I am assuming you are trying to install a switch leg for the disposal and a continuous hot for the dishwasher and the disposal and, dishwasher are on the same circuit, and you are trying to use a split duplex for both devices. I am also assuming that you are trying to surface mount the box inside the cabinet rather than use a cut-in box.
If you are installing a surface mounted box the conductors or cabling would have to protected no mater what kind of box you are using. If you came out of the side you would have to protect the conductors until you could pass into the interior of the wall or some other protected area.
One other problem exists the dishwasher circuit requires GFCI protection and the disposal doesn't. So if you do not have GFCI protection for this circuit you cannot put a split receptacle in under the cabinet. You would have to install two separate receptacles (at least one GFCI protected) or add a GFCI breaker to that circuit.
Taking this one step further. Since the NEC requires at least the dishwasher to be GFCI protected, it would be safe to assume that the area below the sink is considered by AHJ to be a wet location which would mean an "outdoor gang box" would be required in a surface mounted box.
FYI - The new 2020 NEC has modified 210.18 (A) which will require every 120V outlet to be GFCI protected including disposals, as well as any other wet location inside and outside a dwelling.
Hope this helps
Answer from Retired Master Electrician on Stack ExchangeI have single ply construction walls and the boxes for the outlets are visible on the wall. The boxes are shallow and have to be replaced in order to be able to install new receptacles. Problem is, I can't find any electrical boxes that would work. Ideally, it would be 1.5" deep, made of plastic, no cutout lines or designs on boyd, and the box is perfectly rectangular and sides flat. So far, all the plastic boxes I've found are pretty flimsy and the sides are slightly slanted/diagonal and not flat.
edit: Here's a pic of what I'm looking for. This is what I'm looking for.
https://new.abb.com/products/7TAA040460R0007/5070-white
https://www.lowes.com/pd/CARLON-1-Gang-White-Plastic-Old-Work-Shallow-Handy-Wall-Electrical-Box/3420254
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In-Cabinet (sink base) electrical box - Metal or Plastic? - Home Improvement Stack Exchange
Can this box be surface mounted? | Information by Electrical Professionals for Electrical Professionals
Can you still find high quality plastic surface mount electrical boxes like they used to make back in the day? I'm looking for ones without cutout lines all over and the box is perfectly rectangular and sides flat. (everything I find look flimsy and have slightly slanted sides)
Those are wiremold boxes. Look for industrial grade, probably at supply house. The regular grades all you’ll find in big box stores. They are pricey
More on reddit.comSurface mount boxes/conduit not to code?
I am assuming you are trying to install a switch leg for the disposal and a continuous hot for the dishwasher and the disposal and, dishwasher are on the same circuit, and you are trying to use a split duplex for both devices. I am also assuming that you are trying to surface mount the box inside the cabinet rather than use a cut-in box.
If you are installing a surface mounted box the conductors or cabling would have to protected no mater what kind of box you are using. If you came out of the side you would have to protect the conductors until you could pass into the interior of the wall or some other protected area.
One other problem exists the dishwasher circuit requires GFCI protection and the disposal doesn't. So if you do not have GFCI protection for this circuit you cannot put a split receptacle in under the cabinet. You would have to install two separate receptacles (at least one GFCI protected) or add a GFCI breaker to that circuit.
Taking this one step further. Since the NEC requires at least the dishwasher to be GFCI protected, it would be safe to assume that the area below the sink is considered by AHJ to be a wet location which would mean an "outdoor gang box" would be required in a surface mounted box.
FYI - The new 2020 NEC has modified 210.18 (A) which will require every 120V outlet to be GFCI protected including disposals, as well as any other wet location inside and outside a dwelling.
Hope this helps
Given a choice, metal is always the way to go, unless it's impossible for some reason. Metal is both grounded and a good heat conductor, so it will do a much, much better job of containing a variety of wiring faults. It also has standard knock-outs, so you can attach anything instead of only Romex cables.
I have single ply construction walls and the boxes for the outlets are visible on the wall. The boxes are shallow and have to be replaced in order to be able to install new receptacles. Problem is, I can't find any electrical boxes that would work. Ideally, it would be 1.5" deep, made of plastic, no cutout lines or designs on body, and the box is perfectly rectangular and sides flat. So far, all the plastic boxes I've found are pretty flimsy and the sides are slightly slanted/diagonal and not flat.
edit: Here's a pic of what I'm looking for. This is what I'm looking for.
https://new.abb.com/products/7TAA040460R0007/5070-white
https://www.lowes.com/pd/CARLON-1-Gang-White-Plastic-Old-Work-Shallow-Handy-Wall-Electrical-Box/3420254