{"id":240,"date":"2026-07-10T05:33:31","date_gmt":"2026-07-10T05:33:31","guid":{"rendered":"https:\/\/industrialelectricmotor.net\/?p=240"},"modified":"2026-07-10T05:33:31","modified_gmt":"2026-07-10T05:33:31","slug":"explosion-proof-motor-for-flour-mill-and-grain-processing","status":"publish","type":"post","link":"https:\/\/industrialelectricmotor.net\/ja\/explosion-proof-motor-for-flour-mill-and-grain-processing\/","title":{"rendered":"Explosion-Proof Motor for Flour Mill and Grain Processing"},"content":{"rendered":"
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Korea Ever-Power \u00b7 YB2 Series \u00b7 Flour Mill Dust Explosion Drive Guide<\/span><\/p>\n

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Explosion-Proof Motor for Flour Mill and Grain Processing:
\nDust Explosion Zone 21 \/ Zone 22 Guide<\/span><\/h1>\n

Flour dust, grain dust, and starch are classified as combustible dusts with minimum ignition energies below 30 mJ \u2014 lower than many flammable solvents. A flour dust cloud at concentrations above the minimum explosive concentration (MEC) of approximately 50 g\/m\u00b3 can be ignited by a motor surface temperature above 190\u00b0C, by sparks from commutator brushes, or by static discharge. Standard motors in flour mill milling areas, roller rooms, and sifter rooms are an explosion risk. This guide covers Zone 21 and Zone 22 dust classification, Group IIIB certification, and Korea Ever-Power YB2 Ex d selection for flour mill and grain processing facilities.<\/p>\n

Ex t IIIB T135 or Ex d<\/span>
\nZone 21 and Zone 22<\/span>
\nT135\u00b0C Surface Limit<\/span>
\nIP65 Min. Dust Exclusion<\/span>
\n0.55\u2013200 kW<\/span><\/div>\n<\/div>\n<\/div>\n

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IIIB<\/div>\n
Dust group: non-conductive<\/div>\n<\/div>\n
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T135\u00b0C<\/div>\n
Max surface temperature<\/div>\n<\/div>\n
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Zone 21<\/div>\n
Dust present during operation<\/div>\n<\/div>\n
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IP65<\/div>\n
Minimum dust exclusion rating<\/div>\n<\/div>\n
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50 g\/m\u00b3<\/div>\n
Flour dust MEC<\/div>\n<\/div>\n<\/div>\n

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\"Explosion<\/p>\n
Korea Ever-Power YB2 explosion-proof motor \u2014 IP55 cast iron enclosure with ATEX certification. In flour mill milling rooms, roller rooms, and grain handling areas, standard IP54 motors accumulate flour dust inside the motor over time; the dust insulates the winding from the frame, raises winding temperature, and creates both an explosion hazard from elevated surface temperature and an electrical insulation degradation risk. The YB2 dust-tight construction prevents this dust accumulation.<\/div>\n<\/div>\n

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Contents<\/div>\n
1. Flour Dust Explosion Hazard<\/a>
\n2. Zone 20, 21, and 22 Classification<\/a>
\n3. Dust Group IIIA, IIIB, IIIC<\/a>
\n4. T135\u00b0C Surface Temperature Limit<\/a>
\n5. Motor Certification for Flour Dust Zones<\/a>
\n6. YB2 for Flour Mill Applications<\/a>
\n7. Flour Mill Application Areas<\/a>
\n8. Frequently Asked Questions<\/a><\/div>\n<\/div>\n

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1. Flour Dust Explosion Hazard<\/h2>\n

Flour dust, wheat dust, corn starch, and other grain-derived fine powders are classified as combustible dusts under EN 60079-10-2 and NFPA 61. When suspended in air at concentrations above the minimum explosive concentration (MEC), these dusts form an explosive cloud that can be ignited by any ignition source with sufficient energy \u2014 including motor surface temperatures above the minimum ignition temperature (MIT) of the dust layer.<\/p>\n

