Explosion-proof boxes – what they are for
Explosion-proof boxes are used in hazardous areas where there is a risk of explosion due to vapours, dust and other hazardous media. Explosion-proof boxes are installed in hazardous areas only when it is not possible to place the connection or disconnection of power and/or control cables outside the hazardous area.
Junction boxes are made of materials such as polyester, stainless steel, aluminium or cast iron. Each material has its own requirements and its own installation location in the hazardous area. For example, polyester boxes cannot be installed in areas where explosion protection type Exd (“flameproof enclosure”) is required and, correspondingly, cast iron boxes cannot be installed in areas where boxes with explosion protection type Exde (“increased degree of protection”) can be installed without any problems.
The most common opinion in Ukraine, that in any explosive zone to put a distribution box made of cast iron with a type of explosion protection Exd and all problems on explosion protection will be solved. Is that so? It’s actually not quite right.
Let’s take an example, cast iron casings are quite heavy and with little addition of phosphorus (we all know this from school), which lowers the mechanical properties of cast iron and causes cold fracture (formation of cracks in cold castings), which is an unsafe property for explosive areas. Reducing the phosphorus content of some manufacturers’ cast iron boxes reduces the cost of the case itself and the box as a whole, but again we ask the question, is it safe? Additionally, many manufacturers are starting to produce boxes almost from silumin (especially the production of such a country as China), such cases are very fragile and low-quality, although in appearance they look quite good.
The enclosure (box) with Exd type of protection must be reliable and must undergo all tests before installation in a responsible facility in a hazardous area. The cost of such boxes is quite high, bolts are installed along the edges for reliable connection or the lid is tightly screwed into the body. The cable glands in such boxes are metal only with Exd (“flameproof enclosure”) type of protection. These boxes are installed in zones 1/2 (Gases) and 21/22 (Dust).
The enclosure (box) with Exe (Exi) type of protection must also be reliable and fulfil all the functions for use in a less complex hazardous area (“higher degree of protection”). These boxes can be made of polyester, stainless steel or aluminium. Boxes with this type of explosion protection have screws for fixing the cover, which are screwed into the enclosure itself. Cable glands can be installed either plastic or metal. Explosion protection type of cable glands – Exhe (Exi) and/or Exd. These boxes are installed in zones 1/2 (Gases) and 21/22 (Dust).
Boxes with more complex types of explosion protection such as Exp (“purging”), Exm (“pouring”), etc. also have a place for manufacturing. By these boxes it is difficult to describe all their applications and uses. There will be a separate article on them.
Explosion-proof boxes are used in hazardous areas where there is a risk of explosion due to vapours, dust and other hazardous media. Explosion-proof boxes are installed in hazardous areas only when it is not possible to place the connection or disconnection of power and/or control cables outside the hazardous area.
Junction boxes are made of materials such as polyester, stainless steel, aluminium or cast iron. Each material has its own requirements and its own installation location in the hazardous area. For example, polyester boxes cannot be installed in areas where explosion protection type Exd (“flameproof enclosure”) is required and, correspondingly, cast iron boxes cannot be installed in areas where boxes with explosion protection type Exde (“increased degree of protection”) can be installed without any problems.
The most common opinion in Ukraine, that in any explosive zone to put a distribution box made of cast iron with a type of explosion protection Exd and all problems on explosion protection will be solved. Is that so? It’s actually not quite right.
Let’s take an example, cast iron casings are quite heavy and with little addition of phosphorus (we all know this from school), which lowers the mechanical properties of cast iron and causes cold fracture (formation of cracks in cold castings), which is an unsafe property for explosive areas. Reducing the phosphorus content of some manufacturers’ cast iron boxes reduces the cost of the case itself and the box as a whole, but again we ask the question, is it safe? Additionally, many manufacturers are starting to produce boxes almost from silumin (especially the production of such a country as China), such cases are very fragile and low-quality, although in appearance they look quite good.
The enclosure (box) with Exd type of protection must be reliable and must undergo all tests before installation in a responsible facility in a hazardous area. The cost of such boxes is quite high, bolts are installed along the edges for reliable connection or the lid is tightly screwed into the body. The cable glands in such boxes are metal only with Exd (“flameproof enclosure”) type of protection. These boxes are installed in zones 1/2 (Gases) and 21/22 (Dust).
The enclosure (box) with Exe (Exi) type of protection must also be reliable and fulfil all the functions for use in a less complex hazardous area (“higher degree of protection”). These boxes can be made of polyester, stainless steel or aluminium. Boxes with this type of explosion protection have screws for fixing the cover, which are screwed into the enclosure itself. Cable glands can be installed either plastic or metal. Explosion protection type of cable glands – Exhe (Exi) and/or Exd. These boxes are installed in zones 1/2 (Gases) and 21/22 (Dust).
Boxes with more complex types of explosion protection such as Exp (“purging”), Exm (“pouring”), etc. also have a place for manufacturing. By these boxes it is difficult to describe all their applications and uses. There will be a separate article on them.
