Adding a sub panel

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Old 08-09-09, 12:10 AM
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Adding a sub panel

My house has a 200 amp service with an exterior cutoff panel adjacent to the meter base. Breaker 1 is 70 amps for exterior AC/Heating circuits. Breaker 2 is 90 amps and controls the interior load center/subpanel.

According to the 2002 NEC load calc, I currently require 80 amps available from the existing 90 being fed to the interior load center.

I got an electrical permit (based on 2002 NEC), and am starting to wire an addition which includes master bedroom, bathroom, laundry, kitchen expansion. Can I add a third breaker to the exterior cutoff panel/load center and run a new SER, 4 wire cable cable to a new subpanel? The addition needs approx 40 amps. Should I use #4 copper for a 50' run through a crawl space?
 
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Old 08-09-09, 05:58 AM
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Your plan is ok however, I would personally use a 60 amp breaker(same price as a 40), use some #6 copper or #4 aluminum, and get a 100 amp main lug 20 space panel.
 
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Old 08-11-09, 07:26 PM
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Would it be valid for the OP to use a 90A, 70A, and 60A breaker on a 200A service? (220A total) I think that's why a 40A breaker was originally proposed for the subpanel (90+70+40 = 200A)

Since the 70A breaker is for HVAC, maybe it has different rules...?
 
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Old 08-11-09, 08:30 PM
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Originally Posted by Zorfdt View Post
Would it be valid for the OP to use a 90A, 70A, and 60A breaker on a 200A service? (220A total) I think that's why a 40A breaker was originally proposed for the subpanel (90+70+40 = 200A)

Since the 70A breaker is for HVAC, maybe it has different rules...?
The rating of the branch circuits added together has nothing to do with the rating of the main breaker. You can literally have 40 (or even more), 20 amp circuits on a single 200 amp panel. In fact it is done all the time.
 
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Old 08-13-09, 10:48 AM
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Ahh - brain fart.

Thanks Tony - you're right. Same thing with the breakers in any panel. I was envisioning 3 breakers without a main 200A breaker which is protecting the service entrance.

Got it - thanks!
 
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