Attached garage subpanel conduit: drill through concrete or stud wall/joist?

[jvitez]

I'm ready to install a subpanel in my attached garage. The plan is a 100 amp feed for a future detached shop, so I need to penetrate the wall for a 1.5" PVC conduit. It measures 1 7/8" OD so a 2" hole should suffice. I'm planning on 3/3 NMD copper and to use the conduit as a sleeve for it.

I've picked the best spot for the subpanel, but my my problem is where to drill the hole.

The simplest to do myself is to drill through the stud wall just above the foundation wall. Unfortunately, there are a lot of obstacles exactly where the conduit needs to go as in my pic #2. The black flexible duct is for the kitchen cooktop, the white PVC pipe is the central vac, plus there's the 14/2 wire running beside it for the central vac unit itself.

The inside attached garage wall is is 5/8" drywall over 1/2" OSB covering a 2x6" stud wall filled with spray foam insulation. The I-joist in my my pic is over the basement stud wall which is made up of 2x4's placed 3.5" away from the concrete foundation wall, with R12 fibreglass running horizontally behind the stud wall, and the stud bay's filled with vertical R12 batts.

To drill through the stud wall I could use a 2" hole saw, but how do I make a straight hole through 1 1/8" of sheeting, a 5 1/2" foam filled stud bay, then the webbing of the I joist? It will be just shy of 8" deep in total. I've never seen an 8" deep x 2" diameter hole saw, or does something like that exist? But in any case if I go this route I'll have to deal with all the stuff inside the I-joist in the basement.

Or, do I just hire a concrete drilling company and have them drill a 2" hole through the foundation wall? I'd only have to deal with the fibreglass insulation and vapour barrier then. But this means more expense, hoping to find a contractor willing to do a small job (which is a big problem here), the mess of concrete slurry in my garage, etc.

What should I do, and how? Help! Thanks in advance, my illustrious GJ colleagues.

 

[ishiboo]

I'm ready to install a subpanel in my attached garage. The plan is a 100 amp feed for a future detached shop, so I need to penetrate the wall for a 1.5" PVC conduit. It measures 1 7/8" OD so a 2" hole should suffice. I'm planning on 3/3 NMD copper and to use the conduit as a sleeve for it.

I've picked the best spot for the subpanel, but my my problem is where to drill the hole.

The simplest to do myself is to drill through the stud wall just above the foundation wall. Unfortunately, there are a lot of obstacles exactly where the conduit needs to go as in my pic #2. The black flexible duct is for the kitchen cooktop, the white PVC pipe is the central vac, plus there's the 14/2 wire running beside it for the central vac unit itself.

The inside attached garage wall is is 5/8" drywall over 1/2" OSB covering a 2x6" stud wall filled with spray foam insulation. The I-joist in my my pic is over the basement stud wall which is made up of 2x4's placed 3.5" away from the concrete foundation wall, with R12 fibreglass running horizontally behind the stud wall, and the stud bay's filled with vertical R12 batts.

To drill through the stud wall I could use a 2" hole saw, but how do I make a straight hole through 1 1/8" of sheeting, a 5 1/2" foam filled stud bay, then the webbing of the I joist? It will be just shy of 8" deep in total. I've never seen an 8" deep x 2" diameter hole saw, or does something like that exist? But in any case if I go this route I'll have to deal with all the stuff inside the I-joist in the basement.

Or, do I just hire a concrete drilling company and have them drill a 2" hole through the foundation wall? I'd only have to deal with the fibreglass insulation and vapour barrier then. But this means more expense, hoping to find a contractor willing to do a small job (which is a big problem here), the mess of concrete slurry in my garage, etc.

What should I do, and how? Help! Thanks in advance, my illustrious GJ colleagues.

It's easy, you just put an extension on a hole saw. I prefer the Milwaukee Switchblade bits (Home Depot), but Irwin makes one available at Lowes/etc. that is a bit more common and I've used quite a bit including some 12" oak beams with the 2 9/16" bit.

Plus:

If you want to do the concrete, just go to your local mom and pop tool rental place and pick up a core drill and drill it yourself. This is probably the cheapest option.

 

[jvitez]

The extension sounds like just the ticket. Thanks! That will get me through the depth of the wall. But how would the hole saw work going through spray foam? Won't it just gunk up with compressed spray foam? It's not like a fluted drill bit that'll continue to eject material as the drill moves deeper.

 

[sands35]

Spray foam? Like butter. You may need to pull the hole saw out to clear it though. Just go slow.

Seal up the conduit with some caulk and you are good to go.

You can rent concrete hole saws for not much. Might be work thinking about so you don't have to mess with the services by the rim joist. Though you need to miss any bolts put into the concrete.

IMHO, I'd just go to 2" conduit for such a short run. Makes it easier to pull the wires and will cost a couple dollars more.

