【正文】 dust ignition protection type “tD” all relevant measures specified in this standard (. dust ingress protection and surface temperature limitation) applied to electrical apparatus protected by an enclosure to avoid ignition of a dust layer or cloud 4 Construction In addition to the requirements of Clause 4 of IEC 612410, the following applies. Apparatus for use in zone 20: If the enclosure of the equipment is in accordance with the requirements of this standard, and all gaskets preventing the ingress of dust are not stressed by moving parts (. shaft, operating rod), the enclosure is considered as infallible and the fault analysis is only applicable to the electrical circuit. 5 Practice A and practice B Two different types of practice, A and B, are specified in this standard. Both are intended to provide an equivalent level of protection. 6 Supplementary requirements for electrical apparatus protected by enclosures for practice A for use in zones 20, 21 and 22 Dusttight enclosures IP6X shall be applied for use in: – zone 20。 – zone 22 with conductive dust. Dustprotected enclosures IP5X shall be applied for use in: – zone 22 with nonconductive dust. At present, there are no additional requirements for practice A to those given in IEC 612410 and in this standard. Page 8 EN 61241?1:2020 7 Supplementary requirements for electrical apparatus protected by enclosures for practice B for use in zone 20 or 21 Joints Plain joints Plain joints (see Figure 1) shall have a minimum contact width from inside to outside of the enclosure and a maximum allowable clearance between the surfaces as shown in Table 1. Table 1 – Plain joints Minimum contact w idth of the plain joint (mm), W 5 22 Maximum allowable clearance between the surfaces of the joint (mm), G 0,05 0,22 NOTE For widths of joints between 5 mm and 22 mm, the maximum clearance may be increased by 0,01 mm for each millimetre increase in joint width greater than 5 mm. G W IEC 346/04 Figure 1 – Plain joints Spigotted joints Spigotted joints (see Figure 2), which have axial, L, and radial, W, paths neither of which is less than 1,2 mm, may have diametrical clearances as shown in Table 1 for plain joints. The radial section, W, of the spigotted joint shall have a maximum allowable clearance, G, as shown in Table 1 shown for plain joints. L Part 1 Part 2 . W G IEC 347/04 Figure 2 – Spigotted joints Page 9 EN 61241?1:2020 Gasketed joints For gasketed joints (see Figure 3), requirements are given in Table 2. O W IEC 348/04 Figure 3 – Gasketed joints Table 2 – Gasketed joints Maximum opening dimension (mm), O 305 915 915 Minimum required effective width of gasketed joint (mm), W 3 4,8 9,5 For maximum opening dimensions between 305 mm and 915 mm, the effective width of the gasketed joint shall be increased by 0,003 mm for each millimetre increase in the maximum opening dimension greater than 305 mm. Operating rods, spindles or shafts General For apparatus intended for use in zone 20 and 21, dust exclusion shall not depend on running contact seals. The equipment shall meet the design details of Tables 3 and 4 and the tests of without the running contact seal installed. Running contact seals If running contact seals are used, the equipment shall meet the design details of Tables 3 and 4 and the dust tests of without the running contact seals installed. Power shafts Power shafts for transmitting power at rotational speeds of 100 r/min or more (see Figure 4), shall meet the requirements for the length of path from the inside to the outside of the enclosure as given in Table 3. Page 10 EN 61241?1:2020 D1 D2 L IEC 349/04 Figure 4 – Power shafts for speeds of 100r/min or more Table 3 – Power shafts for speeds of 100 r/min or more Minimum length of path for power shafts (mm), L 12,5 38,5 Maximum allowable diametrical clearance (mm), D2 – D1 0,26 0,57 For lengths of path for power shafts between 12,5 mm and 38,5 mm, the maximum diametrical clearance may be increased by 0,012 mm for each millimetre increase in the length of path greater than 12,5 mm. NOTE The minimum length of path may include both the inner and outer lips of the bearing housing. Operating rods Operating rods, spindles or shafts having rotary motion of less than 100 r/min or axial motion, shall have either a threaded joint with three full threads engaging, or have a minimum length of path from the inside to the outside of the enclosure as given in Table 4. Table 4 – Power shafts for speeds of less than 100 r/min Minimum length of path for operating rods, spindles or shafts (mm), L 12,5 25,5 Maximum allowable diametrical clearance (mm), D2 – D1 0,13 0,21 For lengths of path for operating rods, spindles or shafts between 12,5 mm and 25,5 mm, the maximum diametrical clearance may be increased by 0,006 mm for each millimetre length of path greater than 12,5 mm. Clearance of bolts Bolts passing through the enclosure wall shall have a maximum diametrical clearance between the unthreaded shank of the bolt, N, and the clearance hole in the enclosure, DSDH, of not more than 0,26 mm and a length of path, L, of not less than 12,5 mm (Figure 5). Page 11 EN 61241?1:2020 L N DH DS IEC 350/04 Figure 5 – Clearance of bolts 8 Verification and tests General In ad