Over the past two weeks, my 15 amp ARC breaker on my 2nd and 3rd bedroom is randomly tripping. There is no load at all on any of the outlets nor is the ceiling fan/lights on at any time. All the outlets test fine with the plug in/two light circuit checker. It just nuisance trips.

I just opened up the panel to see if any of the wires had perhaps worked loose causing the nuisance trip since a lot of jostling of wires occured when 18 months ago, I had a 100 amp subpanel installed in the basement (eveything worked fine after the panel was installed). The wires are tight but I noticed the pigtail for each of the ARC breakers is attached to what I assume is the ground bus, as all the copper is landing there and the whites are all landing on the left. I don't know if it's always been this way from the original build as I had never removed the panel cover.

So, I understand the pig tail should be on the neutral bus on the left side, but is this configuration based on the pic ok? Is the pigtail on the ground bus finally causing it to trip? Have I gotten lucky all these years? Or is it most likely the breaker is just slowly dying? So my question is, when I bring out an electrician to replace both ARC breakers (might as well, right?), should I insist the pigtails be landed on the left neutral side, because it looks like there's no room left on the neutral bar...

outside panel

Thank you for your comments.

I'm glad to read the pigtails on the right side are acceptable. I don't have a tankless WH. It's a gas water heater and furnace. The big stuff is typical suburban house...Electric double oven plus electric cooktop, electric dryer and then central air.

I have no intentions for adding anything heavy that I don’t already have. I had the subpanel put in to be able to add intermittent use outlets more easily (basement treadmill, fridge, random new outlets, exterior Christmas lights etc) since the main panel was outside and obviously quite full.

I also have no expectations for owning/charging an EV but fully accept that an expensive upgrade would be necessary to the box as well as service as I have buried utilities, unless I went small on the charger per the YT video you posted.

Thank you again.

  • @keshlam This box is not obviously overfilled. It has 20 spaces and 60+ neutral screws. That’s enough to land 40 neutral wires individually and 40 ground wires (at two per screw). That’s enough to handle a tandem (double-stuff) breaker in every single spot. It could be over-subscribed based on load, but not on circuits.
    – nobody
    Dec 6, 2022 at 22:48
  • OK, comment withdrawn. If I see that many tandems, I start being skeptical; I just don't trust 'em as much as I do singles. But that's my own bias, and I admit I have absolutely no evidence to justify it.
    – keshlam
    Dec 7, 2022 at 1:51
  • Believe me I wish I had a panel twice this size but it was what the builder put in outside for the entire subdivision. They're all this small. Thus, a roomy sub panel in the basement.
    – steve0617
    Dec 7, 2022 at 2:32
  • I know you have an answer already, but of note, there are two grounds landed on the left-hand side neutral bar. (Note, too, that it's proper to click the check mark next to the answer that helps you the most, even if there's only one answer. ;)
    – FreeMan
    Dec 7, 2022 at 15:01

1 Answer 1


Your panel does not have any ground bars

This panel has an integral main and utility meter, which means it is intended for use as service equipment i.e. the main disconnect is expected to be here.

The main disconnect is the mandatory location for the Neutral-Ground Equipotential Bond, where neutral and ground bars are bonded. Here, grounds are allowed to be guests on the neutral bar.

As such, panels of this type are NOT supplied with ground bars - only neutral bars. Grounds are expected to be put on the neutral bars. Accessory ground bars are available; however it's extremely unusual for this type of panel to be used as anything other than service equipment.

Now your electrician happened to put only neutrals on the left neutral bar, and all the grounds on the right neutral bar. That is just that person being "OCD" as they say. There's nothing wrong with doing that, but it doesn't make the right bar any less a neutral bar.

Be very careful with the loading of this panel

This panel is VERY heavily subscribed - noting three 40A breakers, a 30A breaker, and a 100A subpanel. I would recommend revisiting the NEC Article 220 Load Calculation on this service, and either managing loads (maybe get rid of a tankless) or adding load-shed features as required, or stepping up to 400A service.

I would use even more extreme caution if EV charging is planned. It can happen within the existing service, but only with careful managment of the Article 220 Load Calculation, sensible charger sizing, and possibly load-shed devices to let things like a water heater pre-empt EV charging.


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