Extending metal boxes for room conversion

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navy_joe

Member
Location
Greeneville TN
Job is to upgrading a basement area to a finished room. Area to be upgraded is 1/2 open to grade level. The original area was wired using conduit and steel boxes mounted to the cinder block. Two inch foam was added later which put all of the existing boxes flush with foam surface, conduit was covered by foam. Now part of the area is being converted to a living space by adding a studded wall, additional insulation, and sheetrock. This will require additional outlets and extending the switchboxes out 4 inches since you can't just extend the original wiring to a new box and covering the old box behind the wall.

Hopefully I have explained this enough to give you an idea of the arrangement.

Here is something I am trying to think out. The existing boxes are steel and attached to the block and basically very cold in the winter (last night it was zero). I can't just bury the boxes and insulate them, they have to be extended BUT I am afraid they will sweat and wet the insulation. Also a lot of cold air actually comes thru those boxes ( was somewhat surprised at this but cinderblock is porous and when the wind blows you can feel a light draft). Have any of you encountered this? You can easy extend a steel box using extenders, but is there any way to have a thermal break there? Surely someone has encountered this before or am I just worrying needlessly. Just trying to not cause a mold or mildew problem in the future.

JD
 

Dennis Alwon

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I am closing this thread, in accordance with the Forum rules. This Forum is intended to assist professional electricians, inspectors, engineers, and other members of the electrical industry in the performance of their job-related tasks. However, if you are not an electrician or an electrical contractor, then we are not permitted to help you perform your own electrical installation work.


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Dennis Alwon

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Occupation
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I have open the thread. The OP is looking for help with the mold/mildew not the wiring so if anyone has experience with this please help out
 

navy_joe

Member
Location
Greeneville TN
Yes I am trying to find out how to set up some type of thermal break, to stop the cold metal boxes from causing condensation. On the outside it could cause a mildew problem in the insulation. I also suspect there is a possibility of harm inside of the box too, but that seems more remote.
I have open the thread. The OP is looking for help with the mold/mildew not the wiring so if anyone has experience with this please help out
 

John120/240

Senior Member
Location
Olathe, Kansas
Could you abandon the existing boxes & re-route your conduit down the new stud wall ? Or better yet intercept the conduit feed in an accessible location then change to romex through your stud wall.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
Could you abandon the existing boxes & re-route your conduit down the new stud wall ? Or better yet intercept the conduit feed in an accessible location then change to romex through your stud wall.

From the OP:

Two inch foam was added later which put all of the existing boxes flush with foam surface, conduit was covered by foam.
 

Smart $

Esteemed Member
Location
Ohio
I would sure hate to have to do any work in these boxes in the future.
I didn't mean fill the extension.

The only thing anyone should be doing in the future where the foam is, is pulling the wire... perhaps a little more difficult than normal, but shouldn't be by much (especially with the somewhat brittle kind like Great Stuff)*. To extend the wires, I recommend using butt splices** and hold the wire taut to the box opening while foam is administered and drying.

*Future pulling could be eased by sleeving the wires with something like unshrunk heat shrink before foaming.

**If solid wire, I'd recommend non-insulated butt splices, crimped with a good crimper, possibly soldered... and approved-method insulated (heat shrink or tape).
 

PetrosA

Senior Member
If the wall is getting packed out anyway, wouldn't it be easier to just rewire the damn thing? Abandon and foam the old stuff and start over. It'll take 1/3 the time at least and it will totally eliminate the temp differences from the old boxes/conduit that would create and kind of moisture issues.
 

navy_joe

Member
Location
Greeneville TN
3M mastic tape

3M mastic tape

My local electric supplier suggested this product, 3M rubber mastic tape #2228,#2210 and #2200

http://multimedia.3m.com/mws/media/223975O/scotch-2200-and-2210-vinyl-mastic-pads-and-rolls.pdf

http://solutions.3m.com/wps/portal/...e-2200?N=5427287+3294317062+3294317063&rt=rud

It is listed for electrical use in insulating, moisture sealing, above and below ground to 600 volts. It could be used to seal the boxes although it is primarily intended for sealing splice connections. It comes in rolls or sheets.
 

navy_joe

Member
Location
Greeneville TN
Is it a violation to fill the original box with expanding foam?

Here is a link to DOW the maker of "Great Stuff" http://greatstuff.dow.com/where-to-use/living-space/electrical-outlets/ about using it with electrical outlets. An excerpt from item #7 " GREAT STUFF? Insulating Foam Sealants are combustible, so it's very important that all electrical switches are turned off before starting your project. Also, never apply foam to exposed wire or inside an electrical box." So I guess that answers the question for sure.

