16
16
Electrical supply Requirements
Explosion
Proof Device
typical Enclosure Wiring Methods
Protected enclosures must be wired similar to explosion
proof enclosures, in accordance with
article 501-504
of the
1999 National Electric Code -
nFpa 70
.
Single conductor wiring must be placed in rigid metal conduit,
seal-flex conduit or other mediums approved for use in the
hazardous location surrounding the protected enclosure.
Although the 1998 edition of NFPA 496 does not require
conduit seals on pressurized enclosures in a division 2 area,
Fuchs strongly recommends the use of a conduit
seal as the most practical way to prevent excessive leakage
through conduit connections.
While explosion proof enclosures require conduit seals on
all cable entries, in accordance with
nFpa 70
,
sections
501-5
, protected enclosure cable entries can be sealed in
accordance with
section 501-5
which permits the use of
compression gland fittings or other sealed cable entry fittings,
as opposed to approved conduit seals, if the wiring method
is otherwise suitable for the hazardous location.
In conclusion, there are two primary goals. First, the installer
should ensure all associated wiring and cable is protected
by pressurization or other means, such as explosion proof
conduit or intrinsic safety barriers. Secondly, the installer
must ensure all associated conduit and wireways are sealed
to conserve protective gas, unless they are used to supply
protective gas to other enclosures or devices.
typical Enclosure Wiring Connections
Seal
Intrinsically
Safe Or Fiber
Optic Device
Adjacent
Pressurized
Device
Independently
Pressurized
Device
Intrinsically
Safe Or Fiber
Optic Device
Seal
Conduit
Conduit
Conduit
General Wiring Requirements
WaRnInG
tHIs DEVICE ContaIns ElECtRICal paRts WHICH
Can CaUsE sHoCK oR InJURY
All electrical connections, conduit and fittings on the protected
enclosure must be suitable for the hazardous location in which
they are installed. In addition, all conduit and wire must be
installed in accordance with NEC articles 500-1, 500-2 or
500-3 as required and all relevant plant and local codes.
note:
Do not use seals on conduit used as a protected
“wireway” to supply protective gas to adjacent protected
enclosures. The same conduit can be utilized for both
electrical and pneumatic service to an adjacent protected
enclosure(s), provided the conduit is oversized to allow a
minimum free clearance equal to or larger than the pipe size
required between multiple enclosures as stated on page 7,
“Getting Started”.
Enclosure power Requirements
The protected enclosure(s) electrical power source must
originate from a circuit breaker or fused disconnect suit-
able for the hazardous location in which it is installed. The
switch must be located within fifty (50) feet of the protected
enclosure(s) and the protection system and be properly marked.
alarm signal Requirements
The protected enclosure(s) alarm signal may originate from
the protected enclosure if the alarm signal is disconnected by
the protected enclosure's circuit breaker or fused disconnect
as stated in Enclosure Power Requirements above.
The protected enclosure(s) alarm signal power may also
originate from outside of the protected enclosure. In this
application, the protected enclosure may be used as a
“wireway” to pass alarm signal wiring from the power source
to the alarm device, if the wiring is isolated and properly
labeled. In addition, appropriate conduit seals must be
provided outside of the protected enclosure separately.
IMpoRtant notE
nFpa 496 requires the use of an alarm or an indicator to
detect the loss of safe enclosure pressure. In addition,
the nFpa 496 requires that if an indicator alone is
utilized, a protective gas supply alarm must also be
installed between the last valve in the protective gas
supply and the protected enclosure. therefore, the
protective gas supply to all lps style systems must
be equipped with the above mentioned protective
gas supply alarm. Exception: systems utilizing an
EpsK or GpsK enclosure pressure loss alarm switch
accessory will satisfy the above mentioned nFpa
requirement.
Gland
Fitting
Cable
Seal
Pressurized
Raceway
Protected Enclosure
Or Device
RSPSupply - 1-888-532-2706 - www.RSPSupply.com
http://www.RSPSupply.com/p-6798-Hoffman-A1001YZUMC2-Purging-Pressurization-System-10-CF.aspx