<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body style="overflow-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;">I agree with Zeke that having two N-G bonds in a supply-side connection is not ideal because of the potential of ground loops and shock risk between the two tie-points. We’ve fought this issue with AHJ’s and as the song goes, “I fought the law, and the law won.” 2023 NEC is pretty clear that it’s required now, regardless of whether it makes sense or not.<div><br id="lineBreakAtBeginningOfMessage"><div>
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<div><br><blockquote type="cite"><div>On Oct 23, 2025, at 3:31 PM, Zeke Yewdall via RE-wrenches <re-wrenches@lists.re-wrenches.org> wrote:</div><br class="Apple-interchange-newline"><div><div dir="ltr"><div>I remember going back and forth with two different Boulder County inspectors on this issue around 2007 -- one made me install the neutral-ground bond in the supply side disconnect switch. The next one inspected that and failed me and made me remove it. Then the first one came back and failed me again and made me put it back.</div><div><br></div><div>My understanding more recently has been that a supply side PV disconnect is not really a separate service and therefore should not have a separate nuetral-ground bond. It is more like when you have two 200A breakers fed by a 320A meter socket -- it is a single service with two outputs. But... we end up with a separate physical box, rather than both outputs being in the same physical box like that example. It still has to be within 6 feet of the main service to that second PV disconnect, but is a separate box. Per Tom's replay, looks like 2023 NEC clarified that if it's a separate enclosure, then it requires a separate neutral-ground bond, and that would make sense for the PV disconnect requiring a separate bond. So... if you are on 2023 NEC, then having that make sense. If on 2020 or earlier... seems like it's still ambiguous.</div><div><br></div><div>What having multiple neutral ground bonds does in practice (other than some bad things with lighting surges) is cause neutral current to flow in the equipment grounds, which is generally not good, because equipment grounds may be much smaller than neutral conductors. </div><div><br></div><div>What I have been doing, if possible, on the two inverters backing up a full 200A subpanel situation like you describe is putting a 200A 8 space feedthrough panel on the exterior of the house. This panel gets the nuetral-ground bond as the first point of disconnect from the grid. Then two 100A breakers feed the two inverters AC-in terminals. And the feed through terminals of the panel go to the grid source for a manual bypass switch. Then you are essentially connecting the PV system per 705.12(B)(3) rather than 705.12(A) like a supply side connection. Have to mark the feedthrough panel that no additional loads are allowed (fill the other two spaces with plug on surge suppressors). The complication is that if you had the bypass switch in inverter bypass, sending the grid to your 200A load panel, the inverters could still be drawing from the grid to charge batteries, or selling PV to the grid, and potentially overloading that feedthrough pane (at least per code... I can't think of how it could actually overload the panel, as if it drew more than 200A total between inverters and the feed through lugs going to the loads while charging batteries, the main 200A breaker would trip to protect the bus. If it sold back 200A from solar while the inverters were bypassed from the load (not that the inverters could, but if they did sell the full amount the breakers were capable of), that 200A could either go fully to the load, or fully to the grid, or somewhere in between, but would never be more than the 200A rating of the bus.</div><div><br></div></div>
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