The basics of dust-explosion protection - STAHL - #21

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The dust type of protection “mD” in accordancewith IEC61241-18is to be based primarily on type of protection “m” according to IEC60079-18, which is currently being revised.Further proceedings on the draft of IEC61241-18will therefore be determined by the development of the new IEC60079-18. > Temperature limits on all outer surfaces of apparatus or their parts whose power limits exceed the operational limits required in IEC61241-11. The surface may consist of an enclosure or an encapsulation.Workis continuing on the standard for the intrinsicsafety “iD” ignition protection type, therefore we refer the reader to current articles in our Ex- Magazine. 6.4 Encapsulation “mD” 21 6.3 Intrinsic Safety “iD” The current draft (CD) largely corresponds to the4th edition of IEC 60079-11: 1999for gas explosion protected apparatus with type of pro- tection Intrinsic safety “i”.The final version should refer for the most part to the directly valid sections of Standard IEC 60079-11 without repeating the text of this standard. This is what is to be expected in practice when the design of “iD” apparatus is derived from existing and already tested intrinsically safe apparatus.The preliminary translation of the introduction to the future standard IEC61241-11mentions the following basic requirements: > Electrical circuits must fulfil the requirements of Group IIB from IEC60079-11, in order to prevent ignitable sparks. > Normally, degree of protection IP 6X or encap-sulation is required to ensure that clearances and creepage distances are not effected. > Power limitation for equipment or their partsthat are not proteced by an enclosure or encapsulation (e.g. for non-insulated sensors). This is the intended to prevent that a dust layer ignites due to a direct transfer of power by conductive dust and to prevent ignition due to heat on the surface of components.
R.STAHL Explosion protection