NM-B cable

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nizak

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I am looking to wire a residential greenhouse so to speak. It is framed with conventional wood studs and will have blown cellulose insulation. The surface finish is going to be a backer board with a stucco type covering. Humidity levels will be as high as 80%. I am being told that NM-B cable will become a problem over time due to moisture. If that's the case, won't the entire structure be subject to problems if there is a concern about moisture actually getting into the walls. I will be using gasketed weather proof receptacle and switch covers as well. I thought about UF type cable but you've got the same type conductor in the box once the outer sheath is removed. Any thoughts?
 
You are correct. why would moisture get in the walls, and if does get in the walls then you'll have mold issue.

I don't know. :?:?
 
nizak said:
I am looking to wire a residential greenhouse so to speak. It is framed with conventional wood studs and will have blown cellulose insulation. The surface finish is going to be a backer board with a stucco type covering. Humidity levels will be as high as 80%. I am being told that NM-B cable will become a problem over time due to moisture. If that's the case, won't the entire structure be subject to problems if there is a concern about moisture actually getting into the walls. I will be using gasketed weather proof receptacle and switch covers as well. I thought about UF type cable but you've got the same type conductor in the box once the outer sheath is removed. Any thoughts?
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What are they using for the walls? Is it Sheetrock ?
 
It sounds to me like they will be using "green board" like you would find around a tub or shower. There will not be a conventional "mud" finish but rather a skim coat stucco type .
 
nizak said:
I am looking to wire a residential greenhouse so to speak. It is framed with conventional wood studs and will have blown cellulose insulation. The surface finish is going to be a backer board with a stucco type covering. Humidity levels will be as high as 80%. I am being told that NM-B cable will become a problem over time due to moisture. If that's the case, won't the entire structure be subject to problems if there is a concern about moisture actually getting into the walls. I will be using gasketed weather proof receptacle and switch covers as well. I thought about UF type cable but you've got the same type conductor in the box once the outer sheath is removed. Any thoughts?
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It's not the conductors that is a problem in wet/damp areas, it's the sheath. NM cable has a thinner sheath and the paper around the bare EGC. The paper wicks moisture into the sheath. UF sheath is thicker and has no paper inside.

If you can't use NM, (I think you can) I would rather run conduit and THWN than to strip the UF cable.:rant:
 
In my opinion , 80% humidity isn't the same as damp anyway , but then I live in south Louisiana .
A damp location would have to be subject to condensate moister .
Never the less , it would be inside a wall and to much moisture wouldn't get to it .
 
scot120 said:
In my opinion , 80% humidity isn't the same as damp anyway , but then I live in south Louisiana .
A damp location would have to be subject to condensate moister .
Never the less , it would be inside a wall and to much moisture wouldn't get to it .
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From the NEC

Location, Damp. Locations protected from weather and not subject to saturation with water or other liquids but subject to moderate degrees of moisture. Examples of such locations include partially protected locations under canopies, marquees, roofed open porches, and like locations, and interior locations subject to moderate degrees of moisture, such as some basements, some barns, and some cold-storage warehouses.
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In my opinion areas of high humidity would be damp locations based on the above definition.
 
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