I have a couple questions concerning a garage wiring project I have coming up. Here is the situation, I have a 200-amp main panel in my basement. I am building a detached garage behind my house and plan to install a sub-panel in the new garage. I plan to pull service from my main panel and the total distance is about 120 feet. Since the main panel is on the opposite end of where the garage will be, it will be about 70 feet from the main panel to the point of exit to the outside and then about 45 more feet from there to the sub-panel in the garage. The outside portion will be underground in 1 ½ pvc conduit. My question is do I run my wiring continuous from the main panel all way to the sub-panel w/o a junction box or anything? If so, does the portion of wire running along the basement ceiling have to be in conduit or can it be run a different way? I am using 4-gauge THHN wiring w/two hots, a neutral and ground.
You are using individual wires, so you need conduit all the way if you don't want a box
Since you are using individual 4AWG THHN wires (instead of some sort of cable), you will need to run in conduit all the way from one panel to the other, unless you wish to have a box somewhere inside the house where you transition from the conduit wiring method to some flavor of cable (SER or NM).
A continuous conduit run inside can be practical, though, depending on what you are running through; the key here is to remember to provide ample pull points using LL and LR conduit bodies instead of bends whenever possible.
The wiring that is run through the house and for that matter that through the new garage, as long as it is free from physical damage, as stated earlier, does not need to be in conduit. However, it does need to be in a cable assembly as in NMB, SER, etc. The wires, at a minimum, must be enclosed in a protective thermo plastic jacket. Junction boxes are acceptable indeed will be required if you change wiring methods. At no place alone the entire run can the wire run without some protective covering, either conduit, cable or junction box. Good Luck.