section of NEC that limits ampacity of sub panel?

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tld38

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Have 1 100 amp 12/24 sub panel for tenant space fed from service disconnect. 2 spares left. I need to add 5 ckts. Can anyone tell me if there is a codse section that limits the size of another sub panel I want to install off of this one? Thanks!
 
tld38 said:
Have 1 100 amp 12/24 sub panel for tenant space fed from service disconnect. 2 spares left. I need to add 5 ckts. Can anyone tell me if there is a codse section that limits the size of another sub panel I want to install off of this one? Thanks!
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Many sections of Article 220 would be on target.
 
Hi iwire! Thanks much. I cannot find a specific section in article 220 that would prohibit me from installing a 60 amp sub off this existing 100 amp sub. I thought I remember haering somewhere that you cannot exceed a certain percantage of a panel. like installing a 100 amp sub off of an existing 100 amp sub. I don,t think you can do that. I just cannot find the referance. How can I be sure that I am allowed to feed this 60 amp sub off the 100 amp sub? Thanks!!!
 
There is no section that contains the limitation that you describe. The rating of a sub panel has to be high enough for the calculated load, and it has to be high enough to be protected by the upstream breaker. You can have a 100 amp panel feed a second 100 amp panel, and have that feed a 225 amp panel, and have that feed another 225 amp panel, and have that feed a 400 amp panel. Not a great design choice, I admit, and probably a huge waste of money. But still code compliant. Panel ratings are not the issue here.

Bob's point, I believe, is that you have to calculate the load, both on the present panel, and on the panel you propose to install. That is why he sent you to article 220: that is where it tells you how to calculate the load. If the total calculated load on the present panel, after all modifications are done, is within its rating, then you are OK.
 
There is no rule regarding the size of one subpanel fed from another. The connected load, as calculated in Article 220 is the real issue.
 
tld38 said:
Have 1 100 amp 12/24 sub panel for tenant space fed from service disconnect. 2 spares left. I need to add 5 ckts. Can anyone tell me if there is a codse section that limits the size of another sub panel I want to install off of this one? Thanks!
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You can have as many circuits as you want as long as the load calculation supports it. You can feed any size panel off any other panel as long as you follow the rules. It makes no economic sense to feed a 400A paenl off a 15A breaker, but it could be legal, code wise.

Do the load calcs first. That will tell you what makes sense.
 
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