I'm employing a Varistor in a simple circuit that will be used in a car. The Varistor is there to ensure that any load dumps / vehicle transients will not result in catastrophe for the circuit.

My question is this: Should I pass VIN through the Varistor, or should the Varistor couple VIN and GND?

Circuit A has VIN passing through the Varistor: enter image description here

Circuit B has the Varistor tied from VIN to GND:

enter image description here

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    \$\begingroup\$ These schematics are not very logically shown. with IN?OUT?Vin and orientation. of shunt device being horizontal wrap around before fuse \$\endgroup\$ – Tony Stewart EE75 Nov 22 '19 at 18:42
  • \$\begingroup\$ Apologies, you're right -- I need to fix my symbols and placement. \$\endgroup\$ – t3ddftw Nov 22 '19 at 18:44

enter image description here

The fuse would always be before voltage-surge "shunt" clamp protection shown as Z_suppressor.

The other series elements are the Z (resistance+inductance) of the source and lines.


  • \$\begingroup\$ Thank you! So I need to move the fuse and then the Varistor will need to be placed between VIN and GND, as poorly shown in schematic "B". \$\endgroup\$ – t3ddftw Nov 22 '19 at 18:46
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    \$\begingroup\$ Yes. Fuse panel locations are designed to minimize Z to surge generating devices like solenoids and ACU clutches thus higher inductance to sensitive peripherals with longer leads \$\endgroup\$ – Tony Stewart EE75 Nov 22 '19 at 18:49
  • \$\begingroup\$ I have updated the schematic for circuit "B" so it's a bit less garbage. Also, that's great to know, thank you! \$\endgroup\$ – t3ddftw Nov 22 '19 at 18:52

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