Understanding Ex d enclosures and using them in accordance with standards

Explosive atmospheres are found in numerous sectors of the processing industry. They require special precautions and protection concepts in order to ensure the safe use of electrical equipment. For example, pressure-tight encapsulated (flameproof) enclosures in the Ex d ignition protection category provide an optimal solution. However, the end user must use them in accordance with the standards in order to prevent compromising the certification of the entire equipment.

Even when an appropriate test and marking have been carried out, when using Ex d enclosures for the pressure-tight encapsulation of electrical equipment in explosive atmospheres, the operator must understand exactly the effects of the encapsulation and the function of the overall device. Plant operators above all must be certain that fitters and the maintenance personnel are qualified to commission and maintain pressure-tight encapsulated enclosures so that the certification of the entire equipment is not at risk.
 

• The primary function of an Ex d enclosure is to prevent an internal explosion from spreading.
• In addition, the enclosure protects the fitted equipment against environmental influences such as moisture, dirt, dust or water.
• Mechanically, an Ex d enclosure is designed to withstand an internal explosion.
• The design of the enclosure – and in particular of the ignition gap – prevents the spread of sparks, flames and hot gases so that any explosive atmosphere surrounding the device is not ignited.
• It is important that the so-called ignition protection gap in Ex d enclosures is not damaged.

The user and operator should always know and understand the effects of modifications to Ex d enclosures whether these are used on an offshore oil platform or in a land-based petrochemical plant. This is because as soon as Ex d devices have left the manufacturer and its quality system, the entire responsibility for safe use is transferred to the end user. However, this is the challenge which faces the plant operator. For example, if modifications to the enclosure are necessary, such as subsequent lacquering, additional wiring, etc., there are no guidelines for the manufacturer or operator to follow.
 

Risks caused by subsequent lacquering

Any subsequent lacquering of an Ex d enclosure, and in particular if paint penetrates the ignition gap, can have a negative effect on the certification. In addition, if paint covers the screws, this can prevent access to the enclosure.
As lacquers are not normally conductive, this can also lead to electrostatic hazards and the occurrence of an additional potential source of ignition. EN / IEC 60079-0 states that electrical equipment must be designed in such a way that under normal conditions of use, maintenance and cleaning, ignition caused by an electrostatic charge is prevented. The standard states precisely which layer thicknesses (e.g. for lacquers) and surfaces (e.g. for plastic inscription labels) must be complied with as maximum values.

ROSE Systemtechnik manufactures flameproof enclosures with pressure-tight encapsulation in various sizes and designs for use in a range of gas groups and operating temperature ranges. In this way, the company provides industry with a large number of solutions for the secure and safe encapsulation of electrical equipment.

Whether as simple distribution boxes for energy, sensor signals or complex control systems – ROSE's Ex d enclosures cover an extremely large and diverse range of requirements in industrial environments. The TBE, EJB, GUB and IJB enclosures conform to Degree of Protection IP 66 in acc. with DIN EN 60529 and are thus dust-tight and protected against the ingress of water.

Consequently, ROSE’s Ex d enclosures are ideal for use in the processing industry. However, they are also used in control and instrumentation applications. The company’s Ex d range includes both stainless steel and aluminium enclosures.