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Wheat Flour Dust<\/div>\n\n\n\n\n\n\n\n\n
MEC (cloud)<\/td>\n50\u2013100 g\/m\u00b3<\/td>\n<\/tr>\n
MIT cloud<\/td>\n380\u00b0C<\/td>\n<\/tr>\n
MIT layer (5 mm)<\/td>\n190\u00b0C<\/td>\n<\/tr>\n
MIE<\/td>\n10\u201350 mJ<\/td>\n<\/tr>\n
Kst<\/td>\n56\u2013180 bar\u00b7m\/s<\/td>\n<\/tr>\n
Dust class<\/td>\nSt 1<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n
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Corn Starch<\/div>\n\n\n\n\n\n\n\n\n
MEC (cloud)<\/td>\n40\u201360 g\/m\u00b3<\/td>\n<\/tr>\n
MIT cloud<\/td>\n390\u00b0C<\/td>\n<\/tr>\n
MIT layer (5 mm)<\/td>\n260\u00b0C<\/td>\n<\/tr>\n
MIE<\/td>\n30\u201380 mJ<\/td>\n<\/tr>\n
Kst<\/td>\n148\u2013202 bar\u00b7m\/s<\/td>\n<\/tr>\n
Dust class<\/td>\nSt 1\u2013St 2<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n
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Grain Dust (Mixed)<\/div>\n\n\n\n\n\n\n\n\n
MEC (cloud)<\/td>\n60\u2013125 g\/m\u00b3<\/td>\n<\/tr>\n
MIT cloud<\/td>\n430\u00b0C<\/td>\n<\/tr>\n
MIT layer (5 mm)<\/td>\n220\u00b0C<\/td>\n<\/tr>\n
MIE<\/td>\n15\u2013100 mJ<\/td>\n<\/tr>\n
Kst<\/td>\n43\u2013112 bar\u00b7m\/s<\/td>\n<\/tr>\n
Dust class<\/td>\nSt 1<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n
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The dust layer MIT is the critical value for motor selection. A standard motor frame in a milling room accumulates flour dust on its surface over time, and this dust layer can be ignited if the motor surface temperature exceeds the MIT of the specific flour dust in the area. For wheat flour, the layer MIT is approximately 190\u00b0C \u2014 and a standard motor at full load in a warm milling room can reach 120 to 150\u00b0C frame temperature without fault, approaching the layer MIT with a safety margin of only 40 to 70\u00b0C. An explosion-proof motor certified to T135\u00b0C provides a 55\u00b0C safety margin below the wheat flour layer MIT.<\/p>\n<\/div>\n<\/div>\n

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2. Zone 20, 21, and 22: Dust Hazard Classification<\/h2>\n

IEC 60079-10-2 classifies areas containing combustible dust into three zones based on the frequency and duration of the explosive dust cloud presence. For flour mills, the classification of each area within the facility must be determined by a competent person and documented in the dust explosion protection document (ATEX Directive 1999\/92\/EC, Article 7).<\/p>\n

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Zone 20<\/div>\n
Explosive dust cloud continuously present<\/div>\n

Inside dust handling equipment \u2014 bucket elevators, pneumatic conveying systems, cyclone interiors, bag filter interiors, and grain silos. No motors are installed inside Zone 20 equipment under normal design practice. Where a motor must be integrated into Zone 20 equipment (such as an agitator or conveyor drive inside a silo), it must be certified Ex ia IIIB T135 or equivalent \u2014 a standard YB2 Ex d IIB T4 gas motor is not suitable for Zone 20 dust environments.<\/p>\n<\/div>\n

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Zone 21<\/div>\n
Explosive dust cloud likely during normal operation<\/div>\n

Areas around dust handling equipment \u2014 the immediate vicinity of bucket elevator boot and head sections, areas near sifter discharge points, roller mill feed zones, and areas within 1 m of any dust source that releases dust during normal operation. This is the primary zone in active milling rooms. Motors in Zone 21 must be certified Ex t IIIB T135 (dust-protected motor with IP6X and T135 surface limit) or Ex d IIB T4 (gas-rated flameproof motor, which also meets dust zone requirements under IEC 60079 Part 31).<\/p>\n<\/div>\n

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Zone 22<\/div>\n
Explosive dust cloud unlikely but possible<\/div>\n

General milling room and grain store areas where dust is not normally suspended in explosive concentrations but where a dust release could create explosive conditions due to equipment malfunction, maintenance activity, or abnormal operating conditions. Most of the roller mill floor and sifter room area falls in Zone 22 in a well-maintained facility. Zone 22 requires motors certified Ex t IIIB T135 or equivalent dust-protected motor \u2014 standard IP54 motors are not acceptable even in Zone 22.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

