I can't resist one last point . The newer codes won't let you downsize the conductors to main dwelling service panel unless it carries the entire load of the dwelling . OK, we use the outside disconnects all the time that have breaker spaces built in and we connect outside loads on that . The inside panel no longer carries the entire load . Also there is a code that says loads like a well pump must have a disconnect in the main panel . I finally asked the inspector why we never get flagged on those things and he looked at me and said "Why would I flag the ser size when all you have done with the out side breakers is take some load off of them ? And why would they sell the outside disconnects with breaker spaces if all the circuits have to originate from the main panel ? " I just said "Good for you"
Nothing in NEC requires a well pump to be supplied from a specific panel - maybe some local code somewhere does.
The 2014 uses a different method for services on a residence. You must take 83% of the service size. For instance if you want a 200 amp service then the wire after derating must be rated for 200 * 83% or 166 amps. It is still the same for a sub panel in that you must carry the full load of the service in order to use the 83% rule.
End result generally gives you same conductor size as in the past - but what is the bigger change is before you did not have to apply ampacity adjustments and now you do if you have a high ambient temp, or number of conductors in raceway is an issue.
Thanks jumper I have never seen it put that way before . I sure see why people did the proposals , if the loads you decide to put on the breaker spaces in the outside disconnect have already been put into the dwelling calculations and the ser size has been determined with that included , then all you are doing is taking some load off the ser that has already been designed to carry that load . Maybe someone can word this better if they can figure out what I tried to say !
Correct the loads in the outside panel are in the total load calc - and the reason the service or main feeder can be sized based on total dwelling load. I agree if you have 100 amp supply in and 100 amp supply out that you have taken some of the load away if there are circuits originating at the outdoor panel, but you have changed the load diversity on the indoor panel, and you are not going to know how much with simple calculations.
Take a situation where you have a 200 amp main supply and a 100 amp sub panel, and it it not quite so simple to say the 100 amp subpanel can have a conductor with less then 100 ampacity supplying it as it could be with the 100 amp main supply and 100 amp subpanel situation.
Does it really cost that much more to increase from 2 AWG to 1AWG or to use a 90 amp breaker instead of a 100 amp breaker?