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.
panels -- is this true? Yes. The
to the main service.
service is larger than
THHN individual
the grounding wire and
from the chassis. The
Even if the original panel had a "combined" neutral and safety grounds?
you can have a 3-wire
connections would have
rules), and you really
The neutral bus stays
breaker handle ratings.
1 breakers would
can not exceed 100A
enough to carry the
install a larger
main breaker protecting
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?
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.
Yes. The only place that neutral and ground are allowed to be the same is at the main disconnect. In your case, the main disconnect is your 100A main panel. Adding a separate panel downstream of that disconnect requires that neutral and ground be separated.
breaker handle ratings.
leg 1 breakers would
calculation can not exceed
100A
enough to carry the
you install a larger
main breaker protecting
maximum current is less than 100 amps? How do you
In your case (a subpanel), the wires feeding the panel must be sized per the breaker protecting it. So no, you can't reduce the size of the wires unless you install a breaker smaller than 100A in your main panel and feed the subpanel through it. Logical sizes would be 60A, and 40A for 60 degree C rated installations (70A, and 50A for 75C rated installations). Since this subpanel will be so close to your main panel, I'd just go with #4 copper and let the existing main breaker be your disconnect.
In a residential setting, there is no specific load for a receptacle. If there is something fastened in place that will connect to this circuit, you count that at its nameplate value. If there is a certain amount of square footage to be served by this circuit, then it is 3 VA per square foot. When adding up circuits based on square footage, you count the first 3000 VA at 100% and then count the remainder at 35%. Motors are calculated per the motor horsepower current listed in NEC 430.6 and then 25% is added only to the largest motor. Some other specific circuits have code minimum values -- the two kitchen and one laundry small appliance circuits are calculated at 1500 VA each, and these numbers can be added into the VA number that gets the 100%/35% demand factor applied.
The original thread said 200A, but then the thread got intermixed with questions. The way I read Art's question was that he has a 100A main panel with a sub next to it. If that main panel is greater than 100A, then he needs a breaker
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