AS NZS 60079.26:2015 pdf download.Explosive atmospheres Part 26: Equipment with Equipment Protection Level (EPL) Ga.
4 Requirements for design and construction
4.1 Protection measures against Ignition hazards of the electrical circuits General
The equipment shall comply with the requirements of 4.1.2 or 4.1.3 in the event of a failure of one equipment means of protection, by the provision of a second independent means of protection.
NOTE 1 Types of Protection according to EPL Ga do not require a second independant means of protection, e.g. Ex IaTM (IEC 60079-11), Ex “maTM (lEG 60079-18), Ex “dan (lEG 60079-1).
Electrical connections and permanently connected cables of the equipment sited within an area requiring EPL Ga equipment shall comply with the same Level of Protection required by this standard, for example a cable suitable for EPL Gb containing non-Ex “ia” circuits additionally protected by a flameproof conduit or a cable suitable for EPL Gb provided with earth leakage protection.
NOTE 2 Detailed cable and installation requirements for Types of Protection accepted as achieving EPL Ga beyond intrinsically safe circuits are under consideration in IEC 60079-14.
NOTE 3 Because of ignition hazards which can arise from faults and/or transient circulating currents in the potential equalization system, galvanic isolation in the power and signal connections to the equipment according to 4.1.2 and 4.1.3 is commonly applied along with minimizing the effect of transient fault currents in the potential equalization network by the use of electrical protection equipment such as sensitive earth leakage monitors.
4.1.2 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.
NOTE 1 An example of a common mode of failure is if an Ex “d” enclosure containing arcing components is installed inside an Ex “e” enclosure. Should the Ex “d” enclosure be compromised, it would also compromise the Ex“e” enclosure.
NOTE 2 The combination of Ex “d” and Ex“q” both depend on the avoidance of flame propagation (same physical protection principle) and may not be useful in combination. In practice, some combinations may not be useful, for example the combination of oil immersion“o” and powder flling“q”. Where combined types of protection are used, it shall be possible for each Type of Protection
to be tested individually (see 5.1). Both Types of Protection shall be assessed using the most arduous fault condition of the other Type of Protection. When combining intrinsic safety, Type of Protection “ib”, with other.
Types of Protection, the second Type of Protection shall be assessed, with the most arduous fault condition applied to the intrinsically safe circuit. 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 combining Ex“ib” with Ex“e”)， the most stringent requirement of both Types of Protection shall be applied. lf 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.
4.1.3 Application of a Type of Protection providing EPL Gb and a separation element
4.1.3.1 General
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 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 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 exceed the maximum surface temperature of the specified temperature class of the equipment (see 5.3).AS NZS 60079.26 pdf download.