Running from my house panel to my garage I currently have a 12-3 wire split into two circuits with a common ground, each circuit has a 15 amp breaker. I know 12 gauge wire can support a 20 amp but my question is can I run one circuit on a 20 amp breaker and the other on a 12 amp breaker with a common ground.
My reason for doing this is I want to run a slightly larger heater in the garage on colder days when I am working in there and once in a while it will trip the 15 amp breaker when it kicks on.
The garage currently has one 15 amp outlet on one circuit (the one I want to change to 20 amp) and the other circuit has a two 15 amp outlets and 2 50 w lights.
I hope this is clear. I look forward to the answers
Best Answer
I believe that it would be against the NEC to have these two seperate circuits with a shared neutral and not have them on a double pole breaker (or at the very least a handle tie between a 15A and a 20A breaker).
A double pole breaker will simultaneously disconnect both circuits and satisfy the code requirement.
20A breaker is required and 12 gauge copper 10 gauge aluminum is the minimum depending on how long the circuit run is.
Furthermore even if it is on a 20A circuit, you are not required to upgrade your 15A outlets to 20A outlets. This is only required if there exists a single receptacle on the circuit. One can only plug in 15A max devices into a 15A outlet, therefore the 20A load circuit load would not be achieved on a single device.
It might also be a code requirement now for a detached building to have its own grounded sub-panel as well but that I will have to look into.