200 Amp main

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  #1  
Old 07-07-02, 11:23 AM
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kpell
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200 Amp main

I was noticing in a post about a 30A main breaker down below(on a previous question) and WG said that the main breaker is supposed to = the sum of all the others? well I think that is what it said, I may be mistaken, if so I apologize. My question is that I have a 200a main, I was told I could put up to 200A(worth of breakers) on each leg, is this true? I assumed so because you are not going to be using all of your outlets at one time. For instance I have a 50A range breaker, 40A ac, 30 A dryer, and 11 20A circuits, if I add all this up it ='s 240A is this correct? also if I can put 200 A on each leg, on the DPST breakers for ex 50 A range, is this counted as 25A on each leg??? or is this 50A on each leg? Thanks for your responses. I hope this makes sense, if not just ask and I'll see if I can explain it better.

KP
 
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  #2  
Old 07-07-02, 12:47 PM
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Wgoodrich
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A panel must be rated equal to the maximum load that can be applied. To discover the load of a dwelling you would perform a demand load calculation. This demand load calculation would dictate the minimum service entrance conductor and main breaker size required to serve that structure. The demand load calculation gives credit for what is called diversification. If a main service panel is with a main breaker that would limit the load that can be applied to the service entrance conductor then the total amp rating of each branch circuit breaker is unlimited.

If you have a panel that is without a main breaker such as a sub panel then the breaker protecting the feeder serving that subpanel would protect that feeder and panel from exceeding their amp ratings.

When you are talking of using the 6 disconnect rule using a panel with a limit of 6 disconects then the sum of the amp rating of those 6 disconnects are not supposed to exceed the amp rating of the service conductor or the amp rating of the panel they are in. This is an entirely different design than what you have.

The discussion I suspect you are referring to never was resolved leaving one opinion claiming an unlimited load that can be applied ot the serivce entrance conductor and the second opinion claiming the panel to be a lighting and appliance panel demanding the total load to be limited by a main breaker.

In you case you have the main breaker and the branch circuit loads can not pull more than the amp rating of that main breker. Therefore you could have an added load of all you branch circuit breakers to be 10 times the amp rating of the main breaker your main breker will limit the maximum load that can be carried by your panel.

Hope this helps

Wg
 
  #3  
Old 07-07-02, 01:35 PM
J
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There are several points, most of which Wg has covered. Here's a summary:
  • The sum of the breakers not exceeding the main does not apply to you.
  • You can in fact have more than 200 amps worth of breakers on each leg -- in most situations, adding up numbers on breakers is a completely meaningless exercise.
  • I hope you know that a "leg" does not equate to the breakers on one side of your panel.
  • A 240-volt breaker counts as a load on both legs, even though it is on one side of your panel. A 50-amp 240-volt breaker is 50 amps on each leg, not 25 amps on each leg.
  • I can't get 240 from your list of numbers (50, 40, 30, and eleven 20s) no matter how I add them. Doesn't matter anyway, however, since as I've already said, this addition is meaningless.
 
  #4  
Old 07-07-02, 01:53 PM
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kpell
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I understand the 200 amp and my main limiting my house to that amperage, what I was referring to was does it matter how many breakers and whatever the size in the pannel for instance, 200A main, 20 20A circuits(this is not practicle in a normal house because of ac, range, ect) that = 400A total, but the main is only rated for 200A so that is all the main will let the house use/pull. I was just wondering I saw it on one of the forums it said a general rule of thumb was to balance the load and for ex if you had a 200A main you could put up to 200A (worth of breakers) on each buss. (in all practical terms a house can not use any more than the main is rated for)(200A) but there is 400A worth of breakers. I didn't understand then nor do I Now. BTW I figured my load calculation and it was 127A so the 200A service is more than enough with enough to supply my shop/storage bldg when I get it built. I don't know if this(about the 200A on each leg as a rule of thumb) was correct or not. My circuits are very underloaded but with 3 kitchen circuits(20A each), 1 bathroom circuit(GFCI 20A), 4 garage circuits(GFCI 20A Each), 2 Bedroom circuits(AFCI breakers 20 A each) 1 outside circuit(GFCI and Lighting 20 Amp), two general lighting circuits(20A each) and 1 living area circuit(20A) along with 1 AC(40A), 1 Range(50A), 1 Dryer(30A), if you add these all up you get 14 (20A), 1 (30A), 1 (40A), 1 (50A), that equals 400A worth of breakers. Is this correct??? That's the only reason I was concerned, was because of so many breakers and only 200A main. And the calculation comes up to be 127A. My house is pretty small 3 bdrm, 1 bath, and I have underloaded most of the circuits but with all the requirements about the kitchen, bath, garage, ac, range, dryer. that equals alone over 200A without even adding in the bedrooms, lights, ect. This is the only reason I was concerned. something just didn't look right. Please post back and thanks WG for the quick response.

KP
 
  #5  
Old 07-07-02, 02:01 PM
J
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does it matter how many breakers and whatever the size in the panel?
No, it does not matter at all (except for the NEC limit of 42 breakers slots in one panel).

You should also understand that your 200-amp main is 200 amps at 240 volts, which can provide 400 amps of power at 120 volts. Furthermore, it is assumed and certainly true that not all of your circuits are being used at full capacity at the same time. This would be virtually impossible.

So there is nothing to prevent you from having 5000 amps of breakers in your panel (although this would be unusual). As Wg said, the demand load calculation is the only thing that counts, and the demand load calculation does not consider what breakers are in your panel, only what loads are in your house.

Once again, do not concern yourself over the number and size of the breakers in your panel. It means nothing.

P.S. Even if you were to add the breakers, you cannot add 120-volt breakers to 240-volt breakers. That's adding apples and oranges. So if you add up 14 20-amp breakers, you get 280 amps of 120 volts. Then add up your three 240-volt loads (30+40+50), you get 120 amps of 240 volts. You'd have to double the 240-volt total to 240 amps before you added it to the 240 amps of 120-volt loads. That adds up to 480 amps of 120-volt load, compared to your panel capacity of 400 amps of 120-volt load. So even if you could conspire to load up every circuit to the maximum at the exact same time, you'd still only be slightly over the main breaker's capacity.

As Wg says, hope this helps.
 
  #6  
Old 07-07-02, 02:03 PM
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kpell
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John I guess we were writing our messages at the same time, because when I replied to the post WG's post was the only one there. I guess I had a Brain FAR* when adding, it should have been 340 from the numbers I gave in the first message (11 20A)220+50+40+30 = 340 not 240. DUUUHHHHH my mistake. Anyway what you said cleared up things I think....... And by the way the correct breakers for my house are in the post above this one. I had to pull out my wiring diagram to see how many 20's there were. Thanks again for the quick response.

Regards

KP
 
  #7  
Old 07-07-02, 02:08 PM
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kpell
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John, Well I guess it happened again(writing at the same time) what you said made perfect sense to me now. And I thought it didn't matter about the number of breakers. I guess I was just confused about the double your service size for breakers, or maybe I just read it wrong on one of the other forums, anyways, it's all cleared up now. Thanks for the quick response, and keep up the good work.

Regards,

KP
 
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