a rare fault malfunction.
Optional:
1) Application of two independent Types of Protection providing EPL Gb
Electrical equipment shall comply with the requirements of two independent Types of Protection that provide EPL Gb. If one Type of Protection fails, the other Type of Protection shall continue to function. The independent Types of Protection shall not have a common mode of failure, except as specified in this clause. Combined types of protection providing EPL Gb shall depend on different physical protection principles.
2) Application of a Type of Protection providing EPL Gb and a separation element
Equipment which is mounted through or forms part of the boundary wall to an area requiring EPL Ga and contains electrical circuits which do not comply with protection level EPL Ga shall comply with at least one of the Types of Protection providing EPL Gb. Additionally, it shall contain a mechanical separation element as part of the equipment to seal off separate the electrical circuits of the equipment from the area requiring EPL Ga.
If the Type of Protection fails, the separation element shall:
a) prevent flame propagation through the equipment into the area requiring EPL Ga,
b) maintain its safety characteristics,
c) not be heated above exceed the maximum surface temperature of the specified temperature class of the equipment.
Examples of marking
Equipment protected by two Types of Protection which is intended to be completely installed inside the area requiring EPL Ga for example:
Ex ia IIC T6 Ga or Ex d+e IIB T4 Ga
Possible application
Equipment installed in the wall of a storage vessel containing Zone 0 (requiring EPL Ga) inside an area defined as Zone 1 (requiring EPL Gb).
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Arpad
