I guess my real question is how do you determine the needed number of circuits for a given number of electrical devices?
I have two new bedrooms to feed from the subpanel. Each BR will have 5 recessed lights @60 watts, a ceiling fan, a bathroom fan and 6 wall receptacles.
I have an existing 40 amp circuit at the main panel that I want to use. The wire is inplace and was used previously for a cooktop (we're now gas).
The goal is to save cutting into the wall at the main breaker box to run another wire (the electrician said he would need to cut). I am trying to determine if a 240v, 40 amp circuit to the subpannel that will be used for the 2 BRs will be acceptable to NEC provisions.
Just from what I have read, the total area in sq feet that you have added to the home, has increased, I may be that your or original electrical was under sized or had out grown todays needs, just a guess, the sub panel that is there is most likely wired wrong, my bet is it does not have a isolated neutral, or you do not have eniough spaces in the old panel, this could be the reason, the electrician needs to open the wall, also I did not see anything about inter connected smokes, and remember another circuit for the bathroom GFCI.
The existing wiring is more than adequate. The house is only 10 years old. The purpose of the subpanel was more to save money running the needed wire back to the main panel since copper is so expensive.
The subpanel will have an 8/3 feed that already exists (no new load). From what I have read it seems the total load calculation can be approximated by ~3 watts (VA) per square foot of new area. Since these are bedrooms, there are no big appliance/motor loads.
In doing the NEC method it seems all I need is ~11 amps@240 volts. I agree I may need many individual circuits (smoke, GFI etc) but the total load this subpanel would need to supply would be significantly less than 40 amps@240 volts I have available... correct?.
Here's the calculation:
General Light and Receptacle Load 600 (2@300)sqft x 3VA = 1800VA
Total General Load Less Demand sum of above less T220.11 demand sum of above = 1800VA first 3000 at 100 % = 3000 next 117,000 at 35% = -420 remainder at 25% = 0 sum less demand = 2580VA
Here you'd need 1 separate 20 A ckt for each bath. Some towns on Long Island require you to also have a separate ckt for an A/C in each bedroom, in addition to the regular outlet circuit (AFCI protected of course). So, the sub-panel doesn't really seem out of line. As a side-note; A fellow sparky who has been working at Home Depot to supplement his income, related this story to me. Seems down the road from his house, a HO wanted to have some high hats installed and contacted an unlicensed "pro." As he's removing some cans from his truck, SCPD pulls in the driveway behind him. When he was asked what he was doing, he replied, "Just doing some electrical work." "Do you have a license?" "Ummm no." The officer was nice enough to provide him with some nice bracelets and a trip to the newly refurbished station house.
"As he's removing some cans from his truck, SCPD pulls in the driveway behind him. When he was asked what he was doing, he replied, "Just doing some electrical work." "Do you have a license?" "Ummm no." The officer was nice enough to provide him with some nice bracelets and a trip to the newly refurbished station house."
Interesting...wheels of justice in Suffolk Cty are really rolling along! What was the charge??
Here in NJ...a formal written complaint has to be filed with the Board of Examiners. Usually, by the time the paperwork is processed, the "pro" is long gone!
So since there's no AC in the bedroom (it's central AC for the house) I will need a 20 amp (bathroom) and 15 amp(lights and receptacles) circuit for each bedroom. So the total for the two bedrooms will be 4 new circuits, if I understand you correctly. A 40 amp feed to a 100 amp subpanel box seems to be more than adequate.