I am afraid to let the potentiometer at full resitence ( ohms ) because i think it may be damaged.

I tried to show in my excel file that at full resistance you have less chance of over heating because your power dissipation goes down. If you can operate at 47ohms, it might provide another clue.

 

It is the load. The term 'short-circuit' is relative. In this case, I would say that it is not short-circuit, since you are trying to do something with this resistance.

And if the motor brake was broken and it had a short-circuit, how I would figure it out if were a sort-circuit or not?

 

How about going through the wiring and see if the wires are shorted or connected to something?

 

I think that this motor brake has some wires from winding in short-circuit, and in that way the rezistence of the winding iz much lower, that's my opinion.