Adding a new sub panel in basement

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Old 12-15-09, 08:01 AM
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Adding a new sub panel in basement

Currently working to finish the basement.
End result - will need @ 6 -20A circuits (Bath, Micro, Frig/Freezer, Lights, Receptacles, Future)to satify needs and allow for future what if's.

Total length of any branch or feeder run from panel to basement would be @ 90 ft.

The main servcie panel is 200A and does have room for the 6 breakers, but would be nearly full.

Is it better to run 3 - 12/3 cables as branch circuits directly to the basement OR to place a sub-panel in the basement?

If a sub panel is recommended - what sub panel size (100 A?), what breaker size at the main panel would be needed to handle the 6- 20A circuits running from the sub and what feeder cable size would be needed at that distance with those loads?
 
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Old 12-15-09, 08:52 AM
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Originally Posted by iowegian View Post
Total length of any branch or feeder run from panel to basement would be @ 90 ft.
That's right about on the break even point for a subpanel. The subpanel will probably be a bit more expensive, but is perhaps better to route just one cable instead of 6+. I would probably lean toward the subpanel route as long as you have a good spot for one.

If a sub panel is recommended - what sub panel size
I would use a 100A 12 space main lugs panel with a 60A feeder. This should be plenty for the loads listed. The feeder would be #6-3g NM-B cable, the breaker in the main panel would be double-pole 60A. The subpanel will require an add-on ground bar kit.

Appx how many sq. ft. will the finished area be?

P.S. The 12/3 idea will not be all that useful because you'll need AFCI breakers for all of the circuits except kitchen and bath. AFCI is not compatible with MWBCs unless you get a really expensive breaker.
 
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Old 12-15-09, 09:04 AM
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Approx finished area would be 1300 sq. ft.

So standard breakers aren't enough anymore even if Bath/Kitchen are GFCI'd as required?
 
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Old 12-15-09, 09:19 AM
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Kitchen and bath receptacles require GFCI. Outlets (incl. receptacles, lights, and smoke detectors) in any living spaces like bedroom, living room, den, etc require AFCI breakers, it's been phased in since 2002 code.

Hmm, 1300 sq. ft. -- will this have a full kitchen? Maybe 60A is a tad low. Could you describe the intended loads a little better? Home theater, office, heaters anything like that?
 
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Old 12-15-09, 09:32 AM
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Propsed loads would include -
Frig/Freezer Combo
Microwave
HDTV w/ Home theater sound system
Bathroom - Full w/ venting
Lights and Receptacles (largest possible receptacle load would be a treadmill and/or small space heater)

About the AFCI if all done via branches - So then every Standard Square-D QO 20A breaker at Home Depot is then meant as a replacement rather than new-construction? Or does the AFCI only apply to using 12/3 and not 12/2's
 
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Old 12-15-09, 09:51 AM
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Originally Posted by iowegian View Post
Propsed loads would include
Okay that sounds good. I was concerned there could be some bigger items.

So then every Standard Square-D QO 20A breaker at Home Depot is then meant as a replacement rather than new-construction?
No there are plenty of applications for standard breakers like bathroom, kitchen, built-in appliances, etc. The AFCI requirement applies to outlets in living areas.
 
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Old 12-15-09, 10:00 AM
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So since I'll have to use AFCI for the living areas per current code, just a matter of are they in the main or the sub (right)?
And the added expense of trying to find an AFCI for a MWBC if kept in the main.
 
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Old 12-15-09, 10:13 AM
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Originally Posted by iowegian View Post
So since I'll have to use AFCI for the living areas per current code, just a matter of are they in the main or the sub (right)?
Right.

And the added expense of trying to find an AFCI for a MWBC if kept in the main.
If you run the circuits from the main panel, I would use a 12-2g cable for each circuit and forget the MWBC idea. I think only Cutler makes a 2 pole AFCI breaker and it's like $200, far greater expense than anything you would save with an MWBC.
 
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Old 12-15-09, 12:21 PM
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Will go the sub-panel route.
Should 60A not be enough, what would be the max A's that it could be bumped up to and still use #6-3g NM-B cable at that distance OR what whout be the next Amperage/Feeder cable size combination that would be needed to go up a step.
 

Last edited by iowegian; 12-15-09 at 12:36 PM.
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Old 12-15-09, 12:37 PM
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60A is the max for #6-3g. If you wanted to go larger I could work out some conductor sizes.

If it's practical to do so you could install a 1-1/4" conduit and pull individual conductors instead of cable. That allows you to upsize in the future if necessary.
 
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Old 12-15-09, 12:50 PM
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If you could work out what the next larger combo would be that would be great.
Trying to avoid conduit as much as possible
 
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Old 12-15-09, 02:35 PM
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Once you get above #6, you will often find cables in type SER (service-entrance) instead of NM-B. These figures apply to either type of cable. You will also find that the cable has a reduced ground and sometimes a reduced neutral (e.g. #2-2-4-8); the size I'm listing applies to the largest hot conductors.

70A breaker = #4 copper or #3 aluminum

80A: #3 copper or #2 alum

90A: #3 copper or #1 alum

100A: #2 copper or #1/0 alum
 
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