Mike Dolt Enterprises
Mike Dolt Enterprises
User: BMacky, Location: Foster City, CA
Asked on: Thursday, June 2, 2011 at 12:13 am EDT
Answered on: Tuesday, May 14, 2024 at 6:07 am EDT
Question: Would someone please direct me to a specific NEC article(s) that would cover that it's OK to put a 200A subpanel downstream from a 100A Main switch? I have to prove to a customer that this is OK, and can't seem to find the specifics in Article 230, or wherever it may be.I realize it does not actually state that it's an approved practice, but that protection must not exceed the stated ampacity of ungrounded conductors, the panel rating, etc.If that's all there is to it, then OK. But is there something more to consider?Thanks!
NEC Articles
Article 110.3(B)
Conductors and equipment shall be protected.
Article 215.2
Overcurrent protection shall not exceed the ampacity of the conductor.
Article 240.6(A)
A panelboard shall have a rating not less than the sum of the branch circuit loads supplied by the panelboard.
Explanation
While the NEC does not explicitly state that a 200A subpanel can be fed from a 100A main switch, it can be inferred from the above articles that it is permissible under certain conditions: The 200A subpanel must not supply branch circuit loads that exceed 100A (the ampacity of the main switch). The conductors feeding the subpanel must be rated for 200A, which is equal to or greater than the ampacity of the main switch. The subpanel must have a rating of 200A or greater to accommodate the load.
Additional Considerations
The main switch should be rated to break the available fault current at the point of installation. The conductors feeding the subpanel should be properly sized and protected to prevent overheating.* The subpanel should be securely connected to the main panel and all electrical connections should be tight and properly made.
Conclusion:
Based on the NEC articles and considerations mentioned above, it is acceptable to install a 200A subpanel downstream from a 100A main switch, provided that the subpanel is properly protected and sized, and the conductors are rated accordingly. Flag for review