Brake Away Switch

Hello to all ,
I am also a member of another message board and
a question about when a brake away switch should engage. There does not seam to be any concrete info
on the subject. Some feel that it should engage when the trailer comes loose from the car but the chains are still connected and the trailer locks up and stops the car pretty much. I feel and so do some other people feel that it should only engage when the trailer becomes completely unhooked from the car chains and all, because if the chains are still hooked up then the plug should be in and you can stop by useing the brake controller.So how do you have it set up and what do you think is right?