200A Sub Panel From 200A Main Panel!!!!!


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Old 11-18-08, 12:14 PM
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200A Sub Panel From 200A Main Panel!!!!!

Hi yes can someone help me out. I'm not that use to residential work as I am a Industrial Electrical Apprentice.

I would like to know how I can hook up a 200a Sub Panel from a 200a Main Panel. The sub panel is going on the second floor to run a home and the main panel was going to be used in a shop on the bottom floor. Later I changed my mind and left the main panel alone.

The electrician put a 30a breaker in and ran the wire to the sub panel. I have a couple more heaters to hook up along with existing lights, heaters, stove, etc.

So I would like to know:

1. What size of breaker should I use to run the 200a sub panel.

2. What size of wire is needed to run between the breaker in the main panel to the sub panel

Thank You, Steveng1979
 
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Old 11-18-08, 12:32 PM
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The size breaker depends on the load. Best to do a load calculation for the area to be served then use a breaker sized to that and wire sized to the breaker.
 
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Old 11-18-08, 02:58 PM
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200A Sub Panel From 200A Main Panel!!!!!

Is there a certain formula to calculate that.

Anyone have the answer to this please. Can someone tell me what it would be when its filled at 200a capicity.

Thank you, steveng1979
 
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Old 11-18-08, 04:00 PM
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You have to google " Load Demand " calucations that is the only safe legit way to do this when you do the expanding the subpanel so that way you can see how much leeway you have left in the system.

Merci,Marc
 
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Old 11-18-08, 04:50 PM
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Originally Posted by Steveng1979 View Post
Is there a certain formula to calculate that.

Anyone have the answer to this please. Can someone tell me what it would be when its filled at 200a capicity.

Thank you, steveng1979
Well, your can't pull 200A off the main panel and then another 200A from the sub panel.

I'm a bit confused by your question. Please help.
Doug
 
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Old 11-18-08, 04:51 PM
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Because both of these panels are serving the same structure, you may not need a load calculation. The load calculation would only be warranted by the additional load, not by the additional panel.

So you can put a 200-amp breaker in the main panel (if you can find one) and run 3/0 copper (if you have 75 degree terminations).

Now I've told you how. But I will also tell you that it is extremely unlikely that you will want to do it at all. This whole design sounds crazy.
 
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Old 11-18-08, 07:23 PM
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200A Sub Panel From 200A Main Panel!!!!!

OK, sorry to confuse you guys.

The main panel box which the service from the light pole is coming from is a 200a box. There is a 200a sub panel box on the second floor of the building running off a 30a breaker which is in the main panel box.

What I wanted to know was how big of a breaker to use and what size of wire I needed to use to connect the sub panel box to the main panel box?

Hope this is better

Thank you, steveng1979
 
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Old 11-18-08, 08:34 PM
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Originally Posted by Steveng1979 View Post
What I wanted to know was how big of a breaker to use and what size of wire I needed to use to connect the sub panel box to the main panel box?
How many watts or amps do you plan to use from the subpanel? Common sizes are 60A, 100A, 125A, 150A varying in cost and difficulty from pretty easy to pain in the butt.
 
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Old 11-18-08, 08:37 PM
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What I wanted to know was how big of a breaker to use and what size of wire I needed to use to connect the sub panel box to the main panel box?
But you already said it was hooked up didn't you?
There is a 200a sub panel box on the second floor of the building running off a 30a breaker which is in the main panel box.
You see why we may be confused? If you mean you want more then a 30amp max load on the panel then you will need to increase the breaker size in the main panel, and increase the wire size. As has been stated that could be anywhere up to 200a or 40 amps or. 60a .. whatever your expected load will require.
 
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Old 11-18-08, 08:41 PM
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Something's amiss here, and I'm not even an electrician.

You have 200 amp service to the first panel, so your feed wire is probably sized for that rating. If you add another 200 amp panel, you are doubling your capacity without having the ability to feed it unless the cable from your pole is oversized.

Maybe you could have a 100 amp subpanel, but then you would not have more than 100 amps available from the main panel.
 
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Old 11-18-08, 08:52 PM
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I don't know if this is what you asked or not (it's all getting very confusing), but wire protected by a 30-amp breaker requires #10 copper wire. That is independent of what the panel is rated for. A panel rating is just the maximum it can handle, not what you have to wire it for.

I am getting a bit concerned that you may be in over your head. Please don't do anything that you are not sure you can do safely. And don't be sure unless it's really true.
 
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Old 11-19-08, 09:36 AM
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Hoping to clarify the situation:

Your main panel is a 200A panel, presumably with the service entrance meeting the 200A requirements (wire size, meter pan, etc). So you have a 200A service.

Now, you need (have) a subpanel. The rating on the subpanel doesn't really matter as long as you don't exceed it. Many people use a panel rated at 100A, but only use a 60A breaker and wire rated to 60A. The subpanel in this case would be able to provide up to 60A (@ 240v) of power.

In your case, it sounds like a 200A panel was chosen to allow a large number of circuits to be added in the future. Though you have 24 or 32 slots for breakers, you're currently limited to 30A total, based on the 30A breaker and probably 10ga wire.

---

So now, on to what you want to do.

Your subpanel is probably adequately sized for anything you want to do. The first question is what do you want to run off of it? If all you need is a couple 15A circuits, each with a 100w lightbulb attached, your 30A setup is quite sufficient. If you want to run an AC, hot tub, sauna, etc, you need to upgrade the wire and the breaker to the subpanel.

Make a list of everything you want to run off your subpanel (current and future). You'll need the amperage and voltage (120v or 240v) of everything. This will help you determine if you need a 30A, 60A, 100A, etc. subpanel setup.

Post back with more details and I'm sure people here will be able to help more.
 
 

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