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I'm considering updating my 20-space/40-circuit Siemens load center (1987 vintage) to a 30-space/48-circuit panel.

Looking at the Siemens offerings in the "plug-on neutral" PN series, I'm noting that the likely panel (model# PN3048B1200C) is only 30" high. This is the same height as my existing panel, yet it has 10 more spaces, meaning the vertical columns of breakers are 5" taller. Seems to me things could get a mite crowded.

I also notice that the "outdoor" version of the same panel (model# PNW3048B1200C) is 35" high, thus allowing the same amount of spaciousness as my existing panel.

So, I'm wondering WHY the outdoor panel is taller ? It simply has the NEMA 3R enclosure, but no additional wiring or hardware, so why ? Secondly, is there any reason I shouldn't use the taller "outdoor" panel even though my panel location is indoors ?

Here is the catalog (Im looking at page 5 of the catalog, which is page 7 of the PDF) ...

https://cache.industry.siemens.com/dl/files/752/109793752/att_1054903/v1/SIE_SA_ResiLoadcenters.pdf

... and here are drawings of the two panels (sorry I can't figure out how to put them side-by-side) ...

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You're really not going to have a problem, unless you put the panel together sloppy. Panels are required to be large because of wire bending space rules.

If you're getting cramped, look at how you are laying the cables in the box. There should be layers. The back layer should be all the ground wires, which should go to the ground bar and then be pushed into the absolute back of the box. The next layer should be neutral wires that don't need to go to AFCI/GFCI. The next layer is hots (and neutrals to AFCI/GFCI).

It's best to cut all wires (but ground) long enough to reach any breaker space in the panel. For neatness sake, fly past the breaker you want then double back. It also helps for wires coming in the top to go to bottom breakers, and wires coming in the bottom to go to top breakers. In between one of these layers is the service wires.


The difference in height for indoor/outdoor panels is a couple of things. First, they need more room at the bottom for side and bottom cable entrances, because top cable entrances are not allowed in outdoor panels. (This is another reason not to use the outdoor version of the panel for your indoor application, since you probably have branch circuits coming in from both above and below, and there are no knockouts on the top of the outdoor panel, just the hub opening).

Second, with an indoor panel, the factory answer for a bottom cable entry is to invert the panel with the main breaker on the bottom. For an outdoor panel entry, you can't invert the panel because that would defeat the water-resistant door! So bottom-entry cables must come to the top and do a "180" to attach to the breaker. Thus, they need lots of wire bending space.

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    the 2nd & 3rd paragraphs are really helpful for people who have read your answers and wondered how to do what you usually recommend. Thanks!
    – FreeMan
    Commented Dec 10, 2021 at 16:36
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    @Rusty When the bus is right where the cables enter, you have a lot of wires maneuvering to land on the bus. That tends to make the area really congested. Whereas a bunch of wires groomed into a bundle don't take much space at all, so it's not so bad to have opposite-end bars, on new construction. You can always add accessory ground bars - what you can't do is put neutral on those. Ground bars are rated for fault current not service current. Commented Dec 11, 2021 at 18:46
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    @RustyShackleford Not a debate, just complicated lol.... Neutrals are never allowed on ground bars because they're not rated for continuous current..... Grounds are allowed on neutral bars in the main panel only because there's a neutral-ground bond there anyway so it makes no difference. Some panels have only neutral bars.... Grounds can be as much as tripled-up on a lug (per labeling/instructions) but neutrals must always be solo. .......... But these days a lot of installations are "meter-mains" where the main breaker is at the meter, and the panel is a subpanel. Separate there. Commented Dec 11, 2021 at 21:51
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    @Rusty your "understood..." comment sounds correct. I would do accessory ground bars myself, but there's no rule against extending grounds with wire-nuts. Commented Dec 11, 2021 at 21:57
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    @RustyShackleford No, you can't get ground connectivity from sheet metal screws. You need a correctly tapped hole and fine machine screws with -32 or finer thread pitch for that. However, the panel label will list some models of ground bar. If you buy those, they'll fit pre-drilled/tapped sites in the chassis. Commented Dec 12, 2021 at 6:45

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