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Types protection

The use of electrical apparatus in potentially explosive atmospheres is quite usual today. This equipment has to be manufactured in such a way that there is no risk of explosion. An explosion occurs when the three following conditions happen:

  • presence of a potentially explosive atmosphere;
  • possibility of transmission of the explosion;
  • existence of an ignition source.

The recognized types of protection eliminate one of these conditions and thus make an explosion impossible. Two types of protection prevent the presence of a potentially explosive atmosphere inside the electrical apparatus:

  • oil immersion (safety “o”);
  • pressurized apparatus (safety “p”).

Two types of protection make the transmission of an internal explosion to the potentially explosive atmosphere surrounding the electrical apparatus impossible:

  • sand filling (safety “q”);
  • flameproof enclosure (safety “d”).

Lastly, three types of protection eliminate any source of ignition such as sparks, overheating, etc...:

  • increased safety (safety “e”);
  • intrinsic safety (safety “i”);
  • protection “n” (restricted to zone 2).

In practice, only four of these seven types of protection are applicable to electric motors:

  • pressurized apparatus (symbol Ex p);
  • flameproof enclosure (symbol Ex d);
  • increased safety (symbol Ex e);
  • non sparking protection (symbol Ex n).

Electric motors have an additional type of protection (symbol Ex de) which is a combination of:

  • flameproof enclosure “d” for motor frame;
  • increased safety “e” for terminal box.