The standard circuit for adjustable, 3-terminal regulators (LM317, LM350, etc) in Fig 1a suffers from a designed-in fault: If the potentiometer R₂’s wiper loses contact, the regulator’s output goes high.

Because the potentiometer is the most unreliable part in the circuit, consider using the circuit in Fig 1b. Now, if the potentiometer’s wiper loses contact, the circuit’s output goes low, and R₃ limits the output-voltage excursion even if the potentiometer shorts out. (DI #1416)

Fig 1—A simple change in the topology of a 3-terminal regulator’s circuit makes the circuit more reliable if the adjusting potentiometer shorts out or if its wiper loses contact.