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Thread: 2017 705.12 (B) Multiple panelboards

  1. #1
    Join Date
    Jun 2018
    Location
    Pasco, WA US
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    1

    2017 705.12 (B) Multiple panelboards

    We have a project where the main service is 200 amps. 100 amp sub feed to a 125amp sub panel in a barn. My electrician installed a 12KW system on the barn. (50amp solar breaker)
    125x1.20=150amps - 100 amp main= 50amps, solar breaker is fine. Question is, do we have to relocate the 100 amp feeder to the bottom of the main panel and derate the 200 amp main to a 175 to be in compliance. I have read 705 (B) in its entirety and it is vague to multiple panels when back feeding from the farthest point. We have passed multiple inspections doing so, and this new inspector is questioning this. I do see his point as to where the power is coming from. The 100amp is backfed but NEC is unclear. In 705.12 (B) (3) it does say it has to be identified as we are supplying power to another busbar. So it seems to me it applies to all panelboards involved. Thoughts?

  2. #2
    Join Date
    Oct 2009
    Location
    Austin, TX, USA
    Posts
    10,026
    Quote Originally Posted by rfry View Post
    We have a project where the main service is 200 amps. 100 amp sub feed to a 125amp sub panel in a barn. My electrician installed a 12KW system on the barn. (50amp solar breaker)
    125x1.20=150amps - 100 amp main= 50amps, solar breaker is fine. Question is, do we have to relocate the 100 amp feeder to the bottom of the main panel and derate the 200 amp main to a 175 to be in compliance. I have read 705 (B) in its entirety and it is vague to multiple panels when back feeding from the farthest point. We have passed multiple inspections doing so, and this new inspector is questioning this. I do see his point as to where the power is coming from. The 100amp is backfed but NEC is unclear. In 705.12 (B) (3) it does say it has to be identified as we are supplying power to another busbar. So it seems to me it applies to all panelboards involved. Thoughts?
    You are correct; you have to qualify every busbar between the PV and the service in compliance with 705.12(D)(2)(3) a, b, c, or d in the 2014 NEC. It's in 705.12(B) in 2017.

  3. #3
    Join Date
    Nov 2015
    Location
    CA, USA
    Posts
    648
    The same reasoning that drives the CB position in the sub-panel that is being back-fed directly from the PV system also applies to all panels in the PV current path back to the utility interconnection. It's hit or miss if AHJs apply this correctly so some contractors can get through quite a few projects before running into an AHJ who points out this requirement.

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