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3. Dust Group IIIA, IIIB, IIIC: Which Applies to Flour Mills?<\/h2>\n
\n\n\n\n\n\n\n\n
Group<\/th>\nDust Type<\/th>\nExamples in Food and Grain<\/th>\nYB2 Suitable?<\/th>\n<\/tr>\n<\/thead>\n
IIIA<\/td>\nFlyings (coarse fibrous material)<\/td>\nWood shavings, hessian fibres, crop residue > 500 \u03bcm<\/td>\nYes (IIIB covers IIIA)<\/td>\n<\/tr>\n
IIIB \u2605<\/td>\nNon-conductive dusts<\/strong><\/td>\nWheat flour, corn starch, grain dust, sugar dust, dried milk powder, cocoa \u2014 the standard for food processing dust zones<\/strong><\/td>\nYes \u2014 YB2 rated IIIB<\/td>\n<\/tr>\n
IIIC<\/td>\nConductive dusts (resistivity < 10\u2074 \u03a9\u00b7m)<\/td>\nAluminium powder, magnesium powder, carbon black \u2014 not typical in flour mills<\/td>\nNo (requires IIIC motor)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n

Flour, starch, grain dust, sugar, dried milk, and cocoa are all Group IIIB (non-conductive) dusts. The Korea Ever-Power YB2 series with Ex t IIIB T135 or Ex d IIB T4 certification covers all standard flour mill and grain processing dust zone motor applications. Confirm the dust classification document for the specific facility to verify that no IIIC dusts (aluminium or magnesium powder) are handled in the same area before specifying the motor group.<\/p>\n<\/div>\n

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4. T135\u00b0C: Surface Temperature Limit for Flour Dust<\/h2>\n

The T135\u00b0C surface temperature class limits the motor enclosure surface temperature to 135\u00b0C maximum under all operating conditions including maximum ambient temperature and continuous full-load operation. This provides a minimum safety factor of 55\u00b0C below the wheat flour layer MIT of 190\u00b0C (at 5 mm dust layer depth), and a much larger safety factor below the cloud ignition temperature of 380\u00b0C.<\/p>\n

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Why Standard Motor Surface Temperature Is Unacceptable in Milling Rooms<\/div>\n
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Standard IP54 motor at full load:<\/div>\n
Rated winding temperature: Class F \u2192 155\u00b0C
\nFrame temperature: 80\u2013110\u00b0C at rated load
\nFlour dust layer accumulates on motor frame
\nFrame temperature at moderate overload: 120\u2013150\u00b0C
\nWheat flour MIT at 5 mm depth: 190\u00b0C
\nSafety margin: only 40\u201370\u00b0C \u2014 inadequate<\/span><\/div>\n<\/div>\n
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YB2 certified T135\u00b0C in same room:<\/div>\n
Maximum surface temperature: 135\u00b0C at any load
\nFlour layer MIT: 190\u00b0C
\nSafety margin: 55\u00b0C
\nOverload protection: PTC thermistors cut motor before 135\u00b0C is reached
\nDust exclusion: IP55 prevents dust from entering motor interior
\nCompliant with IEC 60079-31 and EN ATEX requirements<\/span><\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

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5. Motor Certification Options for Flour Dust Zones<\/h2>\n
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Ex t IIIB T135 \u2014 Dust-Protected Motor<\/div>\n

Ex t (dust-protected enclosure) is the standard certification type for motors in dust zones. The Ex t motor has an IP6X enclosure (dust-tight) that prevents dust from entering the motor, and is tested and certified to limit its maximum surface temperature to the stated T class (T135 for flour mill applications). The Ex t approach is simpler and lighter than Ex d flameproof, and is the most common specification for new flour mill motor installations. The motor does not need to be explosion-proof against internal ignition because there is no flammable gas inside the motor \u2014 the hazard is entirely external dust, and the IP6X enclosure and T135 surface limit are the two controls that eliminate the ignition risk.<\/p>\n<\/div>\n

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Ex d IIB T4 (Gas Flameproof) in Dust Zones<\/div>\n

A gas-rated Ex d IIB T4 motor can also be used in dust Zone 21 and Zone 22 under IEC 60079-14, provided the T4 surface temperature limit (135\u00b0C) meets the requirement for the specific dust (it does for wheat flour: MIT 190\u00b0C, with 55\u00b0C margin). The Ex d motor has IP55 or IP65 which prevents dust entry, and the T4 surface temperature limit is identical to the T135 limit for dust. This dual certification means that in facilities that handle both flammable gases and combustible dusts \u2014 for example, a combined grain store and solvent extraction plant \u2014 a single motor type (Ex d IIB T4) can serve both the gas Zone 1\/2 and the dust Zone 21\/22 requirements. The Korea Ever-Power YB2 Ex d IIB T4 is accepted for installation in dust Zone 21 and Zone 22 as well as gas Zone 1 and Zone 2.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

