Whether the thermal relay and the fuse can use only one of them can play short circuit and overload protection role
Hello: thermal relay only has the role of overload protection, can not play short-circuit protection, because the action is too slow, if the short circuit can not immediately break will cause more serious consequences.
Fuse: fuse only for short circuit protection, can not be used in overload protection, so if you want to play a short circuit protection but also play overload protection, then both are indispensable!
Each have their own characteristics, the main fuse from the fault short circuit protection, action time is less than 0.5 milliseconds, thermal relay called overload relay, from overload protection, action time is greater than 3 seconds. Fuses and circuit breakers are similar, from the reliable on the fuse, from the maintenance of the circuit breaker is good, because the circuit breaker can be recycled, the action does not need to replace, but no fuse is reliable, after all, the circuit breaker is mechanical trip.
For example, the machine is 5.5KW motor, rated current is about 11A, but his starting current is very high, about 30A, you must have more than 30A fuse, but 5.5KW motor in the case of 18A 15 minutes After the temperature reached 80 degrees, but there is no action to the fuse point, so he can not do overload protection. Similarly, we choose the overload relay selection 10-18A, set at 13A, start the current when the current, but the overload relay will delay the action, so when the start will not move, only in a long time to work in more than 13A action, This time varies by load, such as set at 13A, the operating current at 18A, about a minute or so will move.
Can not, you can replace a motor protector can meet the two requirements!
