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Here’s an update on the main panel neutral issues that I raised originally in another question. I relabeled the photo, and made a diagram to show the problem. This post restates the issue, I hope more clearly, and gives more info, but the basics are unchanged.

At the bottom right the neutral from the 100-amp subpanel (labeled SPN) is connected incorrectly to the panel enclosure, rather than the neutral / ground bus where it should be. As a result, current from any unbalanced load in the subpanel flows through the enclosure.

The neutral / ground buses are bonded to the enclosure in two ways I can find, and maybe others.

  1. The bonding jumper BJ at the top is a piece of bare copper, probably #10, which connects the left and right buses together and to a ground screw (BJS) in the enclosure .
  2. A recent solar installation includes the #6 solar ground SolG, which bonds the bushing for the incoming FMC from the solar controller to the neutral / ground bus on the left.

There are also screws in the mounting bar for the buses on each side – you can see the one on the left side in the photo – that look like they might be intended as bonding screws to the enclosure. I can't tell if they are, but both screws are loose and will not tighten.

The neutral / ground buses are connected to the incoming service neutral by a neutral jumper (NJ) on each side; after careful examination it appears there is no other connection. The NJ wires look to be #8. (You can see where they attach to the bus bars in the photo, but due to camera angle the connection to the service neutral is not visible.)

Current from the subpanel neutral will flow as shown in the diagram: through the enclosure, through the bonds between the enclosure and the neutral / ground bus, and finally through the neutral jumpers to the service neutral.

I confirmed this yesterday at a time when most loads in the house were off. I turned on a toaster oven on a 120V circuit in the subpanel. Current in the subpanel neutral was ~13A which is about right. There was ~4A in wire SolG , and ~4A in bonding jumper BJ in the center between the two buses (I couldn't get the clamp ammeter in to measure the current in that wire to the left of the left hand bus). As soon as I turned off the 100A subpanel breaker all of these went to 0. Obviously this current should not be flowing in the ground wires.

It seems to me the solution is to:

  • Move the subpanel neutral to the bus bar using an appropriate neutral lug.
  • Remove jumper BJ, which is not as near the service mains as it looks, but shouldn’t run across them in any case.
  • Add correct bonding jumpers between the bus bars and the enclosure with #6 wire, one on each side.
  • Remove the loose screws in the neutral / ground mounting bars.

Does that seem right?

Main panel

Subpanel neutral current flow

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  • "both screws are loose and will not tighten." As in you've put a driver on them and they just spin because they're stripped?
    – FreeMan
    Sep 8, 2022 at 11:27
  • @FreeMan yes they appear to be stripped. They are not falling out. I could easily and safely remove them with neeedle-nose pliers (with main breaker off). You can tell someone has done something there before, or tried to, because the heads are not quite the same -- so different screws on the two sides.
    – trawson
    Sep 8, 2022 at 11:42
  • I'd like to see a pic of the innards of the 100 amp sub-panel. I'm concerned about one thing there: Do you have a 4 wire feed to the 100A sub? For it to be up to code you need 2 hots (assuming 240v), a neutral and a ground. Sep 8, 2022 at 13:19
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    @GeorgeAnderson I can post a pic later today but I can tell you that the feed is 2 hots and a neutral in EMT with the EMT presumably serving as the ground conductor. Neutral and ground buses are not bonded in the subpanel.
    – trawson
    Sep 8, 2022 at 13:39
  • @trawsonw OK, then never mind about the pic. Since you have EMT for ground, you're OK, at least in that respect, good luck on straightening out the rest of it all. I'm not going to post an answer to your most recent post bc I'm just not sure enough to give the best advice/answer. Sep 8, 2022 at 13:45

2 Answers 2

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The first thing I'd do is search the panel and cover for labeling. Looking for two things: #1 whether 2 or 3 ground wires are allowed on a neutral bar terminal, and #2 the recommended model numbers of accessory ground bars. Because I believe the ITE numbers became Siemens numbers (or a Siemens dealer could steer you right.)

Use either technique to free up some space on the neutral bars. The more the better.

