Help with Choosing Materials for Subpanel Install


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Old 06-07-24, 12:11 PM
C
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Help with Choosing Materials for Subpanel Install

I had a previous post asking about the permit process for installing a subpanel. I reached out to my local Township and confirmed that I am able to do the work. I currently have a Siemens panel with 200 Amp service and would like to add a subpanel. I don't have a ton of room in my existing panel, mainly due to dedicated outdoor receptacles that were installed years ago. I used to have a pretty large Christmas display, but those receptacles aren't used much anymore. My overall load is fairly low.

I'm trying to figure out what Amp subpanel I should go with. I'm installing mini splits, so I'll be adding 4 - 15 amp double-pole breakers. I would like to have room for flexibility down the road, so I would rather go bigger if possible (ie. at least 100 Amps, but I think preferably 125 Amps). I know regardless of what I use, I'm limited by the size of my main service (200 Amps).

As far as the panel, I'm leaning toward a Square D QO or Leviton 42-space 200 Amp. Would either be a good choice, or is there something better I should consider? The only reason I was thinking about using Leviton is that it would be interesting to monitor some of the loads with the smart breakers. This is definitely not a necessity, and I have read some complaints about annoying buzzing, at least with the earlier generation breakers. I believe these will both come with a main, but I can swap that out with a lower 125A rated breaker (not sure if it can be removed entirely, but I have no issue with leaving it).

As far as wiring, I wanted to see if I could get some help with this. Based on Table 310.15(B)(16), I believe my options would be either #2 Cu or 1/0 aluminum. If I'm reading correctly, #2 Cu is rated for 115A, which I think would be okay for 125A, though I have no issue using #1 at 130 if that is better. For the ground, is it 6 Cu or 4 Al? The service entrance cables seems to have larger grounds than this, so I don't think that should be an issue. I am running from my main panel and going two stud bays over in my garage, so it is a very short run. My thought is to run through the top plate, into the garage attic, and then down into the stud bay. In this case, would it be acceptable to use SER wire instead of conduit/THHN? I can use either, and if conduit would look more professional, I'm okay with that. I just want to make sure I don't have any issues with the inspector, and I want everything to look as neat as possible.

I appreciate any advice!
 
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Old 06-07-24, 12:37 PM
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I believe these will both come with a main, but I can swap that out with a lower 125A rated breaker (not sure if it can be removed entirely, but I have no issue with leaving it).
You don't need to replace the main breaker. (You don't need a main breaker at all in this case, but it's nice to have).

If the attic is accessible by ladder, then the cable may need some protection from being stepped on.
 
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Old 06-07-24, 12:59 PM
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Luke - Thank you. If I'm interpreting the attic requirements correctly, for attics with only a scuttle hole entrance, cables within 6 feet of the entrance must be protected. These would be at the far corner of my garage (probably 20+ feet from the entrance), so hopefully, I am okay there.
 
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Old 06-13-24, 09:58 AM
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I'm leaning toward a Square D QO or Leviton 42-space 200 Amp
Square D, Eaton, make good panels. I personally don't buy into the extra cost of the QO panels these days. Leviton has the high-tech niche, but as far as I'm aware, there hasn't been a huge clamor for their new panels. Where will they be in 20 years, who knows. I'm personally an Eaton fan myself, but in the end, you can't go wrong.

I think a 200A panel is likely overkill unless you really need that many spaces. I'm sure a 100A 30 space board would give you more than enough expansion.

Similarly, between 100A and more, 100A is a LOT, and you'd likely want to keep high load items in your main panel anyway. Usually a 60A sub is more than enough.
 
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Old 06-14-24, 05:31 PM
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Square D Homeline is a good balance of cost and quality. Leviton is just a fancy new kid on the block with a shiny new paint color. I would like to see how they are in about 10 years.

My preferred panel/breaker brand is Siemens. You can get them everywhere, they are also a great balance of cost and quality. I also like to keep the panels in a house of the same brand for breaker compatibility between panels.
 
 

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