flush mount load center on exterior wall - insulation / vapor barrier?

[Ashful]

So, I've wired up plenty of load centers / breaker panels over the years, but now I'm looking at doing my first flush-mounted into an exterior wall. It's in my garage, and I'd much rather go with flush mount than surface mount, for several reasons. However, what's normally done with insulation and vapor barrier, when mounting a flush-mount box in an exterior wall cavity? Box depth is 3.5", and wall cavity is 6"+ (2x6 framing plus interior drywall), so I'm anticipating the best plan is simply pushing the box into the cavity from the inside. This will simply squish the insulation (fiberglass with vapor barrier) back toward the exterior sheathing a bit.

A secondary challenge will be fishing wire up to the room above this load center (room above garage) without penetrating vapor barrier. I have 1/2" augers up to 15' long (flex shaft), so I could drill thru header plate from load-center cut-out... but for a neater and easier job, I was actually going to drill down thru header plate from attic above. This will mean I'll be pushing the fish wire or pole down from above, and will not easily be able to choose which side of the vapor barrier / insulation my wiring follows down to the load center.

 

[woodgeek]

I don't think the vapor barrier really does anything in our climate zone...I wouldn't worry about chewing it up a bit.

 

[jharkin]

Fiberglass looses a lot of effectiveness when compressed, so if you want to be really anal and do it textbook: cut out a rectangle where the load center will go then take a that section of bat and peel 3 inches off then put it back in. I saw an episode of TOH where they followed an insulation crew on new construction working around all the electric that way.

In reality you probably won't notice the difference if you just shove the box in there.

 

[semipro]

I'd consider building a box within the wall from xps or polyiso board foam then insert the load center within that box. The seams/edges would be sealed with spray foam.
I'd cut the fiberglass batt at the lower side of the hole to allow it to sit at full depth within the wall cavity below the hole.
I'd consider building the box so that it extends all the way to the top plates. That way, all wiring would be contained within the foam box. This would require cutting out the drywall/fiberglass all the way from the bottom of the box to the upper plates. That way you can also spray foam seal where the wiring penetrates the top plates.
If you don't want to deal with drywall patching you may be able to insert a piece of foam board through the load center hole that reaches to the upper plate. I think that would be tough though.
I did something very similar when I installed a wall mounted ironing board in an outer wall.

 

[Ashful]

Thanks, guys! Some good advice here.

On semipro's idea, I like it... except I have kitchen cupboards on this wall, both lowers and uppers. In fact, I'm still debating on mounting the load center under counter (back of these lower cabinets is open), versus over counter in back splash area. Drywall work is no trouble for me, but I'd like to avoid pulling and remounting the upper cupboards, since I rarely have a second set of hands to help me.

 

[woodgeek]

Fiberglass looses a lot of effectiveness when compressed, so if you want to be really anal and do it textbook: cut out a rectangle where the load center will go then take a that section of bat and peel 3 inches off then put it back in. I saw an episode of TOH where they followed an insulation crew on new construction working around all the electric that way.

In reality you probably won't notice the difference if you just shove the box in there.

Compressed FG has a slightly higher R-value **per inch** than uncompressed. So your plan would actually reduce the overall insulation level. When I put FG batts under my attic decking, instead of getting the R-18 batts for a 5.5" cavity, I got R-24s (which were the same price) and compressed them a bit. According to the intertubes, that should get me R-21 in a 5.5" thickness (neglecting the thermal bypass of the joists). I figure it is also less likely to collapse down later. IOW, a lot of the TOH stuff is sloppy.

So, I think either Joful or semipros plan is aok.

 

[jharkin]

Compressed FG has a slightly higher R-value **per inch** than uncompressed. So your plan would actually reduce the overall insulation level. When I put FG batts under my attic decking, instead of getting the R-18 batts for a 5.5" cavity, I got R-24s (which were the same price) and compressed them a bit. According to the intertubes, that should get me R-21 in a 5.5" thickness (neglecting the thermal bypass of the joists). I figure it is also less likely to collapse down later. IOW, a lot of the TOH stuff is sloppy.

So, I think either Joful or semipros plan is aok.

Hmm then the guys on this old house are wrong again it seems. They had an insulation contractor in and the guys would cut out around the boxes to not squish the batts.

 

[woodgeek]

Of course, if you have a gap because the batts are bent sideways around the box, the loss through the (clear) gap is much bigger than the compression effect. Batts only work when they are perfectly fitted. I suspect that insulation contractor was trying to get a clean fit to eliminate gaps, but explaining it incorrectly.

Sooooo, if adding the load center would pull the batt away from the studs (by compressing the batts in the middle), he should cut out a rectangle of batt the size of the box, and then compress that piece behind the box so the entire remaining cavity is filled.

