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
(PS. This is all new contruction.)
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
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
email@example.com (m Ransley) wrote:
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.
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
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
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.
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
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
firstname.lastname@example.org (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
Why do you need 200
Do you really think I meant that I'll have 200amps of equipment in my
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
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
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?
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
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.
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.
John Hines 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
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
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
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?
Mark or Sue wrote:
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
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
Breaker handle sums typically exceed the rating of each service leg (i.e. leg 1
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
Touched a lot of options here, did I answer your question???
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