The basics of explosion protection - STAHL - #20

Table 10: Types of Protection for Electrical Apparatus in Explosive Gas Atmosphere, Part 1

Type of protection in accordance with IEC, EN, UL, FM and NFPA

Representation (diagram)

Basic principle

Main application

Increased safety "e" EN 60079-7 UL 60079-7 IEC 60079-7 FM 3600

u

Additional measures are applied to increase the level of safety, thus preventing the possibility of excessive temperatures and the occurance of sparks or electric arcs within the enclosure or on exposed parts of electrical apparatus, where such ignition sources would not occur in normal service.

Terminal and connection boxes, control boxes for installing Ex-components (which have a different type of protection), squirrel-cage motors, light fittings

Flameproof enclosure "d"

EN 60079-1 UL 60079-1 IEC 60079-1 FM 3600

Parts which can ignite a potentially explosive atmo­sphere are surrounded by an enclosure which with­stands the pressure of an explosive mixture exploding inside the enclosure, and prevents the transmission of the explosion to the atmosphere surrounding the enclosure.

Switchgear and control gear and display units, control systems, motors, transformers, heating equipment, light fittings

Pressurized enclosure "p" EN 60079-2 NFPA 496 IEC 60079-2 FM 3620

The formation of a potentially explosive atmosphere 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 acting to dilute any com­bustible mixtures.

Switchgear and control cabinets, analysers, large motors

px = use in Zone 1, 2 py = use in Zone 1, 2 pz = use in Zone 2

Intrinsic Safety "i"

EN 60079-11 UL 60079-11

IEC 60079-11 FM 3610

Apparatus used in a potentially explosive area con­tain intrinsically safe electric circuits only. An electric circuit is intrinsically safe if no sparks or thermal effects produced under specified test conditions (which include normal operation and specific fault conditions) is not capable of causing ignition of a given explosive atmosphere.

Measurement and control technology, com­munication technology, sensors, actuators

ia = use in Zone 0, 1, 2

ib = use in Zone 1, 2

[Ex ib] = associated apparatus -

installation in safe area

EN 60079-25 IEC 60079-25

Intrinsic Safety evaluation for defined systems (equipment and cables)

Intrinsically safe systems

EN 60079-27 IEC 60079-27

FISCO Ex ia IIC T4 FNICO Ex ia IIC T4

Definition of the physical and electrical limit values of the intrinsically safe bus string

Fieldbus intrinsically safe concept (FISCO) for Zone 1

Fieldbus Nonincendive Concept (FNICO) for Zone 2