I have a light switch I want to tap into to add another power outlet a few feet away. I believe this switch's junction box is already too full to accommodate adding new wires. I think I would have to re-wire things so my new outlet goes to this switch instead of an existing wire, and then have that splice with the new wire in the outlet's junction box. The only problem is, the existing wires won't reach to the location of the new outlet. Is there any way to splice a wire behind the wall without using an exposed junction box (with blank wall plate) or is that my only option to be within code? Is there some other option I haven't considered?
What is the size of the box holding this switch? Is it 1-gang, 2-gang, 3-gang, etc?
Would a deeper box allow the new cable and connections? There are 3-7/8" deep 1-gang boxes with a 23 cu in capacity which is higher capacity than standard.
Alternatively you could replace a 1-gang box with a 2-gang old work box. Of course, this might be aesthetically unpleasing.
That switch is getting its power from somewhere. Trace that hot line back somewhere to see if it's in another box that you can tap into.
Otherwise, no, you cannot have a junction buried behind a wall - that's not to code and it's dangerous.
Yes, Tyco makes a splice for Romex which is meant to be concealed in-wall.
However, are you sure you are counting your cubic inches correctly? Remember
- all grounds together count as a single wire
- pigtails do not count at all
- a yoke (i.e. The switch) only counts as 2 of the largest wire attached to them
And of course, try to use the cubic inches stamped or molded onto the box itself, rather than the codebook values. That gives you credit for larger-than-stock boxes.