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Forms of Protection

There are several types of protection recognized by the IEC (International Electrotechnical Commission) and CENELEC (European Committee for Electrotechnical Standardization). Each mode of protection is symbolized by a letter that appears on the label ATEX equipment. Since 1 July 2006, the standards of EN50014 to EN50028 series are replaced by EN60079 and EN61241 series listed in the table below. Several types of protection can be used on a single device. In this case the relevant symbols appear one after the other (eg Ex ib IICT4).

Forms of Protection

Safety can be adhered to using two methods: either locating the equipment in a safe area outside the hazardous area, or by having the equipment designed, installed and maintained to the standards for that area. There are a number of standards that equipment can be designed to meet. To understand this we need to explain the different forms of protection.

Exd (Flameproof Enclosure Type d)
Enclosures which contain electrical products which may arc or spark in an atmosphere that may be explosive. The construction of which needs to be designed, so preventing transmission of an explosion to the explosive gas atmosphere surrounding the enclosure. This equipment must be inspected to ensure that the integrity of the product is maintained as per manufacturers instructions.

Exe (Increased Safety Enclosures Type e)
This relates to enclosures which may have mixtures of explosive dusts and gases within them but are not designed to withstand an internal explosion. Instead, the likelihood of explosion is reduced by the following conditions:
• Components fi tted within the enclosure shall not produce a spark/arc in normal operation which is of a high enough energy to ignite an explosive atmosphere.
• Electrical equipment should maintain a high level of reliability within the enclosure.
• Electrical enclosures need to meet a minimum level of ingress protection IP54.
• Electrical enclosures should have a high impact resistance.

Exde
A combination of Exd and Exe type enclosures.

Exi
This applies to intrinsically safe equipment. These are products that incorporate circuits which due to low energy potential are not capable of igniting an explosive atmosphere. This section is split down into Ex ia for equipment in Zone 0/20, Ex ib for Zone 1/21 and Ex ic for Zone 2/22.