What does a varistor do?

Varistors are used to protect a circuit from high voltage surges. When a high voltage surge is applied to a circuit, the outcome is usually catastrophic to the circuit. A capacitor may be installed across the signal lines. However, this capacitor cannot suppress voltage surges.

What is an MOV in a circuit?

An MOV is a voltage dependent device which has an electrical behavior similar to back to back zener diodes. ▪ When exposed to high voltage transients, the MOV’s resistance. changes from a near open circuit to a very low value, thus clamping the transient voltage to a safe level.

How do you identify a varistor?

While it may look similar to a capacitor, you can identify the device by its color, markings and location. The MOV will always be close to the equipment’s power supply and wired to a fuse. Many MOVs have a bright, solid color and are usually coin-sized. Unplug the equipment from the electrical outlet.

How does a voltage dependent resistor work?

A voltage dependent resistor has a nonlinear varying resistance, dependent on the voltage applied. They are often used to protect circuits against excessive transient voltages. When the circuit is exposed to a high voltage transient, the varistor starts to conduct and clamps the transient voltage to a safe level.

What happens when a varistor fails?

Varistors need to absorb the energy deposited by temporary overvoltage, switching surges, or lightning impulses. The energy absorption capability can be divided into thermal energy absorption capability and impulse energy absorption capability. …

How do I know if my varistor is bad?

Touch one meter probe to the free varistor lead and the other probe to the connected lead. Read the resistance on the meter. If it reads nearly infinite resistance, the varistor is still good. If it reads very low resistance, the varistor is blown.

Where is MOV used?

Applications of MOV They can be used for single-phase line to line protection and single-phase line to line & line to ground protection in AC/DC electrical circuits. They can be used for semiconductor switching protection in transistor, MOSFETs or Thyristor and Contact arcing protection in motor-operated devices.

How do I know if my MOV is bad?

How do you test for a bad varistor?

What will happen if the power rating of a resistor is exceeded?

Resistors which exceed their maximum power rating tend to go up in smoke, usually quite quickly, and damage the circuit they are connected to. If a resistor is to be used near to its maximum power rating then some form of heatsink or cooling is required.

Are varistors polarity sensitive?

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.

Why would a varistor burn out?

When the varistor leakage current is too large, and the temperature rises to a certain extent, the low melting point metal is melted, thereby varistor from The cutting in the circuit can effectively prevent the varistor from burning.

How does a varistor work?

This is how a varistor works in a circuit: When the voltage to a circuit is low or within acceptable limits, the varistor has a very high resistance. Since the varistor has such a high resistance, current does not flow through it; instead it flows to the device which needs power in the circuit.

What does varistor mean?

Definition of varistor in English: varistor. noun. A semiconductor diode with resistance dependent on the applied voltage. ‘The range is built by optimising combinations of various styles of inductors with the appropriate capacitors, varistors and other components to give a comprehensive range of suppression levels.’.

What is a MOV circuit protection?

MOV Definition and General Electrical Circuit Protection. MOV Definition. – A Metal Oxide Varistor (MOV) is a voltage suppression device that filters and clamps the transient in an electrical circuit. A Varistor is a Variable Resistor, sometimes referred to as Voltage Dependant Resistors (VDRs) by some manufacturers.

What is a voltage dependent resistor?

A special type of resistor whose resistance can be varied by varying the applied voltage is termed as a voltage dependent resistor (VDR) and is also simply called as varistor. It is a non-linear semiconductor element and its name is obtained from the words variable resistor.

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