My situation is essentially the same as this question, for reference. I am trying to accomplish the same goal: feeding a sub-panel in an outbuilding from my home's main service panel.
I have a 6ga NM wire (3 conductors #8 bare ground) and a set of 4 THHN 6ga (3 conductors w/insulated #8 ground) coming into a space where I need a junction box. What size box would that require, given that this is only for the purpose of splicing the two sets together, there are no devices present, and no other wires in or passing through?
To extend the question a bit, this is happening in the interior space, so a surface mounted box would be ideal. Is there such a thing as a box that fits the bill and doesn't look like it belongs in a factory?