Air Gap when mounting exterior J-Box to Concrete or Brick Wall?

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DM2-Inc

DM2-Inc

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Houston, Texas
We provided a fire & gas system to a project in small town in New York.
When we went to turn it on and test it, we noted water had filled several devices on the exterior of the building. The conduit enters the device from the side and there is no Low Point Drain on the conduit entering the box. The conduit drops down to a GUAT and then from the side of the GUAT it ties to two Strobe lights that are about 9" from the GUAT.

Someone is telling me they believe this to be condensation, and that there is a requirement when mounting junction boxes with an air gap when mounting them to exterior Brick or concrete walls. These device connect to an addressable output module that's installed in a 3' x 3' NEMA 4X box. The conduit from the box runs about 20' horizontal before running down about 5' to the GUAT mentioned above.

I'm trying to find a code reference for the Air Gap requirement, however it does make sense considering the difference in temperature from the inside of the building and the exterior of the building. The walls aren't insulated on the inside of the building.

Someone know the code reference?
 
300.7 is what you should read and use, another is "Mounting of Equipment" in the Index, but I couldn't find a gap
reference there.
I recall that most equipment needs a 1/4" gap that's usually a bump out in disconnect or panel, or offset tab's
on the exterior of NEMA rate equipment. But I couldn't find it.

What is GUAT?
 
312.2 Damp and Wet Locations. In damp or wet locations,
surface-type enclosures within the scope of this article
shall be placed or equipped so as to prevent moisture
or water from entering and accumulating within the cabinet
or cutout box, and shall be mounted so there is at least
6-mm (1⁄4-in.) airspace between the enclosure and the wall
or other supporting surface. Enclosures installed in wet locations
shall be weatherproof. For enclosures in wet locations,
raceways or cables entering above the level of unin
 
I'm trying to follow what you are saying. Without pictures it's confusing. I can say however, that the dimples on the back of most J boxes allow for air circulation. BUT you need to understand that that isn't your problem, water ingress is. The inside of all conduit on the outside of a building is considered a wet location because either from condensation or direct ingress it's going to be wet.

-Hal
 
Air pressure differential between inside and outside will cause drafts to flow inside the conduits, and greatly increase condensation inside them. Same goes for temperature differentials. The conduits should be plugged with some duct seal as close as possible to the transition point to prevent air movement down the conduits.

Do you have an exhaust system inside that pulls air to exhaust, and gives the building a negative pressure. A make up air unit should be used to prevent the building from going to negative pressure. Slightly positive pressure in the building is beneficial.
 
MTW,
I did read in 300.7
(A) Sealing. Where portions of a raceway or sleeve are known to be subjected to different temperatures, and where condensation is known to be a problem, as in cold storage areas of buildings or where passing from the interior to the exterior of a building, the raceway or sleeve shall be filled with an approved material to prevent the circulation of warm air to a colder section of the raceway or sleeve. An explosionproof seal shall not be required for this purpose.

Someone at my office commented on the installation that they mixed steel conduit with aluminum junction boxes. Is there an issue with?

I'm thinking that the requirement for a drain comes from 314.15?
314.15 Damp or Wet Locations. In damp or wet locations, boxes, conduit bodies, outlet box hoods, and fittings shall be placed or equipped so as to prevent moisture from entering or accumulating within the box, conduit body, or fitting. Boxes, conduit bodies, outlet box hoods, and fittings installed in wet locations shall be listed for use in wet locations. Approved drainage openings not smaller than 3 mm (1∕8 in.) and not larger than 6 mm (1∕4 in.) in diameter shall be permitted to be installed in the field in boxes or conduit bodies listed for use in damp or wet locations. For installation of listed drain fittings, larger openings are permitted to be installed in the field in accordance with manufacturer’s instructions.
Informational Note No. 1: For boxes in floors, see 314.27(B).
Informational Note No. 2: For protection against corrosion, see 300.6.
 
Drilling a weep hole in a listed box is an "Approved drainage opening..."?

DM2-Inc said:
Approved drainage openings not smaller than 3 mm (1∕8 in.) and not larger than 6 mm (1∕4 in.) in diameter shall be permitted to be installed in the field in boxes or conduit bodies listed for use in damp or wet locations.
Click to expand...
You answered your own question.

-Hal
 
Daily heating /cooling of outside raceways and enclosures is enough to cause pretty rapid build up of condensation that can fill low points in the system in just days in some instances. It needs to be able to drain. Not only does it promote corrosion but in places where it normally does get below freezing temps, it will split raceways open - I guess once that happens you then have drainage though.
 
kwired said:
Daily heating /cooling of outside raceways and enclosures is enough to cause pretty rapid build up of condensation that can fill low points in the system in just days in some instances. It needs to be able to drain. Not only does it promote corrosion but in places where it normally does get below freezing temps, it will split raceways open - I guess once that happens you then have drainage though.
Click to expand...
I've got a picture somewhere of the ice splitting the 1/2" EMT and pushing a conductor up through the split.
 
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