Catalogue - The basics of dust-explosion protection - STAHL - (Version JPG)

See other catalogues for STAHL

Enclosure, Measuring device, Terminal, Light, Operator interface

Text version of the page

6 ■^|||WIWil4;lillillillJCIIilil

Seals

Type of protection "protection by enclosures" depends on the elastomeric seals used. These are evaluated in accordance with Annex B3.3 of EN 50014. This is an ageing test using specially shaped test objects (ISO 48/ISO 1818) which tests the increase in hardness of the material. This figure must not exceed 20% difference between the initial and the final figure. Materials that have hardened to a greater degree may lose their sealing properties.

Static electricity

An electrostatic discharge is a "very effective" ignition source. When moulded materials is used for enclosures, the outer surface must be prevented from becoming charged. Otherwise, one of the following types of discharge will occur:

> Spark discharge

This type of discharges takes place between grounded and ungrounded components and is able to ignite all gases and vapours, and almost all dust atmospheres.

> Brush discharge

This type of discharge is a special form of the corona discharge. Pipes, elbows, screws, and tools may serve as electrodes at the maximum field strength. This type of discharge represents no risk to most dusts, but caution is advised with regard to gases and vapours.

> Propagating brush discharge

This is a discharge of a chargeable material with a low layer thickness (< 8 mm) on a substrate with adequate conductive.


Table 10: Summary of Requirements for Electrical Equipment
Requirements:	Cat. 1 + 2 - Zone 20+21	Cat.3 - Zone 22
No dust infiltration in enclosure	IP6X	IP5X
No dust infiltration at cable entries	IP6X	IP5X
Propagating brush discharges must be avoided	Insulation resistance s 10⁹ Q Breakdown voltage s 4kV Thickness of insulation a 8mm
Laser radiation (in accordance with EN 50281-1-1)	5 mW/mm² continually 0.1 mJ/mm² impulses
Ultrasonic (in accordance with EN 50281-1-1)	0.1 W/cm² / 10MHz continuous 2 mJ/cm ² puls 0.1 W/cm² average
External connection for equipotential bonding	as in "e"	as in "n"
Plugs, sockets and connectors	Separation with no voltage applied except up to 10A, 250 V; here IP6X sufficient for separation; dust must not fall into opening
Luminaires	Light source with cover, lock or warning label; no low power sodium lamps
Clearance and creepage distance of connecting parts	IEC 60664	IEC 60664
Certification required	yes	no
Label: CE compliance according to Directive 94/9/EC	C€	C€
Conformity to standards		<£>
Surface temp. in °C, (not temperature class)	T ... °C	T ... °C

R.STAHL Explosion protection

The basics of dust-explosion protection - STAHL - #18

Enclosure, Measuring device, Terminal, Light, Operator interface