Total circuits in panel

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  #1  
Old 04-07-06, 06:03 PM
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Total circuits in panel

My panel seems very large. It has a breaker at the top that has 225 on the switch. I assume that this is a 225 amp breaker and controls all of the power to the panel.

Does this mean that the sum of the amps on all of the breakers in the box should be less than or equal to 225?

Here's what I have:
42 spaces in the panel - 40 are used

1 - 220V 50A
2 - 220V 30A
8 - 120V 15A
26 - 120V 20A

These add up to 750A.
Is this normal / correct?
 
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  #2  
Old 04-07-06, 06:27 PM
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Yes, this is normal.

It may seem strange but what is being used is the principle of "Load Factoring" which simply stated means that you will never fully load every circuit in your house at the same time.

For example, a bathroom is required to be served by a 20A circuit but how often is the blow dryer used at the same time as every other electrical item in your house.

You may have a 20A circuit in your bedroom but counting a table lamp, electric clock and an electric blanket you may only have a real load of less than 5A. How often are you in bed with the light and blanket on while someone is cooking a seven-course meal in the kitchen, your entire home-entertainment center is running and all of the house lights are on?

It is this way with most of your circuits.
 
  #3  
Old 04-07-06, 06:52 PM
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Thanks! This makes me feel better.
 
  #4  
Old 04-07-06, 08:41 PM
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Btw, they add up to "only" 400A.

If the actual load load ever goes over 225A for too long or by too much, the 225A breaker will trip. Basically, this never happens.

I think the only times I've actualy seen tripped service breakers, there was a bad short and branch breaker tripped also - pretty amazing considering how people stuff their boxes full of circuits.
 
  #5  
Old 04-07-06, 09:19 PM
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>>Btw, they add up to "only" 400A.<<

I don't understand. Isn't it calculated as follows:

1 - 220V 50A = 50
2 - 220V 30A = 60
8 - 120V 15A = 120
26 - 120V 20A = 520

Total 750
 
  #6  
Old 04-07-06, 10:31 PM
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Nope, they only add up to 400.

You have a mix of 120 volt and 240 volt circuits. The incoming power is 240/120 volts on three wires, two so-called "hot" wires and a "neutral" wire. Between the two hot wires the voltage is (approximately) 240 volts and between the neutral wire and either of the two hot wires the voltage is (again, approximately) 120 volts.

Because of this system, the 120 volt circuits are (approximately) "balanced" with half of the circuits being connected from one hot wire through the load (usage device) and back to the neutral wire with the other half of the 120 volt circuits being connected to the other hot wire in the same manner.

In effect this makes two 120 volt circuits (connected to the two hot leads) into a series-type circuit. If the two 120 volt circuits in the example have the same exact load, i.e. the same amperage draw, then no current will flow in the neutral lead.

Two 120 volt circuits, each rated for a maximum of 20 amperes, will only "draw" a maximum of 20 amperes at 240 volts when connected in the series arrangement I have described. Therefore when you have two circuit breakers, each supplied by its own individual hot wire, you need to add the two together and then divide by two.
 
  #7  
Old 04-07-06, 11:14 PM
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> 1 - 240V 50A = 50
> 2 - 240V 30A = 60

Correct.

> 8 - 120V 15A = 120
> 26 - 120V 20A = 520

No. You add up the two halves separately and use the larger of the two.

A "half" is every other breaker pair left and right.

So you add the odd spaces 1,3,5,7,9,11,13,15,17,19,21,23, ...
and you add the even spaces 2,4,6,8,10,12,14,16,18,20,22,24, ...

(Double-pole "240V" breakers add the same amount to both halves so its easier to add them afterward.)

Your actual number might be 420A or even 460A, but it won't be anywhere near 750A.

Regardless, your dp breakers are always oversized to at least 125% of the actual load, so you could count them at 80% or less.
Dryer? Water heater? A/C? Usually around 20A but have a 30A breaker.
Stove/range/oven? 40A or less, I'd pretty much guarantee it.
I'm sure the same goes for many other circuits.
 
