In our example, the ignition temperature of the 5 mm layer is between 320 ºC and 400 ºC, therefore the middle curve
(320 ºC) should be used. For a layer, say 20 mm thick, the maximum surface temperature derived from fig 30 is:
Tmax = 160 ºC
Where it cannot be avoided that a dust layer in excess of 50 mm is formed on top of the apparatus, or around the
sides, or where the apparatus is totally submerged in the dust (typical zone 20 application), a much lower surface
temperature may be required. This should be investigated under simulated working conditions.
The special requirements for zone 20 can be met by a system of power limitation, with or without temperature control.
Power engineering apparatus e.g. motors, luminaries, plug and sockets, shall wherever practicable be place outside
zone 20 areas or if used at all, be submitted for special testing
In our example, the ignition temperature of the 5 mm layer is between 320 ºC and 400 ºC, therefore the middle curve(320 ºC) should be used. For a layer, say 20 mm thick, the maximum surface temperature derived from fig 30 is:Tmax = 160 ºCWhere it cannot be avoided that a dust layer in excess of 50 mm is formed on top of the apparatus, or around thesides, or where the apparatus is totally submerged in the dust (typical zone 20 application), a much lower surfacetemperature may be required. This should be investigated under simulated working conditions.The special requirements for zone 20 can be met by a system of power limitation, with or without temperature control.Power engineering apparatus e.g. motors, luminaries, plug and sockets, shall wherever practicable be place outsidezone 20 areas or if used at all, be submitted for special testing
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