To create a double cross-arm:
From the Library menu select Constructions to open the Constructions library
Select a cross-arm that has the same number of cables that your desired cross-arm will require
Example
In this example, we will select a single cross arm with three insulators:
Select Make a copy at the bottom right and label it
Select Add new cross-arm and make sure that all the detail feeds mirror the original cross-arm:
Select the same beam
Set the same horizontal/vertical offsets.
Select the correct braces
Now select -X as the offset and this will pin the cross-arm to the other side of the pole:
Select the Usage Type under the insulators header to define the cross-arm as a through unstrained or a termination.
Now save the cross-arm at the bottom right of the pop-up.