What is Metal Oxide Varistor & Its Working

A varistor is also known as VDR (voltage-dependent resistor) is one kind of electronic component. It has VI characteristics that are the same as to a diode. The main function of this component is to protect the devices from high transient voltages. The arrangement of MOV can be done in such a way that it will short itself once the huge current is generated because of the high voltage. So the component that depends on current will stay protected from the unexpected surge within the device. Varistors are non-ohmic variable resistors, whereas rheostat and potentiometers are ohmic variable resistors. There are different kinds of varistors available, in that metal oxide varistor is most frequently used. This article discusses an overview of MOV (metal oxide varistor).

What is Metal Oxide Varistor?

A varistor that is made with a combination of zinc oxide & other kinds of metal oxides such as manganese, cobalt, etc is known as metal oxide varistor. The material is arranged between two metal plates or electrodes to interact with each other. These types of varistors protect from heavy devices from transient voltages.

Metal Oxide Varistor
Metal Oxide Varistor

MOVs are same as resistors because it consists of two leads where they don’t have polarity. So these are connected in both directions. These components cannot resist the transient voltage above the exceeded rating. .Once these components absorb the transient voltage then they tend to dissolve it like heat.

When this method continues continually for a short time, then the device begins to exhaust because of the extreme heat. These varistors are connected in parallel to supply better energy-handling capacities. Metal oxide varistors are also connected in series to supply high voltage ratings.

Working Principle

The term MOV or Metal Oxide Varistor is a variable resistor. But not like a potentiometer, its resistance will change automatically depending on its voltage. Once the voltage across the varistor increases, the resistance will be decreased. This property is very useful for the circuits to protect from high voltage spikes.

MOV Specifications

The specifications of MOV include the following while selecting metal oxide varistors, the following specifications play an essential role.

  • Working voltage is maximum
  • Varistor voltage
  • Once pulse current is given to the varistor, it acquires the highest peak voltage and maximum clamping voltage can be obtained.
  • Leakage current
  • Capacitance
  • Highest Working Voltage.
  • Highest AC Voltage
  • Clamping voltage
  • Surge current
  • Surge Shift
  • Response time
  • The absorption of energy mainly refers to the highest energy that is dissipated for a particular waveform without any problems.
  • Energy Absorption
  • Once surge current is given then surge shift can refer to the change within the voltage.


The features of MOV include the following.

  • The range of AC voltage ranges from 130V to 1000V
  • The range of DC voltage ranges from 175V to 1200V
  • The insulation resistance is 1000Mohm
  • The operating temperature ranges from -55 to +85 °C

Metal Oxide Varistor Circuit

A metal oxide varistor is frequently used in different circuits along with a fuse. These two are connected in parallel to the protected circuit. The circuit of the MOV is shown below. The main components used to protect the circuit are fuse and varistor.

MOV Circuit
MOV Circuit

Once the voltage is in the fixed range then MOV resistance will be extremely high. Therefore, the flow of current is there in the circuit but there is no current flow within the MOV. But once a voltage spike happens within the main voltage, and then it comes into view straight across the varistor because it is located in parallel with the AC mains.

This vast voltage will decrease the resistance value in MOV to an extremely low. So that it forces the current to flow in the varistor and fuse to disconnect the circuit from the supply.

Throughout voltage spikes, the high voltage which is faulted will come back to regular values immediately. In those cases, the duration of current flow will not be high to damage the fuse & the circuit comes back to the normal position once the voltage turns into normal. But, whenever a voltage spike is noticed then varistor separates the circuit for a moment by damaging itself through huge current every time. If the circuit faces with many voltage spikes then varistor used in the circuit will damage,

MOV Performance

The main function of MOV is to work as a surge suppressor. When the voltage across the varistor is below the clamping voltage then varistor will not conduct.

The performance of the varistor gets slow down based on time even if tiny surges flow throughout it. One more reason is that affect the performance of a varistor is the rating of energy. When the number of varistors is connected in parallel then its performance can be increased.

The main feature of this kind of varistor is response time because the voltage spikes are shorted in nanoseconds with the device. However, the response time is affected by the mounting design technique & component leads to inductance.

Metal Oxide Varistor Applications

The applications of MOV include the following

  • Metal oxide varistors are used to protect voltage spike, over-voltage, line to line, arching, and switching.
  • These varistors can be used to protect different kinds of devices from faults.
  • These are used for single-phase L to L, a line to ground protection within electrical circuits.
  • These are used for protecting the switching devices like a transistor, Thyristor, MOSFETs, etc.
  • These are used in the circuits to protect from voltage spikes as well as surges
  • In most of the cases, these are used in strips, adaptors, etc
  • These varistors are used in normal electronic devices like digital cameras, cell phones, mp3 players, etc
  • MOVs are used to protect the industrial ac lines, power systems, data systems, etc

Thus, this is all about an overview of metal oxide varistor, working, circuit, specifications, and applications. MOV is a protection component that can be used for protecting the power supply circuit from surges by changing its resistance. These circuits can be powered through AC mains. Here is a question for you, what is the clamping voltage of a metal oxide varistor?