collision detection between mesh collider and rigidbody boxy collider


I would like to know on how to collide a mesh collider with no rigid body attached to a rigidbody box collider. Based on the documentation provided in unity i see it should be possible but there is no collision detected. Here the mesh collider is the arm of the character and a standard cube object. Please let me know if there is any other way to make this possible.

If the RB is attached by a Joint as you suggest, collisions between those objects are disabled automatically. Use the limit controls in the joint to prevent collision.