Exe Increased Safety Increased safety equipment is based primarily on the elimination of open sparking as at relay and switch contacts or on the commutators or slip-rings of motors and generators, and on the close control of surface temperatures. Also, the construction of the equipment is to a very high standard to prevent faults developing. Extra insulation is used, creepage distances between bare terminals are made longer and special enclosures to protect against damage due to entry of moisture and mechanical damage are also specified.
The enclosure is made to withstand impact and to prevent ingress of solids and liquids. Applications include cage-rotor induction motors, luminaires and connection boxes. Special Exe cable glands, metal or plastic, are used with Exe apparatus.
Exn Non-Sparking Similar to Exe, the designation Exn applies to equipment which has no arcing contacts or hot surfaces which could cause ignition. The Exn requirements are less stringent than for Exe, and designs are very close to that of normal electrical apparatus. The main consideration is extra care to ensure locking of terminal connections to avoid any risk of electric sparking or flashover.
Exp Pressurized Enclosure Clean, dry air or an inert gas is supplied to the equipment slightly above atmospheric pressure to prevent entry of the external flammable gas. This method is sometimes used for motors, instrumentation enclosures and lighting.
The internal pressure may be maintained by leakage compensation or by continuous circulation. A pressurization system requires a purge flow before the internal electrical equipment is permitted to operate. Also, the pressurized enclosure must be fitted with alarm and trip signalling for a reduction of pressure which in turn will switch-off the enclosed electrical circuits.
Exs Special Protection This includes precautions taken to prevent explosions which are not specifically covered by the previous designations. The table below shows the type of protection which is allowed in the three hazardous zones:
ZoneType Of Protection 0Exia, Exs (specially certified for use in Zone 0) 1Any type of protection suitable for Zone 0 and: Exd Exib Exp Exe Exs 2Any type of protection suitable for Zone 0 or 1 and: Exn, Exo, Exq