No, a circuit protection device must open the circuit on a fault current or overload.
A fuse protects a circuit from short circuiting. Also a breaker is used for this same purpose with the additional advantage of protecting the circuit from overloads also.
Varistors are not polarity sensitive. Now I'm pretty sure that the device in question is a varistor. I googled for SAS-820KD05, found several references but unfortunately no data sheet - maybe you have more luck. One main criterium for selecting a varistor is the varistor voltage - as long as the voltage applied to the varistor is below the varistor voltage, it will behave like a capacitor. When the voltage is above, e.g. caused by a transient, it acts as a resistor, shorting this transient. Another important value is the max. pulse current a varistor can withstand.
A varistor is a "variable resistor". When its value changes it then changes the amount of electricity it drops. Some of the energy goes to do the job; some of the energy is "dumped" out as heat. How about this: the volume control on your radio is a varistor. A dimmer switch on your living room lights is a varistor.
The device is called a switch.
No.A fuse is an electrical safety device that operates to provide overcurrent protection of an electrical circuit.
Circuit breakers do not use anything, they are a controlling device. They can automatically open the circuit if the current exceeds the current rating and you can manually disconnect the power from the circuit.
A device with an overload protection used to control a motor is an Overload Relay.
A fuse or circuit breaker will fit this description.
Motor protection circuit breakers(MPCB) are a specialized type of electrical protection device that is designed specifically for electric motors, like their name implies. Electric motors have plenty of applications and are used to drive mechanical devices of all types, so it is very important to protect them adequately with MPCBs.
A switch is often used to activate a circuit.
Circuit breaker or switch
A circuit breaker is a device used to open a circuit if too much current flows through it.