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 electrical safety requires a minimum degree of protection IP20 as basic requirements (according to the IEC 60529 standard) of the live conductors. This is a very bland prescription If we think that the degree IP20 corresponds to a "protection against the access of a finger or similar objects".
Until the early 2000s, explosion-proof enclosures in "Ex db" method of protection had a low 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".
To increase the IP degree it was typical to use silicone grease on the flanges of 'Ex db' enclosures, reaching IP55.
Cortem Group subsequently began to apply special O-rings on the flanges to achieve much higher IP protection degrees, 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.
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) states that the exclusive use of grease to obtain an IP protection level 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 and electrical fittings as 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. However, the use of a suitable grease is also envisaged, if it is non-hardening, non-metallic and non-combustible, and that every connection and ground between the two parts is respected.
For a long time Elfit 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
The legislation provides and promotes the use of grease in explosion-proof enclosures also for the protection of 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. It is necessary to use a grease that does not age and does not contain solvents capable of evaporating and corroding and must be added in the right quantity. 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.