PTC’s act as a type of circuit breaker; the resistance increases as the PTC threshold temperature is exceeded due to the load current passing through the device. This causes high resistance which opens the circuit protecting the device in the event of an over current condition. Unlike fuses, ambient temperature plays a role in how long it will be before a PTC reacts to over current. For this reason, careful consideration should be given to when PTC’s are used for equipment protection.
A PTC is appropriate for battery protection as most battery shorts are heavy shorts quickly tripping the PTC. The PTC is best for devices that can tolerate high current for a substantial amount of time, such as batteries.
Because PTC’s are slow acting and have a less accurate trip threshold, the PTC may not protect the cameras as reliably as a fast acting fuse. Because PTC’s need to cool down to reset and will not do so if the over current condition is not corrected, a service call will probably be needed to address the failure.
A one amp PTC may never blow at 2 amps and may require more than 30 seconds to blow at 5 amps. A one-amp fuse should blow at 1.25 amps in about 1 second, regardless of conditions. It is much more economical for the dealer/customer to replace a simple fuse rather than an expensive piece of electronics.