? sub panel wired from main breaker ?

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Can I legally wire a sub panel from the main breaker of my main panel?
I was planing on having a 200A main service-rated panel in the basement then a 200A non-service-rated panel (i.e. sub-panel or lug panel, without a main breaker) upstairs. I think this will give me a lot of flexiblity as to which branch breakers I put where. The connection for the sub panel would start on the load side of the 200A main breaker of course, if this is even legal.
Also, lets just assume that I've met the requirement allowing me to use my main breaker inside as my means of disconnect and overcurrent device.
(PS. This is all new contruction.)
--wahzoo
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Technically, I believe this is legal. But implementing may be challenging. First question is does your main panel have feed through lugs? If not, you need some way to tap into the bus to continue that 200 amps. Some panels have "sub feed kits", and you'd have to find one rated for 200A. Some panels also have a limitation on the maximum breaker stab current which is less than the total panel rating. So make sure you find a panel with each stab rated to 200A, or it has a feed through lug at the bottom. You'll also need to deal with wire bending space requirements, but these should be OK assuming you find a sub feed lug or feed-through designed for that panel.
You will have to install a 4-wire feeder to the subpanel using 2/0 copper or 4/0 aluminum. The 4th grounding wire must be at least #6 copper. Also make sure you have enough big holes in your neutral bar.
-- Mark Kent, WA
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you are overloading
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Speaking of overloading, shouldn't your head be exploding or something within the next 5 minutes or so?
Sorry, but some unseen force drove me to ask. It was completely against my will.
AJS
snipped-for-privacy@webtv.net (m Ransley) wrote:

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Hi,
You can do it that way but it isn't code. It is safe becasue the main breaker will shut down if you exceed its rating. Check the rating for the main panel. The total amp rating. I am guessing it isn't over 250 amps. Why do you need 200 amps for a basement? that is 10, 20 amp circuits.
candice
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200 amps is a lot more than 10 20amp circuits. It could be 40 or 50 circuits. You don't load each circuit to the max. 200 amps still sounds a lot unless he is welding or running industrial equipment.

breaker
panel.
need 200

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Overload is determined by the Service calculation and not the number of circuits installed. The main panel is rated at 200 amps if the breaker is rated at 200 amps, and that is all he'll get regardless how it is apportioned between panels. Using 100A feeders is a more common approach, but these can be problematic if you have some large items on those feeders like an electric range, clothes dryer, and airconditioning compressor -- doesn't leave much ampacity left. Usually, you leave the big stuff in the main panel and run the general lighting and small appliance circuits form a subpanels if necessary. But if you're trying to keep everything on a single floor in a given panel, this is where it gets tough.
A dual 200A installation will solve a lot of capacity problems, but I don't know why panels are desired on different floors. A single 42 slot panel is usually the least expensive installation. But if more than 42 circuit breakers are needed, then its gets more costly and complicated.
-- Mark Kent, WA
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The house is three floors plus a basement. I just thought by having multiple panels I could save wiring home runs all the way down to the basement. (The main panel is in the basement for security reasons.) Also having 2 200amp panels would allow future flexibility with adding or moving circuits. The thing I forgot to consider is how big that feeder between panels has to be, as you pointed out. Thanks. Maybe it'd be be better to have have 2 100amp sub panels fed from the main 200amp service panel.
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The feeder cable is not only big, but _expensive_. Probably cost more than the panels do...
I'd suggest a 200A main in the basement, and a 100A subpanel upstairs. You should breaker the 100A feed in the main - you don't need a 100A in the subpanel.
If the kitchen isn't wired off the 200A, do make sure you have enough capacity upstairs.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
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snipped-for-privacy@aol.com (CLSSM00X7) wrote in message

I don't get why if a main breaker shuts down it isn't safe. I would think it would be just the other way around: If a main breaker fails to shut down it isn't safe.
Check the rating for the main panel.

In my original post I said I'll have a 200 amp panel. Are you saying there's some other rating, the "total amp rating" could be other than 200 amps?
Why do you need 200

Do you really think I meant that I'll have 200amps of equipment in my basement? The idea was to have two 200 amp panels, one in the basement one on the top floor. Branch circuits would run out from the basement panel to circuits in the basement and 1st floor. The top floor panel would handle the rest of the house. Of course, it would be up to me to make sure the sum of the amps of the branch breakers in both panels did not exceed 200 amps. I like this flexibility.
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wahzoo wrote:

