The use of grease in explosion-proof enclosures (Ex db) and in electrical fittings

1. The use of grease and O-ring gaskets to increase the IP rating In general, the degree of IP protection required in electrical devices...

1. The use of grease and O-ring gaskets to increase the IP rating

In general, the degree of IP protection required in electrical devices varies according to the application. The basic requirements related to electrical safety concern a minimum degree of protection IP20 (according to the IEC 60529 standard) of the live conductors. If we think that the degree IP20 corresponds to a "protection against the access of a finger or similar objects" we understand that it is a very bland prescription.

Until the early 2000s, explosion-proof enclosures in "Ex db" method of protection did not have a high IP rating. Without gaskets, they guaranteed the IP54 degree of protection corresponding to: "allowed dust entry but not such as to compromise the operation of the equipment, protection guaranteed by splashing water".

It was customary to use silicone grease on the flanges of the ‘Ex db’ enclosures to increase the IP rating up to IP55.

Example of a late 90s junction box without an O-ring on the flange

Cortem Group has subsequently made an improvement: the application of special O-ring gaskets on the flanges that allowed to reach much higher IP protection levels reaching the current IP66/67.

This has made the silicone grease an obsolete solution for the improvement of the IP degree, relegating its use to the function of protection of the joint.

Example of explosion-proof junction box of recent production with O-Ring on the flange

Another aspect to take into consideration is that explosion-proof enclosures are often used in environments classified as potentially explosive powders also: zone 21 and zone 22. The product Standard for equipment intended to be installed in such areas (IEC/EN 60079-31) reports that the exclusive use of grease to obtain an IP level of protection is considered unsatisfactory.

In other words, when we talk about powders, the need for an o-ring or other gasket is sanctioned directly by the standard.

A similar concept is contained within the regulations for cable glands, adapters and explosion-proof plugs with parallel threads. To achieve an adequate degree of IP protection, they can be provided with a gasket between the input device and the explosion-proof enclosure. The use of a suitable grease is also envisaged, provided that it is non-hardening, non-metallic and non-combustible, and that each connection and earth between the two parts is maintained.

For a long time Cortem Group has adopted the use of gaskets in cylindrical threaded accessories making the use of grease unnecessary. In conical threads, such as NPT and ISO 7/1 Rp, which themselves can guarantee an IP54 protection degree, Loctite 577 is used to achieve a degree of protection equal to IP66/67.

2. The use of grease to protect the joints

In the explosion-proof enclosures a further use of the grease is foreseen and supported by the legislation: the protection of the joints.

The joints, in fact, are an essential element of the explosion-proof enclosures: they have the purpose of making the gases escape in the event of an explosion allowing the cooling and inhibiting the triggering of the external atmosphere.

The use of grease in the assembly phase can prevent seizure in the cylindrical joints and in the threaded joints facilitating the coupling, considering the tight tolerances involved. Must be used a grease that does not age and that does not contain solvents that can evaporate and corrode. Care should be taken to apply the right amount of grease. A corrosion inhibiting agent could be Vaseline or soap thickened with mineral oils.

The characteristics of the grease should be sought in the material made available by the grease manufacturer.