100A Panel Question


Old 03-04-07, 04:18 PM
Thread Starter
Join Date: Jun 2005
Location: USA
Posts: 106
100A Panel Question

How does one determine the maximum amperage of circuits that can be connected to a 100A panel ?

On the 2nd floor of our home, we have a 100A panel. On the first floor of our home we have a 150A panel. These panels are not connected to each other; they are somehow bonded together at the meter (there used to be 2 meters on the property). I know there needs to be a dedicated disconnect that will shut off both services from one location (future project).

We are installing 2 Central Air condensors in our home (one serving 1st floor and part of 2nd, the other serving the remainder of 2nd and 3rd floor). I am trying to determine if I should connect the AC for the 2nd and 3rd floors to the 100A panel (on 2nd floor) or the 150A panel (on 1st floor).

This is a rough breakdown of what is in each panel currently and what is proposed:

30A Stove
30A Hot Water Heater
30A Dryer
30A AC (NEW)
15A Furnace
General lighting and receptacles for kitchen, living room, dining room, office, basement

30A Dryer
30A AC (New)
15A Furnace
20A (240V) baseboard heaters (will be used very little, not at same time as AC)
General Lighting and receptacles for bedrooms, baths, etc.

Thanks for any suggestions.
Sponsored Links
Old 03-04-07, 06:37 PM
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
You need to do a load calculation. Google that term, "Load Calculation" and go from there.
Old 03-04-07, 07:47 PM
Thread Starter
Join Date: Jun 2005
Location: USA
Posts: 106
Thanks for the suggestion.

I found this site: http://www.electricalknowledge.com/SFDLoadCalc.asp

and plugged in the size of our 2nd and 3rd floors along with the values for the clothes dryer and other misc. stuff. Only problem I had was that I don't know the size of the AC unit, but the installer said it only needs a 30A circuit, so I took the max value it could pull (7200 VA) and used that for the compressor value.

Calculations came back at 76 Amps, so I think I'm in good shape to connect that to the 100 amp panel.
Old 03-04-07, 08:44 PM
nap's Avatar
nap is offline
New Member
Join Date: May 2006
Location: north
Posts: 4,163
didn't look at the calculator you used but just wanted to point out that the AC and the heat are non-coincidental loads (not used at the same time) so you only need to figure in the larger of the two.

also since you do not have an actual load,the number you did use is way overkill for that circuit. 5760 (80%) of the 30 amp circuit is more realistic.

If you were good with your numbers, you are more than safe with the more correct numbers.

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Display Modes