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I am in need of a shallow electrical box. Googling led me to this one, which is 8 cubic inches. Assuming I am using 14 gauge wire, under what scenarios is this even useful, given box fill requirements?

Assuming that I understand box fill calculations correctly, 8 cubic inches would allow for a maximum of 4 conductors with 14 gauge wire (and only 3 for 12 gauge).

If the shallow box had an outlet or a switch, that counts as 2 conductors. The hot and neutral wires would bring the total to 4. Then the ground would bring it to 5 - too much for the box.

If this box were to have two different 14/2 cables enter it, it would again be too small (2 hots plus 2 neutrals plus ground = 5).

The product overview on that page indicates "use with non-metallic sheathed cable" - I am curious to know if that's even possible!

(by the way, I see that there are larger shallow boxes that I can select from. I just want to understand why this particular one is being sold)

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  • The box would be legal as a termination point for a single live wire.
    – Aloysius Defenestrate
    Mar 20, 2022 at 13:32
  • @AloysiusDefenestrate - I suppose that could be done...though is that something that you have ever had a need to do or seen done?
    – susie derkins
    Mar 20, 2022 at 14:56
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    Not suggesting it’s something you’d plan ahead to do, but in renovations, you’ll sometimes find hot wires illegally abandoned. When the client isn’t interested in fixing it properly, this could be a compliant solution.
    – Aloysius Defenestrate
    Mar 20, 2022 at 17:57

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Sconce mounting

As it turns out, NEC 314.16(B)(1) has an Exception that applies to light fixtures which bring their own wiring space with them in the form of a domed cover:

Exception: An equipment grounding conductor or conductors or not over four fixture wires smaller than 14 AWG, or both, shall be permitted to be omitted from the calculations where they enter a box from a domed luminaire or similar canopy and terminate within that box.

So, one could theoretically use a shallow box like the one you linked to wire a 14/2 to a wall sconce that has a domed canopy. I would not recommend using it for that, though, due to the rise of integrated LED fixtures, which do not provide the same types of wiring space that fixtures designed to accept light bulbs do.

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  • Ah...interesting. I was not aware of this exception. Thank you.
    – susie derkins
    Mar 20, 2022 at 4:13
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    @susiederkins Yes, you only pay the "2 units of wire count" penalty for a receptacle or a switch which intrudes into the box. If a device is entirely top-mounted, like many transformers or transformer-relays that mount on a box lid (line voltage thermostat?)... they do not require any cubic inches. Alternately, an extension box could be used.
    – Harper - Reinstate Monica
    Mar 20, 2022 at 21:24

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