IEC 60079-26-2021 pdf free.Explosive atmospheres – Part 26: Equipment with Separation Elements or combined Levels of Protection.
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4 Ex Equipment with two combined Types of Protection
4.1 General
To achieve EPL Ga. electrical equipment may comply with the requirements of two independent Types of Protection each of EPI Gb. If one Type of Protection fails, the other Type of Protection shall continue to function. Then even during rare malfunctions, for example two independent faults, no ignition source can occur.
4.2 Basic requirements
The independent Types of Protection shall not have a common mode of failure, except as specified below (see a) and b)). Combined Types of Protection of EPL Gb shall depend on different physical protection principles.
NOTE I An example for an unacceptable common mode of failure is an Ex “db enclosure containing arcing components installed inside an Ex eb enclosure. Should the Ex db enclosure be compromised, it would also compromise the Ex eb enclosure.
NOTE 2 The combination of Ex db” and Ex q” both depend on the avoidance of flame propagation (same physical protection principle) and are not suitable In combination. In practice, some combinations are not suitable, for example the combination of liquid immersion ob and powder filling
Both Types of Protection shall be assessed using the most onerous malfunction condition of the other Type of Protection. When combining intrinsic safety, i.e. Level of Protection ibN, with another Type of Protection, the second Type of Protection shall be assessed after the application of faults to the intrinsically safe apparatus which result in the most onerous condition as specified in IEC 60079-11. Thermal dissipation shall be considered in case of a fault of one Type of Protection.
When using two Types of Protection, which both rely on the same parameter (for example, the creepage distance when combining Ex “ib with Ex “eb), the most stringent requirement of both Types of Protection shall be applied.
If two Types of Protection are combined which both rely on the enclosure, one of the following shall be met:
a) If two enclosures are used (one totally enclosed within the other), each enclosure shall comply with the requirements of the respective Type of Protection: or
b) if only one enclosure is used, the enclosure and the Cable Glands shall meet the impact test requirements of IEC 60079-0, using the Group I values.IEC 60079-26 pdf free download.