It is a confusing question for some engineers. Actually, for current sensing thermal protectors, there are two current parameters. One is rated current. It is the nominal working current. The other one is tripping off current, also called over-loading current.
For the rated current, for examples, 3A or 5A, it means that the thermal protector can not trip off under this current. It would only cut the circuit off when temperature reaches the preset value.
But for the tripping off current, it means that the thermal protector has to trip off very quickly, like 4 to 10 seconds under this current. It is for overload protection purpose. General speaking, the tripping off current is around triple or 4 times of rated current. For example, if the rated current is 3A, the tripping off current should be set at 9A to 15A. It is only a rough estimation. The accurate value depends on the technical requirements of mock-up test and application.
