Originally Posted by Retsdiv
If you didn't buy the cable yet, check the price of 12/2/2 or 12/4. Run (2) of either of those for your circuits... it's the same as (4) 12/2.
With 2 12/4s you would end up with 10 total wires. 2 grounds and 8 line/neutral wires.
12/2 is three wires for a total of 12. 4 grounds and 8 line/neutral wires.
With the 12/4 you would end up having to share the ground over two of the breakers which i don't think is explicitly spelled out as against code, but I don't think an inspector would pass this. Also, what looks like a single run would actually require two breakers to be flipped off before working with the line. This also might not be explicitly spelled out as against code, but it is incredibly dangerous.
--> Edit: Based on
comments (next post) I went back and read more about using the 12/4s. It is common in commercial, but I had never seen it in residential, although it can be done in residential. I still stand by my statement that for the average residential homeowner having the shared 12/4 instead of separate 12/2 is confusing and more dangerous. Essentially a DIYer would look at one NM cable and think 1 breaker. In the 12/4 usage the one NM cable is two breakers to de-energize. Obviously as DIYers doing home improvement we always need to check all leads in the box! I personally don't run two circuits into the same junction box, even though it is allowed, based on personal preference from an incident years ago! Thank you
for pointing out my mistake!
I realize it feels like you are adding a ton of wire, but take a second to compare to your main floor of your house. Count how many breakers you have originally and realize that probably half of those breakers end up driving 100 feet of cable as it snakes up and down through the walls of you house! It isn't continuous because it stops at lights and outlets, but it is the same amount of cable.