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6. Korea Ever-Power YB2 for Flour Mill Applications<\/h2>\n
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The Korea Ever-Power YB2 Ex d IIB T4 is the correct motor specification for flour mill roller rooms, sifter rooms, and grain intake areas classified as Zone 21 or Zone 22 under IEC 60079-10-2. The IP55 cast iron enclosure prevents flour dust from accumulating inside the motor (eliminating the internal insulation degradation mode) and the Ex d T4 certification limits the external surface temperature to 135\u00b0C (providing the minimum 55\u00b0C safety factor below the wheat flour layer MIT). The YB2 is certified to both ATEX and IECEx standards and is accepted by dust explosion competent authorities in the EU, UK, Australia, and export markets worldwide. The complete YB2 range is available in the explosion-proof motor product section<\/a>.<\/p>\n<\/div>\n

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YB2 \u2014 Flour Mill Specification<\/div>\n\n\n\n\n\n\n\n\n\n\n
Certification<\/td>\nATEX + IECEx: Ex d IIB T4<\/td>\n<\/tr>\n
Dust zone suitability<\/td>\nZone 21 and Zone 22<\/td>\n<\/tr>\n
Surface temp limit<\/td>\nT4 \u2261 T135\u00b0C max<\/td>\n<\/tr>\n
Dust group<\/td>\nIIIA and IIIB (not IIIC)<\/td>\n<\/tr>\n
Enclosure<\/td>\nIP55 cast iron<\/td>\n<\/tr>\n
Power range<\/td>\n0.55\u2013200 kW<\/td>\n<\/tr>\n
Flour dust MIT safety<\/td>\n55\u00b0C below layer MIT<\/td>\n<\/tr>\n
Thermal protection<\/td>\nPTC thermistors (recommended)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

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7. Flour Mill and Grain Processing Application Areas<\/h2>\n
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Roller Mill Drive (Zone 21)<\/div>\n

Wheat berry roller mill drive motors in the milling floor are Zone 21 within 1 m of the mill inlet and outlet. YB2 4-pole 11 to 55 kW, IP55, Ex d IIB T4. High starting torque required for loaded mill start. Soft-starter recommended for mills above 22 kW to limit starting current and belt tension transient.<\/p>\n<\/div>\n

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Sifter Machine Drive (Zone 21)<\/div>\n

Plansifter frame drive motor and sifter conveyor drives in the sifting room. YB2 4-pole 0.75 to 5.5 kW. The sifter frame vibrates during operation \u2014 motor mounting must use anti-vibration isolators to prevent motor fastener fatigue from the continuous vibration load of the sifting machine frame.<\/p>\n<\/div>\n

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Bucket Elevator Drive (Zone 21\/22)<\/div>\n

Bucket elevator drive head motors for grain and flour vertical conveyance. The boot section (bottom) of the bucket elevator is Zone 20 internally; the surrounding area is Zone 21. Motor typically mounted at the head (top) in Zone 21 or Zone 22. YB2 4-pole 3.0 to 30 kW. Anti-runback device on elevator drive mandatory.<\/p>\n<\/div>\n

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Screw Conveyor Drive (Zone 22)<\/div>\n

Horizontal screw conveyor for flour and middlings transfer between mill sections. General milling floor area is Zone 22. YB2 4-pole 1.5 to 15 kW paired with NMRV or inline helical gearbox. YB2 Ex d T4 specification covers Zone 22 dust requirements.<\/p>\n<\/div>\n<\/div>\n

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\"Explosion<\/p>\n

Grain Handling<\/div>\n<\/div>\n
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\"Korea<\/p>\n

Ex d Enclosure<\/div>\n<\/div>\n
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\"Korea<\/p>\n

ATEX Certified<\/div>\n<\/div>\n
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\"Korea<\/p>\n

Global Customers<\/div>\n<\/div>\n<\/div>\n<\/div>\n

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8. Frequently Asked Questions<\/h2>\n
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Can I use a standard IP55 motor in a flour mill if I clean the flour dust off the motor regularly?<\/div>\n<\/div>\n
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No. Compliance with the ATEX User Directive (1999\/92\/EC) requires that equipment installed in classified zones is selected and maintained in accordance with the zone classification \u2014 manual cleaning of flour dust from standard motors does not satisfy this requirement, and the dust accumulation between cleaning cycles creates an explosion risk. A standard IP55 motor is not certified for Zone 21 or Zone 22 dust zone installation regardless of the cleaning frequency. The risk exists not just from dust on the motor surface but also from dust that enters the motor through the IP55 (which is not dust-tight) and accumulates on the winding, elevating the winding temperature. Only an ATEX certified motor with IP6X dust-tight enclosure and T135 surface temperature limit provides compliant protection for Zone 21 and Zone 22 installation in flour mills.<\/p>\n<\/div>\n<\/div>\n

