Subpanel Installation Advice


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Old 12-12-14, 08:37 PM
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Subpanel Installation Advice Needed

I am finishing a basement and I need to know what size subpanel I should use. Service at the main panel is 200 amps and all 30 slots are full. The load calculation for the house is 110 amps.
The main room of the basement will have 23 can lights rated at 65 watts max and 19 duplex electrical outlets.
I thought I would dedicate one 20 amp circuit for the fridge outlet, one 20 amp circuit for a countertop microwave outlet and one 20 amp circuit for a coffee maker/toaster/etc. That leaves me 16 “convenience” duplex receptacles around the room that I thought I would feed with two 15 amp circuits. Since at least one of these 16 receptacles will be used for a surge protected six way for the TV and entertainment system, I thought I would put 8 receptacles on each of the two 15 amp circuits to better distribute the load.
Although, technically, I could put all 23 cans on one 15 amp circuit, I thought I would use two.
In addition to this, there will also be a bathroom with two can lights, an over mirror light, a vent fan and a duplex receptacle. I read somewhere that one 20 amp circuit is acceptable for this, but I thought it might be best to put the lights and vent fan on a 15 amp circuit and the outlet on its own 20 amp circuit.
So here is my question. What size subpanel should I use? I am considering a QO 100 Amp 8 Space 16 circuit subpanel, fed from the main with a double pole 60 amp breaker. Is 60 amps enough or do I need more? The only unknown load is the 16 “convenience” outlets around the main room that I’m not sure how to account for. Also, I will be displacing two circuits in the main panel to accommodate the double pole breaker required to feed the subpanel. Those displaced circuits will have to go in the subpanel, as well (this would total 11 circuits in the subpanel).
Please let me know if my logic makes sense and if the subpanel and amp feed to it is acceptable.
Thanks,
Steve
 

Last edited by homerepairdude; 12-12-14 at 09:00 PM.
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Old 12-12-14, 09:05 PM
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Fridge would be fine on a 15 amp circuit. Two 20 amp circuits for counter top would be a good idea, as would splitting up all of the lighting to two circuits. Bathroom receptacle should be on its own 20 amp circuit. If you are going to have a big TV/audio system it might be a good idea to put that one its own as well. The convenience receptacles I like to keep down to no more than 10 duplex per 15 amp circuit.

All the circuits I mentioned above, with the exception of the bathroom GFCI, will need to be AFCI protected per 2014 code. This means they will take a full space of that 8 space/16 circuit panel. If you want to leave some room for other circuits you might want a bigger panel.

A 60 amp feeder would likely be large enough. You options might depend on where the sub panel is and what wiring method you can use to feed it. If it is going right next to the main panel I would just feed it with 100 amps.
 
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Old 12-13-14, 09:36 AM
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I am considering a QO 100 Amp 8 Space 16 circuit subpanel, fed from the main with a double pole 60 amp breaker.
What version of the NEC is your community on? Even if you aren't required to have these circuits AFCI protected, have you checked the price of QO series tandem breakers? It's outrageous! One mistake many people make when adding a subpanel is not adding enough full size spaces. I cannot even count the times I have seen subpanels replaced because more circuits were needed. I would suggest a subpanel with 16 to 20 full size spaces.
 
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Old 12-13-14, 04:34 PM
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Thank you both for your advice. I think I'll go with a double pole 100 amp feed from the main to the sub. It's probably overkill, but I'd rather have a little more than too little. The sub will be right next to the main, so why not?

Point well made regarding the cost of QO tandem breakers and the amount of circuits in the sub. I know QO is highly touted, but I didn't realize (until I checked) that the prices were that outrageous. I'm not restricted on space, so I'll look for a larger sub with more full size spaces.

The main is a Square D Homeline. What's your opinion of Homeline. I've heard good and bad. I don't know if it matters, but I was thinking of matching the sub with the main. Homeline breakers also seem to a lot less expensive, as well.

Thanks,

Steve
 
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Old 12-13-14, 04:43 PM
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Homeline is on par with other panel manufactures less expensive lines. (IE not QO or Cuttler Hammer CH) I like Homeline panels and just happened to install one yesterday. I also like to use the same brand panel as the other panel(s) in a building, keeps things consistent and professional looking.

I think a 100 amp feed is a good call. You need to use #4 copper or #2 Aluminum.
 

Last edited by Tolyn Ironhand; 12-13-14 at 04:59 PM.
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Old 12-13-14, 07:30 PM
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The main is a Square D Homeline. What's your opinion of Homeline.
Not my favorite, but I would also use another Homeline since that is what you have for your main. Homeline is a competitively priced aluminum bus panel for the residential market to compete with other less expensive aluminum bus panels. The panel and breakers carry a 10 year warranty.
 
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Old 12-14-14, 12:00 PM
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The aluminum bus on the less expensive panels was the reason I was looking at QO. But then again, if the main has an aluminum buss, why upgrade the sub?

Thanks again.
Steve
 
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Old 12-14-14, 04:23 PM
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The aluminum bus on the less expensive panels was the reason I was looking at QO. But then again, if the main has an aluminum buss, why upgrade the sub?
Good point. You don't have to go to the expense of a Square D QO series panel to get copper bus. Both Siemens and Cutler-Hammer BR series offers copper bus at a very competitive upcharge on most of their panels in addition to standard aluminum bus.
 
 

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