Limits of sub panel

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GeorgeW

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I am looking for input on this subject as I cannot find any code guidance. I plan to install a subpanel in an apartment that is seriously lacking in terms of circuits and outlets. The main panel is 100 amp. It has 4 open slots...2 from a 2 pole breaker not being used....2 others that are simply open. I ran two 20 amp circuits from the panel to feed the kitchen and dining room as there were none there. I also plan to run a feeder using the 2 pole breaker slot not being used, to feed a main lug 50 amp sub panel. From there I will run three new 15 amp circuits to different areas to add much needed receptacle. I have to install one more 20 amp circuit to the apartment to feed an airconditioner. My questions is how can I determine what the limit would be in terms of circuits/ amperage draw on the subpanel? I am currently thinking that I do not want to exceed 80% of the 50 amps, but am also realizing that there is no 'continous load', so should I be concerned about having three 15 amp circuits and one 20 amp circuit in this sub panel or should I find a way to put the 20 amp circuit in the main panel?
 
You can't just total the 15's by the breaker size. You could have a fifteen amp circuit feeding receptacles with nothing but a clock plugged in. They may be loaded to 5 amps,,maybe 10 (I doubt it), but my point is don't go by the numbers, go by the calculated load. IMO You will be well within your 80% goal you have imposed, by hooking everything up that you mentioned, if you actually knew the load. What size wire are you running for a feeder?
 
Step one; Do a proper service load calculation.

Adding a subpanel for the sole purpose of adding circuits does not mean the service it completely capable of handling the extra loads.
 
Read the open'n of Article 220 and right on through to all of 220.16 Loads for Additions to Existing Structures and maybe even read some more, depends...that's just a page and half :)
 
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