Now contact your Siemens dealer and get a lug adapters to put large wires on the neutral bar. They have 2-3 prongs which go under 2-3 screws on the neutral bar. Move the subpanel neutral there.


Once you get rid of the various neutral-ground bonds and spurious NJ wires, you can test out the connection between the neutral lug and the 2 banks of neutral bars. That needs to be explained fully. A #8 wire is laughably inadequate; Code requires 2/0 copper for that. There is no way UL approved this panel with #8 neutral jumpers as the primary neutral path. Ergo if removing those causes the neutral bars to fail, the panel is defective.

The spinning screws on the neutral bars are disturbing, and I wonder if there isn't a nut on the backside of them that has been loosened by way of attempting to remove those screws. That might have been what bonded the neutral bars to the lug??

Unfortunately if this 200A neutral connection can't be proved out, the panel is defective and must be replaced (or at least the bus assembly pulled off and torn down for inspection and repair). I suppose you could bring the neutral wire to a 3-port Polaris connector and fork it to dual 2/0s each going to one of the two neutral bars, but this is still "pull the meter" type work.

Eaton makes replacement bus assemblies that can be dropped into old panel enclosures which are obsolete or dangerous. They are costly, however.

Once you prove out the neutral bar, run a neutral-ground jumper of appropriate size to the SPN terminal. Might as well use it!

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  • I agree the first task is to sort out how the service neutral is connected to the neutral busbars. No point in moving the subpanel neutral if there isn't an adequate connection. POCO here turns out to be very difficult about meter pulls ($$$, time, paperwork), but I can safely kill the main breaker, remove all the neutrals and grounds on one side, and see what I can see about how the busbar is connected.
    – trawson
    Sep 10, 2022 at 2:17
  • Whatever the purpose of the NJ jumpers, I don't think they are intended to be "spurious" -- they are part of how the panel is designed and manufactured. I've found two other images of this model panel online that clearly show those jumpers, installed in exactly the same way (i.stack.imgur.com/pCOLc.jpg and i.redd.it/eclag9eywg311.jpg). Of course that doesn't tell us their purpose.
    – trawson
    Sep 10, 2022 at 2:39
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So today I was able to sort out answers / fixes for some of this:

  • I was able to turn off the main breaker, disconnect neutrals from the right side busbar, and loosen the busbar mounting screws. Then I could rotate the upper and lower ends of the busbar forward and backward a bit, but it still was not free to move around much. That suggests there is indeed some other mounting mechanism, presumably an aluminum neutral bar that goes across behind the main breaker. But I still couldn’t see it. I don't think this can be figured out 100% without removing the main breaker, which I'm not going to do because it's so expensive and bureaucratic to get the meter shut off.
  • I very carefully removed the wire that ran across between the neutral bars and to the case (BJ in the original photo). I replaced it with two pieces of green #6 THHN, one on each side, from the neutral bars at the top to lugs at the bottom. The lugs are installed into tapped holes with #10-32 grounding screws. See two new photos below. This is probably overkill -- one side would be adequate -- but there's no harm in it.
  • I was able to determine that the wire for the feed to the 100 A subpanel is actually #2 aluminum so the breaker for that should indeed be 90 A. I ordered one.

Harper, I didn’t take your suggestion to use the lug that currently has the subpanel neutral in it for the new bonding jumpers, because I haven't got the forked lug for the neutral bus yet to move it up there and I wanted to get this part done.

Top of panel

Bottom of panel

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  • I take it your utility won't do shutoffs remotely during business hours? (Most utilities that run smart meters have remote shutoff capacity, and many can cut power for free or not-expensive during business hours as a result since it's just pushing buttons on the keyboard for them) Sep 13, 2022 at 3:43
  • @ThreePhaseEel that's what I figured it would be too when I asked, but they said someone has to come to the house. And they charge $300. And you need a couple of weeks notice because the shutoff has to be "reviewed by a design engineer." Mind you that's not the work you are doing, they don't care about that. Just the fact of a shutoff and reconnection. Also requires a signoff from the AHJ before restoring power.
    – trawson
    Sep 13, 2022 at 9:59

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