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I live in a developing country where there isn't much in terms of electrical codes and electricians often aren't very detail-oriented. I recently had a solar system installed(Victron Multiplus-II –), and I wanted to confirm my setup is correct in terms of bonding neutral and ground. My previous setup was a single main panel with breakers feeding the whole house. Now the setup looks like this:

Panel 1: A new "subpanel" installed next to the old main panel at the front of the house. It receives the service mains and only has a single breaker which passes power along to panel #2.

Panel 2: A new subpanel in the back of the house which feeds into a solar system. The solar system has inputs for solar panels, battery, and grid A/C, and has a charger/inverter that intelligently manages everything. This then has an output that feeds back to panel #3.

Panel 3: This is the original main panel in the front of the house (next to panel #1). It used to take input from the service mains, but its main breaker is now connected to the output from the solar system. This panel has all the breakers for everything in the house and is grounded to a grounding rod.

Currently neutral and ground are bonded in panel #3 (as it was when it was the main panel), and neutral and ground are not bonded in panels #1 and #2. This seems to fit the rule that you only bond neutral and ground in one place, but technically panel #1 is now the "main panel" closest to the service mains, so I'm wondering if neutral and ground should be bonded there and not in panel #3.

Which setup is correct here? If the current setup is wrong, why is it wrong, or what's the risk (so I can try to explain things to an electrician)?

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  • We need to how the panels are grounded. Panel #3 has a heavy ground wire connected from panel to outside ground rods. Panels #2 and #1 have unknown ground setup.
    – crip659
    Dec 12, 2021 at 21:31
  • @crip659, panel #3 is connected to a ground rod outside. And normal insulated ground wires run directly from the ground bar on panel #3 to the ground bars on panels #1 and #2.
    – sahko72
    Dec 12, 2021 at 21:33
  • What make and model is your solar inverter? Dec 12, 2021 at 21:34
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    @ThreePhaseEel Victron Multiplus-II
    – sahko72
    Dec 12, 2021 at 21:35

1 Answer 1

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Your inverter can break neutral, so you need a bond and a grounding electrode connection in the first panel

Assuming your country uses TN-C-S earthing practice (which it seems to from your description), it will require more than just moving the bonding screw to make your system comply with electrical earthing standards. In particular, you'll need to use an irreversible compression splice to add a length of copper wire of the same size as the existing ground rod wire from that wire over to Panel 1 (the new main panel). This is because the Victron inverters will break their neutral in addition to their hot when they disconnect from the mains, so right now, the AC mains side of your system will become ungrounded when the inverter disconnects its output for whatever reason.

Once that's done, you can then remove the bond and grounding electrode connection from panel 3 and install the bond at to panel 1, provided there's an equipment grounding connection on the input side of the inverter. The MultiPlus will internally supply a bond when it breaks the neutral, so Panel 3 needs to be wired as an ordinary subpanel.

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  • Thanks for the detailed response! Basically, it sounds like panel #1 needs to be a main panel with a bond and direct connection to the ground rod, and panel #3 needs to be a subpanel without a bond. Could you elaborate on the safety issue with the current setup? Things are fine while the inverters are feeding in from the mains, but if they switch to the batteries, panel #1 is now ungrounded? It does have a ground wire to panel #3, but because it's not thick enough gauge current could flow elsewhere or something?
    – sahko72
    Dec 12, 2021 at 22:48
  • @sahko72 -- basically, if you switch to battery power, Panel #1 is now unbonded from mains earth, which means that mains current that goes astray onto the ground can't get back to the utility Dec 13, 2021 at 1:24
  • Got it, makes sense. This answer was helpful in understanding why current that can't get back to the utility is a problem: diy.stackexchange.com/a/106776
    – sahko72
    Dec 13, 2021 at 2:54

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