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08-10-2006, 01:22 PM   #1
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## Breaker panel capacity

It is my understanding that if the Breaker box is 200 amps, that technically, you can have up to 200 amps PER LEG, for a total of 400 amps in one box, as long as you keep the box balanced.

Can anyone address this?

08-10-2006, 02:01 PM   #2
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This question usually gets a conversation going even among professionals. But I think that the way you worded your statement if fundimentally correct.

If you have a panel feed with 200 amps at 240 volts, then you could have up to 200 amps at 120 volts on each leg. Except that you cannot load the panel beyond 80 percent so it would be 160 amps not 200.

Another way to look at it is by converting the voltage and amperage into wattage.

160 A x 240 V = 38400 W That is 80 percent of 200 amps at 240 volts.

320 A x 120 V = 38400 W That is 80 percent of 400 amps at 120 volts.

Note that the total wattage is the same.

 08-10-2006, 05:37 PM #3 Licensed Electrical Cont.     Join Date: Feb 2004 Location: NY State Posts: 7,758 Rewards Points: 1,866 Like JW said. A watt is a watt. Amperage moves around according to voltage. Your 200 amp service is NOT 400 amps for both legs. It is 200 amps @ 240v. __________________ Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost.

 08-10-2006, 08:13 PM #4 Member     Join Date: Mar 2005 Location: Welland, Ontario Posts: 12,598 Rewards Points: 11,988 Blog Entries: 11 And all this has NOTHING to do with adding up the numbers on all the breaker handles which most home owners seem to want to do.
 08-11-2006, 03:41 PM #5 Electrical contractor     Join Date: Mar 2006 Location: Philadelphia area Posts: 44 Rewards Points: 25 80% is CONTINUOUS load rating [more than 4 hours]
 08-11-2006, 04:02 PM #6 Member   Join Date: Mar 2006 Posts: 682 Rewards Points: 500 a continuous load is three hours or more. And loading of panels is not the same as loading of branch circuits.
 08-14-2006, 04:42 PM #7 Licensed Electrical Cont.     Join Date: Feb 2004 Location: NY State Posts: 7,758 Rewards Points: 1,866 1 2 3 4 5 __________________ Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost. Last edited by Speedy Petey; 11-20-2007 at 03:17 PM. Reason: Spam gone
 08-15-2006, 11:59 AM #8 Average Joe   Join Date: Aug 2006 Posts: 55 Rewards Points: 79 When I piece everything together, it makes sense! Thanks to all for responding! Dave
 11-20-2007, 02:12 PM #9 Newbie   Join Date: Nov 2007 Posts: 1 Rewards Points: 10 If it has nothing to do with adding up the breakers then what does it relate to? I realize the load should be something less than the breaker size and the breaker is a safety device. It would therefore be possible to run each branch circuit at 85% and exceed design. It should however give a good estimate. If the breakers total up to the 80% watermark certainly I would think you wouldn't want to go any higher???
11-20-2007, 02:14 PM   #10
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Quote:
 It is my understanding that if the Breaker box is 200 amps, that technically, you can have up to 200 amps PER LEG
.......Yes

Edited to clarify,..... although you can have the 200 amps on each leg you will not have 400 amps....unless you add up the total number of amps allowed on each leg and there would be no reason for doing that.

Last edited by 220/221; 11-20-2007 at 04:26 PM.

11-20-2007, 03:32 PM   #11
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Quote:
 Originally Posted by Rze It is my understanding that if the Breaker box is 200 amps, that technically, you can have up to 200 amps PER LEG, for a total of 400 amps in one box, as long as you keep the box balanced. Can anyone address this?
This is incorrect. If you have a 200 amp service, that is your max load. Your 200 amp service should not be exceeded by your total branch circuit calculated load.
Adding the denominations of breakers has nothing to do with it, since a 20 amp breaker may only be hooked to lets say a washing machine which might draw 12 amps and be on a 20 amp breaker but is not even used continuously. Your load calculations are based on demand factors. You add the washer, lighting , general receptacle and small appliance receptacle loads all of those together. The first 25 amps of those loads (3000 voltamperes) will be calculated at 100%. The remainder will be calculated at only 35% for this example. This is just an example of course. There are more calculations involved for range, furnace, etc etc. NEC article 220 explains the rest if you can understand Greek and have a codebook handy. Oh yeah and no more than 42 breakers per panel.

It is considered good practice to balance your loads out on each side of the panel. I hope this helps

Last edited by RichyL; 11-20-2007 at 03:46 PM. Reason: clarification

 11-20-2007, 04:41 PM #12 Electrician philosopher   Join Date: Aug 2007 Location: Lilburn, GA Posts: 838 Rewards Points: 500 42 breaker limit goes away in '08. Just in time for house panels filled with HOT AFCI's.
11-20-2007, 05:24 PM   #13
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Quote:
 Originally Posted by Andy in ATL 42 breaker limit goes away in '08. Just in time for house panels filled with HOT AFCI's.
Are you referring to the combination type arc faults? Will they just be required for bedrooms? I hope so, those breakers are so expensive. And how many breakers will be allowed in the new panels in 08. I guess in the next addition of the NEC we'll have to erect perimeter fences around our panels with fire-rated emergency opening doors

 11-20-2007, 05:36 PM #14 Electrician philosopher   Join Date: Aug 2007 Location: Lilburn, GA Posts: 838 Rewards Points: 500 Wait til you get a load of this.... '08 NEC 210.12(B) Dwelling units. All 12V, single phase, 15- and 20-ampere branch circuits supplying outlets installed in dwelling unit family rooms, living rooms, parlors, libraries, dens, bedrooms, sunrooms, recreation rooms, closets, hallways, or similiar rooms or areas shall be protected by a listed arc-fault circuit interrupter, combination-type, installed to provide protection of the branch circuit. So tell me RichyL...Is a switch an outlet?
11-20-2007, 05:57 PM   #15
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Quote:
 Originally Posted by Andy in ATL Wait til you get a load of this.... '08 NEC 210.12(B) Dwelling units. All 12V, single phase, 15- and 20-ampere branch circuits supplying outlets installed in dwelling unit family rooms, living rooms, parlors, libraries, dens, bedrooms, sunrooms, recreation rooms, closets, hallways, or similiar rooms or areas shall be protected by a listed arc-fault circuit interrupter, combination-type, installed to provide protection of the branch circuit. So tell me RichyL...Is a switch an outlet?
Lmao....Hell no. Closet? whatchatalkin bout willis, thats my hide n seek room. I bet half the states dont adopt the 08 for quite a while, if at all. Makes you wonder if the NEC board is sleeping with the afci manufacturers, Seems a little excessive imo.

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