A “polymeric positive temperature coeffecient device”, commonly called a PPTC, differs from fuses and circuit breakers in that they don’t actually “break” (open) a circuit when a fault is present. Under normal operating conditions, they are in a very low resistive state. When a circuit fault is present, they change to a highly resistive state; however, a very small amount of current still flows through the device to keep it latched in the highly resistive state. Once the circuit fault is corrected, the PPTC cools and returns to its very low resistive state. Unlike thermal circuit breakers, PPTC’s do not need to be reset manually (no buttons to push) – they automatically reset themselves when the circuit fault is corrected. PPTC’s are also less costly than thermal circuit breakers and easy to incorporate into driver's stations.
IMPORTANT: Current ratings listed are the "hold value" for the PPTC - this is the maximum current the PPTC is rated to handle without "tripping". To ensure the PPTC "trips" when a short-circuit is present, be sure your power supply has a continuous current rating at least 3 times the PPTC current rating (hold value). For example, if the PPTC is rated at 3A (hold current), be sure your power supply has a minimum continuous current rating of 9 amps. If your power supply does not satisfy the minimum continuous current rating, use a traditional fuse holder and fuse instead.