FprEN IEC 60079-31:2019

SLOVENSKI STANDARD
oSIST prEN 60079-31:2018
01-april-2018
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Explosive atmospheres - Part 31: Equipment dust ignition protection by enclosure "t"

Explosionsgefährdete Bereiche - Teil 31: Geräte-Staubexplosionsschutz durch Gehäuse

Atmosphères explosives - Partie 31: Protection contre l’inflammation de poussières par

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

SUBMITTED FOR CENELEC PARALLEL VOTING NOT SUBMITTED FOR CENELEC PARALLEL VOTING

This document is still under study and subject to change. It should not be used for reference purposes.

Recipients of this document are invited to submit, with their comments, notification of any relevant patent rights of

Explosive atmospheres - Part 31: Equipment dust ignition protection by enclosure "t"

Copyright © 2017 International Electrotechnical Commission, IEC. All rights reserved. It is permitted to download this

electronic file, to make a copy and to print out the content for the sole purpose of preparing National Committee positions.

You may not copy or "mirror" the file or printed version of the document, or any part of it, for any other purpose without

2 CONTENTS ................................................................................................................... 2

3 FOREWORD .................................................................................................................. 4

4 1 Scope ..................................................................................................................... 7

5 2 Normative references ............................................................................................... 7

6 3 Terms and definitions ............................................................................................... 8

7 4 General .................................................................................................................. 8

8 4.1 Levels of Protection ......................................................................................... 8

9 4.2 General requirements....................................................................................... 8

10 4.2.1 Equipment groups and ingress protection .................................................... 8

11 4.3 Requirements for Ex Equipment with Level of Protection “ta”................................ 9

12 4.3.1 Fault current ............................................................................................. 9

13 4.3.2 Maximum surface temperature ................................................................... 9

14 4.3.3 Overpressure............................................................................................ 9

15 4.3.4 Dust exclusion .......................................................................................... 9

16 4.3.5 Protective devices ..................................................................................... 9

17 4.3.6 Supplementary internal enclosure ............................................................. 10

18 4.4 Requirements for Ex Equipment with Level of Protection “tb” and “tc” .................. 10

19 4.4.1 Fault current ........................................................................................... 10

20 4.4.2 Maximum surface temperature ................................................................. 10

21 4.4.3 Overpressure.......................................................................................... 10

22 4.4.4 Dust exclusion ........................................................................................ 10

23 4.4.5 Thermal protection .................................................................................. 10

24 5 Construction.......................................................................................................... 11

25 5.1 Joints ........................................................................................................... 11

26 5.1.1 General.................................................................................................. 11

27 5.1.2 Threaded joints ....................................................................................... 11

28 5.1.3 Gaskets and seals .................................................................................. 11

29 5.1.4 Cemented joints ...................................................................................... 12

30 5.1.5 Operating rods, spindles and shafts .......................................................... 12

31 5.1.6 Windows ................................................................................................ 12

32 5.2 Entries into enclosures ................................................................................... 12

33 5.2.1 Cable glands .......................................................................................... 12

34 5.2.2 Entries ................................................................................................... 13

35 6 Verification and tests ............................................................................................. 13

36 6.1 Type tests ..................................................................................................... 13

37 6.1.1 Type tests for dust exclusion by enclosures ............................................... 13

38 6.1.2 Tests to determine maximum surface temperature ...................................... 14

39 6.2 Routine tests ................................................................................................. 15

40 7 Marking ................................................................................................................ 15

41 Annex A (Normative) Supplementary requirements for entry devices.................................. 16

42 A.1 General ........................................................................................................ 16

43 A.2 Construction requirements .............................................................................. 16

44 A.2.1 Cable glands, cable transit devices and conduit sealing devices .................. 16

45 A.2.2 Blanking elements and thread adapters ..................................................... 16

46 A.3 Type tests ..................................................................................................... 16

47 A.3.1 Cable glands, cable transit devices and conduit sealing devices .................. 16

48 A.3.2 Blanking elements and thread adapters ..................................................... 16

49 A.4 Marking ........................................................................................................ 17

50 Bibliography ................................................................................................................. 18

52 Table 1 – Level of Protection, equipment group and ingress protection (IP) relationship ........ 8

53 Table 2 – Overload or malfunction conditions for Level of Protection “tb” ............................ 14

64 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

65 all national electrotechnical committees (IEC National Committees). The object of IEC is to promote

66 international co-operation on all questions concerning standardization in the electrical and electronic fields. To

67 this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,

68 Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC

69 Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested

70 in the subject dealt with may participate in this preparatory work. International, governmental and non-

71 governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely

72 with the International Organization for Standardization (ISO) in accordance with conditions determined by

74 2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international

75 consensus of opinion on the relevant subjects since each technical committee has representation from all

77 3) IEC Publications have the form of recommendations for international use and are accepted by IEC National

78 Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC

79 Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

81 4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

82 transparently to the maximum extent possible in their national and regional publications. Any divergence

83 between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in

85 5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity

86 assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any

88 6) All users should ensure that they have the latest edition of this publication.