It is this sort of non-sense that makes building scientists hate batts...real easy to install badly (with corresponding bad performance), a real PITA to install correctly (to get rated performance).

 

[semipro]

Thanks, guys! Some good advice here.

On semipro's idea, I like it... except I have kitchen cupboards on this wall, both lowers and uppers. In fact, I'm still debating on mounting the load center under counter (back of these lower cabinets is open), versus over counter in back splash area. Drywall work is no trouble for me, but I'd like to avoid pulling and remounting the upper cupboards, since I rarely have a second set of hands to help me.

I'm sure you're probably already aware but there are some code requirements for access space around load centers.

 

[btuser]

It's a very small area to worry about. Once you're done pulling you're wires down and refitting the insulation batt (if you bother) pull them through a 2x6 then toenail the board into place. Do the same on the bottom. Spray foam the holes and seams and seal the top plate. Stopping the chimney effect will do the most good. Very important when you figure warm, moist air hitting the inside of a cold electrical panel. I've seen the bottoms of many panels/enclosures rusted to the point they don't have a bottom left.

You only lose 10% through the walls. Divide that by the number of stud bays in the heated space and I wouldn't worry about it. Stop the air infiltration and you've won the battle.

 

[Ashful]

I'm sure you're probably already aware but there are some code requirements for access space around load centers.

Yep! Working only on very old houses, I usually get away with bending some rules, but not in this addition , I suppose . That likely precludes the under counter install.

edit: Actually, after some searching, I find nothing that precludes putting it under the counter, wall mounted in the back of a cabinet. I read many sites citing the NEC, the most complete probably being here:

http://diy.stackexchange.com/questi...e-a-circuit-breaker-box-within-a-storage-room

Summary: the 2m headroom height is only required for 200A and larger centers. There is a max install height, but no minimum install height (except it must be above floor). You must have 30" min working width (got that), and the panel should not be located in the vicinity of easily-ignitable material (linen closets, etc.). The only possible rub would be 110.26(B), space should not be used for storage. Okay... no problem, I won't store anything under there.

 

[Ashful]

Hmm... another fly in the ointment. If doing a flush-mount install, how does one get at the NM-B (Romex) clamps to tighten them? Installed inside to out, I guess I could get at the screws, but not the nuts. Or vise versa.

Surface mount, under the counter, is looking better and better... I can just feed everything thru the back of the panel, and do my welder plug with an offset nipple and a handy box.

 

[Highbeam]

.

A leftover chunk of 2" XPS slips tightly behind the 3.5" deep load center in a 2x6 wall.

Here's mine.

I use those plastic clamps to grab the romex and insulate the romex from the sharp edge of the knockout.

 

[Ashful]

chit! Wiring bundle found right in my install location! I have an idea...

 

[fbelec]

if that counter is permanent inspection wouldn't fly. 30 inches on each side and 36 inches in front floor to ceiling

 

[Ashful]

I like to follow code as closely as possible, but sometimes that's so impractical as to make me go another way, on renovation. If it becomes an issue, it will be easier to remove the counter and cupboards, than to relocate that load center. However, this is a large old house with 6 different load centers scattered about. The likelihood of an inspector ever knowing to look for this one, of finding it, is nil. With 8000 sq.ft. to inspect under two roofs, and endless attics, basements and crawl spaces, our home inspector didn't even get to see the whole place in a 6 hour inspection. He certainly never saw this sub feed, tied off in a type 1 box under the counter, which took me a year to discover, myself.

 

[Swedishchef]

I like to follow code as closely as possible, but sometimes that's so impractical as to make me go another way, on renovation. If it becomes an issue, it will be easier to remove the counter and cupboards, than to relocate that load center. However, this is a large old house with 6 different load centers scattered about. The likelihood of an inspector ever knowing to look for this one, of finding it, is nil. With 8000 sq.ft. to inspect under two roofs, and endless attics, basements and crawl spaces, our home inspector didn't even get to see the whole place in a 6 hour inspection. He certainly never saw this sub feed, tied off in a type 1 box under the counter, which took me a year to discover, myself.

Is this your house?

 

[Ashful]

Nope. Similar vintage, but I wish we were on the water!

 

[Highbeam]

Is this your house?

Wouldn't that be a great place?

 

[Ashful]

Hell yea... I wonder where it is?

In any case... here's where we are:

Load center installed
Rough wiring 60% done
HVAC installed
Spray foam scheduled

To do:
Drywall re-taping / repair
Attic door insulation
Baseboard & chair rail
painting
carpet

Oh... and the line where the wall (actually roof line / cathedral ceiling) meets the ceiling is very not straight. Looking for ways to mask that. May rip some 2x's on the bandsaw for a rough cut look (matching old part of house), and apply on top of drywall, as exposed rafter and collar tie edges, to achieve this end.

This room will house this mess, when done: