I thought you can run a 12/3 and share the neutral to give you the two circuits is this correct.
That is a single circuit...a multiwire circuit.
225.30 Number of Supplies Where more than one building or other structure is on the same property and under single management, each additional building or other structure that is served by a branch circuit or feeder on the load side of the service disconnecting means shall be supplied by only one feeder or branch circuit unless permitted in 225.30(A) through (E). For the purpose of this section, a multiwire branch circuit shall be considered a single circuit.
#101175 - 02/14/0711:49 PMRe: Are two circuit the max for a detached garage
This is an excellent question and I've had to deal with it before. Someone wanted to run a multiwire branch circuit as Don discribed, for lights and plugs. In addition he wanted to run a circuit for a welder. I told him he needed to have a sub-panel and he had a fit. He ultimately put in a sub-panel but he was not happy. The multiwire branch circuit was one circuit but adding the welder was the second circuit.
#101176 - 02/15/0708:24 PMRe: Are two circuit the max for a detached garage
If the welder was using L/L on the same 15/20a MW circuit I would probably question the decision. If you are saying he ran a MW plus a welder circuit I agree 100%. With few exceptions you can only run one set of ungrounded conductors to another building.
In the single circuit situation you still want a disconnect ... ?
#101177 - 02/15/0708:52 PMRe: Are two circuit the max for a detached garage