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Thanks in advance for advice! I just finished framing my basement and am moving on to electrical. Hoping for advice on the subpanel. Main 200A Eaton panel is in the garage. I'll need to run cable up into the attic, cross about half the house, then down into the utility room in the basement. I haven't measured this yet, but I'm guessing about 80' of cable. The basement is about 2200 sf with 2 bedrooms, 2 bathrooms, a wet bar, living room, workout room, utility closet, and large storage area. I haven't finished my drawings yet, but I'm guessing about 15 circuits if I do separate lights and receptacles in most rooms. Mini-fridge, small countertop microwave, and a treadmill are the only notable loads. Everything else will be pretty standard: 2 bathroom GFCIs, bar GFCIs, and a bunch of lighting and receptacle circuits. No heat, range, freezer, AC, etc.

My research is telling me it's much better to "go big" and overdo these things, so I was thinking of installing a 100 amp panel with 24 spaces (48 circuits) from Square D, using a 100 amp breaker at the main panel, and running 1-0/1-0/1-0/2 SER since I'll be crossing insulation in the attic. I also understand the subpanel will need a ground bar installed. Is this overkill for my situation? It's a large basement, but without a fridge, range, baseboard heaters, etc., am I overdoing it? I definitely don't want to run out of space down the road, but I also don't want to spend $2+ per foot on cable (plus wrestle that monster) if half that would do the job.

Anyone have opinions or advice for me? Also, do I sound like I know what I'm talking about enough to attempt this on my own and live to tell about it? :-) Thanks!

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    I don’t have a lot of time right now but I would suggest a panel with more spaces , get it wired prior to the 2020 code taking effect or you will be finding out about the cost of GFCI protection in a basement. These breakers take full sized slots but I agree go big. – Ed Beal Mar 30 at 0:26
  • How big is your existing panel, spaces-wise, and is it CH or BR? – ThreePhaseEel Mar 30 at 0:26
  • I like going big as well but I can't imagine you needing anywhere near 100 amps at 240 for a basement living space. No major loads. If it where a shop with high HP power tools, compressor, dust collector, etc. I would say go for it, but for this space, as you described it, I'd bet a 60 amp feed would be plenty. You may still want to have a large panel, just to allow for breaker space, but that doesn't mean you have to feed it at it's rating. And Ed Beal is right, that that permitted soon, before 2020 goes into effect in your location...cost will go up substantially. – George Anderson Mar 30 at 0:45
  • If you take advice and get a panel with more spaces it is OK to use a 200A panel as a sub-panel with 100A feeder wire and 100A breaker in your service panel feeding it. The rating of sub-panel is just the maximum allowed feed. – NoSparksPlease Mar 30 at 0:59
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    Thanks for the replies! To answer ThreePhaseEel, current panel is BR with 30 spaces -- all filled right now. The basement is fed by two circuits: one for outlets and lights and one for sump pump, so my plan is to move those circuits to the new subpanel down there and use those two spaces on the main panel for the 100 amp (or 60 amp?) breaker that will feed it. After reading these comments I think I'll buy a 200 amp panel with more spaces. If anyone else has opinions regarding size of panel, breaker, and cable, I'd really appreciate it. I'd like to get this done ASAP during quarantine lol! – IndyGopher Mar 30 at 15:38
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That 1/0 SER is good for 125A, so you might as well use it for all its worth

A 1/0 Al SER cable can handle 120A when landed on 75°C terminations, and we are allowed to round up to 125A by the 240.4(B) "round-up" rule as the next standard breaker size above 120A is 125A. As a result of this, and the fact that a BR2125 is only $10-$15 more than a BR2100, along with the fact that the HOM2448L125PGC is a 125A panel to begin with (there is no 100A version in main lug), there is really no reason to go with anything less, although if you wanted to upsize the panel further, the HOM3060L225PGC is only $15 more. (While you could run a 4/0 Al SER cable, you can't pull more than 125A out of your current panel anyway as the double frame breaker or subfeed lug required for a 200A feed takes up more space in your panel than you can make room for.)

Your grounding is good, but you'll need to remember that you'll need new breakers

While you're good to go on the one thing that often gets people in trouble with subpanels, namely grounding, as long as you keep your neutrals and grounds straight, thanks to the fact both panels mentioned above come from the factory with ground bars and a ground lug fitted already, you will have to remember that you'll need new Square-D HOMeline breakers for the circuits you're moving to your new panel, instead of being able to reuse the BR breakers you're pulling out of your existing panel.

TORQUE ALL LUGS TO SPEC

There's one more thing you'll need to do in order to ensure a reliable installation. Your panel and breakers will have lug torque specifications labeled/marked on them (in inch pounds), and 110.14(D) in the 2017 NEC requires that you use a torque wrench or torque screwdriver to set the lug setscrews to that torque. Even if your jurisdiction has not adopted the 2017 NEC yet, it's still a good idea anyway, since you don't want your electrical system to lose you the race, now, do you?

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