  #8  
Old 04-08-06, 08:01 AM
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OK, since they add up to 400, does this mean that I can not use the 2 empty spaces? They are both on the left side of the panel. I don't need them now but it would be good to know.
 
  #9  
Old 04-08-06, 08:09 AM
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Yes, you can use them. The sum of the breakers in your panel means nothing.

What you have to consider is what you want to use them for.

If you are adding circuits because you need a receptacle in a new location or because you want to split a circuit in half then you can surely use them.

However, if you want to use them because you want to add something new, especially something large like a hot tub, then you need to evaluate your service to see if the incoming size (in this case 225) is large enough. Most likely it is, but you still should check for a large load.
 
  #10  
Old 04-08-06, 08:23 AM
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Thanks for the information. I also have another panel with a 200A breaker at the top. It has 4 - 220V breakers (1 is not currently being used and was for a range). The house had an electric or gas range option.

>>evaluate your service to see if the incoming size (in this case 225) is large enough<<

I also have my own transformer in the yard so it will feed only my house. Since I have a transformer and 2 panels, I assume I could add almost anything. Is this correct?
 
  #11  
Old 04-08-06, 08:55 AM
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> Since I have a transformer and 2 panels, I assume I could add almost anything. Is this correct?

Not really. You always have to add up the actual loads. "Almost" is relative.

If you have only 250 kcmil aluminum wire coming in, them you are limited to around 45kVA. Your transformer probably has a similar limit. Is there a two digit number on it?
 
  #12  
Old 04-08-06, 09:05 AM
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One way to think about it is this: you have a 225 amp/240V main. You could think of this as a total of 450 amps at 120 volts.
 
  #13  
Old 04-08-06, 12:48 PM
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Originally Posted by bolide
> Is there a two digit number on it?
It has "15" on the side.

Originally Posted by 594tough
One way to think about it is this: you have a 225 amp/240V main. You could think of this as a total of 450 amps at 120 volts.
This helped.
 
  #14  
Old 04-08-06, 04:38 PM
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> It has "15" on the side.

Yeah, what was I thinking? It's 15kVa. That's typical.
No, you don't have unlimited power. You have 60A, not 225A.
 
  #15  
Old 04-08-06, 04:53 PM
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Originally Posted by bolide
> You have 60A, not 225A.
So, I can only draw 60A at a time? I have 3 AC units which I guess would draw 60A if they were running at the same time according to your previous post. Throw in the electric clothes dryer and that would be over 60A. How would they all work simultaneously?
 
  #16  
Old 04-08-06, 05:14 PM
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I believe that bolide is incorrect.
 
  #17  
Old 04-08-06, 06:08 PM
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don't let the little number fool you

> I believe that bolide is incorrect.

It a 15kVA rating. I know that a 15kVA transformer usually runs five or six houses around here (100A services, gas heat, no central A/C).
 

Last edited by bolide; 04-09-06 at 01:37 PM.
  #18  
Old 04-08-06, 06:23 PM
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Could be "transformer #15 in the neighborhood." Who knows? Who cares?

What's relevant is that the poster has a 225A service. If the utility were foolhardy enough to put a 60A transformer in for a house, then they will upgrade their equipment at their own expense when HDTV burns it up for them.

HDTV, you may use those two spaces in your panel someday if you need to. The question is, how big will the new circuit need to be for the purpose, and will your existing installation be enough for the new load?

Without knowing what the new load is, we can't help you. Rest assured, your 225A service is probably fine with a nearly full 42 space panel, that's not uncommon at all. Those next two spaces will likely be used for a sub-panel, someday.
 
  #19  
Old 04-08-06, 06:41 PM
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Thanks. I see now that it really isn't simple.
 
  #20  
Old 04-08-06, 06:51 PM
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You have no idea.

Service calculations for a house are very difficult, enough so that in general the advice that is given to an electrician sitting for a test on an electrical exam is to check the best guess answer, and return to the question if time permits. There's six main steps, with lots of little potholes in there to trip us up.

