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NEMA 7 or NEMA 4x Enclosure? 2

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Maple2

Maple2

Electrical
Jul 19, 2021
19
I am currently inspecting a site for an upcoming CCTV project, and I found that they were using NEMA 4X enclosures in Class 1 Div 2 and Class 1 Div 1 areas of the site for some of the existing CCTVs. These enclosures house the electrical step-down transformers for CCTVs. However, I have some concerns regarding the suitability of the NEMA 4X enclosure for this particular environment.

In my opinion, a NEMA 7 rated enclosure would be more appropriate for these locations since it is specifically designed for areas with flammable gases. However, there is a significant challenge at the project site - high humidity. Some of the NEMA 4X enclosures have experienced moisture accumulation and corrosion inside due to condensation (see attached photos). This raises doubts about whether using a NEMA 7 enclosure would be the right choice, as it may be even more susceptible to water condensation.

I am looking for an enclosure that can provide both protection against flammable gases and address the issue of water condensation. I have come across information stating that NEMA 4X enclosures are prone to condensation in practice. Considering this, I would appreciate hearing your thoughts and recommendations regarding suitable solution to this problem.

Thank you for your expertise and input.
 
 https://files.engineering.com/getfile.aspx?folder=336377bb-908b-4645-ae81-568ee9f316ca&file=Enclosures.pdf
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Space heaters are normally used to manage condensation.

With that said, I have found many enclosures have poor choices for seal materials. Nitrile o-rings and such crack and fail from UV exposure within a few years of installation. The amount of water in your picture indicates a leak and is not the result of condensation.
 
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I agree NEMA 4X is not suitable for the location. If NEMA 7 enclosures are used, specify them with the proper explosion-proof breather drains for the location - a variety of manufacturers make these accessories.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
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Mr Maple2 (Electrical)(OP)13 May 23 00:07
1. If you accept/accessible to IEC enclosures, you would have a much wider range of choice. IEC IP ratings are much more comprehensive in all expects.
2. Select a proper IP rated enclosure and add a space heater say <20W would be adequate for the size of enclosure shown.
Che Kuan Yau (Singapore)
 
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Explosion proof drains on 4X boxes?


--------------------
Ohm's law
Not just a good idea;
It's the LAW!
 
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Assuming the equipment does not contain any arc producing devices, the Class I, Division 2 location does not require an explosionproof enclosure. Any enclosure suitable for environment can be used.
The Division 1 location will require an explosionproof enclosure. Conduit seal fittings would not be required unless the conduit entries are 2" or larger or the operating temperature of the equipment inside the enclosure exceeds 80% of the autoignition temperature of the flammable gasses.

However the use of seals in either location along with suitable drains or vents may help reduce the moisture problem. Temperature changes cause the conduit to breath and this can result in condensation. Sealing the conduits, even without the use of an explosionproof seal, will reduce air movement and condensation.

If the area is a wet location, rigid conduit couplings in vertical runs will let water enter the raceway and if the conduits enter the enclosures without some type of low point drain that water will end up in the enclosure. I have seen small NEMA 4X enclosures completely filled with water from this issue.
 
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One solution that I’ve seen at our sites for hazardous locations is to pressurize the outdoor control cabinets with dry air. This seems to do a pretty good job of keeping the cabinets moisture-free without the associated concerns of heating elements in hazardous locations. It doesn’t take much - I think it’s regulated to less than a psi (if I recall just a few inches WC) but would have to check.
 
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NFPA 496
4.4.1*
The protected enclosure shall be constantly maintained at a positive pressure of at least 25 Pa (0.1 in. of water) above the surrounding atmosphere during operation of the protected equipment.
 
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Thank you all for your contributions. I have decided to replace them with a NEMA 7 enclosure installed with explosion proof breather/drain.
 
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Explosion proof heaters with built-in thermostats are also available for enclosures if the condensation is too much of a problem for the breather/drains.

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
 
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If the installation is in a wet location, make sure the NEMA 7 enclosure also had a NEMA 4 or other wet location rating. While most do, I have run across NEMA 7 enclosures that are not suitable for use in wet locations.
 
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I agree that NEMA 7 is not called for here if this is a CL1 Div2 environment. A NEMA 4X breather/drain is all that is necessary here, which I don’t see in those boxes.

But certainly NEMA 7 with a breather/drain would work, it’s just kind of over kill. Most NEMA 7 enclosure mfrs offer a NEMA 4X O-ring seal in the flange as an option, so make sure to ask for that.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
 
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Maple2 said:
...I found that they were using NEMA 4X enclosures in Class 1 Div 2 and Class 1 Div 1 areas of the site...
Click to expand...

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
 
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