# how to find the diameter of a varistor

Discussion in 'General Electronics Chat' started by pradeeba, Feb 28, 2008.

Feb 27, 2008
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is there any formula for calculating the diameter of a varistor?????

2. ### jpanhalt AAC Fanatic!

Jan 18, 2008
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Which one? If you have a part number, check the datasheet. If you just want to find one and then its diameter, check a parts house (e.g., DigiKey.com), find what you want, then the datasheet. John

Feb 27, 2008
104
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My Question is what diameter varistor has to be used for a particular range of power suplply?. Like based on what factor that diameter should be choosen?

4. ### jpanhalt AAC Fanatic!

Jan 18, 2008
5,699
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Feb 27, 2008
104
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my intention is not to know about the part number of varistor. i need to know how to choose varistor diameter for particular power supply. for example for 320V varistor 10mm, 15mm are available. i need to know exactly what diameter varistor is to be used?

6. ### hgmjr Moderator

Jan 28, 2005
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I believe the point that jpanhalt is trying to make is that a variator is chosen for a given application based on the manufacturer's voltage rating rather than its diameter. While the diameter of a varistor is directly related to the voltage rating of the particular device, diameter is not the parameter used in selecting a particular varistor for a specific application.

hgmjr

7. ### thingmaker3 Retired Moderator

May 16, 2005
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The varistor should be selected for the needed electrical characteristics. If different sizes are available for the same characteristic, choose the one which is most visually aesthetic. Or pick the one with the prettiest color.

8. ### kubeek AAC Fanatic!

Sep 20, 2005
4,688
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The diameter depends on the technology used, so there is no way to tell universally what diameter should varistor for 320V have.
Look in the datasheets of some brand and maybe you can find some rule.

9. ### rherber1 Member

Jan 6, 2008
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There are no hard and fast rules guiding the selection of a particular diameter varistor for any purpose, only arbitrary recommendations based on the most likely probability of an overvoltage occurrence and the degree of damage it may cause. I regard the varistor as the "centurion at the gate" because it is selected to be able absorb the initial overvoltage hit for sufficient time to allow other protection devices (eg. fuse etc) to activate while not allowing the high voltage through to the more important parts of the equipment. The varistor itself may be destroyed in carrying out this function such as will occur when lightning strikes the power lines or a high voltage main line comes into contact with the domestic 120 or 240Vac supply line.

See the Tech Fundamentals link here http://www.circuitprotection.com/rov.asp