89 7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

90 members of its technical committees and IEC National Committees for any personal injury, property damage or

91 other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

92 expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

94 8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

96 9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of

97 patent rights. IEC shall not be held responsible for identifying any or all such patent rights.

98 International Standard IEC 60079-31 has been prepared by IEC technical committee 31:

100 This third edition cancels and replaces the second edition published in 2013. This edition

103 The significance of changes between IEC 60079-31, Edition 3 and IEC 60079-31, Edition 2

Thermal tests are relocated to IEC 60079-0. Formerly See “Information about the background

105 NOTE The technical changes referred to include the significance of technical changes in the revised IEC

106 Standard, but they do not form an exhaustive list of all modifications from the previous version. More guidance may

115 These are changes which modify requirements in an editorial or a minor technical way. They

116 include changes of the wording to clarify technical requirements without any technical change,

119 These are changes which add new or modify existing technical requirements, in a way that

120 new options are given, but without increasing requirements for equipment that was fully

121 compliant with the previous standard. Therefore, these will not have to be considered for

126 These are changes to technical requirements (addition, increase of the level or removal)

127 made in a way that a product in conformity with the preceding edition will not always be able

128 to fulfil the requirements given in the later edition. These changes have to be considered for

129 products in conformity with the preceding edition. For these changes additional information is

131 NOTE These changes represent current technological knowledge. However, these changes should not normally

134 C1 –Ex Equipment having Level of Protection “ta” shall be rated for connection to a circuit

135 with a prospective short circuit current of not greater than 1.5 kA. For Ex Equipment having

136 Level of Protection “tb” or “tc” which is intended for mains connection and intended to

137 interrupt fault current above 10kA, the equipment shall have a rated maximum short circuit

138 withstand current, be tested according to 6.1.1.1, and be marked according to Clause 7.

139 C2 – For Ex Equipment having Level of Protection “ta” which contains a cell or battery, only a

140 sealed cell or battery shall be used. For Ex Equipment having Level of Protection “tb” and “tc”

141 where there are sparking contacts or hot surfaces, and which contains a cell or battery, only a

143 C3 – Table 2 now includes malfunction conditions for temperature class determination of

145 C4 – Annex A added for entry devices with Type of Protection "t" including cable transit

147 Thermal test formerly located in Clause 6.1.2 are relocated to IEC 60079-0 Ed 7.

150 Full information on the voting for the approval of this standard can be found in the report on

152 This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

155 A list of all parts of the IEC 60079 series, under the general title Explosive atmospheres, can

157 The committee has decided that the contents of this publication will remain unchanged until

158 the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in

159 the data related to the specific publication. At this date, the publication will be

174 This part of IEC 60079 is applicable to equipment protected by enclosure and surface

175 temperature limitation for use in explosive dust atmospheres. It specifies requirements for

177 This standard supplements and modifies the general requirements of IEC 60079-0. Where a

178 requirement of this standard conflicts with a requirement of IEC 60079-0, the requirement of

180 This standard does not apply to dusts of explosives, which do not require atmospheric oxygen

182 This standard does not apply to Ex Equipment or Ex Components intended for use in

183 underground parts of mines as well as those parts of surface installations of such mines

185 This standard does not take account of any risk due to an emission of flammable or toxic gas

188 The following documents are referred to in the text in such a way that some or all of their

189 content constitutes requirements of this document. For dated references, only the edition

190 cited applies. For undated references, the latest edition of the referenced document (including

192 IEC 60079-0, Explosive atmospheres – Part 0: Equipment – General requirements

196 IEC 60034-5, Rotating electrical machines – Part 5: Degrees of protection provided by the

198 ISO 965-1, ISO general-purpose metric screw threads – Tolerances – Part 1: Principles and

203 For the purposes of this document, the terms and definitions given in IEC 60079-0 and the

205 ISO and IEC maintain terminological databases for use in standardization at the following

211 Type of Protection for explosive dust atmospheres where equipment is provided with an

212 enclosure providing dust ingress protection and a means to limit surface temperatures

215 Type of Protection “t” is divided into three Levels of Protection based on the risk of the Ex

216 Equipment becoming an ignition source in an explosive dust atmosphere. Ex Equipment with

221 The construction and marking requirements apply to all Ex Equipment, and in addition, the

222 requirements for "ta" as given in 4.3 and the requirements for "tb" and "tc" as given in 4.4.

