Case #01: Enclosure with Purging
A general purpose lighting source is required to be used in an aircraft
hangar where it is defined as "Class I Division 2" according to NEC
Article 513. However, S-Airline concerned much more safety and treated
the workshop as "Class I Division1". ATE engineer adopted a X-Purge Unit
and customized an air-tight stainless steel enclosure
(500mmx500mmx250mm) to house all "general purpose" electrical devices
such as lighting source, MCB, transformer and magnetic contactor. Relief
valve and spark arrestor with orifice were included as well. Such design
meets the standard of National Fire Protection Association NFPA496. Its
major function is that electric supply will be automatically powered on
after the enclosure is purged for a presetting Purge Time (e.g. 10
minutes) and keep maintaining pressurized at 1 to 4 inch water high.
When pressurization fails, power supply will be cut off immediately.
What is Z-Purge?
Z-Purge Unit makes unclassified equipment be used safely in Zone 2 (or
Division 2). In this case, equipment inside the enclosure can be any
"general purpose" one. In another word, Z-Purge Unit can reduce an enclosed space
from Division 2 (or Zone 2) to unclassified.
What is Y-Purge?
Y-Purge Unit makes Zone 2 (or Division 2) equipment be used
safely in Zone 1 (or Division 1). In this case, equipment inside the
enclosure must be approved or certified for safe use in location of Zone
2 (or Division 2 ) hazardous area. In another word, Y-Purge Unit can reduce an enclosed space
from Zone 1 (or Division 1) to Zone 2 (or Division 2).
What is X-Purge?
X-Purge Unit makes unclassified equipment be used safely in Zone 1 (or
Division 1). However, an enclosure with
X-Purge Unit may have equipment or devices which can cause
ignition of flammable atmosphere so that the X-Purge Unit is required to
control electric power to enclosure automatically and to
provide remote alarm annunciation upon loss of positive purging pressure.