The basics of explosion protection - STAHL - #22

Table 12: Electrical Apparatus for Use in the Presence of Combustible Dust

Type of protection in Repre- Basic principle Main application accordance with IEC or EN sentation

(diagram)

Protected by enclosures "tD" EN 61241-1 IEC 61241-1

Thanks to the tightness, dust cannot ingress the appa- Switchgear and control gear, control, ratus at all or its quantity is limited to a safe degree. connection, and terminal boxes, motors, For this reason, ignitable apparatus can be mounted into light fittings the enclosure. The surface temperature of the enclosure

must not ignite the surrounding atmosphere. td A21 = according to method A for Zone 21

td B21 = according to method B for Zone 21

Pressurized enclosure "pD" EN 61241-4

IEC 61241-4

S

The formation of a potentially explosive atmosphere Switchgear and control cabinets, motors inside a casing is prevented by maintaining a positive internal pressure of protective gas in relation to the surrounding atmosphere and, where necessary, by sup­plying the inside of the casing with a constant flow of protective gas which acts to dilute any combustible mixtures.

Intrinsic Safety "iD" EN 61241-11

IEC 61241-11

u

Apparatus used in a potentially explosive area contain Measurement and control technology, com-intrinsically safe electric circuits only. An electric circuit munication technology, sensors, actuators is intrinsically safe if no sparks or thermal effects

produced under specified test conditions (which include iaD = use in Zone 20, 21, 22

normal operation and specific fault conditions) is not ibD = use in Zone 21, 22

capable of causing ignition of a given explosive atmo- [Ex ibD] = associated electrical apparatus -

sphere. installation in safe area

Encapsulation "mD" EN 61241-18 IEC 61241-18

Parts that are capable of igniting an explosive atmo- Switchgear with small capacity, control and sphere by either sparking or heating are enclosed signalling units, display units, sensors in a compound in such a way as to avoid ignition of

a dust layer or cloud. maD = use in Zone 20, 21, 22

mbD = use in Zone 21, 22