If you were to call an electrician out, they would likely just slap an amp-clamp on your service, crank everything up, take a couple of notes on some key appliances, and not trouble themselves with an official "load calculation" because of the effort involved. A good estimate can be had with a little ingenuity as opposed to a lot of math.

If the day comes when you do add a hot tub, or what have you, be sure to have an electrician verify that you do have a sufficient service for the new load. Better to be sure than sorry.
 
  #21  
Old 04-08-06, 07:08 PM
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I will guess that the transformer is actually a 45kVA (sometimes the 4 looks like a 1).
Even if it was a 15kVA, the utility company is permitted by rules that they make themselves, that the transformer can be overloaded for long periods of time, as long as it doesn't fail. You would be surprised with the load diversity on residential circuits, which would allow what the utility gets away with.
Even on commercial circuits, a design based on the NEC from the building side, is met with half the conductor ampacity on the utility supplied side when it is time to splice together.
 
  #22  
Old 04-08-06, 07:11 PM
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If you wanted to do a home demand calculation, I would suggest you visit http://www.selfhelpandmore.com/homew...calc/index.htm
 
  #23  
Old 04-08-06, 08:43 PM
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Originally Posted by Rocky Mountain
Could be "transformer #15 in the neighborhood." Who knows? Who cares?
You know what? Just go away. Your attitude is contrary to the educational function of this forum.
I care. I want to know more. If you are content with what you know, fine. Don't interfere with those who are here to learn.


Transformers are marked 5, 10, 15, 25, 35, 45, depending on their kVA rating.



> If the utility were foolhardy enough to put a 60A transformer in for a house,

Foolhardy? I assure you that this is very common!

I think Ron is right: either it really is 15 and runs overloaded from time to time, or it is 45 kVA with a defective digit 4.

My guess is 15kVA.
 
  #24  
Old 04-08-06, 09:50 PM
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Originally Posted by HandyRon
I will guess that the transformer is actually a 45kVA (sometimes the 4 looks like a 1).
Even if it was a 15kVA, the utility company is permitted by rules that they make themselves, ...
The transformer has been in place for about 3 years (age of house) and I've lived here for 2. I believe the 1 is really a 1. I'll check again tomorrow in the daylight.

If this is a 15, should I have problems? Sometimes I do see lights dim when one of the AC units comes on. I'm not sure if another unit is running when this occurs or not. As stated previously, the house has 3 AC units.

The house was wired for a shop and has a 220V circuit for a welder and a 220V circuit for an air compressor (both are currently off). Assuming I had these, would I have problems regarding the transformer being a 15 instead of a 45?

Also, thanks for the link. It really does seem very complicated.
 
  #25  
Old 04-08-06, 10:28 PM
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> How would they all work simultaneously?
"Overload" the xfrmr.
The 15kVA is a soft number.


> I believe the 1 is really a 1.

Probably.


> If this is a 15, should I have problems?

No. It's not really something to worry about, at least not unless you add a kiln or something.


> Sometimes I do see lights dim when one of the AC units comes on.

Not bad, practically unavoidable without a lot bigger xfrmr.


> the house has 3 AC units.

There's 60A on the hottest days.


> The house was wired for a shop and has a 240V circuit for a welder and a 240V circuit for an air compressor
> (both are currently off). Assuming I had these, would I have problems regarding
> the transformer being a 15 instead of a 45?

Nope. Those are both intermittent loads. So are your clothes dryer, stove, and water heater (unless you never shut off the water).
 

Last edited by bolide; 04-08-06 at 10:42 PM.
  #26  
Old 04-09-06, 08:48 AM
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I would never consider "slapping on an AMP clamp and turning everything on" to arrive at a load calc figure.

There are a number of available calc aids available that allow a correctly done load calc to be completed in a few minutes after obtaining the REQUIRED values that need to be used (Range, dryer, AC, etc. ratings). The computer and software that does this is just as an important a tool as a screwdriver or linesmans pliers. It does take all of 5 or 6 minutes to do with just a calculator, though. And, I did all the calcs on MY license tests before I answered any questions. But, I digress.

