I have a control panel "hermetically sealed" (purged) in a class 1 DIV 2 area. By the NEC I know that seal-offs are not required. How ever we have them installed at the panel per the owner.
Some of the seal-offs are @ 20" from the panel, some people are stating that if we do install them then they have to be within 18" of the panel.
I am stating being they are not required per NEC they do not have to be within the 18" limit.
Panels purged according to NFPA 496 do
not require seals listed for explosion-proofing(containment) purpose. However, proper design requires that your box minimizes the loss of the purging media AND that you can maintain the required pressure without using up extraodinary amounts of the purging media, therefore your openings must be 'sealed'. This accomplished by gaskets on doors and through-wall mounted devices. Conduit openings should be also sealed by an effective means. Since there is no engineered product available for this specific purpose the two most common way to prevent the purging media leak is to jam ductseal into the conduit and around the conductors, creative use of injectable insulation foam and the use of XP seal fittings on the conduit.
Before energizing the components inside of the purged box in some cases it is required, but in all cases it is prudent that you PURGE the box. The concern here is that you may have had accumulated vapors inside the box upon energization it can explode. Obviously a conduit with a seal that is distance mouted from the box could become a dead space where the pre-purging would be ineffective, eg. ignitable materials trapped. It is of course an esotherically remote possibility IMO, but then the reasonable question comes back, well if you now violate the 18" rule what will prevent the next Contractor from installing the seal 20' away the next time?:lol:
