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I'm replacing my main load center, with this unit, Siemens PN4264B1225C:

enter image description here

Note that the neutral bars extend only about halfway down the columns of breakers. This seems a bit inconvenient, especially for a retrofit where the home runs have already been trimmed to fit the old panel. I intend to install extra ground bars at the bottom, where it says "provision for field installed ground bars".

Since this is the first point of disconnect, grounds and neutrals don't have to be separated here (as they were not in the existing panel). My question: am I allowed to land neutrals on the ground bars, either the factory-installed or the field-installed ones ? (I understand that each neutral must have a dedicated screw).

I imagine the main issue is that the neutral bars are connected to the neutral lug via stout busbar-like connections - whereas the ground bars are connected to the neutral lugs only through the mounting screws and the panel enclosure itself, and the bonding screw on the neutral bar. Would landing neutrals on the ground bars be allowed if I provide jumpers from them to the neutral bars ? If so, what size ?

FWIW, I intend to invert the panel, the feed (from the meter) coming in from the bottom.

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    Most panels also can be used as junction/splice boxes, so extending short wires with wire nuts/wagos in the box is perfectly okay. The bonding screws to the panel should equal any jumpers you might add(not needed).
    – crip659
    Commented Apr 19 at 22:34
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    You didn't provide the model number, or a photograph, but the drawing sure looks like a PON panel, so you won't need most of the neutrals on the neutral bars anyway with modern GFCI/AFCI requirements where they will go to the breakers. Ground can be a guest on the Neutral bar in a main panel. That does not imply that Neutral can be a guest on the Ground bar in a main panel, AIUI.
    – Ecnerwal
    Commented Apr 20 at 0:30
  • Wasn't sure if it was kosher to cite specific models. It's Siemens PN1264B1225C, plug-on neutral as you suggest. Commented Apr 20 at 3:20
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    I would trust Ecnerwal, more than I.
    – crip659
    Commented Apr 20 at 13:07
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    Brand/model is the first question asked of most people posting questions. It's often imperative in getting you a good answer. Asking for brand/model recommendations is off-topic, but providing examples in an answer isn't verboten (unless it's self-promoting/spam).
    – FreeMan
    Commented 2 days ago

2 Answers 2

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Neutral differs from ground in that neutral carries ordinary service currents at full ampacity at any time.

Whereas ground only carries current during a ground fault, which should hopefully end quite soon. As such, there are very different requirements for size and quality of connection. Ground wires can be #8 on a 100A feeder. Switches and self-grounding receptacles can pick up ground via mounting screws (can you imagine doing neutral that way??)

Indeed, in panels, grounds can simply attach to the enclosure and make contact with any screw with -32 or finer thread pitch and Bob's your uncle.

So yeah, the way ground bars attach to the panel is wholly inadequate for neutrals. Also see NEC 200.2(B). There's also the panel instructions and labeling, which is approved by UL (half written by UL) and that functionally extends NEC to include UL rules.

You're always allowed to extend with wire nuts. Or you could consider inline Wagos for a degree of neatness....

...or my favorite: leave the panel with a short EMT conduit nipple, go to a nearby junction box, and splice there. At the cost of junction boxes all over the place, this does two neat things for you: #1 neatens up the panel, and #2 gives you a great place to stick GFCI or AFCI deadfronts/receptacles. When the conduit to the junction box is metal e.g. EMT, that satisfies even new-construction rules for AFCIs.

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  • This doesn't appear to address the suggestion of running a suitable high-current jumper from the neutral bar. Do you have an opinion on that option? Commented Apr 20 at 9:54
  • That does not meet the instuctions/labeling or code, (which requires following the instructions) @SomeoneSomewhereSupportsMonica • 4th paragraph.
    – Ecnerwal
    Commented Apr 20 at 11:27
  • That was exactly my (un-stated) thinking: ground only needs to carry fault current, but neutral is more-or-less continuously carrying its circuit's full current. Commented Apr 20 at 14:37
  • Yes, I will have a stash of inline Wagos. Thinking heat-shrink over them too, veyr secure. AHJ can't see the Wago, but he seems to trust me. Commented Apr 20 at 14:38
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    @Rusty Either bring the home-run cable there and land it there, or since you have to extend it anyway, extend it via the conduit into that box, have your A/GFCI there, and then back to the panel to land on a plain breaker or tandem. Commented May 9 at 5:16
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The question is rather moot, as Siemens provides extension neutral bars. They extend the line of the installed neutral bars and connect via a hefty U-shaped piece of copper.

enter image description here

This isn't obvious, since these aren't mentioned in the list of accessories on the panel's label. However, they are shown in the schematic (right-hand side).

enter image description here

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    Holy smoke, nice find! The power of actually reading the labeling and instructions... Commented 23 hours ago
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    Yeah, still why not in the list of accessories ? Don't they want to sell 'em ? Not even in in the big "Residential Load Centers" catalog. I guess I've spent $70 or so adding ground and neutral bar extensions, but I think it's worth it, for neatness, and esp. because it's a panel replacement and some of the wires may not reach. Commented 22 hours ago

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