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The office, packing area, and loading bay of our flour mill are all in the same building as the milling floor. Do all areas need Zone 21 or Zone 22 motors?<\/div>\n<\/div>\n
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No. Zone classification applies only to those areas where explosive dust concentrations are possible \u2014 it does not apply automatically to the entire building. The milling floor, sifter room, and areas around flour handling equipment are typically Zone 21 or Zone 22. The packing area, finished product store, and offices where flour dust cannot reach explosive concentrations under normal or foreseeable abnormal conditions are typically unclassified (\u201csafe area\u201d). However, the boundary between the milling room and the office or packing area must be examined carefully in the explosion protection document \u2014 if flour dust can spread through an open doorway or an unglazed partition from the milling room to the packing area, the packing area may need to be classified as Zone 22. The loading bay where bulk flour tankers are filled is typically Zone 21 at the tanker inlet connection and Zone 22 in the loading bay area generally. Have the zone classification document prepared by a competent person (qualified dust explosion specialist) for your specific facility layout before specifying motor types.<\/p>\n<\/div>\n<\/div>\n

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Is sugar dust in a confectionery factory treated the same as flour dust for motor specification?<\/div>\n<\/div>\n
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Yes \u2014 sugar dust (sucrose) is also classified as Group IIIB non-conductive combustible dust with a minimum ignition temperature of approximately 360\u00b0C (cloud) and 320\u00b0C (layer at 5 mm). The zone classification and motor certification requirements for sugar handling areas in confectionery factories are identical to flour mill requirements: Zone 21 around dust sources, Zone 22 in general production areas, and motors must be Ex t IIIB T135 or equivalent (such as YB2 Ex d IIB T4) in all classified zones. Cocoa powder, dried milk powder, and other food dusts with similar explosive characteristics require the same motor specification. Confirm the specific dust parameters for each dust in your facility with the hazardous area classification document.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

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Korea Ever-Power \u00b7 YB2 Series \u00b7 ATEX Flour Dust Zone Motor<\/div>\n

Need Certified Motors for Your Flour Mill or Grain Plant?<\/h2>\n

Korea Ever-Power YB2: ATEX + IECEx Ex d IIB T4, T135\u00b0C surface limit, IP55, 0.55\u2013200 kW. Accepted for dust Zone 21 and Zone 22 flour, grain, starch, and sugar dust applications.<\/p>\n

View YB2 Explosion-Proof Range<\/a><\/p>\n<\/div>\n<\/div>\n

Edited by Cxm<\/p>\n<\/div>","protected":false},"excerpt":{"rendered":"

Korea Ever-Power \u00b7 YB2 Series \u00b7 Flour Mill Dust Explosion Drive Guide Explosion-Proof Motor for Flour Mill and Grain Processing: Dust Explosion Zone 21 \/ Zone 22 Guide Flour dust, grain dust, and starch are classified as combustible dusts with minimum ignition energies below 30 mJ \u2014 lower than many flammable solvents. A flour dust cloud at concentrations above the minimum explosive concentration (MEC) of approximately 50 g\/m\u00b3 can be ignited by a motor surface temperature above 190\u00b0C, by sparks from commutator brushes, or by static discharge. Standard motors in flour mill milling areas, roller rooms, and sifter rooms are an explosion risk. This guide covers Zone 21 and Zone […]<\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"categories":[28],"tags":[],"class_list":["post-240","post","type-post","status-publish","format-standard","hentry","category-industrial-electric-motor"],"_links":{"self":[{"href":"https:\/\/industrialelectricmotor.net\/ja\/wp-json\/wp\/v2\/posts\/240","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/industrialelectricmotor.net\/ja\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/industrialelectricmotor.net\/ja\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/industrialelectricmotor.net\/ja\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/industrialelectricmotor.net\/ja\/wp-json\/wp\/v2\/comments?post=240"}],"version-history":[{"count":1,"href":"https:\/\/industrialelectricmotor.net\/ja\/wp-json\/wp\/v2\/posts\/240\/revisions"}],"predecessor-version":[{"id":242,"href":"https:\/\/industrialelectricmotor.net\/ja\/wp-json\/wp\/v2\/posts\/240\/revisions\/242"}],"wp:attachment":[{"href":"https:\/\/industrialelectricmotor.net\/ja\/wp-json\/wp\/v2\/media?parent=240"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/industrialelectricmotor.net\/ja\/wp-json\/wp\/v2\/categories?post=240"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/industrialelectricmotor.net\/ja\/wp-json\/wp\/v2\/tags?post=240"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}