Can Subpanel Total Breaker Amperage Exceed Main Subpanel Breaker Rating? - Electrical - DIY Chatroom Home Improvement Forum
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Old 12-03-2009, 08:26 AM   #1
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Can subpanel total breaker amperage exceed main subpanel breaker rating?


I have a 30 amp subpanel on 10-3 wire....protected by 30 amp bipole at main 200 amp service panel.

The sub panel is rated for 70 amps and has 2 slots that can accomodate 4 circuits using tandem breakers. I'm really not running much in the basement, but for sake of ease of wiring want to use a 20 amp tandem and 15 amp tandem. All basement wiring is 12-2. As I understand this, the 12 wire is protected by the subpanel breakers and the 10 wire protected by the main 30 amp breaker, so at no time is any circuit overloaded.....

SO....is this acceptable? Is there ever a limit to the number of branch circuits off of a subpanel?
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Old 12-03-2009, 08:31 AM   #2
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The only limit would be the amount of breakers that the panel is listed for use with.

The feeder to the subpanel should be sized appropriately, based on the loads.
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Old 12-03-2009, 08:34 AM   #3
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You can technically have as many circuits as you want - as long as you stay within MFG ratings for the panel
But if you add too many then you risk tripping the breaker for the sub all the time
Best way is to calculate the load & do not add more load then the sub will handle



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Old 12-03-2009, 08:41 AM   #4
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Quote:
Originally Posted by Scuba_Dave View Post
You can technically have as many circuits as you want - as long as you stay within MFG ratings for the panel
But if you add too many then you risk tripping the breaker for the sub all the time
Best way is to calculate the load & do not add more load then the sub will handle
I have not done a true calculation, but only because it seems unnecessary based on the following:

The continuous lode is virtually nil....one 20 amp circuit would run a 15 amp treadmill and 15 amp staitmaster, one would power a workbench with very little work done at it , one 15 amp will power about ten 60 watt can lights and the remaining will be a wall recepticle circuit...tv and a couple lamps.

Thanks so much for the fast response......and great advice!!!
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Old 12-03-2009, 09:11 AM   #5
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A lot of garages as small shops have lots of high power tools on a small sub
But since one person is opnly using one machine at a time no problem
I have (way) over 850a of breakers in subs/main panels w/200a Main breaker
I can't remember the last time I have tripped a breaker due to load
Possibly years
I go by what I might have one during a party/get together
Lights, stereo, TV, crock pots etc
That's when you will trip a breaker....not during every day use (normally)



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