Transcript Exe Increased Safety, Exn Non-Sparking, Exp Pressurized

Exe Increased Safety,
Exn Non-Sparking,
Exp Pressurized Enclosure,
Exs Special Protection
(Adapted from:D.T. Hall:Practical Marine Electrical Knowledge)
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:
• Zone
•0
Type Of Protection
Exia, Exs (specially
certified for use in Zone 0)
•1
Any type of protection
suitable for Zone 0 and:
Exd Exib Exp Exe Exs
•2
Any type of protection
suitable for Zone 0 or 1
and: Exn, Exo, Exq