Condensation in wiring conduit?

Reply

  #1  
Old 01-03-11, 03:34 PM
Member
Thread Starter
Join Date: Jan 2011
Location: USA
Posts: 4
Condensation in wiring conduit?

Just moved in to a new house and ran into something I've never seen before. I was moving a ceiling fan from one room to another and had the switch plates off to wire in the fan control. I was pulling out the wires from the box and felt a bit of moisture on my fingers - looking closer I found 2-3 small drops of water along one of the wires coming down through the conduit pipe.

The room is on the second floor, interior wall and the conduit was coming down from an unfinished attic. I went up into the attic to first make sure I didn't have some kind of leak and found none. I did notice the specific conduit pipe in question was not well covered by the insulation and was cold to the touch. The house is 20 years old, in IL and we've been having some fairly sever temp changes over the last week (high 56 and then back to lows in the teens). Checked a bunch of other outlet and switch boxes and found no moisture so it looks to be pretty isolated. Even in the switch box when I did find it, there was no evidence that it had been dripping enough to drip or pool onto the bottom of the box. After the first few drops it appeared to dry up but that was likely because I left switch plate off while I investigated - so it doesn't appear to be a continuous drip.

I assume what I have is warm/humid air going up through the conduit, hitting the cold part in the attic and with the angle just happens to condense and drip back down (there are actually two conduits right next to each other and I only got the drops from one of them).

So - am I interpreting this right - is it just condensation? How common is it and is it a big concern? What is my best approach to address it?

Thanks!
 
Sponsored Links
  #2  
Old 01-03-11, 04:22 PM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,515
Originally Posted by gadgetdude View Post
So - am I interpreting this right - is it just condensation? How common is it and is it a big concern? What is my best approach to address it?
Yes it is just condensation, and it will happen in any conduit that travels from a conditioned space to an unconditioned space. It is a concern because it can cause connection and device failures as well as trip GFCIs. The fix is simple. Get a block of "duct seal" from the electrical aisle at the hardware and stuff a wad of it into each end of the conduit. It's a material like silly putty that will stop up any air flow. About $1 will get you more than you'll ever need.
 
  #3  
Old 01-05-11, 06:26 AM
Member
Join Date: Dec 2010
Location: USA
Posts: 12
this is typically caused from an attic space being under insulated. If you were to pull the wire out of the conduits, I bet they would be wet....and so will the pipes...and they will eventually rust.
the best long term solution... re insulate the cold area.

Did a service call for a lady just not too long ago in Homewood IL...all the pipes in her attic were badly rusted. Could not pull new wire in or the old wire out. We ended up having to repipe....which was not cheap...and she still then had to reinsulate. Stop the warm air from rising into the attic and the condensation will stop.
...so just insulate...cheaper in the long run

...and plugging the ends of the conduit is not a solutions to the problem in my opinion. you will actually make the problem worse doing that by eliminating any chance for the conduit to breath.
 
  #4  
Old 01-05-11, 07:35 AM
Justin Smith's Avatar
Member
Join Date: Dec 2010
Location: Cressona, Pa, USA
Posts: 2,546
If no air with humidity can get in, there is no humidity to condense.
 
  #5  
Old 01-05-11, 07:44 AM
pcboss's Avatar
Forum Topic Moderator
Join Date: Jul 2002
Location: Maryland
Posts: 14,595
Originally Posted by DELEE39 View Post
...and plugging the ends of the conduit is not a solutions to the problem in my opinion. you will actually make the problem worse doing that by eliminating any chance for the conduit to breathe.
Sealing conduits that pass between areas like this is required to prevent the condensation by the NEC.
 
  #6  
Old 01-05-11, 08:15 AM
tldoug's Avatar
Member
Join Date: Jan 2009
Location: USA
Posts: 317
Originally Posted by DELEE39 View Post
Stop the warm air from rising into the attic and the condensation will stop.

...and plugging the ends of the conduit is not a solutions to the problem in my opinion. you will actually make the problem worse doing that by eliminating any chance for the conduit to breath.
Because the symptoms are limited to condensation on and inside the conduit, which is a product of warm moist air from the conditioned living space flowing up the conduit, the objective needs to be to stop the infiltration of the warm air into the conduit. Simplest solution is to use the plastic foam inserts that install behind the cover plates on switches and outlets. This approach has the advantage of not trapping moisture inside the conduit which could happen if you were to plug the ends.

In order for the foam inserts to work, the cover plates must completely and snugly cover the the openings around the boxes.

As for adding insulation, if the attic isn't correctly ventilated, doing that alone will likely not be successful, and just waste time and money.

Doug Thompson
GC Builder/Remodeler
 
  #7  
Old 01-05-11, 08:25 AM
Member
Join Date: Oct 2005
Location: Milwaukee WI
Posts: 1,338
Originally Posted by DELEE39 View Post
...and plugging the ends of the conduit is not a solutions to the problem in my opinion. you will actually make the problem worse doing that by eliminating any chance for the conduit to breath.
A conduit running from a conditioned space, through a conditioned space, to a conditioned space should not need to be plugged with duct seal.

However a conduit that runs from an unconditioned space, through an unconditioned space, or connects to a j-box in an unconditioned space should be insulated. Right?

How does this sound: Even if there is no way for moisture to get in from the unconditioned space, moisture from warm air rising into a conduit will condense in the attic and gravity will carry it back to the ceiling box.

Based on what the OP said originally, the first problem to solve is getting the conduit properly covered with insulation, and properly ventilating the unconditioned space so moisture can escape.

But in addition to that, when conduit runs from an unconditioned space to a conditioned space, it may need to be plugged on both ends: On the inside so that warm air does not enter in winter and condense outside, and on the outside so that warm air does not enter in summer and condense inside. Whether this will in fact be required depends on the specific situation.
 
  #8  
Old 01-06-11, 06:13 AM
Member
Join Date: Dec 2010
Location: USA
Posts: 12
sealing conduits is sealing AROUND them to stop air penetration...not sealing the ends INSIDE the box as I understood was meant by the orginal post. I have seen this done and when that "plug" is pulled....water has built up behind it.

Sealing around the conduits where it passes between floors and into unconditioned areas also has nothing to do with condensation etc...this is a fire code, so fire does not migrate or draw air inside wall cavities.

if not air can get it condensation will stop....there will always be air penetration through a set screw coupling. I doubt the house, being 20 years old, was piped in compression fittings. They stopped using those around here in the late 60's. Sealing the ends of the conduits inside the box will not stop air penetration...it will lessen it, but not stop it...thus he will still have condensation.

Stopping the migration of heated air into the attic space will stop the condensation. The best way to do that is to insulate. sealing around all of the conduits where they leave a heated space into the attic with fire rated caulk would be a good addition as well.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes