IEC 60079-26-2021 pdf free download – Explosive atmospheres – Part 26: Equipment with Separation Elements or combined Levels of Protection.
4.1General
To achieve EPL Ga, electrical equipment may comply with the requirements of two independentTypes of Protection each of EPL Gb. lf one Type of Protection fails, the other Type of Protectionshall continue to function.Then even during rare malfunctions, for example two independentfaults, no ignition source can occur.
4.2Basic requirements
The independent Types of Protection shall not have a common mode of failure，except asspecified below (see a) and b)). Combined Types of Protection of EPL Gb shall depend ondifferent physical protection principles.
NOTE1 An example for an unacceptable common mode of failure is an Ex “db”enclosure containing arcingcomponents installed inside an Ex “eb” enclosure.Should the Ex “db”enclosure be compromised,it would alsocompromise the Ex “eb” enclosure.
NOTE 2 The combination of Ex “db” and Ex “q” both depend on the avoidance of flame propagation (same physicalprotection principle) and are not suitable in combination. ln practice, some combinations are not suitable, for examplethe combination of liquid immersion “ob” and powder filling “q”.
Both Types of Protection shall be assessed using the most onerous malfunction condition ofthe other Type of Protection.When combining intrinsic safety, i.e. Level of Protection “ib”, withanother Type of Protection，the second Type of Protection shall be assessed after theapplication of faults to the intrinsically safe apparatus which result in the most onerous conditionas specified in lEC 60079-11.Thermal dissipation shall be considered in case of a fault of oneType of Protection.
When using two Types of Protection,which both rely on the same parameter (for example, thecreepage distance when combining Ex “ib” with Ex “eb”), the most stringent requirement of bothTypes of Protection shall be applied.
lf two Types of Protection are combined which both rely on the enclosure, one of the followingshall be met:
a) if two enclosures are used (one totally enclosed within the other), each enclosure shallcomply 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 lEC 60079-0, using the Group l values.
Examples of relevant combinations of two independent Types of Protection are as follows:- inductive transmitters (for example proximity switches，electrical position sensors) with intrinsic safety “ib” enclosed by encapsulation “mb”;
NOTE The connections to intrinsically safe “ib” circuits can be protected by increased safety “eb”;
– a luminaire designed as increased safety “eb” included in a flameproof enclosure “db”;- measuring transducers with intrinsic safety “ib” enclosed by a flameproof enclosure “db”;
equipment with electrical circuits of intrinsic safety “ib”, additionally protected by powderfilling “q”;
electromagnetic valves with encapsulation “mb”, enclosed by a flameproof enclosure “db”;- increased safety “eb”, with pressurized equipment “pxb””.
4.3 Electrical Connections
Electrical connections and permanently connected cables of the equipment sited within an arearequiring EPL Ga shall comply with EPL Ga.
NOTEInstallation requirements for equipment with EPL Ga achieved by combined types of protection are inIEC 60079-14。Edition 61.
5Ex Equipment containing parts with different EPLs and a separation element5.1General
Equipment which is mounted through or forms part of the boundary wall between different Zonesmay contain different parts which comply with different EPLs. In this case the equipment shallcontain a separation element between the different parts of the equipment (see Table 1).IEC 60079-26 pdf download.