223 Failure modes as defined in the industrial standard for particular internal components

224 affecting the temperatures of the equipment shall be taken into account when considering

226 When a resistor is used for current limiting, it shall not be considered to fail as short circuit if it

227 is of metal film or of wire wound construction. The resistor shall be rated for the maximum

231 The relationship between the Level of Protection, the group, and ingress protection required is

233 Table 1 – Level of Protection, equipment group and ingress protection (IP) relationship

236 Ex Equipment shall be rated for connection to a circuit with a prospective short circuit current

240 The marked maximum surface temperature shall be determined based upon measurements of

241 the surfaces of the internal components in accordance with 6.1.2. The highest of the

242 measured temperatures shall be the basis for the marked maximum surface temperature. If

243 the equipment includes a supplementary internal enclosure, the temperature shall be

245 NOTE 1 Partial rupture of the external enclosure is considered to be a potential rare malfunction and is considered

247 NOTE 2 Due to the limited thermal dissipation available to Level of Protection “ta” equipment, the maximum normal

250 A positive internal pressure of 4 kPa shall be applied to the enclosure in accordance with

256 If the Ex Equipment is capable of exceeding the marked maximum surface temperature as a

257 result of the temperature test of 6.1.2 under expected malfunction or for rare malfunction

258 conditions, a protective device is required. The protective device may be directly integrated

260 Where the external protective device is not provided by the manufacturer as part of the Ex

261 Equipment, the marking shall include the symbol “X” in accordance with IEC 60079-0, and the

262 Specific Conditions of Use shall detail the required ratings and characteristics of the

263 protective device. The protective device shall be capable of interrupting the maximum current

264 of the circuit in which it is installed. If the Ex Equipment contains a cell or battery, only a

265 sealed cell or battery shall be used. A control device shall be provided to prevent overheating

266 of the cell or battery. The control device may also be considered as a protective device,

267 provided it also protects the complete Ex Equipment from exceeding the maximum surface

270 The Ex Equipment shall be protected by one or more integral thermal protective devices.

271 Thermal protective devices shall not be of a self-resettable type and shall be duplicated

272 unless conforming to the IEC 60127 series, IEC 60691 or ANSI/UL 248 series, in which case

274 Alternatively, if it can be demonstrated that an overcurrent protective device can be used to

275 provide thermal protection, such a device may be used. When an overcurrent protective

276 device is not also used as a thermal protective device, it is permissible for the overcurrent

277 protective device to be located outside the enclosure of the Ex Equipment. In this case, the

278 marking shall include the symbol "X" in accordance with IEC 60079-0 and the Specific

280 The response time of the thermal protective devices should be taken into account and be

283 Where normally arcing and sparking parts are incorporated, these parts shall have a

284 supplementary enclosure inside the main enclosure and the maximum surface temperature of

285 that enclosure is used to determine the marked surface temperature of the equipment in

287 When hot internal components are enclosed in a supplementary enclosure, the maximum

288 surface temperature of that enclosure is used to determine the marked surface temperature of

290 The supplementary enclosure shall meet the following requirements which replace the

292 • A COT of at least equal to the lower specified ambient temperature and at least 20 K

293 greater than the maximum service temperature applies for non-metallic materials,

294 • Resistance to impact test is performed in accordance with 6.1.1.2 with no hot and cold

296 • IP6X in accordance with IEC 60529 following the resistance to impact without thermal

300 For Ex Equipment having Level of Protection “tb” or “tc” which is intended for mains

301 connection and intended to interrupt fault current above 10 kA, the equipment shall have a

302 rated maximum short circuit current, be tested according to 6.1.1.1, and be marked according

305 The marked maximum surface temperature shall be measured on the external surfaces of the

306 enclosure for Ex Equipment with Types of Protection “tb” and “tc" in accordance with 6.1.2.

308 A positive internal pressure of 2 kPa shall be applied to the enclosure in accordance with

309 6.1.1.3 prior to the dust exclusion test, except where the design of the Ex Equipment is such

310 that gaskets or seals are physically constrained from moving e.g. an “O” ring in a groove.

315 For Level of Protection “tb”, if the Ex Equipment is capable of exceeding the marked

316 maximum surface temperature as a result of the temperature test of 6.1.2, a protective device

317 is required. The protective device may be directly integrated into the Ex Equipment or be

319 Where the external protective device is not provided by the manufacturer as part of the Ex

320 Equipment, the marking shall include the symbol “X” in accordance with IEC 60079-0, and the

321 Specific Conditions of Use shall detail the required ratings and characteristics of the

322 protective device. The protective device shall be capable of interrupting the maximum current

323 of the circuit in which it is installed. If the Ex Equipment contains a cell or battery and a

324 control device is provided to prevent overheating of the cell or battery, the control device can

325 also be considered as a protective device, provided it also protects the complete Ex

326 Equipment from exceeding the maximum surface temperature. For Ex Equipment having Level

327 of Protection “tb” or “tc”, only a sealed cell or battery shall be used where there are sparking