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I have a 100Amp Siemens subpanel mc1020b1100sz for the granny unit coming out from the main 200Amp panel of my house. I know that the ground bar and the neutral bar should be bonded at the main panel only, and in the subpanel, ground and neutral should be isolated from each other.

Here is my question: how to isolate the neutral bar and the ground bar in a 100Amp Siemens mc1020b1100sz?

Below is the wiring diagram of my subpanel 100Amp Siemens mc1020b1100sz:

https://assets.new.siemens.com/siemens/assets/api/uuid:7980e6e4-bbf7-4c03-b1ac-1c3b87d96779/sie-wd-mc1020b1100s.pdf

As you can see in the diagram, the neutral bar is bounded to the panel enclosure. Therefore an isolated ground bar was used to keep neutral and ground separated. However I believe that the subpanel enclosure should be grounded. In other words, I believe that the neutral bar should be an isolated neutral bar and the ground should be bonded with the panel enclosure. However I do not understand how the neutral bar can be isolated from the panel enclosure itself.

Does anyone know how this should be done properly? Thank you in advance!

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  • Does this answer your question? Grounding a subpanel box in the same dwelling
    – aaaaa says reinstate Monica
    Mar 3 at 5:16
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    @aaaaasaysreinstateMonica While that does show that ground & neutral should not be bonded at the sub panel, this question is about isolating neutral from the panel chassis. Also, as pointed out in the accepted answer, this isn't a sub panel, so the question is off-basis.
    – FreeMan
    Mar 3 at 13:50

2 Answers 2

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That is not a subpanel! That is a combination meter socket/main panel. By definition, that is the type of panel that always has neutral and ground bonded, so they don't give you the option of undoing it.

Any (or should be any, I'm sure someone will find an exception...) modern panel that does not have a meter socket that is designed as a "main" panel can be converted to a subpanel by removing the neutral/ground bond. That is necessary if you just decide you want to use a big "main" panel as a subpanel, but it is also necessary if you are required to have a main disconnect outside at the meter but want to have a big "main" panel (even though it may technically not be a true "main") inside with a convenient main breaker. Or various other situations.

Similarly, any "subpanel" that is convertible to have a main breaker or that can have a backfed breaker used as an effective main breaker can have neutral and ground bonded together when needed.

But a panel that includes a meter socket is a special case. And in fact you would not normally use it in "subpanel" mode because you would either be wasting a meter socket (jumper it?) or you would run into some legal issues of doing your own submetering. As I understand it, though it may vary by jurisdiction and utility company, in at least some places you can't simply throw in your own meters and bill your tenants for electricity.

There are a few possible solutions here:

  • If you don't actually have any need to meter this building, just put in a nice big ordinary "main" panel and remove the neutral/ground bond.
  • If you do actually need to meter this building yourself, put in a separate meter socket and "main" panel and remove the neutral/ground bond from the panel. Two boxes instead of one, but if you put the meter socket right above the panel it won't be a big deal.
  • If your utility is actually the one supplying the meter, talk to them about how you should handle it. They may have specific exceptions and want you to keep the neutral/ground bond in place, in which case this panel will work fine. Or they may want you to split the feed before your existing main panel. Or something else. Talk to them.

In any case, whether or not you have neutral/ground bonded here or not, assuming this panel is on a separate building from the main panel you will need to have ground rods installed and connected to this panel.

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    Thank you so much for helping me to better understand this matter.
    – Dedde
    Mar 3 at 6:33
  • The granny unit is a separate building 50' away from the main house. The wires from the main house to the granny unit are Qty3 1/0AWG AL, two phases and one neutral. The granny unit has 5 ground rods bonded together and separated from each other with more that 8'. Should the neutral and the ground be separated anyways inside the subpanel? Please consider that we do want to keep metering.
    – Dedde
    Mar 3 at 6:45
  • Do you have a ground wire between the panels?
    – manassehkatz-Moving 2 Codidact
    Mar 3 at 6:51
  • No. There is no ground wire between the panels.
    – Dedde
    Mar 3 at 6:55
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    @Dedde -- who do you have for an electric utility?
    – ThreePhaseEel
    Mar 3 at 12:45
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NEVER ground the panel to neutral!

The idea you mentioned of switching roles, attaching neutral to the panel chassis and isolating ground, is a terrible idea that will send you to jail after it kills someone. Neutral wires break all the time. When they do, neutral is energized at 120V - that's why it has insulation!

If you tie neutral to the enclosure, then when neutral breaks, the enclosure WILL be energized at 120V. What are the chances of the tenant touching the panel right then? Well, close to 100% since their power is out and they're trying to figure out what's going on! This borders on "booby trap" lol and is so severe many DA's would go criminal on it. Given it's a textbook example of a slumlord creating a hazard by pinching pennies on equipment and doing illegal, unsafe DIY. They'll make an example of you.

Yes, it's illegal for landlords to DIY on properties intended for rental. Your requirement of a meter is prima-facie evidence of intent to rent out. With that comes the duty to have a licensed electrician do the job.

This particular box cannot be used!

As discussed, it is labeled "Service Equipment Only" and cannot be used as a subpanel. That will be true of essentially all "combo" equipment on the market.

But I don't understand why you're using combo equipment. You seem to be motivated by "cheap", as apparent from the very small panel... and all-in-ones are specialty items that are more costly than a generic random plain meter pan + a random plain breaker panel + 2 inches of 1-1/2” steel conduit.

Also, all-in-ones are unnecessarily restrictive on panel spaces. You really ought to have at least a 30-space panel on a dwelling, and with plain panels, that's only a few dollars more.

Why a plain 4-jaw meter pan works.

4-jaw meters do not attach to neutral in any way whatsoever. They provide a pair of courtesy neutral lugs which are grounded to the case, but what do we put there? Hmm, let me think - ahh, yes, ground! The neutral can be run right through it without stopping - either in a continuous wire run, or a Polaris connector.

If you have a 5-jaw meter, get a 4-jaw meter.

Also plain meter pans are "on the outs" due to NEC 2020 requiring meter-mains for services. Not your problem.

Consider putting the panel indoors

Since this is a subpanel, NEC 2020 doesn't require a disconnect on the outside of the building. It does require a disconnect but it can be indoors. As such, you need a main-breaker panel (as the cheapest way to get that disconnect) - but you can mount the whole shebang indoors.

Indoor mounting also keeps the costly GFCI and AFCI breakers out of the weather. If you picked a 10-space panel thinking "oh, I'll just use mostly double-stuff breakers", bzzt, not anymore. NEC 2014 required huge numbers of A/GFCI breakers and it's gotten worse and worse on NEC 2017, 2020 and 2023. So yeah, a 10-space panel isn't going to happen. And an "all-in-one" large enough will be VERY expensive.

There's a reason it was on clearance lol.

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