Utilities are as varied in how and why they do things as people are in hair styles and color. The 15 could mean anything as not all utilities may use the same markings.

As to the educational value of getting a homeowner worried about the size of their service transformer - I'm a bit lost here. As long as there isn't a voltage issue the transformer isn't anybody's concern but the utility's. If the homeowner can set the incoming feed on fire or blow up the transformer without tripping his main then the utility is on the hook for replacement costs on both sides of the meter. Frequent popping of the transformer's fuse will get their attention as well and would be the likely result of an overload anyway.
 
  #27  
Old 04-09-06, 11:13 AM
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Originally Posted by bolide
You know what? Just go away. Your attitude is contrary to the educational function of this forum.
You know what? I'm all for education. When you start making broad statements that are completely unsubstantiated, and completely a product of your own imagination, and present them as fact, then you are going against education. That irritates me. If the thread had ended before Racraft posted "I believe Bolide is incorrect" then that homeowner could have walked away thinking his transformer was undersized, and who knows what else.

Transformers are marked 5, 10, 15, 25, 35, 45, depending on their kVA rating.
Now you're an expert again? Three posts ago you were asking what the "15" meant. I didn't answer because I don't know.

My point is not to insult you.

My point is that if you're not sure, you should make that clear when you post, for education's sake.

I agree with Uncle Bill about "the educational value of getting a homeowner worried about the size of their service transformer". (I even agree with him that my "amp-clamp" remark was out of line. )

I have, like, seven POCO's in the areas I work, and there is no discernible pattern in how they operate. I would not be so arrogant as to assume I know what a sticker means on a transformer I've never seen, belonging to a POCO I've never worked with.

Venture a guess, it's a free country. But do not make stuff up, state it as fact, and expect no one to say something.
 
  #28  
Old 04-09-06, 01:33 PM
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just the facts, ma'am

Originally Posted by Rocky Mountain
When you start making broad statements that are completely unsubstantiated, and completely a product of your own imagination, and present them as fact
Obviously you are speaking of yourself.
I did no such thing.


> If the thread had ended before Racraft posted "I believe Bolide is incorrect"

That wouldn't have happened.


> Now you're an expert again?
> Three posts ago you were asking what the "15" meant.

Well, I know what the 15 means. I have known for so long that I kind of forgot whether I actually knew.


>My point is that if you're not sure,

I'm sure.


> I agree with Uncle Bill about "the educational value of getting a homeowner
> worried about the size of the service transformer".

The homeowner asked, " Since I have a transformer and 2 panels, I assume I could add almost anything. Is this correct?"


I didn't bring it up.

The answer, though, is that there is a limit to what the transformer can do.


> I would not be so arrogant as to assume I know what a sticker means on a transformer I've never seen,
> belonging to a POCO I've never worked with.

It works this way because NESC requires that on every transformer the kVA capacity shall be legibly and durably marked where visible...


Furthermore, a transformer over 25kVA can supply more that 10,000A fault current.
This rules out using anything larger with normal breakers and panels.
So unless the homeowner has special equipment, his transformer is 25kVA or less.
This rules out 45kVA.

15kVA makes sense for his installation.


> Venture a guess

No reason to. There are plenty of facts to go on in this case.

The 15 means that it is a 15kVA transformer. That's what is. It's not 45 or anything else. Neither is it unlimited or something to worry about.


Could be "transformer #15 in the neighborhood."
Talk about just making stuff up!

No, it is not transformer #15. It should have a longer premises ID or property number stuck on it. It surely has a serial number and perhaps a barcode. The format, size (letter height), and location of those are specific to the manufacturer and/or the poco.

The transformer is 15kVA. Now you know too.
 
  #29  
Old 04-09-06, 01:56 PM
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We have beaten this issue to death and are not making progress. There is much we don't know and much we are supposing. neither of which are good things to do.

I am closing the thread.
 
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