How about a 100A or 125A main lug panel upstairs, fed from a 2-pole 100A breaker in the service panel in the basement? That would give you plenty of room for expansion, and you could run a lot smaller and easier-to-handle wire to the subpanel -- #4-3/wg, I think, although if the distance is very far you might want to run two #3 hots and #4 neutral and ground. Are you gonna use a conduit to connect the 2 panels, or run a big cable?
Best regards, Bob
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Right that would be better. Or I just might have two 100amp sub panels. Yes I'm using IMT --embedded in concrete block for the risers, surface attached for all other wiring. This is for a completely concrete house, floors too, except for a few internal partitions.
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snipped-for-privacy@hotmail.com (wahzoo) wrote:

There is a limit, I believe it is 6 items, that have to be turned off to shut off power.
To put it another way, unless the two panels are right next to each other, if you have more than 6 circuits in the subpanel, it needs it's own single shut off (service disconnect).
In this case, I don't know if you can get away without feeding the sub from a breaker in the main panel.
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If you don't feed the subpanel through a breaker smaller than the 200 amp main the connection between the entrance panel and the subpanel will have to be made with at least 2/0 copper.
I run 6 subpanels in my home, each fed through 50 or 60 amp breakers in the entrance panel that in turn are fed from one 200 amp breaker. The connections to the subpanels are are made with #6 copper.
Boden
John Hines wrote:

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Amen, but really, 6 subpanels! Pray tell what's the advantage you're getting with that?
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snipped-for-privacy@hotmail.com (wahzoo) wrote:

Same as you, shorter local runs? Concentration of activities, like all kitchen breakers in the same panel?
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(wahzoo) wrote:

You're confusing service panels and subpanels. The 6 switch rule is for service disconnects. A sub panel is by definition fed from a breaker in a panel, so turning off that panel shuts off all of its sub panels..

A subpanel does not require a main breaker if it is protected by a breaker in its feeder. An exception to this rule would be subpanels located in a detached structure -- the structure must also have no more than 6 throws of the hand to shut it down and those disconnects must be located at the structure.

He has no choice but to make the panel a subpanel, which means feeding it from a breaker. If a service rated panel was attempted, he'd violate the requirement that the disconnects have to be grouped, and probably violate the length limitations on how far service conductors can enter a structure.
-- Mark Kent, WA
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One additional question: I have a panel right next to the main panel to add a few more breakers. The original panel has a 100 amp main breaker. The added panel is wired off the main bus in the original panel. (note I'm trying very hard not to use words like sub-panel). What wire size should be used between these 2 panels? Should they be sized for 100 amps? Or, should they be sized for the sum of the breakers in the added panel? Or what? Thanks.
Mark or Sue wrote:

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Depends on a few factors (you aren't NEC guru Joe Todesco's brother are you, trying to see if I step bady in the code?).
First, I'm assuming that the 100A main breaker will remove power to both panels -- is this true? The conductors to the subpanel are not required to be larger than the conductors to the main service. These would normally be #4 copper or #2 aluminum for 100A service. If your service is larger than 100A, then you could use #3 copper if rated for 75C (such as SER cable and THHN individual conductors) or #2 copper if using NM or UF cable. You also need 4 wires, as the grounding wire and neutral wire must be kept separate in the panel and the neutral bus isolated from the chassis. The 4th grounding wire only needs to be #8 copper.
If power in this panel is NOT removed when the 100A main is turned off, then you can have a 3-wire connection to that other panel, but these are unfused service conductors. The connections would have to be made per service conductor rules (usually conduit w/special bonding rules), and you really need to do a load calculation to make sure you're not overloading the service. The neutral bus stays bonded to the chassis in this case.
Panels and services are always sized by calculation and not by adding up breaker handle ratings. Breaker handle sums typically exceed the rating of each service leg (i.e. leg 1 breakers would exceed 100A and leg 2 breakers would exceed 100A). But the service calculation can not exceed 100A or else you need to upgrade it. The breaker that feeds a panel must be large enough to carry the calculated current, and the wires installed must be rated for the load. If you install a larger breaker for future expansion, then the wires must be sized according to the main breaker protecting them.
Touched a lot of options here, did I answer your question???
-- Mark Kent, WA
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I'll try to replay to each part separately:
Mark or Sue wrote:

Don't know Joe Todesco. Just a retired EE working mostly in electronic design, however, I have been known to look at NEC ..... but not in a bunch of years.

Yes. The
Even if the original panel had a "combined" neutral and safety grounds?

So, the conductors can be smaller than #4 CU or #2 AL if the calculated maximum current is less than 100 amps? How do you calculate the current on an outlet string with a 20 amp breaker?

Thanks for the info.
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