Class I Div.1 Conduit Entry to Purged Enclosure

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I found a thread similar to this, but I never found the answer. How can you safely enter a purged sheet metal enclosure in Div.1 and not create a serious leak point for the purge? I must try to maintain a NEMA 4 equivalent seal on my purged box, as it is in a wash down area, and still enter with conduit. As the other thread uncovered, the typical conduit hubs, with NEMA 4 rated gaskets, are rated only for Div.2. No-one ever addressed this quandry in the previous thread. Does the enclosure rating after purge extend to the fittings between the enclosure and the seal, since they are also purged?
 

dicklaxt

Senior Member
IMO,The purge pressure is greater than atmospheric and its generated volume would be greater than leak losses and has built in alarms,,,,I don't see where a problem exists,,,where do you think a problem exists?


dick
 
Maintaining the wash down rating seems a bit sketchy if the conduit does not enter through a Type 4 rated hub. I guess I should have mentioned this is on a portable process skid and will move in / out of the hazardous atmosphere. The wash down is most likely going to occur when the equipment is not in a hazardous atmosphere and therefore, not pressurized. However, with my history of Type 4 panels and UL approval, I doubt the Type 4 would be considered as maintained without a hub, or some gasketed entry port. UL aside, as I have sold Type 1 panels with the understanding that some item lacking the UL Type 4 approval destroys the Type 4 rating, but will still seal out water, I doubt the customer would accept this for wash down service without some gasketing with a NEMA 4 rating. If I must convince them otherwise, I will.
 

dicklaxt

Senior Member
I would agree,,,Nema 4 is listed as providing some degree of protection from hose directed water but if the fitting makeup is not it would be a problem but I think if the hubs were gasketed and thread make up were tight then any problems occuring beyond that would be a secondary failure that is hard to control.

dick
 

petersonra

Senior Member
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engineer
I found a thread similar to this, but I never found the answer. How can you safely enter a purged sheet metal enclosure in Div.1 and not create a serious leak point for the purge? I must try to maintain a NEMA 4 equivalent seal on my purged box, as it is in a wash down area, and still enter with conduit. As the other thread uncovered, the typical conduit hubs, with NEMA 4 rated gaskets, are rated only for Div.2. No-one ever addressed this quandry in the previous thread. Does the enclosure rating after purge extend to the fittings between the enclosure and the seal, since they are also purged?

Pretty common.

Fill the conduit with duct seal or something similar if you need to reduce the leakage.
 
I would agree,,,Nema 4 is listed as providing some degree of protection from hose directed water but if the fitting makeup is not it would be a problem but I think if the hubs were gasketed and thread make up were tight then any problems occuring beyond that would be a secondary failure that is hard to control.

dick

Let's forget about the wash down issue. We are stepping around the real issue here as did the original thread I referred to - is the Div.2 rated conduit hub actually acceptable for entrance to a purged panel in a Div.1 atmosphere? If so, I have no problems for this customer as I routinely use these hubs in their Div.2 purged panels and the wash down is no issue there.
 

dicklaxt

Senior Member
I would say no but not sure what NFPA says about purged panels in this scenario,that ought to be right up your alley.

dick
 
I would say no but not sure what NFPA says about purged panels in this scenario,that ought to be right up your alley.

dick

Okay - NFPA 496 A.4.2.3 says the conduit, if pressurized as well as the enclosure, does not need to have seals installed. That was news to me. What that implies to me, is since the enclosure is not rated for ClI, Div.1, the conduit, also pressurized, would not have to be Div.1 rated either, but that is just my interpretation. Now there are lots of gray area warnings in A.4.2.3 using words like "properly designed", and so on, allowing any inspector to fail an installation with improperly rated fittings.

Note - I just checked with them, and UL will pass the enclosure in an inspection of the panel with the hubs installed. (apparently they consider them part of the pressurized enclosure, or out of the scope of the enclosure inspection) However, I am still concerned about an overall system inspection, which, if it happens at all, won't happen until the machine is on site. And, there is the end user's engineering staff, many of which will call me asking for defined code sections applied to the wiring. This one is a bit difficult.
 
I found a thread similar to this, but I never found the answer. How can you safely enter a purged sheet metal enclosure in Div.1 and not create a serious leak point for the purge? I must try to maintain a NEMA 4 equivalent seal on my purged box, as it is in a wash down area, and still enter with conduit. As the other thread uncovered, the typical conduit hubs, with NEMA 4 rated gaskets, are rated only for Div.2. No-one ever addressed this quandry in the previous thread. Does the enclosure rating after purge extend to the fittings between the enclosure and the seal, since they are also purged?

Since it is a Class I, Division 1 area, even though the enclosure only would require a gastight seal to minimize purging media loss, the conduit itself needs to be explosionproof to contain any explosion that occurs in the conduit system. So you would need to install an explosionproof seal BEFORE it enters the purged enclosure. As far as watertightness goes, the purging pressure usually prevents any moisture entry unless it is directed, washdown hose pressure.
 
Since it is a Class I, Division 1 area, even though the enclosure only would require a gastight seal to minimize purging media loss, the conduit itself needs to be explosionproof to contain any explosion that occurs in the conduit system. So you would need to install an explosionproof seal BEFORE it enters the purged enclosure. As far as watertightness goes, the purging pressure usually prevents any moisture entry unless it is directed, washdown hose pressure.

Okay - as stated before, the water tight problem is dueto the portability of the equipment - the wash down will occur in a"safe" area, not in an area where the purge/pressurization is ineffect. Despite the NFPA ruling allowing pressurized conduit, I would never dothat - sealing subs are most certainly going into my runs.

All that aside, we have come up with the solution - 304ss conduit nippleswelded into the 304ss pressurized enclosure. The sealing sub will thread ontothis ss conduit "stub". Essentially the nipple becomes part of theenclosure. (did I mention we build process equipment - welding/polishing to aseamless finish is what we do every day) Watertight with or without pressureand rated for the environmental condirtions. Essentially what we already do to run from electrical enclosure mounted solenoids to control valves with 304 ss pnuematic tubing runs and maintain a Type 4rating. (try finding a box fitting, or bulkhead, for 1/4" metal tube entry into an electrical cabinet that has a NEMA 4 rating and UL approval sometime)

 
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