As a sideline, it could also get you into a derating area (not to mention that the wires would no longer be accessible) "If multiple Type NM cables pass through the same wood framing opening that?s to be sealed with thermal insulation, caulking, or sealing foam, adjust the allowable ampacity of each conductor per Table 310.15(B)(3)(a)". The point being foam is an insulator and encasing wires in any space adds another consideration.
 

navy_joe

Member
Location
Greeneville TN
If the wall is getting packed out anyway, wouldn't it be easier to just rewire the damn thing? Abandon and foam the old stuff and start over. It'll take 1/3 the time at least and it will totally eliminate the temp differences from the old boxes/conduit that would create and kind of moisture issues.
It is being rewired, but all of this has existing wiring that is now covered with foam. Some of it is behind 6 inches of foam running for 40 feet. But I'll admit that thought has occurred. However to do it would require having a junction boxes imbedded behind the new wall.
 

curt swartz

Electrical Contractor - San Jose, CA
Location
San Jose, CA
Occupation
Electrical Contractor
If the wall is getting packed out anyway, wouldn't it be easier to just rewire the damn thing? Abandon and foam the old stuff and start over. It'll take 1/3 the time at least and it will totally eliminate the temp differences from the old boxes/conduit that would create and kind of moisture issues.

My thoughts exactly. Abandon the existing boxes and wiring. Fill the existing boxes with foam and install new wiring in the new stud wall. Trying to extend the existing boxes and airseal is not worth the trouble. The existing wires are most likely too short to allow for the additional extensions so will need to get re-pulled anyway.
 

navy_joe

Member
Location
Greeneville TN
I didn't mean fill the extension.

The only thing anyone should be doing in the future where the foam is, is pulling the wire... perhaps a little more difficult than normal, but shouldn't be by much (especially with the somewhat brittle kind like Great Stuff)*. To extend the wires, I recommend using butt splices** and hold the wire taut to the box opening while foam is administered and drying.

*Future pulling could be eased by sleeving the wires with something like unshrunk heat shrink before foaming.

**If solid wire, I'd recommend non-insulated butt splices, crimped with a good crimper, possibly soldered... and approved-method insulated (heat shrink or tape).

Doesn't that constitute a junction box? I have read about using some 3M splice devices in trays that are allowed. But I was not aware that this would be allowed in a covered metal box behind a wall. If this were allowed it would be a great solution????
 

Smart $

Esteemed Member
Location
Ohio
That of course would be a great solution except it would have to be approved for that use. I'm also almost certain that foam out of the can is combustable.

Here is a link to DOW the maker of "Great Stuff" http://greatstuff.dow.com/where-to-use/living-space/electrical-outlets/ about using it with electrical outlets. An excerpt from item #7 " GREAT STUFF? Insulating Foam Sealants are combustible, so it's very important that all electrical switches are turned off before starting your project. Also, never apply foam to exposed wire or inside an electrical box." So I guess that answers the question for sure.

As a sideline, it could also get you into a derating area (not to mention that the wires would no longer be accessible) "If multiple Type NM cables pass through the same wood framing opening that?s to be sealed with thermal insulation, caulking, or sealing foam, adjust the allowable ampacity of each conductor per Table 310.15(B)(3)(a)". The point being foam is an insulator and encasing wires in any space adds another consideration.
I used Great Stuff only as an example of expanding foam, without researching it. You are correct about use being approved, and I wasn't aware prohibition in product documentation. I commend you for your diligence.

However, where there is a will, there is a way... :happyyes:
(...well, not always, but an appropriate cliche at the moment ;))

3M? Fire Block Foam FB-Foam


Your concern for derating is also noteworthy. Yet I'm left thinking this is residential, and while it is not out of the question that a box could be a bird's nest of wires, I was and still am assuming that is not the case for most of the boxes of concern. Additionally, though I mentioned filling the box, it is not required to produce the desired effect. I'm guessing a minimally thick layer would suffice.

Nevertheless, it was a idea I had not heard of or explored the practicality and compliance before. Use it or not, I'll not lose any sleep over it either way. :angel:
 

Smart $

Esteemed Member
Location
Ohio
Doesn't that constitute a junction box? I have read about using some 3M splice devices in trays that are allowed. But I was not aware that this would be allowed in a covered metal box behind a wall. If this were allowed it would be a great solution????
I was assuming you were adding extension ring(s) to the box.
 

navy_joe

Member
Location
Greeneville TN
Thanks for your input

Thanks for your input

I want to thank you for your input. You've all been very helpful. I think the basic answer is there is no way to install a thermal break that is code approved. If you do run across something though, let me know.

I hope you all have indoor jobs in a conditioned space until spring! Enough winter for one year!!;) Time for some sunshine:cool:
 
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