 

[bjcouche]

I've drilled some 2.5" holes through studs, foam, studs before. It's not too difficult, especially if you can see what you are doing and have room to get your drill where you need it. I used a combination of tools, but basically, a hole saw with an extension. I would suggest to be cautious when buying the "forstner type" drill bits pictured in a previous post. The ones with the screw on the end to help pull the bit through the wood. These require a very beefy low rpm drill and some cordless drills don't have enough torque when you get to 2" and above in my experience. IF you have a beefy drill though, this is the best bit for what you are doing compared to a hole saw that cut's out a round plug. If you end up using a hole saw, that will work too, you will just have to drill the wood, remove the wood plug, drill 1" of foam and then chip out the 1" foam plug, drill another 1", chip out the plug, etc. until you get through. I've done it this way and it wasn't too difficult. You can get 12" extensions for both hole saws and the forstner type bits, but be sure you get the right one, because the bits have different sized hex ends. Both home depot and Lowes have what you need.

 

[ishiboo]

I've drilled some 2.5" holes through studs, foam, studs before. It's not too difficult, especially if you can see what you are doing and have room to get your drill where you need it. I used a combination of tools, but basically, a hole saw with an extension. I would suggest to be cautious when buying the "forstner type" drill bits pictured in a previous post. The ones with the screw on the end to help pull the bit through the wood. These require a very beefy low rpm drill and some cordless drills don't have enough torque when you get to 2" and above in my experience. IF you have a beefy drill though, this is the best bit for what you are doing compared to a hole saw that cut's out a round plug. If you end up using a hole saw, that will work too, you will just have to drill the wood, remove the wood plug, drill 1" of foam and then chip out the 1" foam plug, drill another 1", chip out the plug, etc. until you get through. I've done it this way and it wasn't too difficult. You can get 12" extensions for both hole saws and the forstner type bits, but be sure you get the right one, because the bits have different sized hex ends. Both home depot and Lowes have what you need.

That's a good point. I have a Dewalt DWD460 I picked up for $35 from a Lowes clearance I use for running those bits. If you don't have a corded drill it may not work. I don't think I've ever tried them with my Bosch 36V.

 

[75gmck25]

Renting a core drill and bit for drilling through concrete or brick works well, but it is relatively expensive for just one hole. Most places have a minimum rental charge of 4 hours, and if you buy breakage insurance on the core bit it adds to the rental fee. In my areas it runs close to $100 for the total rental fees to drill one hole. However, maybe you have some places with cheaper rates.

Bruce

 

[jvitez]

All good points gents, much appreciated.

I've got a Makita D-handle 550 rpm drill so torque shouldn't be an issue with a hole saw or Forstner bit. I checked a Home Depot and another local home centre and neither had Forstner bits, only hole saws. Canadian stock is different than US I guess.

The local Home Depot rents a 2" concrete core drill bit with a rotary hammer for $68 for 24h. I'm going to have to think about it some more, as going through the concrete wall might be less hassle, but then I have to run conduit inside to protect the 3/3 NMD, or have to transition to individual wire which would be even more work.

Anyway, thanks again for the advice. I'll ponder this some more and post again when I'm done.

 

[tfi racing]

I have done this exact job thousands of times,the forstner style bit is best left to dry,clean new wood,I wouldn't even try it for what you are doing.Head over to Princess Auto,buy yourself a cheap hole saw set and and extension(or spend way more if you like but the hole saw will still be likely be junk at the end of the job).You will need to pull the saw out and clean it several times,but it will get it done.

 

[jvitez]

Thanks tfi, the voice of experience is always much appreciated!

Another question I've had: when using PVC conduit as a sleeve for NMD, is there any sort of fitting that needs to go on the opening where the NMD inserts into the conduit? I've found plastic bushings for EMT which makes sense so the wire isn't touching a sharp metal edge, but nothing for PVC conduit, so does that mean nothing is needed?

 

[ishiboo]

For PVC you use what is called an end bell fitting, or bell end.

Not sure about Canadian codes but I don't believe it is necessary for your application.

 

[zmaxmotorsports]

It's easy, you just put an extension on a hole saw. I prefer the Milwaukee Switchblade bits (Home Depot), but Irwin makes one available at Lowes/etc. that is a bit more common and I've used quite a bit including some 12" oak beams with the 2 9/16" bit.

Plus:

If you want to do the concrete, just go to your local mom and pop tool rental place and pick up a core drill and drill it yourself. This is probably the cheapest option.

 

[tfi racing]

No requirement for any bushing or insert(I don't even think anyone manufactures one) when using pvc as a protective sleeve for NMD cable.A little duct seal couldn't hurt to keep critters and insects out.

 

[jvitez]

Many thanks! Glad that's all I need. I've got the duct seal already.

I'm not looking forward to the cost of 3/3 copper, but at least I should get good service from the supply house when I tell them what I need.

 

[bjcouche]

I've used both the forstner type bits and the hole saws. If you have the high torque drill, I prefer the forstner bit types because they are way easier and faster to drill the hole. However if you are buying a tool for just 1 hole, the hole saw is cheaper. Also, if you are not 100% sure there are no nails anywhere near where you are drilling, the hole saw is better because the hole saw can cut through nails and the forstner cannot. The trick to using a hole saw to drill through 1.5" thick wood is to keep pulling the hole saw out to clear the sawdust because the dust doesn't eject, builds up and overheats the saw.
Brian