Most industrial electrical devices follow specific industry standards that ensure their safety. Here the main causes of malfunctions and the presumed faults are investigated. 

The increased safety protection mode takes into consideration electrical equipment which, both in normal conditions and in fault conditions, does not generate arcs or sparks and which does not have temperatures of parts or components that exceed the limit temperatures of the corresponding temperature class. 

A further limitation is the nominal supply voltage which cannot exceed 11kV (15kV for EPL Gc [2]). 

There are not many devices made solely with increased safety, we could give the example of a junction box with relative Ex-e connection terminals (see Figure 1) or an asynchronous motor with squirrel cage rotor. 

It is common to find the Ex-e protection way matched with others. A classic example is when the manufacturer creates an increased safety enclosure where inside there are other components that can be resin-coated (Ex-m), explosion-proof (Ex-d), intrinsically safe (Ex-i) or with segregation at powders (Ex-q).

Figure 2: An Ex-e lighting fixture where the outer casing has increased safety and the internal components are made with different types of protection

What parameters have been modified to increase the safety standard compared to industrial standard devices? 

 We remind you that before responding to the additional requirements of the EN/IEC 60079-7 standard, the device must comply with the general requirements as expressed by EN/IEC 60079-0. Non-metallic materials must therefore pass the test of resistance to aging and UV rays after which they are tested for impact and the required IP degree. We are therefore talking about plastic materials which, compared to common ones, have very wide temperature ranges and excellent resistance to adverse climatic conditions as expressed by the aging test. [3] 

A first distinctive trait is that the increased safety devices are designed with reference to distances in air and surface (between bare conductive parts at different potentials) greater than those required in the industrial standard . This can imply decidedly oversized geometries in the final product compared to industrial standard products, as well as the use of precious materials with a high CTI [4]. 

Secondly, the Ex-e protection mode allows gas to enter the enclosure, therefore the temperature class refers to the maximum temperature measured in the internal components. This means that, evaluating for example a junction box, it is necessary to calculate the power dissipated in the enclosure which allows maintaining the temperature class, considering: the resistance of the terminal (declared by the manufacturer), the resistance of the cable, the current of the circuit and the design ambient temperature. 

 Last but not least the distinctive feature is the IP protection degree of the equipment, pollution from the outside is in fact a trigger for electric arcs and surface currents. The Ex-e standard requires a minimum IP of IP54, where there are live bare parts or IP44 when the parts are isolated. [5] 

They may seem rather low IP degrees, if compared with the market demands (IP 65 or IP 66) but it should be remembered that these are minimum requirements.  

Among the equipment suitable for use in explosive atmospheres with an EPL Gb, those with increased safety are undoubtedly the most similar to an industrial standard product. 

Over the years this method of protection has spread in junction boxes and in particular in lighting. In general, the lighter and more portable constructions of the increased safety products have been appreciated by plant engineers. 

However, it should not be underestimated that knowing the basic rules of systems in explosive atmospheres is necessary in order to be able to carry out correct and safe installation in the field. 

Notes and bibliographical references 

[1] now these devices are marked Ex‑ec 

[2] In alternating or direct current, effective value see summary CEI EN 60079-7:2016-07

[3] These general requirements tend to be associated with the Ex-e protection method because most of the plastic devices have increased safety as well as, symmetrically, Ex-d explosion-proof constructions are more often made in metallic materials. In reality, the type of material used is not a requirement of the protection method, it responds to a need which in explosion proof is resistance to explosion pressure, in increased safety the degree of protection from pollution it can offer. 

[4] CTI Comparative Tracking Index / Tracking Resistance Coefficient 

[5] In rotating electrical machines installed in clean environments and regularly checked by qualified personnel, they must have enclosures with a degree of protection greater than IP20 (excluding terminal blocks and bare conductive parts) - Ex Cortem Guide 3.6.2.2.