What is a Varistor? - A Galco TV Tech Tip | Galco

A varistor, also known as voltage-dependent resistor is an electronic component with a nonlinear varying resistance, dependent on the voltage applied. The impedance is high under nominal load conditions, but will sharply decrease to a low value when a voltage threshold, the breakdown voltage, is exceeded. 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. The energy of the incoming surge is partially conducted and partially absorbed, protecting the circuit. This behavior makes them suitable to protect circuits during voltage surges.

Metal oxide varistors, also known as MOVs are one of the most common types of varistors. They are voltage dependent, nonlinear devices that provide transient suppression. MOVs are composed primarily of zinc oxide with small additions of other metal oxides. The structure of the body consists of a matrix of conductive zinc oxide grains separated by grain boundaries. These boundaries are responsible for blocking conduction at low voltages and are the source of the nonlinear electrical conduction at higher voltages. The use of a metallic oxide within their construction means that MOV’s are extremely effective in absorbing short term voltage transients and have higher energy handling capabilities. As with the normal varistor, the metal oxide varistor starts conduction at a specific voltage and stops conduction when the voltage falls below a threshold voltage.

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With respect to the usage, installation or assembly of any products described in this video, Galco Industrial Electronics, Inc., a Michigan corporation, encourages you to follow the requirements and/or guidelines of: i) the Occupational Safety and Health Act of 1970, Public Law 91-596, as amended, and all laws, rules and regulations implemented in relation thereto; ii) the National Electric Code®; and iii) NFPA 70E®. Any installation, assembly or work described in this video should be performed by a qualified licensed electrician.

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While we have made every attempt to ensure that the information provided is accurate and has been obtained from reliable sources, Galco is not responsible for any errors or omissions, or for the results obtained from the use of this information. All information is provided "as is", with no guarantee of completeness, accuracy, timeliness or of the results obtained from the use of this information, and without warranty of any kind, express or implied, including, but not limited to warrantees of performance, merchantability and fitness for a particular purpose. At all times you should defer to the instructions and safety guidelines issued by the manufacturer. In no event will Galco, its agents or employees thereof be liable to you or anyone else for any decision made or action taken in reliance on the information provided to you or for any consequential, special or similar damages, even if advised of the possibility of such damages.

[RaeesUnboxingwala]

I think this is the only good video available on YouTube regarding vdr 👍🏻

[zutech_italy]

Thank you very much, I am an amateur making small circuits always copied and in fact I don't know how these components work but I see them in different power circuits. Now it remains to know how to connect them in circuits to have surge protection. I have seen in Japanese products connected in both primary and secondary AC transformer lines. Still confusing for me, but many thanks to you. I liked it.

[electricpizzafly]

Thank you, I actually learned something new about varistors. 😀

[mcboomsauce]

The original had a base made out of pre tabulated amululite which controlled the semi lunar wave fluctuations through a series of logarithmic marvel vanes

[michaelbeckerman]

Can you explain how the use of Selenium potentially factors into the usage of zinc-oxide-based MOVs? Also, when would you use other devices like fuses and GDT's in conjunction with MOV's?

[mcboomsauce]

Sooo
Kinda like a person!
I’m a million ohm resistor at 10v but, at 40, 000v I’m not

[larrybud]

Does it seem backwards that they operate with higher resistance at lower voltage? Seems like if it's for transient voltage spikes, it should be the other way around

[yannick]

Thanks for the video. Is there a polarity ?

[salsal]

Hello

Thank you for your educational information.

I have two devices which I want to protect against high voltage (220 V).

The varistor should clamp at (150 V).

1st device:

120 Volts
550 Watts

2nd device:

120 Volts
2, 500 Watts

My question is:

What's the right (MOV) size for each device?
What's is the varistor's:

Diameter
Resistance
Voltage
Ampere. 

Thank you so much.

[corrylaich]

the zinc powder explains why their is so many sparks when I they pop.

[chrishadjipetris]

Yesterday I got a range hood control circuit out with a varistor that was destroyed, causing the mcb to break the circuit when supplying it. There's something I don't understand about this circuit. There are two varistors connected in series, the voltage on these two supplies the primary coil of the transformer, and the spot where the two varistors are connected goes to earth, but why?

[jroalan]

So how are they tested? I have one I suspect is bad for a smart light switch. With 118VAC applied to L1 and C, there is 118VAC across the varistor (model 14D241K). With no power applied, I read 1.4 ohms across the veristor.

[MrLaundrymaster]

do you know the specifications of a pressure Varistor

[Khalil-ps]

What is the value for the varistor by Ohm ?

[jalbz]

How to check MOV with multitester if still functional?

[westbay]

Hi, great video, will definitely subscribe.


I need help, I have something attached to my old relay called a  Contact Protecter.

This vintage relay (1959) with copper leaf springs and it has a contact protector. Part made by "Federal" 15A2PS2

I need to replace this part and not sure the new equivalent part or even how I measure for the value using a multimeter which I do have. 


I'm just not sure what spec I need to look for on Mouser.com. I am ordering a few other parts with them so I'm sure they would have what I need if I knew what to look for. 


Any help, greatly appreciated.


Thanks

[Guds]

so it increases the resistance as the voltage gets higher or.

[mdsharifulislam]

What is diffrence between Varistor and ntc/ptc

[lalkahandawa]

does Varisto has a polarity like a capcitor or diode.