What is the symbol for a varistor?

Varistor symbol The varistor circuit symbol can be seen to be very similar to that of a thermistor. It consists of the basic resistor symbol of a rectangle with a diagonal line through it that has a small added section parallel to the body of the resistor symbol. This indicates the no-linear nature of the varistor.

Is there polarity on a varistor?

Does a varistor have polarity? In the case of metal oxide varistor, a zinc-oxide layer is basically sandwiched between two metal electrodes. As a result, there is no polarity.

How do I select a varistor?

Choose a varistor with an energy absorption rating that equals or slightly exceeds the energy values associated with the event the circuit may experience. If, however, the transient voltage is due to an external event, the magnitude of the source energy is unknown.

Can I replace a varistor with a capacitor?

You can replace it with a new one provided it is for the same voltage levels that it triggers. This AC and DC voltage ratings are the important parts and then the energy capacity. Energy cap. is not a major issue in Computer PSUs since the usually use a small varistor there.

How do you choose varistor voltage?

For example, selecting a MOV or silicon varistor for that matter, for voltage, its maximum continuous rms voltage rating should be just above the highest expected supply voltage, say 130 volts rms for a 120 volt supply, and 260 volts rms for a 230 volt supply.

Can a varistor go bad?

The varistor, normally having a very high resistance, responds to the voltage spike by absorbing its energy with a very low resistance. This will also blow the equipment’s fuse but protect the expensive electronics. If the varistor is visibly burnt through or broken, it is bad; replace it.

What is the difference between fuse and varistor?

Unlike the fuse or circuit breaker which offers over-current protection, the varistor provides over-voltage protection by means of voltage-clamping in a similar way to the zener diode. In many ways the varistor looks similar in size and design to a capacitor and is often confused as being one.

How does a varistor fail?

Under different current conditions, failure modes include electrical puncture (see Figure 4), physical cracking (see Figure 5), and thermal runaway. Cracking happens because varistors are basically a ceramic material, and hitting them with a sharp high-amplitude surge is like hitting a dinner plate with a hammer.