A Different sort of “electrical” issue. EMT Condensation!

New construction here. Everything done in EMT.

Temps here have been below zero, and are currently in the teens.

Two places now I have found wetness in my metal boxes… one in the shop which is a junction box on the ceiling for most of my 220v stuff which leaked (drops) onto my TS top, and another outlet box up stairs which has actually produced a small water-spot on the OSB sub-floor right under a wall plate.

The entire upstairs has not been fully completed, so there are no outlets or conductors in many of the runs yet. So the boxes are all open to warm air, and the EMT runs up into the attic to where it is exposed to very cold air.

All of the shop EMT is similarly run… from ceiling locations up into cold air and over and down. All shop ceiling outlets are installed, but I haven’t put cover plates on yet.

The junction box which leaked onto my TS is open still (no cover-plate).

There’s no question this is condensation because it is impossible that there is something leaking into my EMT runs. The wetness is clearly apparent where EMT runs up into cold air, and then back down to its various and respective locations.

QUESTION: When I get the outlets and switches and cover plates installed, will it minimize warm air creeping up through the EMT and thus keep the condensation down?

The shop junction box… should I stick some foam in there and cover the box… then check it later? It’s still open but has not leaked of late that I can see.

What should I do to minimize the condensation?

Thank you for your attention.

Paul

A couple of questions first.
What type of insulation is in use? fiberglass is renowned for its ability to cause drafts, so that may be something to consider.
Is there an air infultration barrier installed yet? If not, getting the tyvek up could help.
Are you using a portable gas/kerosene/etc heater currently? Those are known to cause moisture to build up and could be raising the humidity enough to cause your issues.

If you are using metal boxes inside stud cavities on exterior walls, that is a definite no no and will cause your electrical inspection to fail, so that is another thing to consider. They can however be surface mounted.

In general, I would suggest spray foam insulation rather than fiberglass for any new house or shop, but it may be too late for you to go that route. That would definitely eliminate the problem. Also, switching from EMT to plastic lines would help too.

I don't think that you can use great stuff or equivalent to seal the pipes up from drafts. Something tells me that violates code. You may be able to use a fire blocking caulk instead. Also, just adding the plates probably won't help much either. Cover plates really don't seal very well.

Eric, we are living in the house and the insulation is all fiberglass batting.

I passed the rough-in electrical inspection with flying colors. Of course I have metal boxes in exterior walls! I have metal boxes everywhere and every place. The entire electrical system was installed by myself.

In the attic over the shop I can throw some extra batting over some of the EMT (which was intentionally bent to be higher than the tops of the joists so as to not interfere with the R-38 batting.)

There's no access to above the upstairs ceilings due to space constraint.

Please explain. I don't follow you about metal boxes not being allowed in exterior walls. Prior to plastic and Romex that's all they used to use.

>>> don't think that you can use great stuff or equivalent to seal the pipes up from drafts. Something tells me that violates code. You may be able to use a fire blocking caulk instead. Also, just adding the plates probably won't help much either. Cover plates really don't seal very well.

I don't want to insert anything into the EMT itself, and would never consider caulk or spray.

My attics are VERY well ventilated, so there is VERY cold air in there during winter.

I'll take a pic later in the day of the shop attic so you and others can see how the EMT is laid out.

I don't know what code says about this - but could you put "elephant noodle" pipe insulation around the conduit? Better yet, stop the air (and moisture) movement all together by inserting a wad of fiberglass in the ends of the conduit. Maybe just covering/wrapping the ends of the conduit in electrical tape would do the trick. All you should have to do is stop the air from moving around and the condensation should stop.

I wouldn't use spray foam or anything that can't be easily "undone".

Maybe check with your electrical inspector - s/he might know a way to mitigate this.

IIRC, code does require firestop AROUND the conduit where it penetrates between floors. I think the ends also need to be sealed.

Quote:

---

Originally Posted by Paul Simmel

I passed the rough-in electrical inspection with flying colors. Of course I have metal boxes in exterior walls! I have metal boxes everywhere and every place. The entire electrical system was installed by myself.

<snip>

Please explain. I don't follow you about metal boxes not being allowed in exterior walls. Prior to plastic and Romex that's all they used to use.

---

Newer housing codes (past year or so) require that an airtight vapor seal be present for all conditioned spaces and that also applies to electrical boxes on exterior walls. That means using the new self sealing outlet boxes that seal around the wire and seal to the plastic vapor barrier (unless spray foam is used). Either your area hasn't adopted the latest building codes yet or the inspector missed it. Up here in MN it wouldn't fly and they would have made you rip all of it out. Part of the reasoning for these new rules is to prevent issues that you are running into. Air leaks cause condensation and mold problems, burst pipes, etc. in addition to heat loss.

Brian,

>>> Better yet, stop the air (and moisture) movement all together by inserting a wad of fiberglass in the ends of the conduit.

That's a good idea, and something I can deal with. Thanks for the suggestion.

I'm also going to be putting a call in to the Inspector and get his take on it. ITMT, the stuffing of the ends with fiberglass makes sense.

Thanks,

Paul