IEC 60079-31 — Ex t Dust Ignition Protection Explained
IEC 60079-31 covers Ex t dust ignition protection by enclosure — the primary protection type for electrical equipment in dust explosive atmospheres (combustible dust zones). Ex t is used in flour mills, grain handling, wood processing, pharmaceutical powder handling, and battery manufacturing.
How Ex t Works
Ex t protects against dust ignition by preventing combustible dust from entering the enclosure and by limiting the surface temperature of the enclosure to below the dust layer ignition temperature. The two key parameters are the IP rating and the maximum surface temperature.
IP Rating Requirements
| Zone | Minimum IP Rating |
|---|---|
| Zone 20 | IP6X (dust-tight) |
| Zone 21 | IP6X (dust-tight) |
| Zone 22 | IP5X (dust-protected) |
Dust Groups
| Group | Dust Type | Examples |
|---|---|---|
| IIIA | Flammable flyings | Wood shavings, textile fibres |
| IIIB | Non-conductive dust | Flour, sugar, coal dust |
| IIIC | Conductive dust | Aluminium, magnesium, graphite |
IIIC dust is the most hazardous — electrically conductive dust can cause tracking failures even if it enters a seemingly sealed enclosure. Equipment for IIIC areas must meet the most stringent requirements.
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