Subpanels

[sjbaugh]

Hello,
I would like to know what the rule (code) is for sub panel feeds. I have a situation that a 200 amp 3 phase service feeds a building. There is a 100 amp (single phase) sub panel being fed off of it. The 100 amp sub panel has another 100 amp sub fed off it!!! Amazing isnt it. You can't make this stuff up!!!
I have been trying to find it in the code book to justify my upgrading the whole service to 400 amps, and give them a 200 amp single phase panel as well as a new 200 amp 3 phase panel..., the customer's position is.... they have no problems with it and don't want to fix it.... typical, but they have no more room in the 3 phase panel. To top it off the 3 phase service has the high leg and most spots are unusable for any 120 volt machinery.

Help!!
Sue J.

 

[haskindm]

There is a difference between the connected load and amperage rating of a panel. Just because you have a 200-amp main panel and 2 100-amp sub-panels does not mean that you are trying to serve a 400-amp load. You will need to do an article 220 load calculation to determine if the 200-amp service is adequate. The ampacity of the sub-panels is not important, your total load is limited by the main service panel. The sub-panels were probably installed for wiring convenience, not in an attempt to provide additional ampacity.

 

[charlie b]

The "rule" is 408.30 (2005 version). It says that a panelboard shall have a rating not less than the minimum feeder capacity required for the load calculated per Article 220 (the calculation that haskindm has already mentioned). That rule does not forbid using a panel that has a higher than needed capacity.